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Chapter 2

Chapter 2Neural Basis for Cognition.docx

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University of Toronto Scarborough
Dwayne Pare

THE NEURAL BASIS FOR COGNITION In this chapter, we will study the brain functioning that makes COGNITION possible. We will also be learning about the methods used in learning about the brain (neuroimaging). What is COGNITION? Very important: Each part of the brain has its own SPECIALIZED function, and or behaviour, thoughts and feelings almost always depend on many brain regions working together. (Even for what you consider the most simplest of actions!) A Preview of the Upcoming Chapter: We will gain an overview of how the brain is built, and how it works, emphasizing the FUNCTION of each region. (Be prepared for a lot of parts!!!!!!) -these functions are identified through neuroimaging data, which can assess the activity level in different areas of the brain… We will be examining the visual system in depth. Why the visual system? Because the visual system is what lets us see and understand the visual system around us, it is a gateway of vast information. The visual system is an example of what we can learn by deeply studying the brain. What is the Key point in Studying the Visual System? Visual system shows that analysis of visual input occurs as soon as visual information enters the nervous system. This analysis depends on many highly specialized regions of the brain working in parallel with each other. -nervous system: Brain damage is deeply unfortunate. It is through brain damage, that we have gained our deepest insights about the brain. –One example in particular: CAPGRAS SYNDROME- What does Capgras Syndrome teach us? Damage anywhere in the brain can produce SPECIFIC, and in this case very disruptive symptoms. How do people get Capgras syndrome? i)In elderly, it may accompany Alzheimer’s disease. ii) Through various injuries to the brain. What is the “HALLMARK” of Capgras syndrome? People afflicted with Capgras syndrome are able to intellectually recognize the people in their world (their spouse, friend, mom etc.), but instead of feeling familiarity and responding with warmth, they believe that their ―close one is actually an imposter, doing an amazing job at impersonating the REAL person. The Capgras patient notes that she sounds just like her and that she looks just like her. However, he believes that there are slight differences between the imposter and the person whom he is impersonating. The real person, is believed to have been kidnapped and replaced (patient offers a bizarre explanation). These belief prompts feeling of suspicion and frustration in the Capgras patient (“Why is nobody else realizing this as well, that my wife has obviously been kidnapped?”) -------You can see how this can lead to violence, by the person with Capgras syndrome, towards the imposter, who is the actual loved one. ________How do researchers explain this? What’s their THEORY? Researchers propose that facial recognition involves TWO SEPARATE systems. What are these two separate systems? 1) INTELLECTUAL recognition, which leads to COGNITIVE APPRAISAL. A judgement is made: (“I know what my dad looks like and I perceive that you closely look like him.”) 2) EMOTIONAL, GLOBAL APPRAISAL-(“You look familiar, and also generate a warm response in me.”) … (1.) + (2) = Concordance of both appraisals lead to certainty of recognition (“You ARE my father.”) In Capgras syndrome, emotional processing is disrupted, leading to (1) intellectual recognition WITHOUT familiarity and warmth. It stops at: (“Hey, you look like my dad, but don’t trigger any sense of familiarity, so you must be someone else.”….Later on…”What did you do with him?”) __________Is the above hypothesis SUPPORTED by evidence? We have 2 types of evidence. 1) Neuroimaging 2) Psychology Laboratory Findings (starts on page 7) 1) We can determine if we are thinking about Capgras syndrome in the right way, by looking at NEUROIMAGING. Neuroimaging: non-intrusive, high quality, 3D images of living brain. Neuroimaging can tell us what is where, the shape of parts and the connection b/w parts, it can show tumors and missing structures.  Neuroimaging tells us, that in Capgras syndrome, there are abnormalities in several brain areas (2 are talked about in the text.): i. In the circuits involving the AMYGDALA (located in right temporal lobe)--CHECK ii. FRONTAL LOBE (particularly prefrontal cortex Brain Abnormality: What do we already What does other What links can know about that biological evidence make between that brain region? say about this brain region, and region? the role it plays in Capgras syndrome? 1) Circuits involving -Amygdala is the 1) Amygdala helps -is important for Amygdala ―emotional people remember supporting feelings of (temporal lobe, evaluator‖, which emotional events of familiarity. With right side of brain) detects + and – their lives. damaged amygdala, stimuli (+: associated 2) Amygdala plays a person WON’T with safety, rewards) experience warm role in decision- sense of feeling good (- associated with making, esp. where threat or danger.) you rely on emotional or secure, when looking @ close evaluation of your one’s familiar face. options. Therefore, face won’t seem familiar to them. 2) Frontal Lobe fMRI shows that the i)absence of planning Damage to this area (specifically) in the prefrontal cortex is and analysis in dream can be attributed to right particularly active, in state, explains why fact that Capgras PREFRONTAL tasks needing careful dreams don’t make patients cannot CORTEX. planning and sense a lot discern real from analysis. unreal, judge the ii) role of frontal lobesensibility of beliefs, is diminished during hallucinations in thus being inclined to Schizophrenia bizarre hypotheses to explain things. (“My patients, rendering them unable to wife was abducted, separate thoughts and a robot is impersonating her.”) from outside voices, and imagined events from real. Temporal lobe: the lobe of the cortex lying inward and down from the temples. The temporal lobe in each cerebral hemisphere involves the primary auditory projection area, Wernicke’s area, and subcortically, the amygdala and hippocampus. When something is subcortical, it means that something is beneath the surface. (i.e., it is beneath the cortex.) Cortex: the outermost surface of an organ in the body Amygdala and hippocampus, are subcortical structures, meaning they exist beneath the cortex. While trying to comprehend the above chart, your eyes must have stumbled upon ―fMRI‖…What is that? What is an fMRI? (A neuroimaging technique) fMRI technique can tell us the moment-by-moment activity level in different sites in a living brain (kind of like giving us sports commentary, I feel)  Can show which part of brain is active when partaking in particular tasks (like: reading these notes, watching TV, listening to music)..from this we can discern what that brain area’s function is, what it does.  WILL BE DISCUSSED LATER. Psychology Laboratory Findings (thanks to: Ellis, lewis, Ramachandran and Blakeslee)  Recognition of ALL stimuli involve two separate mechanisms:  One mechanism is rooted in FACTUAL knowledge.  The other mechanism is more emotional, related to warmth and familiarity. BOTH, cognitive neuroscience (see first column specifically) and cognitive psychology (the psychology laboratory findings, above) confirm the initial hypothesis, researchers used to explain Capgras syndrome. But, by studying Capgras syndrome we also learned a lot about the brain. We learnt that: -amygdala responsible for feelings of familiarity and security -CAPGRAS syndrome has taught us that the emotional evaluator works SEPARATELY from the factual information evaluator, explaining why the head and heart might want different things (in everyday words). (Someone’s evaluation of facts leads to one conclusion, while the emotional evaluation leads to another conclusion.) -simplest of achievements require the integration, cohesiveness and coordination of many brain regions. If you want to recognize your dad, steps taken are: 1) Factual memory stores what your dad looks like 2) You analyze the visual input received when looking at the face, you are presented with 3) You compare 1) and 2). Is there a match? Do (1) and (2) look alike? Also, an emotional evaluation of the input occurs (as we learnt from Capgras syndrome), in a different site (the amygdala0. Yet, again, another different site synthesizes all the data obtained in steps (1) to (4) to reach a sensible conclusion. If it is deemed that he IS your dad, a warm response is evoked. However, if it is your dad, but looks he different from what you remember him as, a plausible explanation is produced (“Oh, he got a haircut.”) Technical Foundations of Brain:  Brain’s weight is 3-4lbs (size of small melon)  Extraordinary: Brain contains both nerve cells and glial cells.  Contains 1 trillion nerve cells, each of which is connected to 10,000 others, for roughly 10 million billion connections  Contains appx 10 trillion glial cells (outnumber nerve cells by 10:1 ratio estimated) Brain is densely packed organ.  Symptoms produced by brain damage depend upon LOCATION of damage. Examples: 1. Phineas Garg: damage in frontmost part of brainsymptom: severe personality and emotional problems 2. Paul Broca discovered damage on left side of brainsymptom: disruption in language skills 3. Edouard Claperede discovered that profound memory loss occurs, when other parts of the brain are damaged. Cherish your brain. SO: Location! Location! Location is everything, like real-estate in the brain!  Now, we will look at the particular where’s of the brain: Human brain is divided into 3 main structures: hindbrain, midbrain and forebrain. Start referring to figure 2.2, from now on. Part of Brain HINDBRAIN MIDBRAIN FOREBRAIN -the LARGEST region. Focus is on forebrain. LOCATION -sits on top of -completely -covered by -WHERE IS IT? spinal chord hidden by CORTEX, so the -mostly hidden forebrain. cortex of from view by forebrain is what forebrain we can we see, when we look @ diagrams of brain. WHAT ARE -includes -coordinate -most important FUNCTIONS structures for movements, esp. in supporting ASSOCIATED controlling crucial precise, eye intellectual WITH IT? life functions movements. functioning. -heartbeat and -has circuits that breathing rhythms relay auditory Tone of body is regulated here: info from ears to areas in forebrain -posture, (where this alertness and sensory input will balance. be processed and interpreted. *********** Its BIGGEST part is the CEREBELLUM -resp for the coordination of body movement and balance, and spatial reasoning, discriminating sounds you hear, & integrating input from your various sensory systems. Comprehension Questions: 1. What is the cortex? –is the outermost covering of an organ. What are the properties of the cortex?  Thin for forebrain, averaging 3mm thick, but still makes up 80% of the brain. Analogy: if stretched out flat, it would be 2 sq. feet.  BUT, cortex is actually CRUMPLED and ―jammed‖ to fit in skull, producing wrinkles the convolutions. Some valleys between the wrinkles are deep grooves, dividing brain into different sections. The deepest groove is the LONGITUNAL fissure, running lengthwise, separating the LEFT cerebral hemisphere from the RIGHT cerebral hemisphere…these hemispheres constitute the major part of the FOREBRAIN in us. (Re: forebrain is what we see, remember? Underneath forebrain is midbrain and hindbrain) -The other fissures are 1. Lateral fissure: (going across; separating top from bottom) and 2.Central fissure, (separating front from back)]. They divide the cortex, in EACH hemisphere into 4 lobes. -Use textbook diagrams to visualize this properly. These divisions occur on both sides of the cerebral hemispheres, concurrently. Frontal Lobe: -forms front of brain, is right behind the forehead Parietal Lobe: -forms brain’s topmost part Both frontal and parietal lobe are divided by central fissure in each hemisphere. The BOTTOM EDGE of frontal lobe is at LATERAL FISSURE, and below lateral fissure are temporal lobes. At back of brain, connected to parietal and temporal lobe, are occipital lobes. Q) What are subcortical parts of forebrain? 1. THALAMUS (fx: is a relay station for almost all sensory information going to cortex (above) 2. HYPOthalamus (underneath thalamus) fx: controlling motivated behaviours like eating, drinking, sex 3. Limbic system surrounds thalamus and hypothalamus and is interconnected. Limbic system consists of amygdala and hippocampus (both are in temporal lobe & subcortical) Fx: needed for learning and memory, and for making of new memories (PROOF: H.M. developed amnesia after removal of these structures).  People have thorough and longer-lasting remembrance for emotional events vs. non- emotional ones (memory is even stronger when amygdala is activated while witnessing this emotional event).  If amygdala damaged, this particular memory advantage diminishes. What is Lateralization?  all brain structures-cortical and subcortical-occur in pairs. o Ex) There is a left side amygala and a right side amygdale o Ex) There is a left side occipital cortex and right side occipital cortex Are left side and right side parts completely symmetrical? Roughly same, in most domains, EXCEPT there are DIFFERENCES in function, between the same left-side and right-side parts. Connections: -both haves work together, functioning of one side is integrated with other side, through COMMISSURES (thick bundles of fibres, carrying info back and forth between both hemispheres).An example of a commisure (the LARGEST) is corpus callosum  Corpus callosum used to be cut in extreme cases of epilepsy, resulting in split brain patient. (communication between both halves limited) SEE FIG 2.5  From these patients we learnt: that both halves are specialized in their unique ways. Left side-Language Capacities, Right Side-needed for spatial judgement tasks. BUT STILL: both halves are partners in almost all mental tasks, each side contributing their own specialized skills for overall task. It’s n ever left side of brain versus right side of brain. They are buddies. Complex skills (ex: creativity and intuition) depend on WHOLE brain, not just one side!!!! Neuropsychology: study of brain’s structures and how they relate to brain function. CLINICAL Neuropsychology: specifically, study of brains with damage, to learn more about functioning of intact brains. The pattern we see: particular symptoms we see in brain damaged patients, depends on site of damage. LESION: particular site of damage in brain. (ex: lesion in hippocampus produces memory problems, and not language problems) Consequences of brain lesions IS FURTHER SPECIFIC to WHICH hemisphere is damaged.  Ex) Damage to frontal lobe, left side: disruption of language use. BUT, damage to right side does not have this effect. The next page chart shows how a neuroscientist can study brain with technology. N E U R O I M A G I N G T E C H N I Q U E S (all 4 give 3D image of brain) MRI (PAGE CT (Computerized PET (Positron Emission fMRI (PAGE 42) Axial Tomography) (PAGE 45, 47) Tomography) 41) How does it -uses magnetic -gives brain -introduce a tracer -closely related work? properties of structure via x- substance (ex. Glucode- to MRI. atoms in brain rays; body’s fuel) -shows brain tissude to give detailed pic of Primary data: x-  These tracer activity like rays molecules PET. brain are tagged with low -shows oxygen dose of content of radioactivity, blood flowing allowing the through each scan to brain region. ―trace‖ the glucose  this through indicates We get stable results in BOTH MRI and CT brain, to see accurately level scans, because brain structure stays consistent (as long as no tumor which tissues of neural growth/accident.) use more of activity in each it, and which region. less, during a task. Primary data: radioactive emissions Whereas, fMRI and PET scans tell us the pattern of activation; the results depend on which TASK you were performing @ time of task. This cements that different brain areas perform different functions….brain is specialized. ELECTRICAL RECORDING:  Neurons do brain’s main work. They vary in size, shape, functions, but usually they communicate with each other through chemical signals called NEUROTRANSMITTERS.  Activated neurons release transmitters, which further activates/deactivates immediately adjacent neurons (these neurons ―receive‖ the chemical message). They can send the message further, to other neurons. But, there is also important messaging that goes on WITHIN a neuron itself..how the message travels through the neuron, from the input end (most sensitive to receiving sisgnal) to the output end. How does this happen?  Via electrical pulse; (b/c of flow of ions (atoms with charges-+ or -, in and out of neuron).  Collectively, considering the brain has ONE TRILLION neurons, when they are active at the same time, the current generated can be detected by electrodes placed on your scalp’s surface.  This is ELECTROENCEPHALOGRAPHY (― records the voltage changes that happen at the scalp, as a reflection of what’s going on underneath). This technique produces an electroencephalogram (EEG)  EEG’s study broad rhytms in brain’s activities (ex: rhythms in different sleep stages See pg 44). EEG’s
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