PSYCH 50: Cognitive Neuroscience
Last modified on May 14, 2022

How does our brain give rise to our abilities to perceive, act and think? Survey of the basic facts, empirical evidence, theories and methods of study in cognitive neuroscience exploring how cognition is instantiated in neural activity. Representative topics include perceptual and motor processes, decision making, learning and memory, attention, reward processing, reinforcement learning, sensory inference and cognitive control

We are our brains. The overall goal of this class is to introduce you to the scientific study of how our brains work to make us who we are. This class should prepare you to take more specialized upper level classes in specific areas of cognitive neuroscience.

After taking this course you should be able to…

…demonstrate familiarity with basic anatomy and physiology of the brain. You should gain familiarity with fundamental terminology and basic knowledge about brain systems and functions. You should be able to recognize and understand these terms when you encounter them in reading literature (both popular press and primary) or listening to lectures about cognitive neuroscience. Chapter reading and quizzes will be used to build this knowledge. Examples of basic factual knowledge:

What are neurons and glial cells? What functions do they preform?
What is an action potential? Why is it important for cognitive function? How do ionic currents make it possible?
Where is prefrontal cortex? What might happen to someone if they had damage to it?
What is dopamine? What it is thought to signal in the brain?

…explain how the brain allows us to do everyday behaviors. Cognitive neuroscience aims to provide explanations for how the brain gives rise to behavior. You should be able to take any behavior that you engage in like walking, talking or deciding whether to drink a cup of coffee or eat cheese and be able to discuss what might be going on inside the brain to allow you to preform that behavior. This is not just knowing what parts of the brain are involved in different functions, but being able to apply conceptual models derived from cognitive neuroscience to new situations. We will practice this through weekly thought questions discussed in section. For example:

I decide to swing at a pitch while playing whiffle ball. How would a diffusion model explain my reaction time and choice?
I recognize someone I just met, but I can’t remember their name. What are the processes in the brain that have and have not worked properly?
I slowly learn to balance on my new RipStik casterboard. How do I sense balance? Would reinforcement learning provide a good theory for how I have learned to do this? If so, what would my dopamine neurons be doing when I fall off the board?

We will not cover everything there is to know about cognitive neuroscience in one quarter. Cognitive neuroscience is a rich field that draws on many disciplines from biology, chemistry, psychology, computer science, engineering, mathematics, philosophy and beyond. The objective is not to be exhaustive (and exhausting!) in what we cover. Instead the goal is to give you basic background and conceptual knowledge as outlined above by going in to depth in a few areas to illustrate the concepts and knowledge that structure the scientific study of cognitive neuroscience.

How does our brain allow us to do what we do? – that is, cognitive neuroscience = how cognition is implemented in the brain, whereas cognitive science = how we think and behave.

different “scales” of the same system – genes => intracellular signals => neurotransmitters/receptors => synapses => neurons => local circuits => populations => areas => interacting brains

different processes: input · output · feedback · broadcast

Key framework: Marr’s Levels. What goal? What algorithm? What implementation? – interesting bit from Marr here. We can’t study the brain just by looking at neuron implementation – we need to ask what they’re trying to accomplish, and how.

Experiment types: observe brain, add something to brain, remove something from brain. observe is cheaper, but add/remove can establish causality (since you’re essentially doing the “wiggle” test.) So, when FB/Twitter/whatever do A/B testing, they’re basically doing add/remove (psych not neuro) experiments lol…

Visual cortex is the cleanest example of hierarchical processing. Can draw an analogy to convolutional neural networks in the building up of increasingly complex representations in deeper layers.

LGN => V1: go from circular receptive fields to orientation-selective receptive fields (in one synapse!) by just overlaying the circular receptive fields.

V1 simple => V1 complex: similar idea. V1 complex are still orientation-selective, but now position invariant.

(side note, laterality: representations switch sides)

And so on, V2 => V4 … unlike convnets, though, not all the connections are feedforward. Some go back to previous layers. What do those do, I wonder?

“where” / action stream

“what” / perception stream

Vision isn’t just about copying the pattern of light in the eyes – it’s about making meaning out of that. That semantic meaning isn’t at the level of neurons – i.e. no “grandmother cell” specifically for grandma, but rather a distributed representation. (Ok fine they found this one neuron that’s dedicated to Jennifer Aniston LOL, but it def wouldn’t be the only/encapsulating neuron for Aniston representation)

Fusiform Face Area (FFA) – area of ventral cortex that is specifically selective to faces. (Observe: seeing face <=> FFA activity, Add: stimulation leads to distorted perception, Remove: loss of FFA causes prosopagnosia, inability to recognize faces)

Middle Temporal: needed for motion detection (Remove: lesioning flattens psychometric curve.) We have “integrator neurons” that sum up the responses from leftward-motion and rightward-motion neurons, and once a threshold is crossed either way make a decision.

Chemical basis: resting membrane potential is increased by synaptic input from another neuron above threshold potential => Na+ channels open + Na+ enters and depolarizes cell (spike up), Na+ channels close, K+ channels open + K+ leaves cell (spike down), Na+/K+ pump uses ATP to restore resting potential

Myelination + axon width => Action potentials vary in speed in different brain regions (!)

Why do we have a brain? Simple (evolutionarily): to move. Motion is incredibly complex

This is a pretty interesting thing to think about. Like yes, we have brains to think and plan and all that super intelligent human stuff – but ultimately all that doesn’t really mean anything unless it eventually translates into motor movement (and especially motor movement that leads to viable reproduction LOL.)

Central pattern generator in brainstem/spine can generate rhythmic movements (like walking) with /no cortical input/(!!) – cortex just flips them on/off like a light switch.

Basal ganglia = gateway, timing, value

Premotor and supplementary motor areas: Planning, movement sequences.

Cerebellum = learning + error correction

Motor cortex = Volitional control. shaped like homunculus. This is too simplistic though – some stimulations generate complex movements with many muscles..

How does the brain use energy? + vasculature that supports it

Brain uses a LOT of energy relative to rest of body…yet compared to computers are extremely efficient 😅.

Can measure BOLD (Blood Oxygen use) as a proxy for brain activity => basis for fMRI.

Frontal cortex = higher order thinking. Oh god, no lobotomies plz.

Frontal plays a role in executive control – what are we doing, what rules are we following, etc. Prefrontal cortex might play a role in category judgment.

Possibly a hierarchy of policy abstraction in PFC (i.e., goals on goals on goals.) Makes me wonder tho…cuz at some point in the hierarchy, at least for me, I don’t feel like I have the highest-level goals in active memory. Like, they might be stored somewhere, but policy here feels more like “in the moment”…

These stories are vague / simplistic. We really don’t know what the hell’s going on in the PFC. => level of abstraction that’s useful here is populations of neurons performing cognitive functions. Looking at a neuron is like looking at a transistor.

overt attention: you physically move your eyes (or other sensors) to pay attention
covert attention: the attention shift is only mental, not physical (i.e. looking out of the corner of your eyes)

Posner cueing task: Give a cue that’s supposed to tell you where the stimulus appears. RTs are faster when the cue is valid, i.e. in the same direction as the stimulus.

Weber – ability to notice small differences is increased when the cue is valid, as opposed to when the cue is neutral.

Biased competition model – this one is interesting. Attention suppresses the representation of the things you are not attending to. As if the stimuli are competing for representation, but attention biases the race.

Response gain / sensitivity enhancement – improvement in the representation due to attention.

Control of Attention: interesting observation is that world “stays stationary” when moving eyes. Hypothesis: whenever you move, an “efference copy” of the command is sent to the visual system to update your representation of the world. Hemholtz did a crazy experiment to test – paralyzed himself and tried to move his eyes…indeed, he experienced shifting perception.

Frontal Eye Field (FEF): Responsible for voluntary saccades, fires for visual receptive field and motor fields – but also “delay period” activity…involved in shifting attention / carrying cognitive signals related to working memory. Stimulating monkeys in FEF leads to overt (and at lower levels, covert) attention shift.

So what about the other senses, though? Is there a “Frontal ear field” or something? Cuz sometimes when listening to a podcast or something, I’m totally transfixed on the audio, barely even noticing / suppressing the visual stimuli around me.

Feels like…we’re going with a neuroscientist’s definition of consciousness here. One that presupposes Identity Theory…

I think he tried to apply the Marr’s Levels construct here – top points are the physical / algorithmic ways consciousness happens, bottom is big picture, what’s the purpose of consciousness?

Good example of broadcast system in the brain: broadcasts signals far and wide in the brain.

broadcast: neurochemical signals that are sprayed widely over the brain. “Dopamine neurons” in the ventral-tegmental area and substantia nigra pars compacta. Striatum involved in value representation.

dopamine represents perceived value (not pleasure) – its signal serves as a measure of prediction error. Dopamine = wanting, not liking.

Pavlovian conditioning: stimulus (bell) becomes associated with reward (food.) Thus, the conditioned response (salivation) shifts backward from the time of receiving reward to the time of receiving stimulus (can show causality b/c after conditioning, dogs salivate upon hearing the bell even when no food is given.).

drugs hijack dopamine circuitry, motivating drugseeking behavior.

Rescorla-Wagner: value of stimulus is updated by the difference between reward and the current value. (cf. gradient descent)
\(V_{pred} += \alpha(R - V_{pred})\)

TD learning: takes time into account (reward propagates backwards) further and further in time – like a basic form of reinforcement learning
\(R_{t=n} - (V_{t=n} - V_{t=n+1})\) = 0

Going lower-level to the neuronal level … how are new memories formed + consolidated synaptically?

Place cells in hippocampus fire for location
Grid cells fire regularly depending on where you are in a locale
direction cells = a sort of mental, locale-local compass.
border cells = detect borders of an environment

Oxytocin <=> pair bonding (for females)
increase in trusting behaviors for humans w/ oxytocin inhaled (well…maybe)

toxoplasmosis – holy crap that’s creepy. Mice eat cat poop infected with toxoplasma => become unafraid of cat urine => get eaten by cats => infect another cat with toxoplasma. (Reason: toxoplasma affects/damages the amygdala)

Kluver-Bucy syndrome: loss of fear reactions.

Endocrine system also controls emotions. A bunch of hormones in the pituitary gland => stress, pain, reproductive functions, mating behaviors lol…

Autonomic nervous system: control bodily responses.

• Sympathetic system uses norepinephrine (adrenaline) for fight-or-flight signaling
  
• Parasympathetic system uses acetylcholine for rest-and-digest signaling
  

Rabies: virus that takes over central nervous system, makes behavior more aggressive/salivating (perfect for transmission to others). So efficient at spreading through nervous system that scientists use it to trace neural connections(!)

Enteric nervous system: the gut practically has a mind of its own (lots of neurons down there.) Interesting bit – some bacteria might be producing serotonin + hijacking the enteric system…

Somatic marker hypothesis: instead of emotions => bodily response, bodily response => emotions. see Iowa gambling task: people have a “skin conductance response” whenever hovering over a bad deck, as a bodily “marker” that influences emotion / decision making. (Interesting – we think with our bodies??)

video of random shapes moving around – but the (neurotypical) brain sees a social scene, the big triangle bullying the others, the lil circle and square dancing(?) and maybe even in love(?). autistic doesn’t see the social construction – just sees literally.

Neurotypicals’ and Autistics’ eye patterms are different too – autistics care less about faces and eyes, social cues, etc.

Theory of mind = theory theory = our ability to reason about others’ mental states. Develops in childhood (Remember that whole Mary and Sally story…)

Genes + environment => Autism.

Currently, can just replace sensory organs (and kinda badly.) Future…interface with cognitive parts of brain? Cortex? Cue Neuralink