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10. Principles of Neocortical Function.docx

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PSYC 3530
Guy Proulx

10. Principles of Neocortical Function Tuesday, October 15, 2013 9:16 AM A Hierarchy of Function from Spinal Cord to Cortex  Dysphasia-- impairment of speech caused by damage to the central nervous system  Subcortical structures are capable of mediating complex behaviors  The brain’s considerable capacity to change its structure in response to experience, drugs, hormones, or injury is due to its plasticity, as is its ability to compensate for loss of function caused by damage   The Spinal Cord and Reflexes o Spinal animal-- an animal whose spinal cord is disconnected from the brain o A spinal animal is alert; a person who has sustained such an injury can still talk, express emotion, and so on  The Hindbrain and Postural Support o If the brain is injured such that the hindbrain and spinal cord are still connected but both are disconnected from the rest of the brain, the subject is called a low decerebrate o A low-decerebrate animal no longer shows any alertness, because many essential inputs to the brain regions above the injury are now disconnected, presumably leaving the forebrain ―in the dark,‖ with difficulty maintaining consciousness o A characteristic aspect of behavior accorded by the hindbrain is a peculiar kind of stiffness called decerebrate rigidity. This stiffness is due to excessive muscle tone, particularly in the antigravity muscles that hold the body up to maintain posture and are the body’s strongest o The neural centers that produce sleep are located in the hindbrain  The Midbrain and Spontaneous Movement o Damage that separates the diencephalon from the midbrain regions containing, in the tectum, the coordinating centers for vision (superior colliculus) and hearing (inferior colliculus) and, in the tegmentum, a number of motor nuclei, produces this condition, called high decerebration o These experiments demonstrate that all the subsets of voluntary movements— movements that take an animal from one place to another, such as turning, walking, climbing, swimming, and flying—are present at the subcortical level of the midbrain o High-decerebrate animals can also effectively perform automatic movements, units of stereotyped behavior linked in a sequence o The forebrain is not important in producing movements but is important in attenuating and inhibiting them  The Diencephalon and Affect and Motivation o A diencephalic animal, although lacking the basal ganglia and cerebral hemispheres, has an intact olfactory system, enabling it to smell odors at a distance (see Figure 10.2). The hypothalamus and pituitary also are intact, and their control over hormonal systems and homeostasis no doubt integrates the body’s physiology with the brain’s activity. Diencephalic animals thermoregulate, for example, but they do not eat or drink well enough to sustain themselves o In addition to sham rage, another pronounced feature of a diencephalic animal’s behavior is its constant activity (sham motivation)  The Basal Ganglia and Self-Maintenance o Decortication is the removal of the neocortex, leaving the basal ganglia and brainstem intact o Decorticate animals are able to maintain themselves without special care in laboratory conditions o They have normal sleeping–waking cycles; run, climb, and swim; and even negotiate simple mazes o They can also sequence series of movements such as copulation and grooming  The Cortex and Intention o The cortex is not essential for learning itself. However, decorticate animals fail at learning, for example, complex pattern discriminations and how to find their way around in space o The cortex appears to extend the usefulness of all behaviors or to make them adaptive in new situations The Structure of the Cortex   A consistent theme in neuroanatomy throughout the past century is that cortical regions can be categorized as primary sensory cortex, primary motor cortex, and association cortex. Association areas are usually also categorized as secondary cortex, which elaborates information coming from primary areas, and as higher-order areas (sometimes called tertiary areas), which may combine information from more than one system  Cortical Cells o Nerve cells are easily distinguished in the cortex as spiny neurons or aspiny neurons by the presence or absence, respectively, of dendritic spines  Spiny neurons are excitatory and are likely to use glutamate or aspartate as neurotransmitters  Spiny neurons include pyramidal cells, whose pyramid-shaped cell bodies generally send information from a region of the cortex to another area of
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