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Chapter 2

PSYB57- Chapter 2.doc

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Dwayne Pare

Chapter 2: The Neural Basis for Cognition Capgras Syndrome: An Initial Example Capgras Syndrome – a relatively rare disorder, resulting from specific forms of brain damage, in which the afflicted person recognizes the people in his or her world but denies that they are who they appear to be. Instead, the person insists, these familiar individuals are well-disguised impostors. Facial recognition involves two separate systems • Cognitive appraisal: understanding that the other person is recognized • Global emotional appraisal: the warm response to familiarity These two together results in: Of course you’re who you are. The emotional appraisal is disrupted in this syndrome leading to the intellectual identification without the familiarity response. The Neural Basis for Capgras Syndrome Neuroimaging Techniques – allow researchers to take high-quality, 3-d pictures of living brains Current studies rely on MRI scans, before researchers relied on PET scans. Right temporal lobe is damaged in Capgras patients and this damage disrupts circuits involving the Amygdala –serves as an “emotional evaluator” helping an organism to detect stimuli associated with threat or danger and for detecting positive stimuli – indicators of safety or available rewards. • This means people won’t experience the warm sense of feeling good (and safe and secure) when looking at a loved one’s familiar face. Capgras patients also have damage in the right Prefrontal Cortex – the outer surface (cortex) of the front most part of the brain. It has many functions but is crucial for the planning of complex or novel behaviours, so it is one of the main sites underlying the brain’s executive functions. • fMRI allow us to track moment-by-moment activity levels in different sites in a living brain o Prefrontal cortex is less active when dreaming dreams are illogical • Capgras patients are less able to keep track of what is real and what is sensible; weird beliefs can emerge unchecked, including delusions. What Do We Learn From Capgras Syndrome? Damage to the amygdala is probably the reason Capgras patients experience no sense of familiarity when they look at faces they know well The damage to prefrontal cortex helps us understand why Capgras patients offer crazy hypotheses about their skewed perception. Capgras syndrome can be used to illuminate broader issues about the nature of the brain and of the mind It suggests that the amygdala plays a crucial role in supporting the feeling of familiarity and the biological evidence suggests that the amygdala also plays a central part in helping people remember the emotional events of their lives, and it’s important in decision-making, particularly emotional decisions. The Study of the Brain Brain weighs about 3-4 pounds Contains 1 trillion nerve cells with 10 million billion collections. Contains about 10 trillion glial cells Phineas Gage: damage to front-most part of his brain led to severe personality and emotional problems Hindbrain, Midbrain, Forebrain The brain is divided into 3 main structures: 1. Hindbrain – sits atop the spinal cord and includes several structures crucial for controlling key life functions • It maintains the body’s overall tone; it helps maintain the body’s posture and balance and helps control the brain’s level of alertness • Cerebellum – largest area of hindbrain and damage to this can cause problems in spatial reasoning, in discriminating sounds, and in integrating the input received from various sensory systems 2. Midbrain - plays important role in coordinating movements and it contains structures that serve as “relay” stations for information arriving from the sensory organs. • There are circuits that relay auditory info from the ears to the areas in the forebrain where this info is processed and interpreted. It also helps regulate the experience of pain. 3. Forebrain - the largest region; it plays a crucial role in supporting intellectual functioning • Cortex – the outer surface of the forebrain; it covers 80% of the human brain o Convolutions – wrinkles visible in the cortex that allows the enormous surface area of the human brain to be stuffed into the relatively small volume of the skull. “valleys” between the wrinkles are actually deep grooves that divide the brain into different sections. Longitudinal Fissure – deepest groove which separates the left Cerebral Hemisphere from the right Cerebral Hemisphere – one of the two hemispherical brain structures – one on the left side, one on the right – that constitute the major part of the forebrain in mammals. Cortex is divided into 4 lobes: Frontal Lobes – front of the brain behind the forehead Central Fissure – divides the frontal lobes on each side of the brain from the Parietal Lobe – the brain’s topmost part Lateral Fissure – the bottom edge of the frontal lobes is marked, and below it are the Temporal Lobes. Occipital Lobe – at the very back of the brain, connected to the parietal and temporal lobes Subcortical Structures Subcortical – parts of the brain hidden from view, underneath the cortex • Thalamus – acts as a relay station for all sensory info going to cortex • Hypothalamus – under the thalamus; plays crucial role in controlling motivated behavior such as eating, drinking and sexual activity Limbic System – surrounding the thalamus and hypothalamus; it include the amygdala and hippocampus; essential for learning and memory Amygdala is key in emotional processing • Eg. we remember emotional events more than emotionally flat events Lateralization Cortical and subcortical structures appear in both sides of the brain in roughly the same structure Commissures – integrates the 2 hemispheres with its thick bundles of fibers that carry information back and forth from one hemisphere to the other • Corpus Callosum – largest commissure Split-brain procedures severed the commissures between the two hemispheres as treatment for epilepsy; this taught us the left-brain is specialized in language and the right in a number of tasks-spatial judgment. Data from Neuropsychology Neuropsychology – study of the brain’s structures and how they relate to brain function Clinical Neuropsychology – understand the functioning of intact, undamaged brains by careful scrutiny of cases involving brain damage Symptoms developing from brain damage depend heavily on the site of the damage Lesion – specific area of damage – In the hippocampus produces memory problems but not language disorders, in the occipital cortex produces problems in vision but spares the other sensory modalities. Damage to left side of frontal lobe = disruption of language use the right doesn’t have this effect Data from Neuroimaging Computerized Axial Tomography (CT) – study brain structure Uses X-rays and provides 3D image • • Tells size, shape and position of structures within brain Positron Emission Tomography (PET) –study brain activity • Uses a radioactive tracer substance and tells which tissues are using more of it Eg. glucose • Tells which regions are active at any point in time Magnetic Resonance Imaging (MRI) – uses magnetic properties of atoms that make up brain tissue to show detailed pictures of the brain Functional Magnetic Resonance Imaging (fMRI) – measures the oxygen content in blood flowing through each region of the brain; this is a very accurate index of the level of neural activity in the brain from moment-to-moment. CT and MRI scans are stable while PET and fMRI are variable, depending on what task the person is performing. Data from Electrical Recording Neurons – trillion nerve cells that do the brain’s main work Neurotransmitters – chemical signals neurons use to communicate with one another When a neuron is “activated”, it releases the transmitter and this • chemical can then activate or de-activate other, immediately-adjacent neurons. The adjacent neurons “receive” the signal and send it to other neurons. • 2 types of communication: between neurons & within neuron (input and output ends that receive and sends neurotransmitters) Because millions of neurons are active at the same time, the current generated by them is enough to be detected by electrodes on the scalp. Electroencephalogram (EEG) – a recording of voltage changes occurring at the scalp that reflect activity in the brain underneath. EEGs study broad rhythms in the brain’s activity Eg. Sleep cycles • • Event-Related Potentials (ERPs) - measure of the changes in EEG in a brief period just before, during and after an event The Power of Combining Techniques Researcher combine the scans and techniques from different sources so as to use the strength of one technique to make up for the shortcomings of the others. Neuroimaging data can tell us that a brain area’s activity is correlated with a particular function, but we need to ask whether the brain site plays a role in causing that function. Transcranial Magnetic Stimulation (TMS) – creates a series of strong magnetic pulses at a specific location on the scalp, causing temporary disruption in the brain region directly underneath this scalp area;provide crucial info about functional role of that brain area. Localization of Function Localization of Function – aims toward figuring out what’s happening where within the brain The Cerebral Cortex The cortex includes regions divided into 3 categories: Motor Areas – contain brain tissue crucial or organizing and controlling body movements Sensory Areas – contain tissue essential for organizing and analyzing info we receive form senses Association Areas – support many functions, including the essential activity of thinking Motor Areas Primary Projection Areas – regions of the cortex that serve as the brain’s receiving station for sensory information or as a dispatching station for motor commands. • Primary Motor Projection Areas – departure point for signals leaving the cortex and controlling muscle movement o Evidence: electrical current in different areas of the brain of an anesthetized animal produce movements  Contralateral Control – stimulation to the left hemisphere leading to movements on the right side of the body and vise versa • Primary Sensory Projection Areas – arrival points for info coming from eyes, ears, and other sense organs Sensory Areas Somatosensory Area – information arriving from the skin senses is projected to this region in
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