Cognitive Neuroscience Week 3 Notes
Cognitive Neuroscience Week 3 Notes PSYC 3122
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This 16 page Class Notes was uploaded by Freddi Marsillo on Friday September 16, 2016. The Class Notes belongs to PSYC 3122 at George Washington University taught by Dr. Shomstein in Fall 2016. Since its upload, it has received 21 views. For similar materials see Cognitive Neuroscience in Psychology at George Washington University.
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Date Created: 09/16/16
Cog Neuro Week 3 9/16/16 4:11 PM *Dorsal means top – it also means superior *Ventral means bottom – it also means inferior *Rostral means towards the front *Caudal means toward the back *Superior – top; inferior – bottom *Anterior – front; posterior – back *Sagittal – straightforward; middle of the brain Revealing the brain • Tracts: bundles of axons • Gray matter o Cell bodies of neurons and glia • White matter o Myelin surrounding axons • Corpus callosum connects the two hemispheres • Sylvian fissure separates frontal lobe from temporal lobe (Inferior to Sylvian fissure lies the temporal lobe; superior to the Sylvian fissure lies the frontal lobe) • Pre-central gyrus lies antierior to central sulcus • Longitudinal fissure separates left hemisphere from right hemisphere • Parietal occipital sulcus separates parietal lobe from occipital sulcus • Cerebral spinal fluid produced in the ventricles o Cerebral spinal fluid acts as a cushion between skull and brain o Protective layer o 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) • M1 = primary motor • S1 = primary somatosensory • Heschl’s gyrus ▯ auditory cortex (A1) o Heschl’s gyrus (auditory) is in the temporal lobe • Primary visual cortex (V1) is on the medial view of the brain, along the calcarine sulcus • Area 18 is V2 The Limbic System Also called the mesocortex – consists of 4 important brain regions • Cingulate gyrus (right above the corpus callosum) • Hypothalamus • Hippocampus • Amygdala The function of the limbic system is emotional processing, also playing a role in learning and memory • One of the oldest structures in the brain The Basal Ganglia Function: motor control Thalamus – gateway to cortex • All the modalities – synaptic relay in the thalamus – the modalities synapse in the thalamus before they reach the cortex • LGN = visual • MGN = auditory • VPN = somatosensory Hypothalamus – endocrine regulation, vasopressin (kidneys), oxytocin (arousal), circadian rhythms (wake/sleep cycles) Midbrain • Reticular formation: sensorymotor – arousal, respiration, cardiac modulation, pain, muscle • Red nucleus: motor coordination • Pineal gland – endocrine system (wake/sleep, seasonal functions) • Superior and Inferior Coliculi – visuomotor functions, auditory relay Cerebellum • Posture, walking, coordinated movement o Contains 11 billion cells • Consists of cerebellar lobes, which contain deep nuclue (dense cell bodies) the fasitigial nuclei are the most medial, the interposed nuclei is in the middle, and the dentate nuclei are the most lateral Methods Outline • Cognitive psychology • Techniques with animals • Neurology • Converging methods 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) o Isomorphic = identical/similar • Emphasis on construction (assumptions about the structure of the world) • In order to reconstruct, sometimes decisions are arbitrary • Study of mental activity as information processing problem • Internal (mental) representations o What format do they take? • Their transformation and computation of these representations Chronometrics • Measure reaction time or accuracy • Finer analysis of internal representations • Handle on mental events which are rapid and efficient Mental Operations • Memory retrieval o Serial or parallel? • AVXL o Target: V • AV o Target: V • Encode, compare, decide, respond • Manipulate, elaborate and generate mental representations Mental Operations: Parallel Word superiority effect • Brief exposure duration • Stimulus contains A or E o RACK – 90% accuracy o KARC – 80% accuracy o XAXX – 80% accuracy Mental Operations Stroop • See names of colors written in different colors (e.g. the word RED in blue ink) o Task is to say the name of the color, not to read the word • Interference from word o 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? o When a cell fires, it increases action potential • Visual system Recording in visual cortex Receptive Field Properties of neurons: • Receptive Field – location in space where presence of a stimulus will alter firing • Neurons have preferences – what is within the receptive field Retinotopy/Tonotopy Complex Preferences Limitations • Only one neuron (or very few) • Correlation • Not sure how it functions (feedforward/back) • Even if we understood every neuron, it is not clear whether we would understand brain and behavior 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) • 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 o Gliomas (glial cells) ▯ Astrocytomas, oligodendrogliomas o Meningiomas (dura, pia, arachnoid maters) o Metastatic ▯ From elsewhere Degenerative and Infectious Parkinson’s • Dopaminergic cell death • No mention in pre-industrial Alzheimer’s • 5% inherited • Aluminium • Protein overproduction • AIDS dementia (lesions within white matter) • Herpes simplex (cortical and limbic structures) • 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 o Temporal lobe damage in the vicinity of Fusiform gyrus (the area in the brain that recognizes faces) • Patient BB o Temporal lobe damage – inferior temporal cortex (IT) Neuropsychology – Double Dissociation Patients AA & BB Induced Lesion Method Transcranial Magnetic Stimulation (TMS) Pros: Reversible lesion Cons: Superficial surface of the brain, 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) EEG traces from a series of trials • Measure: neural activity related (sensory & motor) • Benefit: superb temporal resolution Magnetoencephalography (MEG) Synaptic activity produces small magnetic field • Average many trials – event-related fields (ERFs) • Same temporal resolution as ERP • But, more accurate solution to the inverse problems MRI vs. fMRI • MRI studies brain anatomy • Functional MRI (fMRI) studies brain function o fMRI – Blood Oxygenation Level Dependent (BOLD) signal indirect measure of neural activity o Increased neural activity ▯ increased blood oxygen ▯ increased fMRI signal 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 fMRI Experiment Stages: Prep Prepare subject • Consent form • Safety screening • 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 images fMRI Experiment Stages: Functionals Functional images • Images are indirectly related to neural activity • Usually low resolution images 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: o T1: Hit a button when you see a light o T2: Hit a button when the light is green but not red o T3: Hit the left button when the light is green and the right button when the light is red o T2 – T1 = time to make discrimination between light color o 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 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 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 9/16/16 4:11 PM 9/16/16 4:11 PM
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