Physiological Psychology PSY 3803
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Otha Treutel DDS
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CH 4 What are the six formal criteria for establishing that a particular chemical serves as a neurotransmitter The chemical exists in presynaptic terminals 2 The enzymes used to synthesize the chemical are found in presynaptic neurons 3 The chemical is released when action potentials arrive in sufficient quantities to have postsynaptic effects 4 The postsynaptic membrane contains receptors for the chemical 5 Experimental application of the chemical also changes postsynaptic potentials 6 Blocking release of the chemical prevents presynaptic nerve impulses from altering the activity of the postsynaptic cell A classic neurotransmitter can affect the postsynaptic neuron if its release from the presynaptic membrane is stimulated by an action potential true A classic neurotransmitter must be able to affect receptors at great distances from its origin false A drug that binds to a receptor and blocks the effect that the endogenous neurotransmitter would have is termed an antagonist while a drug that mimics the effect of the endogenous substance is called an agonist A compound that binds to a receptor and causes it to have an effect opposite to the normal effect of the endogenous compound at that receptor is termed an inverse agonist Some drugs are noncompetitive ligandsithey do not bind at the transmitter s normal binding site but rather exert their effects through an modulatory site It is misleading although a fairly common practice to identify a cell on the basis of its transmitter release eg cholinergic neuron doparninergic neuron serotonergic neuron because an individual neuron may co localize more than one type of transmitter ACh was first identified as a transmitter in the neuromuscular junction Large numbers of ACh producing neurons are found in the basal forebrain region especially the medial septal nucleus the nucleus basalis and in the diagonal band nuclei Muscarinic ACh receptors are metabotropic and therefore respond more slowly than nicotinic receptors They are blocked by the drug atropine The loss of cholinergic cells in Alzheimer s disease suggests that they are important in learning and memory Approximately 1 million dopaminecontaining neurons exist in the human brain The mesostriatal system is a dopamine projection that originates in the substantia nigra and innervates the striatum the collective name for the caudate putarnen and globus pallidus as well as the olfactory tubercle and nucleus accumbens These latter projections may be important in mediating the effects of psychostimulant drugs such as cocaine A second major DA system is the mesocorticoljmbic system which originates in the ventral tegmental area and projects to the nucleus accumbens cortex including the insula and limbic system the collective name for the amygdala septum hippocarnpus and associated areas The three main sources of norepinephrine in the brain are the locus coeruleus the lateral tegmental system and the dorsal medullary group Noradrenergic projections course throughout the brain particularly to the cortex true thalamus true cerebellum true and spinal cord true Approximately 200000 neurons of the human brain contain serotonin 5HT Most serotonergic projections emanate from the raphe nuclei of the brainstem There are at least 19 subtypes of receptors for 5HT Drugs that increase serotonergic activity such as Prozac tend to be effective antidepressants For each of these four prominent amino acid transmitters identify whether their activity is primarily excitatory or inhibitory l GABA inhibitory 2 Aspartate excitatory 3 Glutamate excitatory 4 Glycine inhibitory There are 3 classes of GABA receptors GABAA receptors are ionotropic GABAB receptors are metabotropic and GABAc receptors are ionotropic Drugs that block GABA receptors can produce seizures Along with metabotropic receptors glutamate acts through three types of ionotropic receptors the NMDA receptor which has been implicated in learning and memory the kainate receptor and the AMPA receptor Prolonged excitation of postsynaptic neurons through glutamate exposure can kill them through excitotoxicity Glutamate is cleared from synapses by being taken up by astrocytes a type of glial cell A prominent group of peptide transmitters is the opioid peptides one of which is Bendorphin Other members of this group of peptides include met and leuenkephalin and dynorphin A second major group of peptides is the gut peptides one of which is cholecystokinin Other peptides from this group include substance P neurotensin and neuropeptide Y The third major group of peptide transmitters is composed of the pituitary peptides of which vasopressin and oxytocin are examples These peptides act as transmitters at some synapses but they also act as hormones elsewhere There may be subtypes of receptors for any given neurotransmitter for example there are 5 subtypes of receptors for dopamine Dopamine binds to all the subtypes of course but dopaminergic drugs may tend to bind more readily to some of the subtypes than it does to others This selectivity is how subtypes of receptors are identi ed in the rst place The drug haloperidol is thus said to be a selective Dz antagonist because it has high af nity for D2 receptors Overthecounter medicine and psychoactive substances are both types of drugs true Most but not all drugs of interest in biological psychology interact with receptor molecules The presence of a receptor to which a drug binds implies the existence of an endogenous ligand for the receptor An important principle of neuropsychology is that transmitters tend to act on more than one kind of receptor A pharmacological approach to targeting particular receptors involves devising synthetic human made compounds that preferentially affect only a subset of a transmitter s receptors Such exogenous compounds may thus mimic or modify some of the effects of the endogenous neurotransmitters Drugs diffuse widely and nonspecifically ie they do not hunt out certain tissues so in order for the drug to show an effect a neural mechanism must have appropriate receptors to which the drug can bind For each of the following modes of drug action 1 indicate whether the effect is primarily presynaptic or postsynaptic 2 indicate whether the action is classified as agonistic or antagonistic inverse agonistic or neuromodulatory and 3 complete the brief description of the change produced by the drug s action 1 Activation of postsynaptic receptors postsynaptic agonist direct stimulation of postsynaptic receptors mimicking the transmitter s actions 2 Axonal sodium channel blockade presynaptic antagonist prevention of action potentials 3 Inhibition of reuptake presynaptic agonist less transmitter resorbed into synaptic vesicles thus more transmitter present in synapse 4 Upregulation induced increase in postsynaptic receptors postsynaptic agonist increased responsiveness to transmitter 5 Calcium channel blockade presynaptic antagonist inhibition of transmitter release 6 Stimulation of transmitter release postsynaptic agonist increased receptor activation 7 Stimulation of presynaptic receptors ie autoreceptors presynaptic antagonist inhibition of transmitter release 8 Blockade of postsynaptic receptors postsynaptic antagonist decreased response to neurotransmitter 9 Inhibition of transmitter storage in vesicles presynaptic antagonist neurotransmitter not available for release 10 Downregulation of postsynaptic receptors postsynaptic antagonist decreased responsiveness to neurotransmitter ll Inhibition of cAMP or other second messenger postsynaptic antagonist decreased response to neurotransmitter after binding to postsynaptic receptors Inhibition of axonal transport presynaptic antagonist raw materials unavailable in axon terminals for production of neurotransmitters hence decreased neurotransmitter release Inhibition of breakdown enzymes eg AChE presynaptic agonist neurotransmitter remains available longer and therefore has greater effect on postsynaptic receptors Facilitation of transmitter release presynaptic agonist increased availability of neurotransmitter increases activation of postsynaptic receptors N LA 4 Drugs that block sodium channels are used as local anesthetics One such drug is called procaine For each of the following drugs indicate which of the effects it produces LSD activation of postsynaptic receptors Reserpine inhibition of transmitter storage in vesicles Black widow venom stimulation of transmitter release Curare blockade of postsynaptic receptors Physostigmine inhibition of breakdown enzymes e g AChE Tetrodotoxin axonal sodium channel blockade Cocaine inhibition of reuptake Colchicine inhibition of axonal transport Lithium inhibition of cAMP or other second messenger 509089 59 N1 Benzodiazepines such as Valium generic name diazepam bind to the GABAA receptor complex and enhance the effects of GABA resulting in larger inhibitory postsynaptic potentials Because a benzodiazepine does not bind to the same binding site as GABA does it is classified as a noncompetitive agonist The presence of benzodiazepine receptors in the brain implies that the body naturally produces an endogenous ligand but this hypothesized substance has not yet been demonstrated conclusively One current contender is allopregnanolone which may mediate the calming effects of alcohol About 5 different types of receptors for dopamine have been described Members of an important class of drugs called neuroleptics such as the drug haloperidol reduce the severity of the symptoms of the disease schizophrenia by blocking D2 receptors Newer antipsychotic medications have additional activity at receptors for the neurotransmitter serotonin Alcohol is produced by the fermentation of grains or fruit and it has a biphasic effect in the nervous system involving an initial stimulant phase followed by a prolonged depressant phase Although it affects other transmitter systems too alcohol particularly alters GABA transmission activating the GABAA receptor s chloride channel The destructive effects of alcohol may be mediated by secondary consequences of alcoholism a severe deficiency in thiamine Chronic alcohol exposure affects many parts of the brain especially frontal cortex Restoration of many functions is evident in the brains of people with alcoholism who abstain from drinking including a reversal of atrophic changes and improved metabolism Chronic use of alcohol damages various types of neurons especially Purkinje cells of the cerebellum hippocampal pyramidal neurons and cells of the superior frontal cortex Alcohol directly activates GABAA receptors leading to postsynaptic inhibition Opiate systems also seem to be involved because the opiate antagonist naloxone may suppress alcohol consumption For each of the drugs listed below identify the transmitter system it particularly affects Lysergic acid diethylamide LSD7ser0t0nin Phencyclidine PCP iNMDA glutamate Mescalineinorepinephrine Muscarineiacetylcholine Psilocybiniserotonin KetamineiNMDA glutamate MDMA Ecstasy iser0t0nin QP39HeP NE Drugs that reduce anxiety are collectively known as anxiolytics examples include neuroleptics false haloperidol false alcohol true barbiturates true amphetamines false opiates true and benzodiazepines true The major active substance in opium is morphine which has very powerful analgesic properties and which can be modi ed to produce the highly addictive compound heroin A major discovery about opiates in the 1970s was the identi cation of opiate receptors in the brain These are found especially in the limbic and hypothalamic regions and they are particularly rich in the locus coeruleus and periaqueductal gray regions This discovery provoked a search for endogenous ligands the first to be identified were the enkephalins The three main kinds of opiate receptors that have been described are the 5 delta K kappa and mu receptors all of which are metabotropic receptors The main active ingredient in marijuana is delta9 tetrahydrocannibinol this and related substances are collectively known as cannabinoids Cannabinoid receptors have been identified in the cerebellum true spinal cord false cerebral cortex true substantia nigra true and brainstem false There are now known to be 2 different cannabinoid receptors Genetic disruption of the CB1 receptor in mice blocks the rewarding properties of cannabinoid drugs The search for endogenous THC receptor ligands such as anandamide offers the hope of drugs that will provide the beneficial effects of marijuana for instance marijuana seems to be helpful in the eye disease glaucoma provides decreased sensitivity to pain and offers protection from excitoxicity Nicotine activates a class of acetylcholine receptors found especially at neuromuscular junctions but also in the CNS By stimulating the sympathetic nervous system nicotine increases heart rate and activates reward circuitry such as the VTA Aside from its wellknown harmful effects on the lungs and circulatory system nicotine also has been shown to improve cognitive performance Stimulants may act by increasing excitatory postsynaptic potentials or by decreasing normal inhibitory in uences Cocaine acts by blocking monoamine transporters especially those for dopamine and thus it inhibits the reuptake of transmitters from synapses prolonging their effect Cocaine produces changes in cerebral blood ow and decreases in glucose utilization that are evident for months after a person stops using it The molecular structure of amphetamine resembles that of the catecholamine family of transmitters Amphetamine potentiates the actions of these transmitters in three ways facilitation of release inhibition of reuptake and competition for breakdown enzymes In the short term amphetamine produces heightened alertness and euphoria Longerterm use induces tolerance to the effects of the drug so higher and higher doses are needed to produce the same effect The higher doses however often result in sleeplessness weight loss general deterioration and in some cases a psychotic state that resembles schizophrenia Longterm users exhibit lasting symptoms of brain damage for an extended period of time after they have stopped using amphetamine Cocaine and amphetamine treatments lead to the production of cocaine and amphetamine related transcript CART peptide by the brain which when injected in the ventral tegmental area provides a strong reward cue Drugs that alter sensory perceptions are collectively known as hallucinogens This term is inaccurate because the drugs rarely induce perceptual experiences in the absence of sensory stimulation rather they distort ongoing perceptions Identify which of the Four Cs toxic reactions of phencyclidine use go with each statement 1 PCP users frequently exhibit combativeness and will attack others 2 PCP may induce catatonia in which the user displays stupor and stereotyped behavior 3 PCP users may exhibit convulsions seizures or enter a coma and be unconscious for days 4 PCP use may induce confusion that lasts for weeks The drug Ecstasy or MDMA is a 39 quot 39 39 form of I 39 39 Persistent memory problems have been reported in humans following its use However controversial work with nonhuman animals suggests that chronic use of Ecstasy has persistent effects on serotonin containing neurons in the brain changes that have been noted in these cells include damage to fine axons although cell bodies appear to be spared According to the study conducted by Fischer and colleagues in 1995 as much as 18 months after administration of 40 mgkg of Ecstasy to monkeys marked anatomical changes in the brain have been noted especially in the neocortex and hippocampus Such results remain controversial given that this dose is rather high a typical recreational dose for humans is less than 2 mgkg It is difficult to determine which mechanisms are most important in the development of addiction because addictive substances tend to have multiple effects For example cocaine has anesthetic effects produces pleasurable feelings is a stimulant and produces adverse effects at high doses A comprehensive theory of drug abuse and addiction has yet to account accurately for the diversity of effects related to drug use According to the DSM I V the substancerelated disorders include what we commonly refer to as addiction Of these disorders drug dependence is more severe than abuse Forapersontobe 139 Jasjl J ona 39 met Identify four of these criteria at least three of seven criteria must be 1 Larger quantities are consumed than intended or more time is spent consuming than intended 2 Attempts to reduce or stop use of the substance are unsuccessful 3 Much time is spent procuring using or recovering from the substance 4 Important activities work recreation etc are curtailed due to the use of the substance The moral model of drug use is exempli ed by the famous saying Just say N 0 This campaign did not appear to significantly reduce drug abuse The moral model of drug use attributes drug abuse to a lack of moral character Societal pressure in this form was effective in reducing alcohol consumption in the Us by 33 during the time of the temperance movement The disease model of drug use stipulates that drug abusers require medical treatment however a problem with this model is that there does not appear to be an abnormal physical or biochemical condition involved in the causes of drug abuse The physical dependence model of drug use explains drug abuse as a desire to avoid symptoms of withdrawal in the case of morphine abuse some these symptoms include tremors true stupor false irritability true convulsions false confusion false elevated heart rate and blood pressure true and sedation false The phrase going cold turkey derives from the appearance of the skin of an addict during morphine withdrawal which looks like that of a plucked turkey In the general experimental setup for studies of the positive reward model of drug use an animal presses a lever to get small injection of the test drug rewarding properties of the drug are proportional to the willingness of the animal to press the lever Experiments using the drug selfadministration approach have shown that physical dependence is are not a requirement for drug selfadministration For instance animals will leverpress for morphine at doses too low to produce physical dependence and will leverpress for drugs that do not produce withdrawal symptoms It is possible that drugs of abuse share activation of a generalpurpose reward system that arises in the ventral tegmental area and projects to the nucleus accumbens where rewarding experiences stimulate a release of dopamine Treating rats with a weak agonist for dopamine reportedly reduces cocaine craving perhaps by activating this system Four factors have been identi ed as contributing to the likelihood of drug abuse They are bP NE biological factors such as sex or genetic predisposition personal characteristics such as aggressiveness lack of education etc social and community factors such as peer group drug use and family situation such as divorce of parents or the presence of an antisocial sibling Five categories of drugs for use in the treatment of drug addiction have been identified Identify the category of which each of the following is an example bP N Naltrexone antagonist to the addicted drug Antabuse medication that blocks drug metabolism Methadone agonist of addicted drug Drugs that reduce the desire to drink certain antidepressants have this action anticraving medication Drugs such as benzodiazepines that control withdrawal symptoms drug for detoxi cation Antabuse causes an accumulation of acetaldehyde which is a sickening metabolite of alcohol Therefore it is a treatment based on the positive reward model of drug abuse Everyone who uses an addictive drug becomes addicted false CH 5 The glands that produce most of the hormones that have effects within the body are called endocrine glands The exocrine glands secrete products to the outside of the body and have ducts Hormones are secreted by organs other than glands Identify the four humors to which temperament was historically attributed based on the personality trait each was believed to cause when produced in excess Humor Personality trait Phlegm Sluggishness Blood Cheerfulness Choler Hottemperedness Bile Irritability Sugar metabolism is regulated by the pancreas the gland that secretes insulin from a cluster of cells called the islets of Langerhans The first major endocrine experiment was conducted by Adolph Berthold Describe the three main treatment conditions in Berthold s experiment with roosters and the conclusion suggested by the pattern of results 1 Condition 1 no treatment The bird develops into a normal rooster with comb and wattles crowing aggressive behavior and mating with hens 2 Condition 2 early castration The bird develops with small combs or wattles weak crowing and reduced sexual behavior 3 Condition 3 early castration with reimplantation of one of the testes into the abdomen The bird develops into a normal rooster with an normal comb 4 Because the neural connections to the testes were cut in the third condition this experiment indicates that a blood home factor must be responsible for masculine characteristics For each of the following select the correct form of hormone action 1 Hormone released from body to affect individuals of a different speciesiallomone 2 Hormone released into bloodstream with effects that may be distantiendocrine 3 Hormone released from body to affect another individual of same speciesipheromone 4 Released hormone that affects neighboring cells by diffusion through extracellular spaceiparacrine Hormone that affects same cell that released itiautocrine 6 Neurotransmitter released into synaptic cleft to signal postsynaptic neuronineurocrine V39 Complete the following statements summarizing nine general principles of hormone action 1 Hormones act gradually so the effect of a hormone treatment may emerge long after the treatment 2 Hormones affect the probability that a behavior will occur or they alter the intensity of the behavior they generally do not switch on behavior 3 Hormones are sensitive to environmental factors 4 A hormone affects perhaps multiple targets a given target may respond to multiple hormones 5 Hormones are generally produced in small quantities and are released in pulsatile fashion 6 Hormone secretion shows pronounced biological rhythms 7 Hormone systems interact and alter one another s functions 8 The chemical structure of hormones tends to be maintained among vertebrate species 9 A given hormone can affect only tissues that contain the appropriate receptor proteins for that hormone Indicate the hormone actions that are exemplified by the scenarios presented below 1 Two male students have a tiddlywinks grudge match and after the game blood samples are drawn from each of them and tested for hormone concentrations The loser of the contest may show a reduction in testosterone This result would demonstrate the principle that hormones are sensitive to environmental factors 2 An athlete abuses steroid hormones testosterone and after a few months shows increased muscle mass kidney damage testicular atrophy and mood changes The observed changes occurred slowly and the single hormone affected multiple targets 3 Your female dog is usually very well behaved but occasionally she becomes agitated and leaps the fence to spend some quality time with the male dog next door Her condition of heat or estrus which occurs in a periodic manner involves a biological rhythm The overlap of hormonal and neural communication systems is exemplified by the neuroendocrine cells of the hypothalamus they are similar to neurons in that they receive synaptic contacts move material down their axons and release substances peptides in response to the arrival of action potentials They are like endocrine cells in that the material released is a hormone and it is released into the bloodstream Neural communication is relayed to specific targets and therefore can be likened to a telephone A hormonal system conveys its messages either to nearby structures or throughout the body and therefore can be likened to a radio Neural messages are transmitted very rapidly usually taking only a few milliseconds to reach their destination Hormonal messages are much more gradual usually spanning a range of time from seconds to minutes to be transmitted Neural transmission may be considered digital because neural messages are allornone action potentials hormonal messages by contrast may be considered analog because they are graded in strength ie the quantity of the secreted hormone varies The fact that you cannot by force of will secrete more or less of a given hormone suggests that hormone release unlike many neural systems is not under voluntary control Complete the statements below describing the five ways in which neural transmission and hormonal signals resemble each other 1 Both systems manufacture chemicals used for signaling and also store them for later use 2 Cells of both systems communicate with other cells through secretions 3 Both systems employ a variety of different chemicals for signaling 4 In both systems a target tissue must contain the correct receptors in order for it to respond to the chemical message Both systems feature signaling pathways that employ second messengers V39 Hormones made up of long strings of amino acids are called protein hormones while hormones made up of shorter strings are called peptide hormones Unlike the protein hormones steroids have a molecular structure featuring four rings of carbon atoms Steroid hormones are soluble in lipids this has implications for diffusion because cell membranes consist of a lipid bilayer The amine hormones are so named because the molecular structure of each is based on one amino acids These substances are also known as monoamines The steroid hormones are composed of four interconnected rings of carbon atoms Hormones are crucial to the early development of the body with effects on proliferation generation of new cells growth and differentiation assignment of cells to particular roles An example of their in uence is the brain s requirement for thyroid hormones during development A shortage of these hormones leads to production of fewer brain cells and thus stunted intellectual development Facts about the interaction of various hormones with receptors are listed below In the space provided after each item identify the type of hormonal signal primarily associated with it Receptor Fact Primarily Applicable to Binding to DNA Steroids Surface membranebound receptors Protein and amine hormones Speci c receptors Both Regulation of gene transcription Steroids Secondmessenger system Protein and amine hormones In order for a cell to be responsive to a particular protein or amine hormone it must have the correct receptors for that hormone These are made of protein inserted into the cell membrane in such a way that the extracellular portion interacts with molecules of hormone causing the receptor to change its shape This change induces the intracellular portion of the receptor to change the functioning of the cell often by activating a second messenger Hormones also affect cells by altering the cells rate of function For example luteinizing hormone regulates the rate of production of sex hormones by the testes The initials CAMP stand for cyclic adenosine monophosphate which is a common second messenger Although many protein and amine hormones act through a cAMP system their effects are highly variable The cAMP system is able to mediate a variety of hormone effects depending on which cells are affected which part of the cell is affected the cells prior biochemistry and the selectivity of the receptors Other secondmessenger compounds include cyclic guanosine monophosphate and phosphoinositides Up regulation refers to an increase in the number of hormone receptors produced whereas down regulation refers to a decrease in the number of hormone receptors produced The protein and amine hormones have their effects within seconds to minutes There are exceptions to this In order for a cell to be responsive to a steroid hormone it must have the correct receptors typically located in the cytoplasm In many cases the cell also must contain appropriate steroid receptor cofactors proteins that determine the genes to be regulated when the steroid is present Because the cell membrane is a lipid bilayer and steroids are lipidsoluble steroids diffuse into and out of all cells but only those cells that contain receptors for that steroid are affected In cells that do contain the receptor the receptor binds to the hormone and the hormoneireceptor complex then binds to DNA in the cell nucleus and alters protein synthesis Steroids can sometimes have a rapid effect on neurons suggesting the existence of membrane bound steroid receptors that may alter the excitability of neurons This rapid effect is called the nongenomic effect The basic control mechanism of hormone release is negative feedback In this system the actual levels of hormone present are compared with an set point and if the hormone level meets or exceeds this point secretion of hormone is reduced This system is often likened to the heating system of a house according to this analogy the set point is located in the thermostat A more complex endocrine system involves the brain specifically the hypothalamus which directly governs the pituitary through the use of releasing hormones The presence of releasing hormones stimulates the secretion of tropic hormones by the pituitary In the table below identify experimental techniques used for determining hormonal control over a behavior Question Techniques A m 39 39 y false 39 39 39 false I 39 Which true hormone replacement true hormone removal true implantation false hormone autoradiography false Where are the I 39 39 y true 39 39 39 39 false I 39 target cells false hormone replacement false hormone removal false implantation true autoradiography true 4 I L m 39 y false 39 39 true I 39 true hormone replacement false hormone removal false implantation true autoradiography false What happens there What is the hormonal control of sexual behavior in male rats according to the major questions asked in behavioral endocrinology research Which hormone Where are the target cells What happens there 1 Castration of male rats eventually abolishes sexual behavior and testosterone replacement restores it Studies employing radioimmunoassay reveal that sexual behavior does not vary with testosterone levelsionly castration reduces testosterone to levels at which sexual behavior is curtailed 2 Autoradiography and immunocytochemistry have identi ed numerous regions in the nervous system that contain androgen receptors 3 Implantation of tiny pellets of testosterone in the brains of castrated male rats reinstates sexual behavior only when they are placed in the medial preoptic area of the hypothalamus The androgens estrogens and progestins are derived from cholesterol and all share a basic four ring molecular structure In fact estradiol can be synthesized from testosterone which in turn is synthesized from progesterone The two principal hormones of the thyroid gland are thyroxin and triiodothyronine which are secreted under the control of thyroidstimulating hormone a tropic hormone of the anterior pituitary A unique feature of the thyroid is its capacity to store enough hormone to last 100 days Another unique feature is that although its hormones are structurally classi ed as amine hormones their receptormediated activity is more like that of steroids The pituitary is a relatively tiny structure measuring about 1 cm3 and weighing about 1 g It is located just below and is controlled by the hypothalamus of the diencephalon to which it is connected by a piece of tissue called the pituitary stalk The pituitary has two major anatomical and functional divisions the anterior pituitary or adenohypophysis and the posterior pituitary or neurohypophysis One of the two major hormones of the posterior pituitary is arginine vasopressin which is also called antidiuretic hormone because of its effects on the formation of urine It also has effects on blood pressure and acts as a transmitter in various locations in the brain The second major hormone of the posterior pituitary is oxytocin This hormone is involved in feeding behavior false salt metabolism false milk letdown re ex true sexual behavior and orgasm true uterine contractions true parasympathetic activation false and social behavior true Nursing mothers become conditioned to the sound of their babies cries such that this stimulus alone is suf cient to induce oxytocin secretion and milk letdown The pituitary stalk contains both blood vessels and axons The axons of the stalk terminate in the posterior pituitary only The two principal hormones of the posterior pituitary are synthesized in neurons located in the supraoptic nucleus and the paraventricular nucleus of the hypothalamus In response to action potentials the hormones are released from the neurons axon terminals into the vascular bed of the neurohypophysis from which they can enter the general circulation The neurosecretory cells of the hypothalamus can respond to circulating factors because they are not shielded by the bloodibrain barrier Hormones released by the anterior pituitary that stimulate endocrine tissues elsewhere in the body to release their hormones are called tropic hormones Their rate of secretion is controlled by releasing hormones from the hypothalamus These hypothalamic hormones are produced by neurosecretory cells and released into the capillary bed known as the hypothalamicpituitary portal system which is located in the median eminence Complete the following table of releasing hormones tropic hormones targets and hormonal responses 39 3 Releasing hormone Anterior pituitary hormone Primary Target S hormonal target response Corticotropin Adrenal Glucocorticoids and Adrenocortlcotroplc hormone releasrng hormone cortex mineralocortrcords Pmlacnnmhlbmng Prolactin Mammary None identi ed factor glands Gonadotropin Luteinizing hormone and Testosterone estrogen Gonads releasrng hormone folllclestlmulatlng hormone progesterone somatocnilm and Growth hormone Bones Somatomedin from liver somatostatrn Thyrotropin Thyroidstimulating hormone Thyroid Thyroid hormones releasrng hormone True to its name GH or growth hormone stimulates the development of cells by altering protein metabolism GH is secreted particularly during sleep GH secretion is under hypothalamic control and also can be modulated by a substance called ghrelin which is secreted by the stomach The two gonadotropins gonadtropic hormones are LH which is short for luteinizing hormone and FSH which is short for folliclestimulating hormone In females FSH induces the release of estrogen and LH prepares the uterus for implantation In males FSH stimulates sperm production and LH induces testosterone release A prominent role of prolactin is the stimulation of mammary development for lactation in female mammals although it has different roles in other vertebrates Psychosocial dwarfism is caused by extreme social and familial deprivation during development and is marked by three hormonal changes de cient GH secretion abnormally low levels of somatomedin and excessive adrenocorticoid secretion The adrenal glands are located on top of the kidneys Each consists of two divisions 1 an outer cortex which secretes hormones known collectively as the adrenocorticoids under the control of the pituitary hormone ACTH and 2 an inner medulla which releases amine hormones under the control of nerve impulses from the sympathetic nervous system For each of the following items indicate if it is a product of the adrenal cortex AC or the adrenal medulla AM Amine hormonesiAM GlucocorticoidiAC EpinephrineiAM Steroid hormonesiAC MineralocorticoidiAC NorepinephrineiAM AndrostenedioneiAC QP39HeP NE C01tisol is a glucocorticoid involved in metabolism and the control of in ammation Androstenedione is a sex hormone that contributes to secondary sexual characteristics such as body hair distribution Aldosterone is a mineralocorticoid involved in sodium balance The major regulating mechanism for thyroid hormone secretion is a negative feedback system in which the thyroid hormones act directly on the pituitary to reduce TSH secretion This system is balanced against the secretion of thyrotropin releasing hormone by the hypothalamus The major role of the thyroid hormones is the control of metabolic processes within cells Deficient secretion of thyroid hormones during development leads to cretinism characterized by deficient growth reduced brain size and mental retardation Inadequate dietary supply of iodine provokes enlargement of the thyroid called a goiter in response to steadily increasing levels of TSH Within the testes the Leydig cells produce the steroid hormone testosterone under the control of the pituitary tropic hormone LH The Sertoli cells of the testes produce sperm Production of steroids by the ovaries occurs in cycles under the control of the two gonadotropins LH and FSH The two primary classes of ovarian steroids are the estrogens the most important of which is estradiol and the progestins the most important of which is progesterone FSH stimulates growth of the ovarian follicle whereas LH selectively affects the corpus luteum Oral contraceptives contain steroids that exert a negative feedback effect on the hypothalamus thus inhibiting the release of GnRH The primary secretion of the pineal gland is melatonin which is an amine hormone and is regulated by sympathetic activity via the superior cervical ganglion The pineal is located in the midline on top of the brainstem and surrounded by the cerebral hemispheres Melatonin is secreted at night and melatonin secretion tracks day length In seasonal breeders this variation governs the regression of the gonads which respond to changes in the feedback sensitivity of the hypothalamus to steroid levels The pineal in birds is sometimes called the third eye because its photosensitive cells respond directly to light coming through the thin skull In humans melatonin administration induces sleep sooner than usual and may be helpful in treating jet lag Oxytocin released during delivery in mice appears to protect fetal neurons from injury and improves the mother s ability to navigate a maze During orgasm both men and women release oxytocin and rodents given supplementary doses of oxytocin spend more time in physical contact with each other Male mice with the oxytocin gene knocked out are unable to produce the hormone and display social amnesiaithey seem able to recognize the scent of female mice they ve met before In female mice there is evidence that the oxytocin released during delivery and lactation may improve the mother s ability to navigate a maze In the prairie vole Microtus ochrogaster in which couples form stable monogamous pair bonds infusions of oxytocin in the brains of females help them bond to their mates In male prairie voles vasopressin facilitates their forming a preference for their female partners in fact the distribution of receptors for this hormone in the brains of male prairie voles may account for their monogamy In the closely related montane voles M pennsylvanicus which have multiple mating partners the males have far fewer vasopressin receptors in certain brain regions Review Table 53 For each of the following endocrine abnormalities identify their effects on cognition and emotion and their role in psychiatric disorders Problem Cognitive Impairment Anxiety Depression Psychosis Hypercortisolism sometimes often often often Hyperthyroidism sometimes often sometimes sometimes Panhypopituitarism none sometimes often often Hypocortisolism none sometimes often often Hyperinsulinism sometimes often none often One of the keys to understanding the functioning of the endocrine system is to appreciate that it acts in concert with the nervous system to produce integrated adaptive responses to the environment in both the short and longer term In many ways the hypothalamus of the brain can be considered the interface between the neural and hormonal systems since the neural impulses generated by incoming information from brain regions such as the cortex and the cerebellum are translated here into hormonal changes In the fightor ight response the nervous system controls muscular activity but the hormonal system mobilizes energy In the milk letdown response which is mediated by oxytocin environmental cues translated into neural impulses bring about the hormonal secretions required for nursing Complete the following statements illustrating the four types of communication between the neural and hormonal systems that are involved in the mating behavior of the ringdove l Neuraltoneural communicationiVisual perception of a female by a male ring dove comes about by this means of communication 2 Neuraltoendocrine communicationirlhe visual stimulus provokes release of LH by secretory cells in the male s hypothalamus and pituitary 3 Endocrinetoendocrine communicationiThe secreted LH provokes the production and release of testosterone by the gonads of the male 4 Endocrinetoneural communicationiTestosterone alters the excitability of neurons in the male resulting in the display of courtship behavior CH 8 The sensory worlds of different species are very different from our own and suited to each species ecological requirements What can the following animals detect that humans cannot l Snakesiinfrared radiation 2 Batsiultrasound Specialized body components collectively called sensory receptor organs are sensitive to energies of various sorts that come into contact with the body The job of these organs is to convert environmental energy into electrical signals There is great diversity in receptor organs across species re ecting the particular ecology of each species For example some migratory animals can sense magnetic elds some snakes have detectors adapted to perceiving infrared radiation and some species of fish are sensitive to electricity The type of stimulus for which a given sensory receptor organ is adapted is termed the adequate stimulus In the case of the human eye this stimulus is photic Humans do not hear sounds above 20000 Hz The type of sound above this range is ultrasonic Electricity is considered an adequate stimulus for the eye false An illusory sensation of light is called a phosphene Complete the following statements about hearing in different classes of animals based on Figure 1 Fish hearing is adapted to much lower frequencies than that of humans with best detection typically below 1000 Hz and little sensitivity above 1100 Hz 2 Birds and humans have similar auditory sensitivity with peak detection in the range of about 500 to 4000 Hz 3 Humans are least sensitive to lowfrequency sounds The idea that each sense has its own unique receptors and independent neural channels is called the doctrine of speci c nerve energies If you press on your eye you will experience various whorls of color and shapes this phenomenon is consistent with this doctrine The concept of labeled lines states that particular nerve cells are at the outset labeled for distinctive sensory experiences The notion of a labeled line refers to the idea that the sensory qualities of any particular sensory afferent are predetermined For instance activity in the touch receptor pathway can be perceived as touch only A receptor cell is a specialized device for detecting particular energies or chemicals Such cells produce a change in their membrane potential when exposed to an adequate stimulus a process formally known as sensory transduction The change in the membrane potential of the receptor cell when it is stimulated is called a generator potential which in many ways is similar to an EPSP Since these changes are the sole means of transducing environmental signals into a neural code they are said to be necessary and suf cient for generating nerve impulses Work on the Pacinian corpuscles has revealed that they produce a graded electrical potential in response to mechanical stimulation and that the amplitude of this potential is directly proportional to the strength of the stimulus Mechanical stimulation causes the Pacinian corpuscle to deform which stretches the tip of the axon embedded within it This causes mechanically gated Na channels in the cell membrane to open leading to a depolarization Whereas early investigators thought that sensory nerves transmit accurate information to brain centers we now know that a good deal of processing and transforming of sensory information occurs in the peripheral nervous system The first step in the processing of sensory information is the conversion of stimuli into patterns of impulses a process called coding Because action potentials are allornone they are akin to digital information Sensory information is therefore encoded in the frequency of action potentials or in the rhythms in clusters of action potentials The maximal rate of firing for an individual neuron is about 1200 per second Once a cell reaches its maximum firing rate it is no longer able to convey any new information Therefore either the range of stimulus intensities that the cell can encode is limited to a small subset of all the possible intensities or else the sensory cell may encode the whole range but only in large steps One solution is to recruit additional cells as stimulus intensity increases allowing more cells to fire A different solution is to use an array of receptors each of which is sensitive only to one part of the complete spectrum of stimulus intensities In this latter case as stimulus intensity increases different cells fire a solution called range fractionation In order for a sensory system to avoid being overwhelmed by sheer volume it needs to have the ability to selectively not respond to some of the stimuli that impinge upon it One way of determining the location of a stimulus involves the use of a spatial array of receptors For touch receptors are arrayed across the skin for vision they are arrayed across the retina In either case if a receptor is stimulated within the array the location in the array is encoded relative to the rest of the array This information is passed on to brain mechanisms that are generally arranged like topographic maps Another way of determining location involves the use of bilateral receptor systems In auditory localization of a stimulus for example the information processing involves comparison between receptors on the left and right Disparities in amplitude time of arrival and so on encode the position of the stimulus In many sensory systems receptors show progressively less and less response to a stimulus that continues unchanged for some period of time This process is called adaptation and is characteristic of phasic receptors but not tonic receptors The process of adaptation underscores the idea that the sensory system does not provide an accurate re ection of what is going on in the environment Adaptation is useful in two key ways 1 It prevents the nervous system from being overwhelmed 2 It lters out unchanging stimuli Adaptation involves both neural and nonneural events In some receptors adaptation involves a change in the generator potential of the cell In contrast if the accessory cell of a Pacinian corpuscle is removed leaving only the free nerve ending mechanical stimulation produces a sustained discharge of nerve impulses Evidently adaptation in the Pacinian corpuscle is a mechanical property of the corpuscle Each sensory modality has a distinct collection of tracts and stations in the brain that are collectively known as the sensory pathway for that modality Identify two major ways of suppressing sensory inputs 1 Accessory structures can limit sensitivity for instance closing the eyelids reduces photic input Higher nervoussystem centers can exercise direct neural inhibition of sensory pathways for example descending brain projections can inhibit pain signals at the level of the spinal cord N A midbrain way station that relays sensory information in several modalities is the thalamus Sensory information enters the CNS through the brainstem and then reaches the thalamus The thalamus shares the information with the cerebral cortex which directs the thalamus to suppress some sensations Primary sensory cortex swaps information with nonprimary sensory cortex The olfactory sensory system does not go through the thalamus on the way to primary sensory cortex The somatosensory information that enters the nervous system travels upward in divergent pathways and may therefore connect to numerous representations of that sensory modality at various levels of the nervous system These representations are often laid out like topographical maps of the body and they may be studied by recording the electrical activity of their constituent cells A cortical neuron can be individually recorded by means of an intracranial recording electrode The receptive elds for the cell are mapped by stimulating the periphery in this case the skin while recording the frequency of neural impulses generated by the cell when the stimulation falls in the center and in the surround of the cell s receptive eld Receptive elds vary in size true shape true and the stimulus properties to which they respond true Cells at many levels of the brain not just cortical cells exhibit receptive elds true The most recent evidence suggests that brain regions representing the same receptive surfaces nevertheless receive different inputs and process information differently Complete the following statements supporting this position 1 The different representations of the same receptive surface tend to receive sensory inputs from different divisions of the thalamus 2 The maps all tend to be orderly but they differ in their internal arrangement For each sensory modality one particular cortical representation is typically referred to as the primary sensory cortex It provides input to other regions designated secondary cortex although these regions also typically receive their own unique inputs directly from the thalamus the main way station for sensory information Primary somatosensory cortex is also known as S 1 and it maps the opposite side of the body Nonprimary somatosensory cortex is also referred to as S II and it maps both sides of the body Individual neurons that respond to inputs in more than one sensory modality such as touch and vision are termed polymodal neurons For example recent evidence indicates that humans detect a visual object more accurately if it is accompanied by a sound emanating from the same location There is a lack of agreement on the nature of attention Complete the following statements regarding three competing models of attention 1 A generalized arousal mechanism may enable an animal to pay close attention to all inputs from the environment 2 A mental process may allow for selection of particular sensory inputs to be attended to A state of mental concentration may direct one s attention to a particular task like a mental spotlight while casting others in a shadow E One brain region that has been especially implicated in attentional processes is the posterior parietal lobe This area contains many polymodal neurons that track environmental events in several different sensory modalities Lesions in this region result in neglect of stimuli on the other side of the body The cingulate is are implicated in motivational aspects of attention the posterior parietal lobe is are implicated in attention to spatial locations the frontal eye fields is are implicated in visual exploration of space What is the explanation for the peculiar appearance of the homunculus in Figure 810 The somatosensory cortex is a1ranged as an orderly map of the body surface and all pa1ts of the body are not represented equally The most sensitive parts of the body contain the highest densities of receptors and therefore account for larger amounts of the sensory cortex CH 19 There are about 7000 different languages in the world of which only about 1000 have been studied The sounds that make up a language are called phonemes and the set of rules that govern how they are put together to form sentences is called grammar Humans are remarkably sensitive to speech sounds We can distinguish the sounds of different languages at birth Babies start paying special attention to sentences with unfamiliar structure by 7 months suggesting that at this point they understand grammar People with a specific mutation of the gene FOXPZ take a long time to learn to speak and display longlasting difficulties with particular language tasks Children raised in isolation develop no language implying that there is a sensitive period for language acquisition This period probably closes at about 11 years of age because learning a second language after this point activates different brain regions compared to those activated by the first language People who learn a second language early in life tend to exhibit better uency in that language than people who learn a second language later Some theories concerning the origins of verbal communication argue that speech and language may have evolved from gestures Some experimental data support this position For example preventing people from gesturing causes them to make speech errors In general studies of nonhuman vocalization may provide clues about the basic control and evolution of human language Birdsong probably is not an evolutionary precursor to human language this is an example of analogy In male songbirds song acquisition proceeds by three stages 1 exposure to a tutor usually the father 2 successive approximations ie practice and 3 the crystallization of the acquired song This process is complete by about 90 days of age which corresponds to sexual maturity A developing songbird that is deafened during this sensitive period produces abnormal song The songs of adult birds can be changed on the basis of feedback The selection of a tutor from which a young bird learns its song is governed by social stimuli The main songproducing organ of songbirds is the syrinx which is directly controlled by the RA which in turn is controlled by the HVC Lesions of the LMAN seem to specifically disrupt song development only in adolescents Furthermore there is an asymmetry in this system cutting the left twelfth cranial nerve disrupts song production but cutting it on the other side does not This asymmetry extends to the brain lesions in the left hemisphere s songcontrol system have marked effects on song production In squirrel monkeys stimulation of regions of the limbic system can produce vocalizations but stimulation of regions of the cortex generally does not Monkeys tend to favor the right ear When listening to the vocalizations of conspecifics Chimpanzees appear to be capable of learning ASL short for American Sign Language and one researcher claimed that a gorilla learned a vocabulary of hundreds of signs Fill in the blanks in the following brief overview of the ape language employed for training apes Yerkish is a computerbased symbol language involving the use of combinations of different keys on a console to communicate novel chains of concepts On the basis of studies in which apes have learned many words in this language some researchers have claimed that language comprehension may have preceded speech production by millions of years Some researchers have noted that while chimps may generate series of symbols their language behavior lacks grammar and their use of language seems to re ect subtle imitation In about 90 to 95 of cases of language impairment due to brain damage the damage involves the left hemisphere In an important nineteenthcentury case study of a man who lost the ability to speak postmortem examination showed that the patient had suffered damage to the inferior frontal part of the left hemisphere That region is now known as Broca s area after the neurologist who conducted the study The most common symptom of aphasia is the production of an incorrect sound or word when another was intended this is called paraphasia At times an entirely new wordlike utterancei called an neologismimay be produced due to the substitution of phonemes Additional symptoms may include aleXia which is a difficulty with reading and agraphia which is difficulty with writing Some aphasias are nonfluent meaning that speech is truncated labored and nonconversational if it is produced at all In uent aphasia an overabundance of speech may be produced but it is full of errors Brain lesions that produce aphasia also produce apraxia an inability to execute smooth movements in the absence of any apparent weakness In the Wada test the drug sodium amytal is injected directly into the carotid artery supplying one hemisphere and later the same procedure is followed for the other hemisphere Sodium amytal is an anesthetic and it produces a reversible lesionithe hemisphere on the side of the injection essentially shuts down Ifthe injected hemisphere contains language mechanisms the patient will show characteristic language disturbances during this time such as speech arrest Complete the following table on the symptoms of the major classifications of aphasia Broca s aphasia Wernicke s aphasia Quantity of speech produced little uent Quality of speech labored if any much paraphasia Comprehension usually good impaired Reading often impaired often impaired Writing usually impaired Motor problems hemiplegia apraxia Associated brain damage left anterior left temporoparietal Global aphasia Conduction aphasia Quantity of speech produced little uent Quality of speech labored if any impaired repetition Comprehension impaired usually good Reading often impaired Writing usually impaired Motor problems Associated brain damage left frontal temporal parietal arcuate fasciculus The traditional WernickeGeschwind model of aphasia is a connectionist model According to this view language disturbances occur when communication between areas is severed for instance lesions of the angular gyrus which spans between visual areas and Wernicke s area result in difficulty reading aloud ASL consists of both an elaborate set of signs that convey meaning and formal rules grammar for arranging these signs Compared to spoken language ASL is at least as complicated for instance ASL does have dialects Researchers have been interested in ASL users because if hardwired language mechanisms exist in the brain one might expect that a visual form of language would depend on them The neural mechanisms involved in signed and verbal language are fundamentally similar Research evidence supporting this conclusion includes the observations that l damage to the left hemisphere in a man uent in both verbal and signed languages resulted in similar impairments in both languages 2 damage to temporal lobe language areas impaired signing ability in a deaf woman and 3 in three deaf signers with lesions of differing parts of the left hemisphere language impairments paralleled the impairments of verballanguage users who had suffered damage to the same areas Recent imaging work shows extensive activation of the right hemisphere during signing The neural mechanisms underlying ASL therefore remain controversial Dyslexia tends to be more prevalent in males and left handed people and it appears to be unrelated to IQ Abnormalities that probably occurred during fetal development are observed in the brain tissue of people with dyslexia Complete the following statements about the brain abnormalities seen in dyslexia l The regions of the brain that tend to be particularly affected are the frontal and temporal cortical regions 2 Cortical layers are grossly abnormal especially featuring abnormal groupings of cells in outer layers that distort layers and columns 3 Under a microscope neurons are often disoriented 4 There is abnormal excessive folding of the cortex called micropolygyria and abnormal nests of cells called ectopias 5 It is thought that the normal developmental process that has been disrupted is cell migration More recently fMRI studies of brain activity suggest that the posterior language area of the brain of people with dyslexia is underactivated during reading while an abnormal increase in activity in the region of the anterior area is evident Patients with dyslexia also show abnormal transmission across the angular gyrus when reading Recently 4 different genes have been implicated in dyslexia The DYXCl gene has been implicated in Finnish family members with dyslexia and in 9 of the general population Reading a word as an entirely different but related word for instance cow may be read as horseisame category wrong word is an example of deep dyslexia Pioneering research on the effects of electrical stimulation of the brain showed that stimulation within large anterior regions of the left hemisphere often results in speech arrest and that other effects on language such as misnaming and poor repetition may result from stimulation of anterior or posterior temporoparietal regions of the left hemisphere Complete the following statements summarizing stimulation mapping experiments performed by Ojemann and colleagues 1 Stimulation revealed that separate areas are involved in English versus Spanish speech errors in a bilingual subject 2 Stimulation of the anterior inferior premotor area causes speech arrest and impaired facial movements this area may be a final common output zone 3 Stimulation of broad regions in frontal temporal and parietal regions may produce impairments of sequential facial movements and phoneme identification 4 Subtractive PET scan imaging has been used to study the areas of the brain activated during successively more difficult verbal tasks Complete the following table describing the four experiments Verbal task Brain regions activated Passive exposure to visually posterior left hemisphere presented words Passive exposure to spoken words left temporal region Oral repetition of words bllateral motor and supplementary motor c01tex msula and cerebellum Generation of semantically Broca s area posterior temporal and cerebellar areas assoc1ated words Native speakers of Italian reading aloud in Italian use slightly different brain regions from those used by native English speakers reading aloud in English This may be attributable to more irregular speech sounds in English Imaging research suggests that different categories of verbal material are stored in different regions of the brain particularly in the frontal lobes In ERP studies it has been found that sentences containing a word that is grammatically correct but with a meaning that does not fit the sentence provoke an N400 wave which is centered over the temporal lobe of the left hemisphere A grammatically incorrect word however induces the appearance of an P600 wave originating in a different region of the brain Williams syndrome results from the deletion of one copyies of more than a dozen genes found on chromosome number 7 People with this disorder exhibit el ike features due to the absence of a protein encoded by a gene named elastin They have better than average mathematical ability and poor language ability in early childhood In adulthood they show good language ability and poor mathematical ability A brain asymmetry in the region called the planum temporale which is involved in language has been noted in both humans and chimps Historical analyses of the function of the two hemispheres considered the left hemisphere dominant more recently it has been recognized that various intellectual functions are lateralized This pattern of function is usually masked in the normal functioning of the individual due to the interconnections of the two hemispheres This masking is reduced or absent in splitbrain patients The splitbrain procedure performed as atreatment for epilepsy involves transection of the corpus callosum Such surgery has no obvious effect on IQ scores After such surgery stimuli presented to one side of the body tend to be processed only by the hemisphere on the other side In splitbrain cats who have also undergone a transection of the optic chiasm each eye is connected only to the hemisphere on the same side of the body In one such experiment cats using just the left eye learned that an upright symbol but not an inverted one signified reward and then with the right eye they were able to learn the reverse This study implies that each hemisphere can learn a different rule without interference from the other hemisphere Studies of right handed splitbrain patients have revealed 1 that reading and speaking are unimpaired when information is presented to the left hemisphere 2 the right hemisphere has limited linguistic ability including a vocabulary and 3 the right hemisphere outstrips the left hemisphere on tests that emphasize spatial relations Tests of lateralization of function in which different stimuli are presented to the left and right ears simultaneously are called dichotic listening tests Each ear has a stronger and more direct connection with the auditory areas of the hemisphere on the other side of the body Consequently stimuli presented to the right ear would be expected to be preferentially processed by the left hemisphere and vice versa Using this technique a rightear advantage has been found for verbal material in righthanded individuals implying that verbal material is preferentially processed by the left hemisphere Visual stimuli can be presented to just one hemisphere if the stimuli are ashed for less than 100 to 150 ms in just one visual halffield The right visual halffield is processed by the left hemisphere and the left halffield by the right hemisphere Verbal material presented in the right halffield is processed better than the same material presented in the other halffield The reverse pattern is found for material such as faces and forms Visual information such as light hue and simple patterns is processed equally well in the left and right half fields Early work showed that the planum temporale which is located on the superior surface of the temporal lobe is larger on the left in 65 of adults and larger on the right in 11 of adults The degree of asymmetry tends to be lesser in lefthanders This asymmetry may re ect the importance of the left hemisphere for language functions as lesions of this region in the left hemisphere tend to impair speech perception The asymmetry also appears to be present in fetuses by about the 30th week of gestation Using MRI the shape of the planum temporale has been studied in relation to musical ability in three groups of experimental subjects 1 nonmusicians who showed normal asymmetry 2 musicians without perfect pitch who showed an intermediate degree of asymmetry and 3 musicians with perfect pitch who showed an exaggerated leftward asymmetry Musical ability is more seriously impaired by right hemisphere damage than by damage to the opposite hemisphere Damage to both hemispheres can abolish music ability altogether It has been estimated that 10 of people are lefthanded but the actual incidence may be a bit higher In prehistoric humans righthandedness was probably prevalent as the skulls of prey animals tend to show hunting fractures on the left side Complete the following statements about lefthandedness 1 In a comparison of the cognitive abilities of left and righthanded children neither left nor right handers had a slight advantage 2 There is slightly more left handedness in mental retardation In such patients EEG abnormalities are more common in left handers 3 It has been argued that a small proportion of people are left handed as a consequence of early brain damage to one hemisphere which caused handedness to shift to the other hemisphere In the disorder called astereognosis unseen objects placed in the hand opposite the damaged parietal lobe cannot be identified This deficit is not attributable to a loss of sensation on the affected side In prosopagnosia there is a selective loss of the ability to recognize faces recognition of objects may be retained Damage to the right parietal lobe causes prosopagnosia although it is argued that bilateral lesions are required for full expression of the disorder Prosopagnosia for other categories such as types of cars or animals may occur Damage to the fusiforrn gyrus located at the junction between the temporal and occipital may cause impairments in discrimination between types of birds or an inability to recognize individual faces Such damage may be accompanied by agnosia an inability to identify objects The characteristic pattern of progressive cognitive impairment that emerges in many boxers is formally known as dementia pugilistica A study described in the text looked at CT scan data for ten boxers varying in age and success all of whom had been knocked out Abnormalities were found in the brains of 50 of these boxers A more recent MRI study of 338 boxers clearly revealed atrophic changes in 7 and borderline damage in a further 12 Mild symptomatology is also observed in players of soccer Following brain lesions that cause aphasia there is usually some recovery of function The degree of language recovery may be predicted by several factors For instance recovery is better if the damage was caused by trauma and left handed people tend to show better recovery Most language recovery in aphasia takes place during the period up to 3 months following the brain injury and recovery tends to be negligible after 1 year Recent work raises the possibility that we may be able to use undifferentiated cells known as embryonic stem cells as replacements for neurons lost to damage or disease This research is very controversial because currently the main source of these cells is human fetuses although we may soon be able to grow these cells in culture In considering the effects of training on recovery of function after CNS damage it is important to be able to distinguish between actual restoration of function and compensation as an example of the latter patients can be trained to make large eye movements if they have large scotomata Nevertheless recent work suggests that training may restore at least partial ability to walk after spinal injury for example Forcing a recovering stroke patient to use an affected limb by splinting the good limb is called constraintinducedm0vement therapy Recent research found that patients receiving this treatment showed about 75 recovery of function in the affected limb within two weeks and a corresponding remapping of motor cortex
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