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Chapter 3

PSYC31 - Clinical Neuropsychology Ch. 3

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Pare, Dwayne

PSYC31 – Chapter 3: The Behavioral Geography of the Brain  New neurons are produced in some brain regions of adults in a number of mammalian species, playing a role in brain injury repair, new learning, and maintenance of healthy neural functioning  Adult neurogenesis has been identified in the hippocampus and olfactory bulb in mammalian brains and implicated in other limbic regions, in the neocortex, straitum, and substantia nigra  Neurogenesis in the hippocampus is thought to be especially critical for maintaining normal cognition and emotional well-being  Basal ganglia and cerebellum are increasingly appreciated for their influences on cognition and psychiatric disorders  Motor cortex appears to play an active role in processing abstract learned information  Strategically occurring lesions or abnormalities albeit small may nonetheless influence neuropsychological functions Brain Pathology and Psychological Function  any given behavior is the product of a myriad of complex neuropsychological and biochemical interactions involving the whole brain  one focal lesion may affect many functions when the damaged neural structure is either a pathway, nucleus, or region that is central in regulating or integrating a particular function o these disruptions can produce a neurobehavioral syndrome (cluster of deficits that tend to occur together with some regularity)  knowledge of the localization of dysfunction, the correlation between damaged neuroanatomical structures and behavioral functions also enables neuropsychologists and neurologists to make educated guesses about the site of a lesion on the basis of abnormal patterns of behavior  similar lesions may have quite dissimilar behavioral outcomes  localization cannot imply a “push-button” relationship between local brain sites and specific behaviors as the brain’s processing functions take place at multiple levels within complex integrated, widely distributed systems o lesions at many different brain sites may alter or extinguish a single complex act as can lesions interrupting the neural pathways connecting areas of the brain involved in the act The Cellular Substrate  primary function of neuron is to provide network of connectivity between neurons and different regions of the brain  brain connectivity is key to brain functioning  at birth, the full complement of neurons appears to be present, indicating an astonishing growth pattern from conception to birth  glial cells (astrocytes) facilitate neural transmission and probably play a more direct role in synaptic functioning and neural signaling  Glial cells serve as structural supports and also appear to have nutritional scavenger functions and to release growth factors; additional role as a component in the BBB  Oligodendrocytes = form myelin for axonal insulation for high-speed conduction  Surface of dendrite may change in response to neural activity forming a spine o Spine development is thought to be important in the formation of new memories and neural plasticity  Stimulation applied to neural pathway heightens that pathway’s sensitivity and increases the efficacy with which neuronal excitation may be transmitted through synapse  Long-lasting synaptic modifications = long-term potentiation and long-term depression o These are critical neurophysiological features of memory and learning  Each neurotransmitter can bind to and thus activate only those receptor sites with the corresponding molecular conformation, but a single neuron may produce and release more than one of these chemical messengers  When a circuit loses a sufficiently great number of neurons, the broken circuit can neither be reactivated nor replaced  During development, some neurons initiate apoptosis which enhancing organization and efficiency of specific neuronal pathways in a process called pruning  While apoptosis occurs normally in the development of the nervous system, some nervous system diseases may result from apoptotic processes gone awry or other forms of cell deaths which are normally prevented by neurotrophic factors The Structure of the Brain  Embryological development has major anatomical divisions of the brain o Hindbrain (pons, medulla, and cerebellum) o Midbrain o Forebrain (telencephalon and diencephalon)  The lowest brain centers are the most simply organized and mediate simpler and more primitive functions  Hemispheres mediate the highest levels of behavioral and cognitive function  Brain has 4 ventricles which have CSF running through them  CSF is also running between arachnoid membrane and dura mater (meninges)  CSF is produced in the choroid plexi  CSF is pressured in the ventricles, serving as a shock absorber and helping to maintain shape of the soft nervous tissue of the brain by creating an outward pressure gradient that is held in check by the mass of the brain  Blockage within the ventricular system affects CSF flow, producing obstructive hydrocephalus o In disorders in which brain substance deteriorates the ventricles enlarge to fill the void space  When vascular pathology occurs, its effects are typically associated with one or a combination of the major blood vessels of the brain  It is in the intimate interaction between individual capillaries and neurons that neural function or dysfunction occurs  It is the interplay between vascular damage and brain damage that gives rise to neuropsychological impairments  3 major blood vessels of the brain o Anterior cerebral (frontal lobe) o Middle cerebral (lateral temporal, parietal and posterior frontal lobe) o Posterior cerebral (brain stem and cerebellum)  Most frequent vascular source of neuropsychological deficits is associated with arterial side of blood flow  The site of disease or damage to arterial circulation determines the area of the brain cut from its oxygen and nutrients supply and to a large extent, the neuropathologic consequences of vascular disease The Hindbrain  Medulla Oblongata o Lowest part of the brain stem o Lowest section is medulla oblongata (bulb) o Site of basic life-maintaining centers for neural control of respiration, BP, and heartbeat o Pathology results in death or profound disability o Contains nuclei involved in movements of mouth and throat structures necessary for swallowing, speech, gagging, control of drooling etc…  Reticular formation o Contains many nuclei which mediate important and complex postural reflexes , contribute to the smoothness of muscle activity, and maintain muscle tone o The site of the RAS which controls wakefulness and alerting mechanisms; modulates attention o Brain stem lesions involving the RAS give rise to sleep disturbances and to global disorders of consciousness and responsivity  The Pons o High in the hindbrain o Pons and cerebellum together correlate postural and kinesthetic info, refining and regulating motor impulses relayed from the cerebellum at the top of the brain stem o Lesions of the pons may cause motor, sensory, and coordination disorders including disruption of ocular movements and alterations in consciousness  The Cerebellum o Attached to the brain stem at the posterior base of the brain o Connections with vestibular and brain stem nuclei, hypothalamus and spinal cord; has strong connections with the motor cortex o Influences programming and execution of actions and background motor control o Damage is known to produce problems of fine motor control, coordination, and postural regulation, dizziness and jerky eye movements o L
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