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Chapter 2

CH.2 cognition.docx

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University of Toronto Scarborough
Dwayne Pare

CH.2: The Neural Basis for Cognition Capgras Syndrome: An Initial Example  Rare on its own, accompanies Alzheimer’s syndrome and is observed among elderly. It can result from injuries to the brain  They could recognize the ppl in their world like family members but convinced they are not who they appear to be  Facial recognition involves 2 separate system in the brain; one which leads to a cognitive appraisal (I know what my father looks like, I can perceive that you closely resemble him) and the other to a more global emotional appraisal (you look familiar to me and also trigger a warm response in me). Concordance of these 2 appraisals then leads to certainty of recognition (you obviously are my father). in CS, emotional processing is disrupted leading intellectual identification without familiarity response The Neural Basis for Capgras Syndrome  Capgras patients have damage in the temporal lobe on the right side of the head. It disrupts circuits involving the amygdala (emotional evaluator) which helps an organism to detect stimuli associated with threat or danger.  It is also important for detecting positive stimuli, indictors of safety or indicators of available rewards.  With damaged amygdalae, ppl with capgras syndrome won’t experience the warm sense of feeling good (and safe and secure) when looking at a loved one’s similar face.  MRI scans tell us about structure of the brain and fMRI scans tell us which portions of the brain are especially active during the scan (color images with each hue indicating a particular activity level)  CS also have brain abnormalities in the frontal love (prefrontal cortex). PC is active when a person is engaged in tasks tht require planning or careful analysis and is less active when someone is dreaming. This latter pattern reflect absence of careful analysis of the dream material which in turn helps us understand why dreams are often illogical or bizarre What Do We Learn From Capgras Syndrome?  Recognition of all stimuli involves 2 separate mechanisms, one that hinges on factual knowledge and one’s that more emotional and tied to the warm sense of familiarity.  Damage of amygdala is probably the reason Copgras patients experience no sense of familiarity when they look at faces they know well. The damage to prefrontal cortex help us understand why Capgras patients when they experience lack of familiarity offer crazy hypotheses abt their skewed perception  Different areas of the brain work together to match factual and emotional information The Study of the Brain Hindbrain, Midbrain, Forebrain  Hindbrain sits directly atop the spinal cord and includes svrl structures crucial for ctrllng key life function. Ex: rhythm of heartbeats and breathing regulated here. It also maintains the body’s overall tone; specifically, the hindbrain helps maintain the body’s posture and balance, and it helps control the brain’s level of alertness  Phineas Cage- intellectual and emtl impairments for valuable cues abt function of the brain’s frontal lobes  Cerebellum: largest area of hindbrain. It coordinates bodily movement and balance. It also plays a diverse set of other roles and damage to this organ can cause prblms in spatial reasoning, in discriminating sounds and in integrating input recvd frm various sensory system  Midbrain: coordinates movements, including skilled, precise movement of your eyes as you explore visual world. There are also circuits tht relay auditory information frm ears to the areas in the forebrain where this info is processed and interpreted, it also helps to regulate experience of pain  Forebrain: not as visible as other parts of the brain. It is only the outer surface of the forebrain, the cortex. Cortex refers to an organ’s outer surface and may organs each have their own cortex.  Cortex constitutes 80% of human brain. Its crumpled up as it has a very large sheet of tissue hence brain has a lot of wrinkles or convolutions that cover the brain’s outer surface  Some of the valleys are deep grooves tht divide brain into diff sectns. Deepest groove is the longitudinal fissure running from the front of the brain to the back which separates the left cerebral hemisphere from the right  The frontal lobes form the front of the brain, right behind the forehead. Central fissure divides frontal lobes on each side of the brain from the parietal loves, the brain’s topmost part. Bottm edge of frontal loves is marked by lateral fissure and below it are temporal lobes. At the very back of the brain, connected to the parietal and temporal loves are occipital lobes Subcortical Structures  Underneath cortex are subcortical parts of forebrain. The thalamus acts as a relay station for nearly all the sensory information going to the cortex. Underneath thalamus is the hypothalamus, a structure tht plays a crucial role in ctrllng motivated behaviours such as eating, drinking, and sexual activity  Surrounding the thalamus and hypothalamus is another set of interconnected structures tht together form the limbic system. Included here is amygdala and close by is the hippocampus both located underneath cortex in temporal lobe Lateralization  The limbic system includes a number of subcortical structures tht play a crucial role in leanring and memory and in emtl processing  2 halves of the brain wrk together. Integration made possible by commissures which are thick bundles of fibers tht carry info back and forth btwn 2 hemispheres. Largest commissures is the corpus callosum  Each hemisphere proves its own specialized skills tht contribute to overall performance. Complex skills like creativity, intuition, etc. depend on the whole brain. Our hemispheres are not cerebral competitors each trying to impose its styles of thinking on the other. Data from Neuropsychology  Neuropsychology is study of brain’s structures and hw they relate to brain function. Clinical neuropsychology seeks to understand functioning of intact, undamaged brains by careful scrutiny of cases involving brain damage  Lesion (a specific area of damage) in the hippocampus produces memory problems but not language disorders; a lesion in the occipital cortex produces prblms in vision but spares the other sensory modalities.  Consequences of brain lesions depend on which hemisphere is damaged: damage to the left side of frntl lobe will produce disruption of language Data from Neuroimaging  Rsrchers used computerized axial tomography (CT) to study brain’s structure and positron emission tomography (PET) to study the brain’s activity  CT scans rely on x-rays and provide a 3 dimensional x-ray picture of the brain. PET start by introducing a tracer substance such as glucose into body, molecules tagged to low of radioactivity and scan keeps track of it which allows to tell which tissues are using more of the glucose and which are using less.  Both scans collects primary data frm detectors arnd the head.  Magnetic resonance imaging (MRI) relies on magnetic properties of the atoms tht mke up brain tissue and yields fabulously detailed pictures of the brain  Functional magnetic resonance imaging measures oxygen content in the blood flowing through each region of brain and turns out to be an accurate index of the level of neural activity in tht region. It gives precise picture of brain’s moment by moment activities  Results of a CT or MRI scan are relatively stable, changing only if person’s brain structure changes due to injury or growth of tumour  PET or fMRI results are higly variable because result dpnd on wht task the person is performing. Data from Electrical Recording  Neurons do the brain’s main work and communicate with each other via chemical signals called neurotransmitters  Once a neuron is activated, it leases transmitter and this chemical can activate or immediately adjacent neurons that receive this chemical signal can send the signal to other neurons  This process requires 2 types of communication: between neurons and involves chemical signals to other neurons AND within neuron is demanded by the fact tht neurons have an input end and output end. Input end is portion of neuron tht’s most sensitive to neurotransmitters where signal frm other neurons is received  Output end is the portion of the neuron tht releases the neurotransmitter, sending signal on to other neurons.  Electroencephalography is a recording of voltage changes occurring at scalp tht reflect activity in the brain underneath. The result of this procedure is electroencephalogram (EEG)  EEG studies brain’s activities and it can measure changes in EEG in the brief period jst before, during and after the event; these changes are referred to as an event related potential The Power of Combining Techniques  CT and MRI don’t tell us abt activity levels within these brain structures. PET and fMRI are less precise abt activity when they actually take place  EEG gives more info abt timing but weaker in telling where activity took place  EEG combined with fMRI or fMRI combined with CT  Limitation is tht many of the techniques described so far provide only correlational data.  Fusiform face area is active when face is being perceived and parahippocampal place area when they see pictures of places. Activation level only reflects wht subject is aware of not the pattern of incoming stimulation  Transcranial magnetic stimulation (TMS): this technique creates a series of strong magnetic pulses at a specific location on the scalp, causing a (temporary) disruption in the brain region directly underneath this scalp area Localization of the Function  It is referred to figuring out what’s happening to where within the brain  Brain active more when actually looking at pictures and less activity while visualizing mental pictures The Cerebral Cortex  Cortex includes many distinct regions each with its own function and are divided into 3 categories: motor areas which contain brain tissue critical for organizing and controlling bodily movements; sensory areas which contain tissue essential for organizing and analyzing the information we receive from the senses; and association areas. These latter areas support human activity we call “thinking” Motor Areas  Specific areas of cerebral cortex serve as the departure points for signals lvng the cortex and ctrllng muscle movement  Specific areas of the cerebral cortex serve the departure points for signals leaving the cortex and ctrllng muscle movements. other areas are arrival points for info cmng frm eyes, ears and other organs  These areas are called primary projection areas with the departure points known as the primary motor projection areas and arrival points contained in regions known as the primary sensory projection areas  Contralateral control: stimulation to the left hemisphere leading to movements on the right side of the body and vice versa Sensory Areas  Information arriving from the skin senses (your sense of touch or your sense of temperature) is projected to a region in the parietal lobe, just behind motor projection area; this is labeled the somatosensory area  If a patient’s brain is stimulated in this region (with electrical current or touch) the patient will typically report a tingling sensation in a specific part of the body  Sensory projection areas differ frm each other but also have features in commons and they’re features tht parallel the attributes of the motor projection area. 1. Each of these areas provides a map of sensory envrmnt. In somatosensory area, each part of body’s surface is represented by its own region on the cortex; areas of the body tht are near to each other typically represented by similarly nearby areas in the brain. 2. In each of these sensory maps the assignment of cortical space is governed by function not by anatomical proportions. In parietal loves, parts of body tht aren’t discriminating with regard to touch, even if they’re physically large, get relatively little cortical area. Other sensitive areas like lips, tongue, and fingers get far more space. Advantaged frequencies are those essential for perception of speech. 3. Contralateral connections; visual protection areas, although here the projection is not contralateral with regard to body parts; instead it’s contralateral with regard to physical space. Visual projection area in the right hemisphere receives info frm both left eye and right but info receives corresponds to the left half of visual space (i.e., All of things visible to your left when ur looking straight ahead) Association Areas  The remaining cortical areas are referred to as association cortex, these areas perform the task of associating simple ideas and sensation in order to form more complex thoughts and behaviours  Lesions in the frontal love produce apraxias, disturbances in the initiation or organization of voluntary action. Other lesions (generally in occipital cortex, or in the rearmost part of the parietal lobe) lead to agnosias, disruption in the ability to identify familiar objects. It usually affects one modality only, so a patient with visual agnosia, for example can recognize a fork by touching it but not by looking at it. auditory agnosia, can’t identify familiar faces but can recognize the person speaking  Other lesions produce neglect syndrome in which individual seems to ignore hlf his face (shave half the face, eat hlf his plate, or write half of a word like pigpen)  Disruption to language capacities is called aphasia  Damage to the frontmost part of frontal love, the prefrontal
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