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This 13 page Class Notes was uploaded by Emily Wu on Sunday February 7, 2016. The Class Notes belongs to PSYCH 50 at Stanford University taught by Justin Gardner in Winter 2016. Since its upload, it has received 25 views. For similar materials see Intro to Cognitive Neuroscience in Psychlogy at Stanford University.
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Date Created: 02/07/16
Emily Wu firstname.lastname@example.org Lecture 1: Introduction (1/5/16) ● Neurons work like transistors → about 86 billion ○ action potentials, “all or none” electrical signals used to communicate with other neurons ○ communicate with other neurons by sending neurotransmitters across synapses ○ receptors on cell membrane concert chemical neurotransmitters to electrical signals ○ neurotransmitters can be excitatory or inhibitory ● scope of study: ○ genes→ intracellular signaling → neurotransmitters → synapses→ neurons → local circuits → neuron populations → brain areas → interacting brains ● how to approach a study: ○ What computation do we want to study? ○ What algorithm should we use to study it? ○ What implementation should we use to carry it out? ● Add, Remove, or Observe: ○ add: stimulation of brain area ○ remove: lesions or removal of brain area ○ observe: record brain activity while associating it to certain cognitive behaviors Emily Wu email@example.com Lecture 2 (1/7/16): Sensory Processing ● Retina: light detected by retinal ganglion cells → axons project into central nervous system for processing ○ light receptors include rods and cones ● Macular degeneration: degenerating rods/cones, lose sight especially in elderly people ● General brain pathways: ○ ventral stream: what/perception stream (object discrimination) ○ dorsal stream: where/action stream (landmark discrimination) ● Visual prosopagnosia: damage to ventral temporal lobe ○ fusiform face area damaged → area related to face recognition ○ study: add electrodes and stimulate fusiform gyrus during brain operation → patient reports distorted facial features ○ study: place electrodes to measure action potentials in hippocampus → some cells fire more when seeing faces you’re accustomed to seeing → perhaps neuron selectivity for specific faces (“grandmother cell”) Emily Wu firstname.lastname@example.org Lecture 4 (1/14/16): Perceptual Judgment ● perceptual illusion rotating face ○ no eye sensors that directly detect depth/motion → we must infer from inputs ○ depth and motion are ambiguous → unconscious inference creates the illusion ● Akinetopsia: loss of movement perception ● Bill Newsome: performed studies on rhesus monkeys and perceptual judgment of motion ○ studied middle temporal (MT) area in dorsal stream ○ monkeys trained to shift their gaze towards direction they believe the dots are moving ○ motion coherence: 0% = dots aren’t moving in a particular direction; 100%= all dots are moving in one direction ○ experimenters varied motion coherence, plotted against %correct responses from monkeys ○ if MT is damaged, monkeys’ performance decreases ○ conclusion: MT is necessary for motion perception ● another study: stimulated cortical columns of neurons ○ all neurons arranged in a column share similar properties ○ findings: stimulating a specific cortical column caused increased perception of a specific direction → neurons selectively prefer/detect certain directions of motion ● Drift Diffusion Model: ○ the firing rate of a neuron depends on how easily it detects a specific direction of motion (increased firing rate = increased perception of a certain direction) ○ a neuron accumulates “evidence” of a stimulus until it hits a threshold and makes a decision on how to perceive the stimulus ○ model predicts that the harder it is to gather evidence the longer it takes to make a decision ○ also predicts that the more “noise” and lack of clarity of stimulus the less accurate our perceptual judgment will be Emily Wu email@example.com Lecture 6: Action Potential (1/21/16) ● reaction time depends on many things: ○ sensory delays → takes time for senses to pick up stimuli and transfer information to cortex ○ evidence accumulation → takes time for us to make a perceptual judgment ○ motor delays → takes time for cortex to send out signals to motor system ○ action potentials traveling slower/faster ● NaCl exists intra and extracellularly → only Na+ passes through Na+ channel of cell membrane → enters cell and goes down its concentration gradient, exits cell and goes down its potential gradient → reaches equilibrium potential (about 58mv), where concentration and potential gradients equally oppose each other ● KCl exists intra and extracellularly → only K+ passes through K+ channel → exits cell to go down its concentration gradient, enters cell to go down its potential gradient → reaches equilibrium potential (about 58mv) ● at rest, cells are highly permeable to K+, resting potential is about 70mV ○ cell receives synaptic input → membrane depolarizes to 50mV → voltagegated Na+ channels open → Na+ rushes in → membrane potential increases to +58mV → Na+ channels close → K+ channels open → K+ flows out → membrane potential drops to 83mV → K+ channels close ○ ion channels inactivate so that action potentials don’t travel backwards ● passive flow of current opens subsequent voltagegated channels → allows action potentials to move along length of axon ○ passive flow is fast but leaky → solved by myelination by glia ○ action potentials jump across Nodes of Ranvier between each Schwann cell and travels faster down the axon ● wider axons = quicker passive flow Emily Wu firstname.lastname@example.org Lecture 7: Energetics of Brain (1/26/16) ● brain imaging techniques rely on BOLD ● BOLD is a measurement based on these facts: ○ deoxyhemoglobin (deoxyHg) is paramagnetic (attracted to a magnetic field) ○ cortical vascular supply is tightly regulated ● blood vessels with higher concentrations of deoxyHg appear darker in MRI image ○ magnetic activity disrupts the imaging at that area ● brain supplies oxygen and blood to metabolically active areas of the brain ● BOLD response lasts about much longer (2030s) than the stimulus duration (12s). Why?: ○ cerebral metabolic rate of oxygen consumption: brain area needs oxygen, consumes oxygen → increase concentration of deoxyHg → causes initial dip in graph ○ cerebral blood flow: blood vessels bring in new blood with oxyHg that washes out the deoxyHg → BOLD image signal increases ○ cerebral blood volume: veins expand and accumulates more deoxyHg in a given area → BOLD signal decreases ● the imaging we see (brain areas “lighting up”) is based on the change in deoxy and oxyHg levels ● What happens if brain activity changes too quickly?: ○ in experiments stimulus must be presented for a longer duration to ensure BOLD signal doesn’t change too fast ○ if stimulus is shown in quick succession, the BOLD curves are addeemporal lineari : f(a+b) = f(a) + f(b) ● Why is cortical vasculature tightly regulated? ○ it’s costly for the brain to create action potentials ○ Na+/K+ pumps use ATP to push Na+ against its concentration gradient ● How does the vasculature know to bring in fresh blood? ○ when neuron gets excited by synaptic input, neurotransmitter bonds to neuron which signals for dilation of blood vessels ○ glial cells connect principle neurons to astrocytes to arterioles+capillaries ■ astrocytes take glutamate (excitatory neurotransmitter) from neurons and dilates arterioles to avoid excitotoxicity ■ glutamate bonds to neurons and cause pericytes (which have local control over capillary dilation) to expand and allow blood to flow through capillaries Emily Wu email@example.com Lecture 8: Attention (1/28/16) ● change blindness: directing attention towards one thing causes you to miss changes in other places ● without selective attention we wouldn’t be able to function ○ we can’t function while receiving all information all the time ● What is attention? according to William James: ○ accommodation of sensory organs to something of interest (overt attention) ○ anticipatory preparation from within the brain to pay attention to something in periphery (covert attention) ● Helmholtz study: ○ asked subjects to focus on fixation point in middle of screen ○ asked them to focus their covert attention to a specific area ○ they could tell what letters were in that specific area without moving their eyes to that area ○ since there was no motor movement, something must be changing in the brain ● “bottom up” → stimulus pops out to us, reflexive, fast/transient, stimulusdriven, exogenous ● “top down” → effortful to find stimulus, goaldriven, slow/sustained, endogenous ● Posner cuing task: ○ look at fixation cross in middle, arrow will appear and tell you which direction to look → respond when you see the stimulus ○ 80% valid cues, 20% invalid cues ○ results: slower reaction times for invalid cues ● study done on attention and sight: ○ premise: higher contrast of image means higher visibility ○ subjects asked to pick which of two pictures with difference contrasts is easier to see ○ in later trials, the contrast difference between the pictures becomes smaller until reachingpsychophysical threshold:ust noticeable difference ● followup study: ○ cue was given that directed subject’s visual spatial attention to a specific location ○ asked to pick which picture (of differing contrasts) was easier to see ○ valid cues: smaller just noticeable difference (subjects could better detect differences) ○ neutral cues: larger just noticeable difference (subjects did worse in detecting difference) ○ conclusion: giving attention allows you to notice smaller differences between stimuli theories for explaining how you improve detecting small differences between stimuli 1) increased contrast = increased neuron response in primary visual cortex = contrast response ○ sensitivity to contrast differences = response differenc (signaltonoise ratio) noise ○ bigger response difference to two different contrasts and smaller “noise” = smaller just noticeable difference/better sensitivity ● hypothesis: greater slope means greater sensitivity to contrast difference ● results: there was no difference in slope between valid cue and neutral cue conditions, so contrast response didn’t improve! 2) biased competition: ● measuring the firing rate of a specific neuron ● let’s say this neuron prefers horizontal bar orientation vs. vertical bar ● if two stimuli ( a horizontal and vertical bar) are displayed in the same visual field, you might expect that the neuron will respond to the horizontal bar as long as it’s in your visual field ● findings: directing attention to horizontal bar increased firing rate, but directing attention to vertical bar showed little neuron response, even though the horizontal bar was still present in the visual field ● conclusion: the brain suppresses unwanted signals and only allows signals that you want ● there are two stimuli in the same visual field, but the neuron acts as if there’s only one stimulus (the one you’re paying attention to) → gives a larger response to the attended stimulus ● from the contrast studies: although the slope (contrast sensitivity) did not change, the curve was shifted upwards in the valid cue condition, indicating that the brain gives a larger cortical response to the stimulus you’re attending to Emily Wu firstname.lastname@example.org Lecture 9: Attention part 2 (2/2/16) ● hemineglect syndrome: lesion in right parietal cortex → ignores stimuli in left visual field ● Balint’s syndrome: lesions in both 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 ● every time we voluntarily move our eyes, something in the brain adjusts, so the world doesn’t move as our eyes move ○ hypothesis: so if we have the “effort of will” to move our eyes but actually can’t move them, then our world perception will adjust ○ some crazy grad student injects self with chemical to stop eye muscle movement and finds that this is true → his perception of the world changed even though he couldn’t move his eyes ○ “effort of will” motor plans can change perception? ● study: stimulate monkey brain areas to find localization of function ○ stimulate the frontal eye field (FEF): monkey turns eyes and head to contralateral side ○ FEF projects onto superior colliculus, which maps eye saccade directions in the neurons of the FEF (i.e., specific neurons code for specific saccade directions) ● study: removing FEF disrupts voluntary eye movement, also partial neglect of certain visual fields ● smooth pursuit and saccade study: ○ we can’t make a smooth pursuit with our eyes without following a moving target ○ tracked eye movement of monkeys after displaying two moving dots on a screen ○ results: monkey’s eyes move in the averaged vector direction of the two moving dots, then makes a saccade to select one of the moving dots to follow ○ followup study: stimulate the FEF → results: the monkey immediately makes a saccade and focuses on one of the moving dots with its eyes ○ conclusion: FEF controls the choice of the pursuit of a moving target ● study: monkey must detect the dimming of a target in periphery while looking at a fixation point ○ over different trials, the amount of dimming is varied → trying to find the dimming threshold/just noticeable difference ○ experimenters stimulated the FEF enough to give it a signal, but not enough to make an actual saccade ○ results: monkeys were able to detect smaller dimming differences with subthreshold stimulation of the FEF ○ conclusion: we can evoke the function of covert attention by microstimulation of brain ● all of this supppremotor theory of atten overt and covert attention are controlled by common mechanisms → attention and the overt movement of eyes are linked ● motor system generates plans for us to act on the world, influencing cognitive functions at the same time ○ motor plans can alter our choices and cause attention ● mirror neurons: show activity both when doing an activity and watching someone else do the same activity Lecture 10: Executive Control (2/4/16) ● frontal lobotomy: remove parts of the prefrontal cortex to alleviate certain psychoses ○ we don’t actually do this anymore (for good reason) ● Multiple Errands Test: patients with frontal lobe lesions asked to run several simple errands ○ showed normal intelligence scores, but impaired strategy application ● Environmental Dependency Syndrome: person acts on direct environmental stimulis rather than own plans ○ driven by “bottom up”/reflexive processing rather than effortful, top down processing ● frontal lesions impair planning, selecting appropriate behavior, application rules, suppressing unwanted responses ○ but how do we operationalize these functions for study? different methods used for studying executive control: ● Wisconsin Card Sort: ○ dorsolateral frontal cortex damage correlates with perseverance errors ○ patients can learn new rules, but will make more perseverance errors than healthy people ● Matching rule tasks → tests capacity to apply rules ○ monkeys trained to respond to whether a picture matches the picture that’s shown first ○ monkey is presented a cue when first shown a picture ■ juice cue → indicates monkey should respond if next picture is matching ■ sound cue → indicates monkey should respond if next picture isn’t matching ○ results: found that there are rulespecific neurons in the dorsolateral frontal lobe → firing rate of neuron depends on which rule is being used ● does this apply to categorization, not just rules? ○ study: monkey is shown a cat or dog picture ○ monkey responds if the next images shown are of the same category ○ the firing rate of neuron depends on whether monkey is trying to categorize based on dog or cat ○ firing rates of different stimuli of the same category are similar ○ conclusion: prefrontal cortex can code for categories as well as rules ● Eriksen Flanker Test → testing for selection of appropriate behavior ○ presented a set of arrows: > > > > > or < < < < < or > > < > > ○ subjects asked to say which direction the middle arrow is pointing ○ when middle arrow is facing opposite direction, must suppress urge to say direction the other arrows are facing ● Stroop task → also tests for selection of appropriate behavior ○ tests conflict monitoring ○ when color of word and meaning of word are incongruent (e.g., the word “green” is colored yellow), anterior cingulate gyrus has increased activity → in the next trial, the prefrontal cortex has increased activity ○ interpretation: in the previous trial, anterior cingulate gyrus monitors conflict → tells prefrontal cortex to work harder and engage cognitive control in the next trial ● however, lesion in anterior cingulate gyrus doesn’t show any effects on performing in Stroop task ? ● simple rules → activity towards posterior prefrontal cortex ● complex rules → activity towards anterior prefrontal cortex ● much of this is still debated, since frontal cortex is responsible for many cognitive functions
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