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The Nervous System - Advanced Version / The Brain
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 The thalamus has long been regarded as the key to understanding the organization of the central nervous system. It is involved in the relay and distribution of most, but not all, sensory and motor signals to specific regions of the cerebral cortex. Sensory signals generated in all types of receptors are projected by complex pathways to specific relay nuclei in the thalamus, where they are segregated and systematically organized. The relay nuclei in turn supply the primary and secondary sensory areas of the cerebral cortex. Sensory input to thalamic nuclei is crossed for the somesthetic and visual systems, bilateral (but mainly crossed) for the auditory system, and ipsilateral (on the same side) for gustatory (taste) and olfactory (smell) sense.
The somesthetic relay nuclei of the thalamus, collectively known as the ventrobasal complex, receive input from the medial lemniscus (originating in the medulla), from spinothalamic tracts, and from the trigeminal nerve. Fibers within these ascending tracts that terminate in the central core of the ventrobasal complex receive input from deep sensory receptors, while fibers projecting onto the outer shell receive input from cutaneous receptors. This segregation of deep and superficial sensation is preserved in projections of the ventrobasal complex to the primary somesthetic (i.e., sensory) area of the cerebral cortex.
The medial and lateral geniculate bodies form what is called the metathalamus. Fibers of the optic nerve end in the lateral geniculate body, which consists of six cellular laminae, or layers, folded into a horseshoe configuration. Each lamina represents a complete map of the contralateral visual hemifield, and all laminae are in perfect registration. Cells in all layers of the lateral geniculate body project via the optic radiation to the visual areas of the cerebral cortex. The medial geniculate body receives auditory impulses from the inferior colliculus of the midbrain and relays them to the auditory areas on the temporal lobe. Only the ventral nucleus of the medial geniculate body is laminated and tonotopically organized; this part projects to the primary auditory area and is finely tuned. Other subdivisions of the medial geniculate body project to the belt of secondary auditory cortex surrounding the primary area.
 Major output from the cerebellum projects to specific thalamic relay nuclei in a pattern similar to that for somesthetic input. The thalamic relay nuclei in turn provide a major input to the primary motor area of the frontal lobe. This large system appears to provide coordinating and controlling influences that result in the appropriate force, sequence, and direction of voluntary motor activities. Output from the corpus striatum, on the other hand, is relayed by thalamic nuclei that have access to the supplementary and premotor areas. The supplementary motor area, located on the medial aspect of the hemisphere (see figure to left), exerts modifying influences upon the primary motor area and appears to be involved in programming skilled motor sequences. The premotor area, rostral to the primary motor area, plays a role in sensorially guided movements.
Other major thalamic nuclei, besides those involved in relaying sensory impulses or controlling influences from the cerebellum and corpus striatum, include the anterior nuclear group, the mediodorsal nucleus, and the pulvinar. The anterior nuclear group receives input from the hypothalamus and projects upon parts of the limbic lobe (i.e., the cingulate gyrus). The mediodorsal nucleus, part of the medial nuclear group, has reciprocal connections with large parts of the frontal lobe rostral to the motor areas. The pulvinar is a huge posterior nuclear complex that, along with the mediodorsal nucleus, has projections to association areas of the cortex.
Output ascending from the reticular formation of the brain stem is relayed to the cerebral cortex by intralaminar thalamic nuclei, which lie in laminae separating the medial and ventrolateral thalamic nuclei. This ascending system is concerned with arousal mechanisms, maintaining alertness, and directing attention to sensory events.
The amygdala, (which means “almond-shaped”), controls our aggression and emotions. Many autistic individuals are aggressive towards themselves or others, or conversely, extremely passive. Furthermore, autistic children and adults often appear emotionless or ‘flat’ (even though they obviously do have emotions). Experimenters have also shown that when the amygdala is removed or damaged, animals exhibit behaviors similar to autistic individuals, such as social withdrawal, compulsive behaviors, failure to learn about dangerous situations, difficulty retrieving information from memory, and difficulty adjusting to novel events or situations. In addition, the amygdala is responsive to a variety of sensory stimuli, such as sounds, sights, and smells; as well as emotionally or fear-related stimuli. We know that autistic individuals often have problems with each of these senses. Interestingly, Georgie, whose childhood was described in her mother’s book, The Sound of a Miracle, often mentioned being afraid of many sounds prior to receiving auditory integration training from Dr. Guy Berard.
 The hippocampus, (shaped like a “sea horse”) appears to be primarily responsible for learning and memory. Damage or removal of the hippocampus will lead to an inability to store new information into memory. This sounds similar to Dr. Bernard Rimland's cognitive theory of autism. In his 1964 award-winning book Infantile Autism, Dr. Rimland theorized that autistic children had difficulty relating new information to previously stored information. In addition, when the hippocampus is damaged or removed, animals will display stereotypic, self-stimulatory behaviors and hyperactivity.
The diencephalon consists of a pair of egg-shaped nuclear masses that lie on each side of the third ventricle and medial to the posterior limb of the internal capsule. Four subdivisions are recognized: (1) the epithalamus, (2) the thalamus, (3) the hypothalamus, and (4) the ventral thalamus, or subthalamus.
The epithalamus is represented mainly by the pineal gland, which lies in the midline posterior and dorsal to the third ventricle. This gland synthesizes melatonin and enzymes sensitive to diurnal light. Rhythmic changes in its activity in response to cyclical photic input suggest that the gland serves as a biological clock. With age it tends to accumulate calcium deposits.
The ventral thalamus is represented mainly by the subthalamic nucleus, a lens-shaped structure lying behind and to the sides of the hypothalamus and on the dorsal surface of the internal capsule. The subthalamic region is traversed by fibers related to the globus pallidus. Discrete lesions in the subthalamic nucleus produce hemiballism, the most violent form of dyskinesia known. Take this preliminary to see if your condition could respond to treatment.
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