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From: MichaelI Grynbawn
Date: 09 Oct 2008
Time: 16:51:53 -0500
Remote Name: 189.81.34.37
The innermost relationship between stuttering and many of its concomitant disorders maybe comes from the fact of stuttering also involve basal ganglia dysfunctions. Traditionally, the basal ganglia have been regarded as motor structures that regulate the initiation of movements. However, the basal ganglia are also central structures in anatomical circuits or loops that are involved in modulating non-motor aspects of behavior. These parallel loops originate in broad regions of the cortex, engage specific subdivisions of the basal ganglia and thalamus, and ultimately terminate in areas of the frontal lobe outside of the primary motor and premotor cortices. These non-motor loops include a “prefrontal” loop involving the dorsolateral prefrontal cortex and part of the caudate, a “limbic” loop involving the cingulate cortex and the ventral striatum, and an “oculomotor” loop that modulates the activity of the frontal eye fields. The anatomical similarity of these loops to the traditional motor loop suggests that the non-motor regulatory functions of the basal ganglia may be generally the same as what the basal ganglia do in regulating the initiation of movement. For example, the prefrontal loop may regulate the initiation and termination of cognitive processes such as planning, working memory, and attention. By the same token, the limbic loop may regulate emotional behavior and motivation. Indeed, the deterioration of cognitive and emotional function in both Huntington’s disease and Parkinson’s disease could be the result of disruption of these non-motor loops. In fact, a variety of other disorders are now thought to be caused, at least in part, by damage to non-motor components of the basal ganglia. For example, patients with Tourette’s syndrome produce inappropriate utterances and obscenities as well as unwanted vocalmotor “tics” and repetitive grunts. These manifestations may be a result of excessive activity in basal ganglia loops that regulate the cognitive circuitry of the prefrontal speech areas. Other psychiatric disorders, including obsessive-compulsive disorder (by the way, a very often comorbidity of Tourette's), depression, and chronic anxiety, may also involve dysfunctions of the limbic loop. Why most theories on stuttering have a tendency to ignore these so revealing relationships that it maintains with others basal ganglia conditions?