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Krasnow Institute > Monday Seminars > Abstracts THE HUMAN BRAIN Ann Butler, Research Professor, Krasnow Institute The human central nervous system consists of the brain and the spinal cord. The spinal cord has regional divisions, while the brain can be divided into forebrain, midbrain and hindbrain. The brainstem (hindbrain, midbrain, and part of the forebrain) contains numerous nuclear regions and fiber tracts, as well as some cortical (laminated) parts. Among the latter are the midbrain roof (colliculi), which relay sensory information to the thalamus in the upper (rostral) part of the brainstem, and the cerebellum, which is a highly laminated and complex structure involved in, motor, sensory, and integrative functions. The brainstem relays ascending inputs from the spinal cord and from most of the sensory cranial nerves to the cerebral cortex in the forebrain and also relays and serves as a conduit for the descending output systems from the cerebral cortex. Several of the nuclear groups of the lower (caudal) part of the brainstem give out long ascending axons that terminate in large areas of the cerebral cortex and serve generalized functions such as waking and attention functions. Both noradrenaline and serotonin-containing neuronal cell groups are most active during wakefulness, decrease during slow wave sleep, and are almost completely quiescent during REM sleep. Another major ascending system of axons are from dopamine-containing neurons in the midbrain; these axons terminate in the motor-related basal ganglia of the forebrain and also in a large region within the cerebral cortex. The latter part of the cortex, located in the frontal lobe, is involved in a number of higher cognitive functions. Within the forebrain above the level of the brainstem, several major brain regions are present. The largest and most prominent is the cerebral cortex. It is divisible into four major lobes (frontal, parietal, occipital, and temporal) and contains a myriad of identified, specific functional areas. Also present are two other cortical areas, the olfactory cortex, and the hippocampal formation. The latter is part of the limbic system, which also includes the amygdala; these structures are essential for many aspects of learning, memory, and emotion and lie in the deep part of the temporal lobe. Different forms of memory are observed in humans. The case of H.M., who underwent removal of part of his temporal lobes on both sides, led to a deeper understanding of the complexity of human memories. The memory deficits associated with damage to structures such as the hippocampus, amygdala, cerebellum, and different regions of the cortex will be discussed. A brief video showing the dramatic affects of severe hippocampal damage in humans will be shown.
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