Lectures 1, 2, 3-Neuroscience cognitive Flashcards

Question

What electrical function does the brain do?

Answer 1

It's moving electricity all around from neuron to neuron. For information processing

Answer 2

More than a century modern research on the brain and cognition, neural theory, and cognitive theory. Neural theory (neuroanatomy, physiology) * Cognitive theory (psychology, cognitive science The integration of neural and cognitive theory is RECENT * The first Cognitive Neuropsychology textbook: 1998! Cognitive neuoscience , young field, cognition long time, basic of neuroscience. Both research integrated together is fairly recent.

Answer 3

1)Cardiocentrism: Mind located in the heart poetic 2) Ventricular localization:So it was a major focus on fluids as the key sort of underlying physiological substrate for lots of different things, including the mind. And they thought, oh, here's this area that has a lot of fluid inside of the head. The head seems to be important for cognition. Maybe this fluid is what underlies the mind. Very detailed theories. Not all true. 3)cerebral localization: Tissue in the brain is responsible for thinking since we had the same ventricular as other animals and supposedly we are smarter and different thus it has to be the brain 4) cortical localization: People had accidents that were very specific to some type or regions.

Answer 4

Cardiocentrism: the belief that the heart is the seat of intellectual and perceptual functions * Aristotle (384-322 B.C.) * “broken heart”, “heartfelt thanks”, “learn by heart”

Answer 5

1)Ventricular localization: the fluid-filled ventricles are the location of cognition: 2)Perception/imagination: lateral ventricle 3)Cognition: third ventricle 4)Memory: fourth ventricle Widespread view from the 1st century through the Middle Ages and Renaissance

Answer 6

Realization that the ventricles are unlikely to be the seat of higher mental functions because the ventricles of humans are not dissimilar from those of animals with clearly inferior mental abilities * The localization of respiration to the medulla and sensory and motor functions to the dorsal and ventral roots of the spinal cord led to the idea that other parts of the brain might support other, higher-level mental functions

Answer 7

Cortical Localization: * The brain is composed of as many organs as there are mental faculties (aka: cognitive functions) Phrenology: * These mental organs vary in size and their size affects the shape of the skull * One can study a person’s character and faculties by studying the external configuration of the skull * Sought evidence by studying the skulls of people with exceptional traits: poets, statesmen, people with mental illness, etc.

Answer 8

Phrenology: * Correct about cortical localization of function * But wrong about evidence from skull shapes It turned out to be a pseudoscience, but at the time there were a lot of adherence to this idea that that there are different specialized functions in different parts of the brain and that That just like in the way that if you use a muscle a lot, the muscle will grow. That if you use a particular cognitive function a lot, that part of the brain will grow. And actually that you could then even tell this by looking at the surface of the skull. That there would be bumps in the skull, that would tell you something about people's mental faculties because they have an enlarged part of the brain that's involved in memory or something like that. turned out not to be true, but This person, Franz Gahl, developed a whole theory about this. It became very popular. There were journals and societies dedicated to it. Now, it turned out that he was wrong about this, but there was one sort of element of this idea of phrenology that actually turned out to be right, which is that there is functional specialization of the brain. Different regions of the brain do have different specialized functions, right? It's just that those regions don't get larger if you are better at that function. You definitely can't see anything on the skull, right? You can't tell if somebody has a good memory by likegetting some information about the shape of their skull.

Answer 9

Functional localization: Specific cortical areas perform specific cognitive functions * There may be interactions between cortical areas, but these interactions are sufficiently limited, such that we can usefully understand the brain by identifying its cognitive functions and their localization in the brain And the idea is that of course there are interactions across brain regions and we need to, you can't just like, we can't fully understand the brain by just studying. each brain region of isolation. At some point we need to understand how they interact with each other. But there's enough localization of function. Study each section individuality. Holism: The cortex is a dynamic whole which is more than the sum of its parts * Music cannot be understood as individual notes * Squareness cannot be understood by individual lines * The brain cannot be understood via decomposition into local areas and component functions The contrast to this is something like holism where The idea here is that the neural basis of cognition is so widespread and so dynamic in the brain. That You can't possibly go in and study one brain region and try to characterize what its cognitive function is. It's so interdependent on every other region of the brain that you're just misleading yourself. That's like trying to understand music by studying the individual notes or whatever, not understanding how the notes work together to form a piece of music that gives an aesthetic experience. You're missing the sort of bigger picture by focusing on individual regions.

Answer 10

French physician * Tested the hypothesis that language is a faculty of the anterior frontal lobes Tan (Leborgne): extreme difficulty in speaking but no paralysis of lips or tongue, and no language comprehension difficulties * Autopsy revealed damage to the “3rd convolution of the frontal lobe of the left hemisphere” (which we now call the inferior frontal gyrus) * Turned the tide in favor of functional localization (as opposed to holism) And he had no difficulty with language comprehension. It was clear that you could talk to him, he could follow directions, but he couldn't speak. He had this difficulty generating speech.

Answer 11

Fused neural networks (Golgi) Independent units (Ramon y Cajal)? If all neurons are fused, how can there be localization of function, as suggested by Broca’s findings?You know, the microscopes weren't as powerful, the techniques for isolating cells weren't as good. So it was actually really difficult to try to resolve this debate. It turned out that the key piece of evidence for resolving this debate came from Golgi.

Answer 12

So Golgi had been arguing in favor of this like Fuse network idea and he was experimenting with different types of stains so he had these like you know dishes of slices of neural tissue that he was staining and trying to characterize the structure of the neurons and he just hit upon this particular stain that would get picked up by specific neurons. It's actually not fully understood why. Specific neurons would pick up the stain and it would diffuse through that neuron And it would give you like a very clear picture of that neuron and it wouldn't go to any other neuron. And so a lot of people saw these results and thought. Well, this is very clear evidence that all the neurons are not fused together because there's clearly like an endpoint to where this goes. It doesn't just fuse to all the other cells. It seems to be restricted to this one cell. It suggests that it's an independent unit. Interestingly, Golgi himself was not convinced of this idea from this evidence. He went on to win a Nobel Prize, and even in his Nobel Prize acceptance speech, he still argued for the fused neural network idea. But most of the rest of the neurophysiology community was convinced and then of course we then later learned that indeed that was correct and it sort of was the starting point of what's called the neuron doctrine. The idea that the sort of most basic element of the brain is the neuron and each neuron is an independent Silver nitrate stain: Stains random neurons. Discovered by Golgi (1873) in a kitchen, working by candlelight * Convinced most (but not Golgi himself) that neurons are not continuous and connected—instead, they are independent units * The Neuron Doctrine * Neurons are separate physiological units * Electricity travels in one direction down a neuron Purkinje cell (cerebellum)

Answer 13

Presynaptic neuron receives signals-> Moves current down an axon-> Triggers release of neurotransmitter at the synapse-> Passes signal to post-synaptic neuron Addition and Subtraction: Excitatory signals (EPSP): increase the probability that the post-synaptic neuron will fire (generate a signal) Inhibitory signals: (IPSP) decrease the probability that the post-synaptic neuron will fire (generate a signal) Electrical signals are the basis of information processing in the brain what's happening when neurons are communicating with one another is that Neurons send signals to one another either synapses by releasing neurotransmitters. One neuron releases a neurotransmitter and the neurotransmitter lands on a downstream neuron. It changes the likelihood that that downstream neuron will itself send signals to other neurons. So at a very simple level, we can think of this as either exciting the downstream neuron or inhibiting the downstream neuron. So it excites the downstream neuron. It's increasing the probability that the downstream neuron will fire an active potential and then some electrical activity will travel down the downstream neuron and it will release neurotransmitters that it's synapses. If it's inhibitory, then it decreases the probability that the downstream neuron will fire an actual potential. So at the simplest level, we can think about it as like neurons are sending signals to one another that basically increase or decrease the probability that the next neuron will then send some other signals to another set of neurons. So it's like, well, pluses and minuses. You have a bunch of neurons doing this, and it determines when neurons are finding their action potentials. So this is the basis of information processing in the brain.

Answer 14

100 billion neurons in the human brain * typical neuron has 1,000-10,000 synapses * ~60-100 trillion synapses * A LOT of computational capacity! We talk about neural representations when we talk about sending signals, when we go on information processing. It's all really instantiated in neurons sending signals to one another. And as we're going to see, we can get a picture of that by recording the actual potentials of neurons. It tells us when they're sending signals to other neurons. or using other methods to indirectly tell us about when neurons are firing action potentials. Okay, so

Answer 15

earning neuroanatomy is analogous to learning a language or geography; it is a slow process of building inch by inch and learning by repetition.” (DeArmon, Fusco & Dewey. Structure of the Human Brain. 1989)

Answer 16

Directional terms * Dorsal or superior = top * Ventral or inferior = bottom * Anterior or rostral = front * Posterior or caudal = back * Medial = middle * Lateral = sides Note that these are relative terms * Bilateral = on both sides (hemispheres) * Ipsilateral = on the same side (hemisphere) * Contralateral = on the other sid

Answer 17

Dorsal or superior means at the top. And by the way, these directional terms are relative terms, right? So we can say... Like this, you know the superior part of the brain overall So it's like the very top of the brain or I could say like the superior part of the temporal lobes We'll see what that is soon, which would be like actually like halfway up the brain, right? This is like the top part of the temporal lobes Ventral or inferior means the bottom. Anterior or rostral means the front and a posterior or caudal means the back. Medial means in the middle and lateral means on the sides. Again, these are relative. I could talk about like the medial aspect of a particular gyrus or something like that, right? doesn't necessarily mean the middle of the brain, it means like the middle, you know, the part of that gyrus that's closer to the middle. here are other terms that describe the laterality. So you could say bilateral, meaning on both sides of the brain. You could say ipsilateral, meaning on the same side. So this will come up when we talk about like lesions. So you could think about like the effect of a lesion on cognition or on like say motor control for example and you can talk about that as being ipsilateral or contralateral. So for example if you have a lesion to right motor cortex it will result in difficulty controlling the left side of your body right so that that's a contralateral lesion right or the impairment is contralateral to the lesion, right? You can say it either way, right? Whereas if's lateral would mean on the same side.

Answer 18

400 miles of blood vessels

Answer 19

Ventricles contain cerebrospinal fluid (CSF), produced by blood vessels in the ventricular wall * CSF is also present between the brain and skull to protect the brain, like a shock absorber

Answer 20

Thalamus * Limbic system * Cerebral cortex

Answer 21

Central relay for all sensory and motor information to and from cortex * Lateral geniculate nucleus: visual information * Medial geniculate nucleus: auditory information * Ventral posterior nucleus: somatosensory information And then also there's another part of the thalamus that is a relay station for auditory processing, the medial geniculate nucleus. So we won't talk much about what happens in the thalamus. For our purposes, it's really basically just a path, it's a relay station along the pathway.

Answer 22

The limbic system is this set of structures that's a realm, the thalamus. the hippocampus, the amygdala, and the cingulate jar. So all of these are going to come up in this course. The hippocampus is particularly important. We're going to learn about this when we learn about memory. It's really a key structure for memory. Hippocampus * Medial temporal lobe * Key for memory formation * Amygdala * emotion * Cingulate gyrus * Motivation, error detection You can see on a coronal slice of the brain, you can see the hippocampus in this medial part of the temporal lobes. It's an eventual part of the brain and it's medial and it has a sort of like coiled up structure. The amagal is this sort of this like ball shape structure that's right in front of the hippocampus. It's really important for emotion. And then the cingulate gyrus is this large gyrus that goes around this white matter structure which you'll see here called the corpus venosum that connects the two hemispheres. And we're going to see that the singular chirus is important for controlling our behavior. We're going to see how it's involved in monitoring when we're making mistakes. and so on.

Answer 23

And then the white matter is all of the connections between the neurons. It's all the axons. It's all the wiring of the brain. And it's covered in lipids. It's fatty. That's why it shows up with white in these images. and It's the part of the brain where neurons are sending signals to one another, axons to one another, sort of a wiring that connects different neurons to one another

Answer 24

for (singular-gyrus): protruding * Sulci (singular=sulcus): furrows * Some large sulci are called fissures

Answer 25

Commissures are white matter tracts that connect the two hemispheres: * Anterior commissure * Corpus callosum (callosal commissure) * Posterior commissure * Within-hemisphere tracts connect gray matter regions within a hemisphere

Answer 26

So the first is about disruption and stimulation methods where where, either there's, like, a naturally occurring lesion, like a stroke or something, just disrupted, some, some functioning in the brain, and then you're trying to characterize how did that affect cognition. Or there's actually as we're gonna see, there's methods for directly going in and sort of stimulating the brain and seeing what happens when specific brain regions are stimulated. Disruption/stimulation approach: * Disruption/stimulation of a specific brain region can disrupt/enhance specific cognitive functions * We can use experimental tasks to determine which cognitive functions are impaired (or enhanced) when a specific brain region is disrupted (or stimulated) * This approach can determine which cognitive functions are supported by the disrupted/stimulated brain region So this is a really, powerful method for trying to understand which regions of the brain have a causal function in causal relationship to a specific cognitive function.

Answer 27

* Design experimental tasks to isolate a cognitive function * Measure brain activity and determine which brain regions are activated by the task

Answer 28

Stroke * Stroke in the middle cerebral artery, damaging most of the frontal lobe) and the superior temporal gyrus * Tumor * Tumor in ventromedial right hemisphere * Degenerative diseases (Alzheimer's, Parkinson's, Huntington's, Pick’s, and others) * Frontal and temporal lobe atrophy (gradual loss of grey and white matter, more distributed than damage from stroke) * Trauma * Ventral frontal head injury

Answer 29

So I'm gonna show people images in the scanner. Some of them will be faces, some of them will be other things. And I wanna see what effect that has on the brain activity, what region of the brain is activated when people are perceiving faces. So notice the direction of the sort of causal arrow here. Right? So in the first thing that we talked about, disruption, you start with some manipulation of the brain. Right? So naturally occurring, lesion of the brain or a direct experimental manipulation of the brain. And you assess the effect on cognition. Right? So that that's a situation in which you can see the causal effect of this brain region on this cognitive function. Right? In the recording approach, you're manipulating cognition and you're looking at the effect on brain activities. Right? So your starting point is to manipulate some task and see what happens in the brain. Right? Now there's an important thing to keep in mind, which is when you're doing this recording approach, you you can't say for certain with certainty that this brain region say a certain brain region is activated during face perception, for example. You don't know for sure that this brain region has a has a causal role in face perception. Right? Because you don't know, like, maybe it's the case that you thought it was about face perception, but it was really something else.

Answer 30

1) Association 2) Dissociation 3) double dissociation

Answer 31

Now there's an important thing to keep in mind, which is when you're doing this recording approach, you you can't say for certain with certainty that this brain region say a certain brain region is activated during face perception, for example. You don't know for sure that this brain region has a has a causal role in face perception. Right? Because you don't know, like, maybe it's the case that you thought it was about face perception, but it was really something else. Like all those in all those photos had some other thing in them that was correlated with faces that you didn't take into account. Right? And that was causing activation of this brain fusion. Like, they all tend to be brighter photos than the other photos that you showed to the subjects. Right?

Answer 32

Damage to brain region 1 is associated with poor performance on cognitive function A * E.g., damage to the occipital lobe is associated with poor vision * Inference: brain region 1 is involved in function A You need to show that when that brain region, its activity has been disrupted, that the cognitive function is also disrupted So the first method is showing you, like, the causal role that a brain region has in specific cognitive functions, and the second region is just determining associations between brain regions and cognitive functionsyou can study, say, one person or multiple individuals that have a damage to a particular brain region, say, brain region 1, and, you find that when you administer some tasks, it's like a visual perception task, they're really bad on that task. Their accuracy is, like, 20%, and healthy individuals have an accuracy of, like, 100%. Right? So what you found is that you found an association. Right? So you found that damage to brain region 1 is associated with worse performance on the task that you administered. Right? For example, maybe damage to the occipital lobe is associated with poor, performance on vision test. Right? Okay. So this is one type of finding. It's it's showing you that this brain region is involved in this task. Right? But what's lacking is a degree of specificity. Right? And the way to think about this is maybe it's the case that damage to this brain region makes you bad on lots of different types of tests. Right? Like, for example, let's say it was, like, the occipital lobe is, like, is is important for vision. Okay? And so let's say what you did was you administered, like, a math exam. And then the the subjects were really bad at doing the math exam. And you said, how much is the occipital lobe? Makes people worse in math. Right? But then really, what's going on, and if you did more studies, you realize, well, actually, they just have bad vision, and they can't do, like, any exam. Right? So, yeah, it's like, has a causal role in doing, like, math exams where you have to, like, read something and and do an exam, but it's not really about math. Right? That's not the specific association that you would you would wanna draw. It's really vision. And so one way in which you can rule out these kinds of explanations, these more general explanations, is to find dissociations.

Answer 33

1. Identify/generate brain lesion 2. Evaluate cognitive functions 3. Across multiple individuals (or studies) determine if there is a systematic relationship between a cognitive function and a brain area

Answer 34

Double dissociation * Requires two groups or subjects with damage to different brain regions * Group 1: damage to region 1 is associated with poor performance on function A but not function B * Group 2: damage to region 2 is associated with poor performance on function B but not function A * E.g., damage to the fusiform gyrus is associated with poor perception of faces but not places, and damage to the parahippocampal gyrus is associated with poor perception of places but not faces * Inference: brain region 1 is involved in function A but not function B, and brain region 2 is involved in function B but not function A * Strong evidence for more specific brain-function mappings and very strong evidence against more general explanations (e.g., general deficits in intelligence, attention, etc.) Right? That's not the specific association that you would you would wanna draw. It's really vision. And so one way in which you can rule out these kinds of explanations, these more general explanations, is to find dissociations. So you can show that, like, okay, well, the, the subjects with, damage to brain region 1 have poor performance on task a, but they're fine on task b. ike, there's a region of the visual system that's really important for face perception. And when people have damage to that brain region, they have a specific impairment in face perception. Right? So you would find the damage to the fusiform gyrus is associated with poor perception of faces, but not objects or other types of visual stimuli. Right? And we're gonna we're gonna have, like, a whole lecture where we get we talk about, like, how people figured out that this brain region is specifically involved in face perception. But just at a broad level, just to give you an idea of what this means. Right? So you're like, you know, you're trying to find other tasks, so it's like, oh, I think it's about face perception. You're trying to find other tasks that are similar to face perception as possible. Right? They're visual stimuli. They're doing the same kind of responses, but yet if you can find that they are still doing this task just fine, right, but yet they're bad on the taste task, that gives you more confidence that you sort of identified the specific cognitive function that's affected here. Okay. So, so an association's result is one where you found an association between a performance on a particular task that you think is tapping into some cognitive functio ecause you've only tested this one task, so you haven't ruled out other sort of more general explanations. Like, for example, maybe the reports on every single task you give them. Right? There's, like, ban on everything you give them. Right?

Answer 35

So, classically, the the most common way in which people studied the effect of disruption of brain activity on cognition was by studying naturally occurring lesions of the brain. This still this is still a, you know, a very common method in the field, but now we have a lot more sort of technologies that allow us to, to go beyond just the study of naturally occurring lesions

Answer 36

Double dissociation * Requires two groups or subjects with damage to different brain regions * Group 1: damage to region 1 is associated with poor performance on function A but not function B * Group 2: damage to region 2 is associated with poor performance on function B but not function A * E.g., damage to the fusiform gyrus is associated with poor perception of faces but not places, and damage to the parahippocampal gyrus is associated with poor perception of places but not faces * Inference: brain region 1 is involved in function A but not function B, and brain region 2 is involved in function B but not function A * Strong evidence for more specific brain-function mappings and very strong evidence against more general explanations (e.g., general deficits in intelligence, attention, etc.) nd the idea here is that, you can you're looking for a group of patients that have damage to one particular brain region. And they're, they're bad at task a, they're good at task b. Alright. So let's say they're bad at face perception, but they're good at object perception. And then you wanna find another group of patients that that have damage to a different brain region where test a their test a performance is fine, or their face perception is fine, but they're worse on the other thing, right, test b. Right? So they're worse on, like, object perception in this example. Right? So let's go to double association. You found 2 different patterns of of dissociation that go in the opposite direction, right, in 2 different groups of patients that have different brain functions. Right? This is the strongest type of of finding that you can get, because it really shows you that you found something that's highly specific, highly specific association between these brain regions and these cognitive functions. Right? Just to give you an example of, like, why this might be important, let's say you found this first result. You found this dissociation. You found that, okay. Patients who have damage to the fusiform gyrus are worse on face perception, but they're fine on object perception. So I found this dissociation. So I think there's something specific about face perception in the ang in the fusiform gyrus. Right? But what if what's going on here is that, like, let's say you tested other patients that have damage to other brain regions, and you find that they also look like this. Right? And then what you realize is that you created a test that you didn't you didn't you weren't aware of this, but the face task is just more difficult than the object task. So, like, damage to any brain region is just gonna make people worse at any challenging task. Right? Like, anytime you give them something that's a little bit challenging, they're gonna do worse because they just have difficulty concentrating or something like that. Right? So you thought it was something specific, but it was something more general, just like a task difficulty thing. Right? So you can rule that explanation out with a double dissociation

Answer 37

Similar logic applies to brain recording methods * E.g., perception of faces but not places is associated with strong activation of the fusiform gyrus, and perception of places but not faces is associated with strong activation of the parahippocampal gyrus d

Answer 38

Many ways of characterizing lesions * Gray matter * Presence/absence of lesion * Thickness * White matter * Presence/absence of lesion * Thickness And then the white matter is all these sort of fibral fiber bundles that are connecting all the different brain regions to one one another. It's like the wiring of the brain. We're gonna see them that can characterize the degree of the lesions to break to the gray matter or the degree of the lesions to the white matter. And both of these techniques that we're gonna focus on use, MRI magnetic resonance imaging.

Answer 39

We're gonna see them that can characterize the degree of the lesions to break to the gray matter or the degree of the lesions to the white matter. And both of these techniques that we're gonna focus on use, MRI magnetic resonance imaging. here is 3d. Measures the difference in water (hydrogen) density in brain tissue to visualize brain structures (static MRI) * Spatial resolution is determined by the size of the voxels (3D volumetric pixels) in the MRI image * If voxels are 3x3x3 mm, there are ~80,000 voxels in a 3D image of a human brain

Answer 40

MRI: spatial resolution * Spatial resolution: ability to resolve small differences in an image * Spatial resolution in MRI is determined by the size of the voxels. * Only very advanced machines can obtain voxels smaller than 1 mm. * A: 8 mm, B: 4 mm, C: 2mm, D: 1.5 mm, E: 1 mm

Answer 41

Brain locations: X,Y,Z coordinates in 3D space, each unit =1 mm * X (left-right/lateral-medial) distance from vertical plane between the hemispheres (mid- sagittal) * 0 = medial plane * Positive = right hemisphere * Negative = left hemisphere * Y (posterior-anterior) distance from vertical plane through the anterior commissures (AC) * 0 = AC plane * Positive = anterior * Negative = posterior * Z (ventral-dorsal) distance from horizontal plane through the anterior and posterior commissures * 0 = AC-PC plane * Positive = superior * Negative = inferior 35, -45, -12? It was created in Montreal, the Montreal Neurological Institute Coordinate System. t was created in Montreal, the Montreal Neurological Institute Coordinate System.

Answer 42

By overlaying images of brain lesions for a group of subjects who all have a similar pattern of cognitive impairment, we can identify common areas of lesioning across the group * Bottom row: the color coding in each voxel indicates the percentage of subjects in the group who have a lesion in that voxel

Answer 43

Parietal lobe lesion and surrounding axonal fibers imaged with DTI * Note the right/left asymmetry in the fiber tracts. And so you lose basically, what happens in in your DTI data, diffusion tensor imaging data, those track like, you no longer can trace out those tracks. Basically, it looks like those tracks are missing on the brain. Right? So this is an example of, like, a patient who had, a lesion affecting some of the white matter tracks tracks in one hemisphere, but not the other hemisphere. The point here is that on, on one hemisphere, you see all those bright yellow tracks, and then they're just missing in the other hemisphere. That's where the lesion is.

Answer 44

Advantages: * Powerful method for testing the causal role of brain regions in cognitive functions * Reveals brain areas that are NECESSARY for the function * Double dissociations provide strong evidence for separable processes (e.g., face perception vs. place perception. DISAVANATAGES In humans, these are not “controlled” experiments * E.g., Damage may not occur in brain areas one would like to investigate. Subjects may have various cognitive, educational or other differences that complicate interpretation * Damage is not always narrowly localized, and multiple functions can be impaired. * Damage is never identical from person to person You're not like the the lesion of the brain was not an experimental manipulation. Right? You didn't have control over that. Right? And so as a result, you're Right? You didn't have control over that. Right? And so as a result, you know, the lesions can be I mean, the lesions are messy. Right? They're, like, not in one specific brain region.

Answer 45

Transcranial magnetic stimulation (TMS) 2. Brain electrodes 1. intra-operative 2. long-term implants 3. temporary implants

Answer 46

Most common in front of the head Dammage to the occipital lobe.

Answer 47

Cortical stimulation * For research purposes: cortical stimulation can be used for studying brain- cognition relationships * What’s the logic? * Stimulation affects neural activity of underlying tissue * If this tissue supports a cognitive function, then the ability to carry out the function should be affected. * Researchers can draw inferences about the underlying cognitive functions from performance on one or more tasks under stimulation conditions * There are also clinical uses of brain stimulation (we will see some examples)

Answer 48

Wire coil encased in insulation * Electrical current sent through the coil à generates a magnetic field * Magnetic field passes through skin and scalp à produces a physiological current à can increase or decrease neuronal firing * The current can impact (disrupt) cognitive processing * The effects are limited to a local region of ~1-1.5 cubic cm, allowing researchers to test hypotheses about the localization of cognitive functions * It is akin to a temporary, reversible “lesion” * Advantage: Can be used in healthy volunteers have agents in skull

Answer 49

How can surgeons avoid damaging critical cognitive areas during brain surgery? * Map brain regions during awake brain surgery (e.g., for brain tumor, epilepsy, etc.) * Apply focal stimulation and ask individual to perform tasks (e.g., name a picture, count, move hand, etc.) * Brain lacks pain receptors * Penfield was an early pioneer using this technique Left: Intraoperative view of parietal tumor before resection Above: * The letter tags mark the tumor boundaries. * The number tags show areas identified using electrical stimulations: * primary somatosensory areas of the hand and fingers (10, 11, 12); language sites (20: counting, 21: naming); calculation areas (30: multiplication, 31: multiplication and subtraction, 33: subtraction). An: anterior; P: posterior; M: midline

Answer 50

Parkinson’s Disease: Loss of dopamine producing cells in substantia nigra (basal ganglia) Placement of DBS electrodes in subthalamic nuclei of the basal ganglia

Answer 51

* Subdural arrays of electrode pairs embedded in plastic strips are placed on the surface of cortex * Recording (to identify epileptic focus) (ECOG) * Stimulation (injection of current into electrodes) Stimulation: * For clinical purposes: cognitive mapping used by surgeons to limit cognitive impact of surgery. * For research purposes: Disruption of function to understand brain-cognition relationships

Answer 52

We cannot directly measure a “cognitive function.” Instead, we design tasks that rely on that cognitive function (e.g., picture naming). * However, a single task typically involves multiple cognitive functions * And a single cognitive function can be used in many different tasks

Answer 53

Isolating a brain region – creating disruption or measuring activity in a limited brain region * Isolating specific cognitive functions – Comparing tasks that are matched for all functions but the one under investigation (experimental and control tasks)

Answer 54

Disruption/stimulation techniques: Strengths and weaknesses * Extremely powerful for hypothesis testing, esp. to test if an area is necessary for a cognitive function * Limitations in terms of available neural locations, invasiveness, spatial resolution, temporal resolution, etc.

Answer 55

Brain activity Brain activity” is neurons firing action potentials * Action potentials cause the release of neurotransmitters at synapses * This is the primary way in which neurons send signals to one another * Communication between neurons is the basis of information processing in the brain * All measures of brain activity are either directly or indirectly related to neural firing * Directly: e.g., electrical recording from single neurons * Indirectly: e.g., changes in blood oxygenation (fMRI)

Answer 56

1. Identify what cognitive functions a brain region is associated with * E.g., face perception Kanwisher et al. * Fusiform Face Area F = face stimuli O = object stimuli fMRI data Kanwisher et al., 1997

Answer 57

Measuring curves. Two thirds (67%) of tuning curves with a maximum at one extreme showed the minimum at the opposit

Answer 58

Characterize the functional organization of the brain * E.g., brain maps

Answer 59

Identify what cognitive functions a brain region is associated with * E.g., face perception 2. Identify what information a brain region sends to other parts of the brain. * E.g., information about specific facial features 3. Characterize the functional organization of the brain * E.g., brain maps

Answer 60

Record the electrical activity of neurons by invasively placing electrodes inside the skull * Key measure is firing rate * Number of actions potentials (spikes) per second * Determine what causes the neurons to fire: * What stimulus features? * What cognitive tasks? * If a neuron responds strongly to a specific stimulus, we infer that the neuron is involved in processing that stimulus

Answer 61

High temporal resolution (milliseconds) * High spatial resolution (as small as single neurons) * Can allow for the recording of individual neurons * Single cells can be highly selective in what they respond to

Answer 62

Invasive * Samples only a small percentage of neurons in the brain * Which brain region should I target? * Cannot demonstrate causal function of neurons in cognition * Need disruption methods to address this issue * What happens when these neurons are disrupted (e.g., lesioned, turned on/off)?

Answer 63

functional Magnetic Resonance Imaging * Non-invasive technique for indirectly measuring brain activity * Uses a strong magnet (often 3 tesla or more) to detect small changes in the magnetic properties of blood that occur when the neurons in a brain region are active * often 3 teslas or more

Answer 64

Blood Oxygenation-Level Dependent (BOLD) signal * When neurons fire, they require more glucose and oxygen, which is carried in red blood cells * When neurons fire, excessive amounts of oxygen are sent to nearby blood vessels * More neural firing = more oxygenated hemoglobin in local blood vessels * fMRI is sensitive to the ratio of oxygenated to deoxygenated hemoglobin * More oxygenated hemoglobin = greater fMRI signal

Answer 65

Increased neural activity * Increased local blood flow * Increase in oxygenated hemoglobin relative to deoxygenated hemoglobin * Increased BOLD fMRI signal

Answer 66

The hemodynamic response detected by fMRI is slow relative to the speed of neural activity * Peaks at 4-6 seconds after activity onset * This lagged response limits the kinds of experimental questions that can be addressed with fMRI * Cannot examine rapid fluctuations in neural firing

Answer 67

When experimental events are close together in time, their responses overlap * Challenging to determine the amount of activation that can be attributed to each even

Answer 68

fMRI data are 3D images (volumes) collected every few seconds (repetition time) * Typically collected every 1 to 3 seconds * Each image is composed of voxels * Voxels = volume pixels * Typically cubes with a length of 1 to 3 mm on each side

Answer 69

One of the primary ways that fMRI is used is to identify the cognitive functions that a brain region is associated with * E.g., face perception * In the scanner, subjects see images of faces, objects, scenes, etc. * Compare levels of fMRI signal across stimulus categories * Are there selective responses to certain categories and not others?

Answer 70

Our data allow us to reject alternative accounts of the function of the fusiform face area (area “FF”) that appeal to visual attention, subordinate-level classification, or general processing of any animate or human forms, demonstrating that this region is selectively involved in the perception of faces.

Answer 71

MRI results are often displayed as maps of activation across the brain * These activation maps show which brain regions respond most strongly to an experimental condition (e.g., faces) * fMRI results are simply numbers that indicate the activity levels of voxels. * Activation maps convert these numbers into color scales. A R T I C L E S Cortical surface rendering Slices through the 3D data

Answer 72

Non-invasive * Can examine activity across the whole brain * Moderately good spatial resolution (millimeters)

Answer 73

Low temporal resolution (seconds) * Cannot examine activity of individual neurons. * A single voxel may contain 10^5 to 10^6 neurons * Cannot demonstrate causal function of brain regions in cognition * Need disruption methods to address this issue * What happens when these regions are disrupted (e.g., lesioned, turned on/off)?

Answer 74

EG = Electroencephalography * MEG = Magnetoencephalography * MEG and EEG are different views of the same neural source * Electromagnetic signals generated when large groups of neighboring neurons (10^3 to 10^5) exhibit synchronous activity

Answer 75

When neurotransmitters are released at synapses, they allow charged ions to flow into the postsynaptic neuron * This creates a difference in electric potential along the axis of the neuron, which can be detected as a change in voltage * The electric signal from a single neuron is very weak and hard to detect from outside of the head (non-invasive)

Answer 76

When the activity of thousands of neurons fluctuates synchronously, their electrical signals sum and can be detected with electrodes on the scalp * This is the signal that is detected by EEG

Answer 77

Electric currents produce magnetic fields, which curve around the current * When the activity of thousands of neurons fluctuates synchronously, their associated magnetic fields can be detected outside of the head * This is the signal that is detected by MEG

Answer 78

These magnetic fields are very weak (10^-12 tesla) relative to the magnetic fields generated by the earth, electrical equipment, and many other environmental sources * “a challenging problem akin to listening for the footsteps of an ant in the middle of a rock concert” Magnetically shielded room Big box. Very expensive MEG

Answer 79

EEG can be used to assess the overall state of the brain (arousal, sleep, etc.) * These measurements reflect large-scale changes in overall brain activity

Answer 80

EEG and MEG can also be used to assess the timing of brain responses to experimental events * EEG or MEG responses to an event are averaged over many repeated trials * These are called event-related responses

Answer 81

Average event-related MEG signals from the back of the head contain face-selective responses at 100 and 170 ms

Answer 82

* The response at 100 ms is associated with face categorization * Is this a face? * The response at 170 ms is associated with face identification (and also categorization) * Who is this person?

Answer 83

We found a face-selective MEG response occurring only 100 ms after stimulus onset (the 'M100'), 70 ms earlier than previously reported. Further, the amplitude of this M100 response was correlated with successful categorization of stimuli as faces, but not with successful recognition of individual faces, whereas the previously-described face- selective 'M170' response was correlated with both processes. These data suggest that face processing proceeds through two stages: an initial stage of face categorization, and a later stage at which the identity of the individual face is extracted.”

Answer 84

Spatial resolution of MEG and EEG is much worse than fMRI * Localizing the spatial source of the signal is challenging, because the responses detected at the scalp contain a mixture of signals from many parts of the brain * Known as the ”source-localization problem”

Lectures 1, 2, 3-Neuroscience cognitive Flashcards

Pictures will be in Gradescope, exam Tuesday.