Neurobehavioral Disorders of Childhood: An Evolutionary Perspective by Robert Melillo;Gerry Leisman

Author:Robert Melillo;Gerry Leisman [Leisman, Robert Melillo;Gerry]
Language: eng
Format: epub
Published: 2008-05-17T06:24:00+00:00

CORTICAL-SUBCORTICAL CIRCUITS

AND AFFECTIVE DISORDERS

In considering how cerebellar, thalamic, or basal ganglionic dysfunction may lead to depression or mania, it has been proposed that it is the result of the disruption of frontal cortical function. The caudate is thought to share common pathways with frontal cortical structures either directly or through the dorsomedial nucleus of the thalamus. Alexander and colleagues (1986) described five functionally segregated parallel frontal cortical- striatal-thalamic loops, both motor and non-motor with variable degrees of limbic input. Part of the non-motor loop, a dorsolateral prefrontal network would be used for storage in working memory of spatial locations (Goldman-Rakic, 1987). A lateral orbito-frontal circuit, proceeding from the orbito-frontal cortex to a specific area of the caudate and globus pallidus would then project to the thalamus and the orbito-frontal cortex again. This loop is thought to be responsible for learning and recognition tasks requiring frequent shifts of set. This interpretation is thought to explain the pronounced perseveration seen in orbito frontal damage. In addition, there is an anterior cingulate circuit, which includes the ventral striatum, nucleus accumbens, and medio-dorsal nucleus of the thalamus. The hippocampus and entorhinal cortex also send information in this loop integrating information from the para-limbic association cortex. It is thought that the nucleus accumbens is a target of dopaminergic terminals from the mesencephalic ventro-tegmental area (VTA).

Mayberry (1992) conducted PET studies of basal ganglia stroke patients. They found that compared to euthymic patients, all of the patients with mood change showed hypometabolism in the orbital-inferior frontal cortex, anterior temporal cortex, and cingulate cortex. Of course the cerebellum could be considered a primary source of many of these findings as well. Recent reports on human emotional behavior show that disorders in control of affect can follow atrophy of the midline cerebellum (Gutzmann and Kuhl, 1987). Lack of behavioral self-control, including episodic rage, is sometimes seen as an early symptom of tumor of the paleo-cerebe!- lum (Elliot, 1982). It has been reported that after the surgical removal of a benign tumor, several weeks of explosive behavior follow. The cerebellum is connected to the neocortex and the limbic system. One route connects the cerebellum to the thalamus and the cerebral neo-cortex. The other route connects the cerebellum to the hypothalamus and therefore to older structures of the brain (Haines et al., 1984, 1990; Haines and Dietricks, 1987; Dietricks and Haines, 1989). It is thought that the midline paleo-cerebellum is connected primarily to the limbic system and limbic neocortex, whereas the lateral cerebellum is more connected to the neo-cortex especially the prefrontal cortex. It has been noted that a large percentage of children with learning disabilities and affective disorders like ADHD present with motor deficits that are consistent with cerebellar and or basal ganglia dysfunction.

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