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This 8 page Study Guide was uploaded by Emily Wu on Monday February 8, 2016. The Study Guide belongs to PSYCH 50 at Stanford University taught by Justin Gardner in Winter 2016. Since its upload, it has received 136 views. For similar materials see Intro to Cognitive Neuroscience in Psychlogy at Stanford University.
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Date Created: 02/08/16
Section 1: Interpreting Cognitive Neuroscience Receptive field:the part of a neuron that, when stimulated, elicits a response ● in the visual system, retinal ganglion cells and lateral geniculate cells are excited or inhibited by light going on or off in the center of their receptive fields ● singlecell recordings measure neuron activity by placing an electrode near the neuron of interest ● for example, certain neurons fire more rapidly when seeing a certain orientation of a bar (i.e., vertical vs horizontal) → single cell recordings can determine the receptive field of a neuron and which kind of stimulus the neuron prefers Retina: lining the back of the eye, contains photoreceptors called rods and cones ● rods: perception of low levels of light ● cones: perception of higher levels of light, color and detail ● fovea: center of retina where cones are most densely packed, where acuity is highest Lateral geniculate nucleus (LGN): in the thalamus, receives info directly from retinal cells ● primary visual pathway: input→ retinal ganglion cells → leaves retina via optic nerve → LGN → primary visual cortex of occipital lobe ● consists of two magnocellular system layers (process spatial detail, color, brightness) and four parvocellular system laters (process changes in stimuli that result in motion perception) V1:the primary visual cortex, also known as striate cortex ● middle temporal (MT) area especially important in generating motion percepts ● ascending pathway example: input → LGN → V1 → MT → LIP (going up the hierarchy) ● descending pathway example: FEF → V1 (going down the hierarchy) V4: an area in the extrastriate cortex (which usually deals with higherorder processing) ● especially important in processing information about color vision ventral stream starts in primary visual cortex and leads information to inferior temporal lobe ● “what” pathway, deals with object recognition, analysis of form and color ● thus, neurons in temporal lobe show selectivity for shape, color, texture dorsal stream: starts in primary visual cortex and leads info to parietal lobe ● “where” pathway, analysis of motion and spatial relations between objects ● thus, neurons in parietal lobe show selectivity for direction and speed of movement fusiform face area in the temporal lobe ● neurons here show selectivity for face recognition ● prosopagnosia: inability to recognize faces due to damage in FFA topographic map: organization of receptors in the retina corresponds to spatial organization of areas in the visual cortex ● also present in somatosensory systems ● stimulating adjacent area of brain elicits response in adjacent area of receptor insular cortex in the temporal and frontal lobes, receives information from the thalamus about taste ● also associated with a bunch of things like interpersonal awareness, empathy, anxiety, depression, pain, disgust, addiction (from thought question 1) forward inference: if a specific brain region is activated by a certain cognitive task, then the neural activity in that region must depend on that cognitive task ● ex: FFA shows more activity while subject views faces instead of houses or cars, so FFA activity must depend on viewing faces reverse inference: if a specific brain region is activated then a subject must have been doing a specific cognitive task that has been associated with that brain region before ● ex: prefrontal cortex is activated while subject is doing a mental rotation task, therefore subject must have been using working memory (since PFC has been associated with working memory) ● usually logically incompatible with forward inferences → you can’t be sure that working memory was actually used since other processes could have been happening to activate the PFC during the mental rotation task Section 2: Drift Diffusion Model The Drift Diffusion Model: ● explains the process of perceptual judgment ● used to test judgment of motion perception in the random dot coherence test (such as the one used in Newsome’s monkey experiments) ● in the model, there are two alternative choices, and the neuron being measured accumulates evidence of the stimulus over time, then makes a decision when the evidence reaches the threshold ● since we detect many different stimuli at once, the evidence accumulated will include “noisy” stimuli → the “noisier” the other stimuli, the longer it takes to reach a decision, and less accurate the decision will be ● when shown moving dots of 100% coherence, there is less “noise” and neuron will reach a perceptual judgment quickly and accurately since the evidence accumulated is straightforward ● when shown moving dots of 0% coherence, there is a lot of “noise” and neuron will reach a perceptual judgment more slowly and less accurately since evidence accumulated includes a lot of noise/other stimuli sensory transduction: the process of transforming physical stimulus into neural signals that eventually reach the central nervous system retinotopic organizatio the mapping of specific retinal sites and their corresponding areas in the primary visual cortex firing rat the amount of action potentials a neuron creates per unit time ● greater firing rate corresponds to greater neuron activity, meaning there was more excitatory presynaptic input unconscious inference: coined by Helmholtz ● in perception, the idea that we involuntarily perceive illusions even though rationally we know they’re not true ● there is a difference between the real world and the world our brain constructs/perceives ● ex: theinverse optics problem:objects are 3D, but they’re projected onto retina as 2D, so the actual properties are not accurately reflected ● theories: the visual system tries to solve this problem by gathering empirical evidence based on prior experiences MT and MST: in the temporal lobe, most relevant regions for motion processing ● neurons in MT show selectivity for specific directions of motion, which is important in perceptual judgment of motion ● stimulation of certain neurons in MT increased the probability that a monkey would make the correct perceptual judgment in direction in the random dot coherence task evidence accumulation: in the drift diffusion model, neurons will accumulate evidence about a stimulus and make a perceptual judgment based on the quality of evidence necessary and sufficient: ● removal of MT area in monkeys showed impaired motion perception → MT is necessary for motion perception ● MT alone is sufficien for motion perception since stimulating MT will affect the judgment of motion perception psychometric function: a function that objectively measures psychological behavior computational model: a mathematical model that uses computer simulation to study complex behavioral systems ● RandomWalk generator we studied in section is an example of computational model of perceptual judgment speedaccuracy tradeoff: ● the faster you make a judgment, the less accurate it might be ● the slower you make a judgment, the more accurate it might be ● supposed by the drift diffusion model → making a judgment too early on a “noisy” stimulus doesn’t allow enough time to accumulate quality evidence; allowing enough time to accumulate evidence allows you to make a more accurate judgment Section 3: Action Potential ● Ions K+, Na+, and Cl exist both inside and outside cell (more Na+ outside, more K+ inside because of Na+/K+ pump that actively maintains this imbalance), Cl moves around to balance the differences in positive charge ● cell membrane is selectively permeable to K+ at rest, so constant efflux of K+ down its concentration gradient through passiion channelsis the main reason for the negative resting membrane potential ● when the cell receives synaptic input, oltage gated channelopen and allow an influx of Na+ (which ends up traveling downoncentration gradien which depolarize the membrane potential towards a more positive voltage (rising phase) → influx continues untilelectrical gradie is equally opposed to concentration gradient, creating anequilibrium potential ● at this point, Na+ channenactivat, and K+ channels open, allowing efflux of K+ down its concentration gradient until electrical gradient opposes it equally and creates equilibrium potential → cell membrahyperpolarizestowards more negative voltage (falling phase) so that the action potentials don’t go backwards ● delayed rectificati the K+ channels are slow to open and close, helping control the duration of the action potential → the slow closing of K+ ion channels is the reason why the membrane potential undershoots the resting membrane potential ● Na+/K+ pump: uses ATP energy to transport three Na+ ions outside the cell and bring two K+ ions into the cell against their concentration gradients in order to bring the cell back to resting membrane potential Section 4: Methods fMRI: uses the differences in BOLD signals to image brain activity ● noninvasive ● good spatial resolution, less temporal resolution BOLD: blood oxygenation leveldependent signals ● based on the fact that brain brings in more blood when more active ● also based on fact that deoxyhemoglobin is paramagnetic ● active brain areas will have higher concentration of deoxyhemoglobin which will disrupt the magnetic imaging and appear darker fNIRS: similarly uses BOLD signals like fMRI but uses infrared spectroscopy by shining light through the skull to image the brain ● less costly and more portable than fMRI ● noninvasive ● good spatial resolution, less temporal resolution DWI: diffusionweighted imaging ● noninvasive ● detects the movement of water as it diffuses across different cell membranes ● water moves differently according to the structure of matter in the brain ● used to map the white matter fiber tracts and connectivity of the brain ● good spatial resolution, less temporal resolution TMS: transcranial stimulation ● transient stimulation of a superficial brain area by pulsing with a rapid magnetic field over the skull ● noninvasive ● some temporal resolution, spatial resolution limited to area affected by the pulse EEG: placing electrodes on the scalp ● noninvasive ● good temporal resolution, spatial resolution only limited to areas near surface ● measures fluctuations in charge along neuron’s dendrites when it receives input ● eventrelated potentials (which are due to specific cognitive tasks/events) can be extracted from EEG recordings MEG: magnetic version of EEG ● measures magnetic fields from the dendrites fluctuations in current flow, rather than voltage changes ● noninvasive Optogenetics: ● genetically designing ion channels that will open/close in response to light ● can control the firing of action potentials in specific neural circuits ● invasive ● high temporal resolution ● high spatial resolution but limited to the selected circuits being studied calcium imaging: ● measures changes in calcium concentrations by chemically dyeing/marking Ca2+ ions ● high temporal resolution, high single cell spatial resolution lesion studies: ● invasive if done in animals, otherwise noninvasive if observing naturally occurring lesions ● no spatial/temporal resolution singleunit electrophysiology: ● placing an electrode directly on a neuron to measure its firing rate of action potentials ● invasive ● high temporal resolution, high spatial resolution of a single neuron ECoG: placing electrodes directly onto surface of the brain to measure neuron activity ● invasive ● good temporal resolution, good spatial resolution but limited to the areas near surface Psychophysics: the study of the relationships between stimuli and sensations/perceptions Section 5: Attention covert vs overt attention: ● overt: directly moving your eyes/head towards a stimulus ● covert: directing attention to something in the periphery without moving eyes/head topdown vs bottomup: ● bottomup: more basic processing, reflexive and fast ● topdown: more complex processing, effortful and slower endogenous vs exogenous: ● endogenous: voluntary attention, actively directing your attention towards something, effortful, topdown, slower ● exogenous: involuntary attention, reflexive, having something catch your attention, bottomup, faster/transient premotor theory of attention: preparing goaldirected actions and directing attention are controlled by same sensorimotor mechanisms sensitivity enhancement: increased attention towards a certain area increases sensitivity to small differences between stimuli (such as small contrast differences between two pictures) perceptual threshold: the just noticeable difference → can you tell between the small difference between two similar stimuli? ● sensitivity enhancement reduces the just noticeable difference → you can detect smaller differences Posner cuing: subject fixates attention on fixation cross and is cued which direction to look → must respond when they see the stimulus → 80% valid and 20% invalid cues ● reaction time is faster for valid cues instead of invalid cues Balint’s syndrome: lesions in left and right parietal cortices ● simultanagnosia: can’t see two objects at the same time, even in the same visual field ● optic ataxia: can’t coordinate movement with visual feedback → lack of order and coordination ● oculomotor apraxia: can’t plan voluntary eye movement Hemineglect: lesion in right parietal lobe ● neglects stimuli in left visual field functional anatomy of PFC: anterior PFC processes more complex/abstract rules, posterior processes more simple rules conflict monitoring: anterior cingulate gyrus plays large role in conflict monitoring ● when ACG detects that there is conflict in stimuli processing it signals to PFC to use more resources for processing this complex stimulus ● evident in the Stroop task Wisconsin Card Sort: used to test learning and applying rules ● prefrontal lesions will impair the application of new rules → more perseverance errors Working memory: temporary maintenance/manipulation of information ○ an active process that also keeps out irrelevant information ○ Activity in lateral prefrontal cortex: ● typically lasts entire length of delay period ● increases as more information is held in working memory ● increased activity is associated with better working memory ● increased activity is associated with resistance to distractions ● tends to be greater when information needs to be manipulated in working memory rather than simply being held there
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