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Chapter 2

PSYB57 – Chapter 2 Notes.docx

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University of Toronto Scarborough
Dwayne Pare

PSYB57 – Chapter 2 Notes  One form of evidence does need its own presentation: evidence concerning the brain functioning that makes cognition possible  Capgras Syndrome: rare disorder on it’s own, but it seems to be one of the accompaniments to Alzheimer’s disease, and is so sometimes observed among the elderly o Patient is fully able to recognize the people in her world, but she is utterly convinces that these people are not who they appear to be - the person on the scene therefore isn’t the genuine article; instead, he or he must be a well-trained, well-disguised imposter o What is going on here? The answer to some researchers, lies in the fact that facial recognition involves two separate systems in the brain, one of which leads to a cognitive appraisal, and the other to a more global, somewhat emotional appraisal o In Capgras Syndrome, the emotion processing is disrupted, leading to the intellectual identification without the familiarity response: “You resemble my father but trigger no sense of familiarity, so you must be someone else”  PET scans suggest a link between Capgras Syndrome and the abnormalities in several brain areas; one site of damage is in the temporal lobe, particularly on the right side of the head o This damage probably disrupts circuits involving the amygdala – the amygdala is the “evaluator” (it is essential for making the judgment of “you look familiar to me and trigger a warm emotional feeling” – one half of our two-systems hypothesis)  Patients with Capgras Syndrome also have brain abnormalities in the frontal lobe, specifically in the right prefrontal cortex o With damage to the frontal lobe, Capgras patients may be less able to keep track of what is real and what is not, what is plausible and what is not o Evidence supports our hypothesis: the damage to the amygdala is likely to be the reason why Capgras patients experience no sense of familiarity when they look at faces they know quite well  The damage to the prefrontal cortex, in turn, helps us understand why Capgras patients, when they experience this lack of familiarity, offer such crazy hypotheses about their skewed perception  The human brain is divided into three main structures: the hindbrain, the midbrain, and the forebrain o The hindbrain sits directly atop the spinal cord, and includes several structures crucial for controlling key life functions – it’s here, for example, that the rhythm of heartbeats and the rhythm of breathing are controlled; also plays an essential role in maintaining the body’s overall tone (helps maintain the body’s posture and balance and helps regulate the brain’s level of alertness) o The largest area of the hindbrain is the cerebellum; plays a role in the coordination of our bodily movements and balance, and also other roles o Damage to cerebellum can cause problems in spatial reasoning, in discriminating sounds, and in integrating the input received from various sensory systems  The midbrain plays an important part in coordinating our movements, including the skilled, precise movements of our eyes as we explore the visual world  The forebrain is the largest region – the outer surface of the forebrain is the cortex o The cortex constitutes 80% of the brain  The deepest groove in the brain 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 four lobes, and these are named after the bones that cover them o The frontal lobes form the front of the front of the brain – right behind the forehead o The central fissure divides the frontal lobes on each side of the brain from the parietal loves, the brain’s topmost part o The bottom edge of the frontal lobes is marked by the lateral fissure, and below this are the temporal lobes o Finally, at the very back of the brain, connected to the parietal and temporal lobes, are the occipital lobes  Hidden from the view, underneath the cortex, are the subcortical parts of the forebrain o One of these is the thalamus, a brain region that acts as relay station for nearly all the sensory information going to the cortex o Directly underneath the thalamus is the hypothalamus, a structure that play a crucial role in the control of motivated behaviours such as eating, drinking, and sexual activity  Surrounding the thalamus and hypothalamus is another set of interconnected structures that together form the limbic system o Included here is the amygdala, and close by is the hippocampus, both located underneath the cortex in the temporal lobe; these structures are essential for learning and memory, and for emotional processing o Patient H.M., developed his profound amnesia after surgeons removed these structures  Commissures make it possible for the two halves of the brain to work together; the functioning of one side is closely integrated with that of the other side o Commissures = thick bundles of fibres that carry information back and forth between the two hemispheres o The largest commissure is the corpus callosum  A lesion on the hippocampus produces memory problems but not language disorders; a lesion on the occipital cortex produces problems in vision but spares the other sensory modalities  CT (computerized axial tomography) scans use X-rays to study the brain’s anatomy  PET scans provide a precise assessment of how blood is flowing through each region of the brain; they are used to study the brain’s functioning – this method rests on the fact that when a particular brain area is more active it needs – and receives – a greater blood flow  MRI (magnetic resonance imaging) relies on the magnetic properties of the atoms that make up the brain tissue, and it yields fabulously detailed pictures of the brain  fMRI (functional magnetic resonance imaging) measures the oxygen content in the blood flowing through each region of the brain; this turns out to be an accurate index of the level of neural activity in that region  The results of a CT or MRI scan are relatively stable, changing only if the person’s brain structure changes  The results of PET or fMRI scans, in contrast, are highly variable, because the results depend heavily on what task the person is performing  Fusiform Face Area (FFA): an area that seems highly representative to faces and much less responsive to other visual stimuli  Parahippocampal Place Area (PPA): a brain site that seems to respond actively whenever pictures of places are in view  Binocular Rivalry: the visual system is unable to handle both stimuli at once, or to fuse the stimuli into a single complex perception; instead the visual system seems to flip-flop between the stimuli, so that for a while the person is aware only of the face, then for a while aware of only the house, and so on  BOLD (blood oxygenation level dependent) signal: measures how much oxygen the blood’s haemoglobin is carrying in each part of the brain, and this provides a quantitative basis for comparing activity levels in different brain areas  We can use brain scanning, first, to figure out the special function of different brain regions, and thus learn which brain regions are crucial for the perception of faces, and which for the perception of other stimuli o Second, we can use measurements like the BOLD signal to track activity levels across time and to ask how the brain activity changes in response to new stimuli or new thoughts o Third, we can ask what exactly a brain state corresponds to  Striking suggestion from Tong et al. that we can use brain scans as a means of studying some of the bases for conscious awareness  Localization of function – questions related to the different jobs carried out by different bits of the brain  Neuroimaging data tells us whether a brain’s area activity is correlated with a particular function, but we need other data to ask whether those brain sites play a role in causing that function  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 small brain region directly underneath this scalp area  Primary projection areas: certain areas of the brain seem to be the arrival points for information coming from the eyes, ears, and other sense organs; other areas are the departure points for signals leaving the forebrain and controlling muscle movement (both cases, these areas are called PPA) o The arrival points = primary sensory projection area o Departure point = the primary motor projection area  Contralateral control – stimulation to the left hemisphere leading to movements on the right side of the body, and vice versa  The sites stimulated in the anaesthetized animals (where evidence for motor projection area comes from), are in a strip of tissue located toward the rear of the frontal lobe  Areas of the body that we can move with great precision (fingers and lips) have a lot of cortical area devoted to them; areas of the body over which we have less control (the shoulder and the back) receive less cortical coverage  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 the motor projection area; this is labeled the “somatosensory area” o In the somatosensory area, each part of the body’s surface is represented by its own region on the cortex; areas of the body that are near to each other are typically represented by similarly nearby areas in the brain  In each of these maps the assignment of cortical space is governed by function, not by anatomical proportions  The left parietal lobe receives its main input from the right side of the body, for example; the right receives its input from the left side of the body  The visual projection area in the right hemisphere receives information from both the left eye and the right, but the information is receives corresponds to the left half of visual space  Association cortex: such named on the idea that this section of the brain performs the task of associating simple ideas and sensations in order to form more complex thoughts and behaviours  Aparaxias: disturbances in the initiation or organization of voluntary action  Agnosias: disruptions in a person’s ability to identify familiar objects  Neglect syndrome: in which the individual seems to ignore half of the visual world  Aphasia: lesions in the left frontal lobe, usually at sites just above the lateral fissure, that result in disruption to language capacities  These various clinical patterns make it clear that the so-called association cortex contains many su
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