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PSYC*2650 Ch 2.doc

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PSYC 2650
Anneke Olthof

Wednesday, Jan 16, 2012 Chapter 2: The Neural Basis for Cognition - evidence concerning the brain functioning that make cognition possible needs its own presentation - each part of the brain has its own specialized function so that our behaviours, thoughts, and feelings almost invariably depend on the the coordinated action of many brain regions Capgras Syndrome: An Initial Example - rare disorder which seems to be one of the accompaniments to Alzheimer’s syndrome - someone with Capgras syndrome is fully able to recognize the people in their world but is convinced that these people are not who they appear to be - they believe the person has been kidnapped or worse - they think the person in front of them is a well-trained imposter - the sufferer developed paranoid suspicions - the answer of what is going on lies in the fact that facial recognition involves 2 sepa- rate systems in the brain, one of which leads to a cognitive appraisal (I know what my father looks like) and the other to a more global, somewhat emotional appraisal (you look familiar to me and also trigger a warm response in me) - the concordance of these 2 appraisal then leads to the certainty of recognition - in capgras syndrome, the emotional processing is disrupted leading to the intellectual identification without the familiarity response The Neural Basis for Capgras Syndrome - must use neuroimaging techniques to study the brain - PET scans tell a great deal about the structure of the brain - PET scans show a link between Capgras syndrome and abnormalities - one site of damage is in the temporal lobe on the right side of the head, this probably disrupts circuits involving the amygdala that seems to serve as an “emotional evaluator” - the amygdala is also important for detecting positive stimuli - safety and rewards - another abnormalities is in the frontal lobe, specifically in the right prefrontal cortex - an fMRI allows us to track moment-by-moment activity levels in different sites - an fMRI of schizophrenic patients reveals diminished activity in the patients’ frontal lobes whenever they are experiencing hallucinations - with damage to the frontal love, Capgras patients may be less able to keep track of what is real and what is not Wednesday, Jan 16, 2012 What Do We Learn From Capgras Syndrome? - Capgras syndrome suggests that the amygdala plays a crucial role in supporting the feeling of familiarity - it also tells us that this emotional evaluator works in a fashion separate from our evalu- ation of factual information - this syndrome tells us how parts of the brain work together for even the simplest achievement - recognizing your family The Principal Structures of the Brain - the human brain weighs between 3 and 4 pounds, its roughly the size of a small melon - contains estimated a trillion nerve cells Hindbrain, Midbrain, Forebrain - the brain is divided into 3 main structures: 1. Hindbrain - sits directly atop the spinal cord and includes several structures crucial for controlling key life functions - here the rhythm of heartbeats and breathing are controlled - plays an essential role in maintaining the body’s overall tone - posture and balance, level of alertness - largest area of the hindbrain is the Cerebellum which controls coordination of our bod- ily movements and balance, spatial reasoning, discriminating sounds, and integrating the input received from various sensory systems 2. Midbrain - important for coordinating movements, including the skilled, precise movements of our eyes as we explore the visual world - also are circuits that relay auditory information from the ears to the areas in the fore- brain where this information is processed and interpreted - other structures help regulate our experience of pain 3. Forebrain - the largest and most interesting region, this structure surrounds the entire midbrain and most of the hindbrain - the Cortex is the outer surface of the forebrain, it is 3 mm think but it is 80% of the brain - it is convoluted which produces the brain’s most obvious feature - the wrinkles Wednesday, Jan 16, 2012 - the deepest groove is the Longitudinal Fissure, running from the front of the brain to the back and separating the left Cerebral Hemisphere from the right - other fissures divide the cortex in each hemisphere into 4 lobes - the Frontal Lobes form the front of the brain - the Central Fissure divides the frontal lobes on each side of the brain from the Pari- etal Lobes (the brain’s topmost part) - the Lateral Fissure marks the bottom edge of the frontal lobes and below this are the Temporal Lobes - at the very back of the brain are the Occipital Lobes Subcortical Structures - the Thalamus is the brain region that acts as a relay station for nearly all the sensory information going to the cortex - underneath the thalamus is the Hypothalamus, a structure that plays a crucial role in the control of motivated behaviour such as eating, drinking and sexual activity - the Limbic System surrounds the thalamus and hypothalamus, it included the Amyg- dala and the Hippocampus - these structures are essential for learning and memory and for emotional processing - subcortical structures come in pairs so there is a hippocampus on the left side of the brain and another on the right - the 2 halves of the brain work together, made possible by Commissures, thick bun- dles of fibers that carry information back and forth between the two hemispheres - the largest commissure is the Corpus Callosum Neuroimaging Techniques Computerized Axial Tomography (CT scans) - use X-rays to study the brain’s anato- my Positron Emission Tomography (PET scans) - provide a precise assessment of how blood is flowing through each region of the brain, used to study functioning Magnetic Resonance Imaging (MRI) - relies on the magnetic properties of the atoms that make up the brain tissue and it yields a fabulously detailed picture of the brain Functional Magnetic Resonance Imaging (fMRI) - measures the oxygen content in the blood flowing through each region of the brain, it is an accurate index of the level of neural activity in that region, precise picture of moment-by-moment activities - results of CT or MRI are relatively stable Wednesday, Jan 16, 2012 - results of PET or fMRI are highly variable because they depend on the task being per- formed Neuroimaging: An Example - in one condition, participants looked at pictures of faces while their brains were scanned, the data showed high levels of activation in an area called the Fusiform Face Area (FFA), an area that seems highly responsive to faces - in the second condition, participants were looking at pictures of houses while their brains were scanned, the data showed high levels of activity in the Parahippocampal Place Area (PPA), a brain site that seems to respond actively whenever pictures of places are in view - in the third condition, a picture of a face was put in front of one of the participants eyes while a picture of a house was put in front of the other eye - this produced Binocular Rivalry: the visual system is unable to handle both stimuli at once or to fuse the stimuli into a single complex perception, the visual system flip-flops between the stimuli - participants pressed buttons to indicate whether they saw a house or a face and at the same time researchers used an fMRI to keep track of the activity levels - the researchers relied on the BOLD signal (blood oxygenation level dependent) which measures how much oxygen the blood’s hemoglobin is carrying in each part of the brain - when the person reported seeing a house, PPA activity went up etc - suggests we can use brain scans as a means of studying some of the bases for con- scious awareness Correlation Versus Causation - answers the questions of what areas of the brain do is referred to as Localization of Function - there are limitations to neuroimaging data e.g. because activity levels increase in FFE when a face is being perceived, doesn’t mean the FFA is needed for face perception - FFA activation could be a by-product of face perception and not play a crucial role - e.g. a car’s speedometer becomes more activated when a car goes faster but it doesn’t cause speed - neuroimaging data tell us whether a brain area’s activity is correlated with a particular function but we need other data to ask whether those brian sites play a role in causing Wednesday, Jan 16, 2012 Transcranial Magnetic Stimulation (TMS) - creates a series of strong magnetic pulses at a specific location on the scalp, causing a temporary disruption in the small brain re- gion directly underneath this scalp area - can be used to find out if that brain tissue plays a causal role Primary Motor Projection Area - Primary Projection Areas is where signals arrive and depart - arrival points are Primary Sensory Projection Areas and departure points are Pri- mary Motor Projection Areas - evidence for the motor projection area comes form studies in which investigators apply mild electrical current to this area in anesthetized animals - stimulation produces specific movements which show a pattern of Contralateral Con- trol - the primary motor projection area seems to form a map of the body - areas of the body that we can move with great precision have
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