Cog Neuro Exam 1 Study Guide
Cog Neuro Exam 1 Study Guide PSYC 3122
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This 36 page Study Guide was uploaded by Freddi Marsillo on Sunday October 2, 2016. The Study Guide belongs to PSYC 3122 at George Washington University taught by Dr. Shomstein in Fall 2016. Since its upload, it has received 50 views. For similar materials see Cognitive Neuroscience in Psychology at George Washington University.
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Date Created: 10/02/16
Cog Neuro Exam 1 Study Guide 10/2/16 4:31 PM What is Cognitive Neuroscience? • Cognition o Variety of higher mental processes (thinking, perceiving, imagining, speaking, acting, planning, etc.) • Neuroscience o Biological investigations of the brain Cognitive Neuroscience consists of cognitive science, cognitive psychology, biology, and neuroscience (it is an interdisciplinary field) Multiple memory systems • Long-term memory o Declarative memory (explicit memory) • Short-term memory o Sensory memory o Short-term/working memory Localization vs. Mass Action • ▯ Localization wins (has the most evidence) o Different parts of the brain have different functions Cajal’s Neuron Doctrine • Individual cells (neurons) with small gaps • Connectional specificity o Connections not random but specific pathways/circuits • Dynamic polarization o Parts of neurons take in information o Parts send information Building Blocks Neurons • Like other cells but some specific properties Glia • Non-neural cells playing supportive function Neurons 100-1,000 billion neurons in the brain • Each makes ~1000 connections (on average) What do neurons do with all that information? • Collect input • Process/decide in some way • Produce output • Transmit information over a distance (big toe to spinal cord) Postsynaptic versus presynaptic neurons • Presynaptic – neuron that sends info to another neuron • Postsynaptic – the neuron that receives the information o Once that neuron has the information, it then becomes the presynaptic neuron Neuron: Soma Soma • Cell body • Metabolic machinery o Nucleus, ribosomes, mitochondria, Golgi apparatus o Enclosed in membrane, suspended in cytoplasmic fluid Neuron: Dendrites Dendrites – afferent (accepting) • Receive input from neurons at synapses (postsynaptic) • Treelike – may be large arbors (Purkinje) or small (thalamus) • Spiny endings Neuron: Axons Axons – efferent (entering) • Before synapse (presynaptic) • Communicates output of neuron • Originates at axon hillock • Insulated with myelin sheaths • Ends at presynaptic terminal button • Release neurotransmitters Glia = “nerve glue” • There are ten times more glia in the brain than neurons • Brain volume • Support systems for neurons o Guide growth o Remove metabolic waste o Grow and maintain myelin sheaths Central Nervous System (CNS) – different types of Glia • Astrocytes • Microglia • Oligodendrocytes Astrocytes • Surround neuron • Form blood-brain barrier – they protect neurons from any type of bleeding that can occur from the blood vessels – brain is protected from blood • Dopamine cannot cross but L-dopa, precursor, can • Blood-brain barrier is very selective in what it lets pass into brain Microglia • Assist in repair • Proliferate (multiply rapidly) in damaged region • Phagocytic function – remove waste Oligodendrocytes • Produce myelin • Generate axon potentials Neuronal Signaling • Communication between neurons • Input contact at dendrites (or cell body) o Synapse at terminals • Output from axon terminals • Long and local distance circuits of networks How it works – the overview • Neurons receive chemical or electrical signal • Signals change membrane of postsynaptic neuron • Changes in flow of electrical currents • Neuron integrates signals • Triggers spike or action potential • Travels down axon • Releases neurotransmitter Neural Membranes • Bilayer of lipids does not dissolve • Barrier to chemicals - ions, proteins, and molecules – that are floating in the extracellular space (outside the cell) and intracellular space (inside the cell) • Bilayer is permeable – some things can pass through Neural Membranes • Resting potential • Voltage differences (-70mV) across membrane Membranes Ion channels • Non-gated: passive (more potassium K+) than sodium (Na+ or Cl-) – selective permeability • Gated: opened/closed by stimuli (electrical, chemical, or physical) Concentration of Ions Ionic (chemical) gradient • More Na+ outside, more K+ inside • Membrane is more permeable to K+ • Some K+ escapes to the outside Electrical gradient • As K+ escapes out, the inside of the cell becomes more negative • As the inside becomes more negative, it is harder for K+ to escape • The struggle continues until electrochemical equilibrium is achieved Resting Potential • Electrical current ionic (charged atoms = ions) o Na+, K+, Cl-; also some large charged proteins in solution • Electrochemical equilibrium o More Na+ outside and K+ inside o Membrane more permeable to K+ o K+ tries to move out o Electrical gradient develops ▯ + move out and so remaining – attracts positives o Electrical and ionic concentration in opposition but balance Conduction Conductors • Cytoplasm and extracellular fluid Insulators • Membranes with variable resistances • Myelin is a great insulator Active/passive currents Synapse activated • Electrical currents generated • Flows in local region Passive currents across postsynaptic membrane through dendrites and soma If current is strong, ▯ action potential If not, passive flow and decrement (reduction) in current (bad for long distance communications) Action Potential Long distance communication • Regenerative electrical signals Action potential • Rapid depolarization and repolarization of membrane in local area • If sufficient potential, cross threshold • All or none once crossed threshold So, what happens? • Voltage gated ion channels open when membrane is depolarized • Opens and lets some Na+ in, further depolarizes • Lets in more Na+ etc. THEN • Open voltage = gated K+ channels • Repolarizes • Overshoots resting as repolarizes (hyperpolarizes) • Refractory period Neurotransmitters • Synthesized by presynaptic neuron • Transported to axon terminal • Stored in vesicles • Binds with postsynaptic neuron • At cleft o Active reuptake o Enzymatic breakdown o Diffusion Terminology *Dorsal means top – it also means superior *Ventral means bottom – it also means inferior *Rostral and anterior mean towards the front *Caudal and posterior mean toward the back *Superior – top; inferior – bottom *Sagittal – straightforward; middle of the brain Gray matter • Cell bodies of neurons and glia White matter • Myelin surrounding axons Corpus callosum connects the two hemispheres Cortex = the bark of the brain • Increase surface area: gyri and sulci • Reduce axonal distance • Multiple layers o But only 3 mm thick o Neurons o Dendrites o Some axons Cortical Lobes 4 lobes: frontal, parietal, temporal, and occipital • Central sulcus: frontal/parietal • Lateral Sylvian fissure: temporal from frontal and parietal • Parieto-occipital sulcus: occipital from parietal and temporal • Corpus callosum; longitudinal fissure (“hard body”) – divides the lobes Motor Cortex • Frontal lobe • Motor cortex – Betz cell Somatosensory – parietal • Touch, pain, temperature, limb proprioception Auditory cortex • Lateral view of the left hemisphere Visual Cortex • Primary visual cortex = V1 Limbic System The Limbic System: for emotional processing, memory, learning • Surrounds brain stem; older cortex • Also called mesocortex Basal Ganglia: Function is motor control Thalamus • Gateway to the cortex: modalities make synaptic relay • LGN = visual; MGN = auditory • Ventral posterior nuclei (VPN) = somatosensory • Receives input from basal ganglia, cerebellum, medial temporal lobe Hypothalamus • Endocrine regulation • Vasopressin (kidneys); oxytocin (arousal); circadian rhythms Cerebral spinal fluid produced in the ventricles • Cerebral spinal fluid acts as a cushion between skull and brain • Protective layer • If impact is too hard, concussion can occur Pre-central gyrus = primary motor cortex function Post-central gyrus = primary somatosensory function – touch, pain, pressure, temperature, limb proprioception (the signal that’s projected into the brain about where your muscles and joints are relative to your body – for example, if you close your eyes, you know exactly where your hands are) Cognitive Psychology Construction and reconstruction of biologically relevant aspects of the external world • There is not an isomorphic relationship between the world and how you see it – the brain makes assumptions (often wrong assumptions) • Isomorphic = identical/similar Mental Operations Stroop task • See names of colors written in different colors (e.g. the word RED in blue ink) • Task is to say the name of the color, not to read the word • Interference from word • Reading is an automatic process • Reduction if response is manual, not verbal • Reduce interference with dual task or with practice Techniques with animals Careful experimental (unlike human lesions) • Control lesion • Measure neural activity • Examine physiology • Intracellular best but difficult o A probe is inserted into the cell body • Extracellular most frequent o Likely small set of neurons at once Single Unit Recording What is baseline activity? (What is the cell doing at rest?) • Measure changes to experimental manipulation • What increases or decreases firing? • When a cell fires, it increases action potential Animal Lesions • Neural structure contributes to task o Lesion ▯ impairs performance on task • Necessary for task • Some caveats o Area may be bypassed to other regions and not involved itself o Animal may learn to compensate for deficit so system is reorganized Procedure • Aspirate tissue (draw out tissue from brain) • Electrolytic lesion: electrical charge • Chemical lesion: kainic affects cell bodies only • Reversible lesion o Cooling o Pharmacological Neurology • As in Broca and Wernicke • Link cognitive processes to neural structures o Harder to do with diffuse lesions o Focal lesions are best • Appropriate diagnosis Computed Tomography (CT): Structure • Like an x-ray but from all possible directions • Intervening tissue absorb radiation (bone a lot; blood a little) • Reconstruct differential absorption Magnetic Resonance Imaging (MRI) • Measures magnetic properties of organic tissue • Protons of hydrogen atoms spinning, weak field, random orientation • In scanner, all protons aligned • Perturb with radio waves, absorb energy and spin • Measure relaxation: different tissues, different relaxation rates Acquiring Brain Damage • Neurosurgery – severe epilepsy (HM, split brain) • Strokes (or cerebrovascular accident; CVA), aneurysm • Traumatic head injuries – most common in under 40 year old males • Tumors – new cells are produced in a poorly regulated manner o Tumors are formed from supporting cells (meningiomas and gliomas) o Pressure is applied to neurons disrupting functioning and leading to cell death • Neurodegenerative disorders – 1900 4% over 65 years old; in 2030 20% will be over 65. Alzheimer’s, Parkinson’s, Huntington’s, dementia, etc. • Deprivation of oxygen o Embolism (blockage) o Aneurysm (dilation of a blood vessel) o Ischemia (occlusion) • Tumors Degenerative and Infectious Parkinson’s • Dopaminergic cell death Alzheimer’s • 5% inherited • Protein overproduction AIDS dementia (lesions within white matter) – not STD Herpes simplex (cortical and limbic structures) – not STD Multiple sclerosis (white matter) HIV-1 encephalopathy and AIDS dementia complex (ADC) – CT scan of the brain of a patient with ADC shows diffuse atrophy and ventricular enlargement and attenuation of periventricular white matter MRI scanning provides detailed pictures of the brain and spinal cord. Areas of scar tissue may be identified as MS lesions Highlighted areas of scar tissue within the brain cells Other Cortical Problems Trauma Functional neurosurgery Epilepsy Neuropsychology – Single Dissociation Patient AA • Temporal lobe damage in the vicinity of Fusiform gyrus (the area in the brain that recognizes faces) Patient BB • Temporal lobe damage – inferior temporal cortex (IT) – low and up front in brain o Damage is bilateral o Patients may experience difference between faces but not objects Neuropsychology – Double Dissociation Patients AA & BB • Patient AA performed very poorly on processing faces – face processing is impaired • Patient BB 98% accurate on faces, but only 25% accurate on objects • Bilateral IT is responsible for object recognition • Double dissociation allows you to infer that a specific part of the brain is responsible for a specific process Neural Imaging Induced Lesion Method Transcranial Magnetic Stimulation (TMS) • Magnetic pulse delivered to brain via metal coil • Delivers small magnetic field o Perturbs normal functioning of the neurons o Prevents neurons from firing action potentials o Creates a short-lived reversible lesion • Experimenter shows letters on a screen and acts patient to identify letters o When pulse is delivered simultaneously with letter shown, it interferes with processing the identity of the letter o From the onset of the letter, it takes about 100 ms for the info to reach the occipital cortex • Pros: Reversible lesion, great temporal resolution (because you can draw inferences about the timing) • Cons: you are restricted to the superficial surface of the brain, very simple tasks Cognitive Deficits – Lesion Method • Nature’s experiments o Poor control of lesion o Reversible lesion in nonhumans • Groups vs. single case studies vs. multiple case studies o Cases rare o Average data, get nothing • Pros and cons of each o Variability in lesion location, extent; see lesions next o Individual differences and premorbid skills o Etiological differences Functional Imaging: Event-related potentials (ERP) ERP looks at the EEG trace according to a particular event of interest (event- related potential) • Measuring neural activity in response to a particular event EEG traces from a series of trials • Measure: neural activity related (sensory & motor) • Benefit: superb temporal resolution • Drawback: poor spatial resolution Example ERP study • Faces, animal faces, objects • Human faces are processed similarly to animal faces • Takes 170 ms to commute facial recognition Magnetoencephalography (MEG) Synaptic activity produces small magnetic field • Average many trials – event-related fields (ERFs) • Same temporal resolution as ERP o Fantastic temporal resolution • But, more accurate solution to the inverse problems o Inverse problem: the process of calculating from a set of observations the causal factors that produced them MRI vs. fMRI • MRI studies brain anatomy o Very high spatial resolution o Simply one image; static • Functional MRI (fMRI) studies brain function and where in the brain something occurs o Lower spatial resolution o Many images, like a video over time, you can track changes o fMRI – measures Blood Oxygenation Level Dependent (BOLD) signal indirect measure of neural activity – tracking/measuring blood oxygenation o As neural activity increases, there is greater need for blood oxygenation; the more the neuron is working, the more blood oxygen it needs ▯ You are measuring oxygen consumption of the neurons ▯ There is localized change in neural activity that causes local increase in oxygen consumption; this consumption triggers even more blood rushing to the area. Then oxygen is extracted (deoxygenation) and that causes a more uniform magnetic field, and that is what you’re measuring. You are not measuring neuron activity directly. o Neural activity increases ▯ blood oxygen increases ▯ fMRI signal increases The BOLD Effect • Localized change in neural activity • Local increase in oxygen consumption • Local increase in blood flow • Local decrease in deoxyhemoglobin • More uniform local magnetic field • Increase in MR signal fMRI Activation Off for 60 seconds, then on for 60 seconds, repeatedly When flickering checkerboard is on, the posterior part of the brain looks lit up • The signal intensity in the occipital cortex is higher when there is visual stimulus • Even when the stimulus is off, there is still SOME signal intensity. That’s because retinal cells are constantly firing – they need oxygen • If a neuron is alive, it is consuming oxygen A Simple Experiment: LOC Localizer Lateral Occipital Complex (LOC) ▯ responds when subject views object (part of the brain that computes object recognition) fMRI Experiment Stages: Prep • Prepare subject o Consent form o Safety screening o Instructions and practice trials if appropriate Decide on how much brain you want to cover • Number of slices fMRI Experiment Stages: Anatomical Anatomical images • High resolution anatomical images fMRI Experiment Stages: Functionals Functional images • Images are indirectly related to neural activity • Usually lower resolution images Baseline • There really is no baseline • Brain activation levels must always be considered relative to another condition o Many contributing variables to signal strength: inherent metabolic rate, location with respect to the coil, etc.) • Thus, the absolute level of signal is relatively meaningless on its own • Consequence: Neuroimaging experiments rely on subtraction logic to make sense of the data fMRI Experiment Stages: Superimpose • Functional images onto the anatomical images Statistical Analysis • An example of an experiment: objects & scrambled objects & rest o We are looking for areas that show greater activity to objects as compared to scrambled objects Subtraction Logic • Brain activation levels must always be considered relative to another condition o Many contributing variables to signal strength: inherent metabolic rate, location with respect to the coil, etc. • Thus, the absolute level of signal is relatively meaningless on its own • Consequence: Neuroimaging experiments rely on subtraction logic to make sense of the data Subtraction Logic Cognitive subtraction originated with reaction time experiments • Measure the time for a process to occur by comparing two reaction times, one which has the same components as the other + the process of interest Example: • Task 1: Hit a button when you see a light • T2: Hit a button when the light is green but not red • T3: Hit the left button when the light is green and the right button when the light is red • T2 – T1 = time to make discrimination between light color • T3 – T2 = time to make a decision Assumption of pure insertion: you can insert a component process into a task without disrupting the other components Subtraction Logic: Brain Imaging Example: Object recognition area (LOC) localizer T1: View intact objects T2: View scrambled objects Subtract regions of the cortex that activate with the scrambled objects and the regions of the cortex that activate with the intact objects • T2 – T1 = “object” areas Pure insertion • Possible factors added: o Object-selective processing o Attentional salience (objects are more interesting than scrambled objects) o Memory (you’ve seen an apple before but probably not a scrambled apple) fMRI BOLD • An indirect measure of neural activity • Is a ratio of oxygenated hemoglobin to deoxygenated hemoglobin o NOT a direct measurement of neural activity – it is an indirect measure since you’re measuring oxygen consumption of the neurons fMRI results are always based on subtraction logic/pure insertion Statistical Analysis • Are a result of subtraction logic (pure insertion) Spatial Resolution • 2-3mm, very good Temporal resolution • Order of seconds, about a 6 second lag Motor System • Cortex & subcortical (cerebellum & basal ganglia) • Spinal cord o Cortical o Subcortical • To muscles o Effectors: proximal and distal Muscle Signals • Paired agonist and antagonist • Released via acetylcholine • Innervations from own stretch spindles and also spinal cord • Excitatory to one, inhibitory to other Knee Reflex: Stretch Sensory signal ▯ stretch receptor ▯ alpha motor ▯ contract quadriceps Cortex Cortico-spinal tract • Motor neurons from motor cortex • Premotor cortex • Supplementary motor cortex Organization • Topographic • Importance of effectors and precision of movement • Cross body (decussate) at medulla/spinal cord juncture • Hierarchical arrangement o Abstract cortex regulates o Simple reflex at bottom Hierarchy: Cortex and Periphery Sherrington • Cut input from cortex (efferent) • Reflexes exaggerated • Animals still move • Cut sensory root (afferent): no longer move • Sensory feedback crucial Brown • Actually, sensory is not necessary • Humans with neuropathies can still make movements • Although they do make errors and if complex, they are not coordinated • Central pattern generators o Hierarchy ▯ Cortex simply activates pattern generator neurons: command into movement ▯ Postural adjustments Motor Representation Hierarchical sequences • Chunks • Seems non-cognitive, as we cannot verbalize it • Independent of particular muscle group o Several distributed anatomical structures Directional tuning of motor cells • Georgopolous: neurons like particular directions of action Direction of movement (M1 cells) Population Vector Summed activity over all neurons = population vector Population Vector: Action or Intention? ▯ Intention! Motor Planning vs. Execution Hierarchical ideas • Primary and somatosensory activated for simple movements • More complex motor planning: supplementary motor area (SMA) and prefrontal cortex • When you are imagining yourself making these movements: only SMA is activated, because you are not actually making the movement – no muscles are being stretched or flex (abstract motor plan) Evidence from TMS study • You interfere with actual execution of movement o Over motor cortex: movement halted or wrong key pressed o Over SMA: delayed movement Movement occurs when M1 cells fire (nothing else activates movement) Internal vs. External Guidance Internal guidance • “Muscle memory” – you just know what to do • SMA is the major contributor (along with prefrontal cortex) to internal guidance External guidance • You have to see something in order to know what to do with it (for example, you need to read a sign to know where to go) • Premotor cortex (PMC) (visually-guided) is the major contributor to external guidance Internal vs. External Guidance Effects of Learning • New sequences: lateral premotor and prefrontal cortex (the red areas = brain regions that are activated when you are just learning a new task) • Previously learned sequences: activate SMA and hippocampus (the blue areas = the brain regions that activate after you’ve already learned) o Hippocampus is activated because it is involved with memory Summary • Parallel circuits • Parietal, PMC (and cerebellar) ▯ spatially directed or guided movement, dominate in early acquisition • SMA (and basal ganglia) ▯ when skill is learned and driven by internal representation Functional Analysis ▯ and produce movement Movement Disorders Hemiplegia • Damage in M1 (Example: with damage in left side of M1, it is impossible to move right side of body – reflexes are still there because they do not engage the motor cortex) • Loss of voluntary movement • Reflexes return (but they are hyper, exaggerated – this shows how the cortex, when not damaged, can inhibit muscles so that they do not move accidentally; when you remove the cortex, you remove the inhibition) o Therefore, increased spasticity (increased muscle tone; muscles are overly active) Apraxia (left hemi, parietal) • Loss of motor skill (not muscle related; they have the muscular capability) • They can describe the steps they need to take to carry out an action, but cannot physically carry out that action o Ideomotor – knows sequence but cannot implement o Ideational – disrupted knowledge of action Cerebellum Vestibulocerebellum • Balance, VOR, etc. Spinocerebellum • Sensory info from spinal cord • Also from auditory/visual o Polysensory • Output to spinal cord and motor cortex Neocerebellum • Has inputs from all the regions spinocerebellum has • Innervated by cerebral cortex and goes back to the thalamus; integrating a lot of info that comes from the motor and sensory systems and brings it back to spinal cord and back to the motor cortex • Newest part of cerebellum Cerebellar Lesions Vestibulocerebellum • Damage to this area affects balance Damage to the spinocerebellum • Affects having smooth control of action o Especially axial muscles (body and trunk) o Alcohol • Hypermetria o Good initiation of movement but it’s clumsy, irregular, erratic (like a drunk person) • Neocerebellum o Similar to spinocerebellum but with prolonged initiation (planning role) – difficult to start the movement Cerebellar Atrophy – ataxia Cerebellar function • Not clear – it receives a LOT of inputs • Timing hypothesis (think of cerebellum as a conductor; tells each muscle when to start and when to stop) – controls the timing of activation of particular muscles Basal Ganglia • Input to basal ganglia is excitatory; output to basal ganglia is inhibitory o Movement initiation/motor control • Function of basal ganglia is to inhibit unwanted movements and to facilitate wanted movements • Inhibition keeps motor system in check, while motor plan is emerging • As specific motor plan is derived, inhibitory signal is decreased for selected neurons Basal Ganglia: Disorders Parkinson’s (damage in the substantia niagra) • Bradykinesia – slowness in execution (initiation) of movements • Hypokinesia – reduction in voluntary movements (hypo = not enough) Huntington’s chorea (striatum) • Clumsiness, balance problems, increase in involuntary movements o Not restricted to the motor system, general dementia Fluorodopa – radioactive tracer Uptake at the striatum Summary 10/2/16 4:31 PM 10/2/16 4:31 PM
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