Q. I am studying communication disorders. I was wondering if you could tell me what type of processing deficits may occur with damage to the extrapyramidal system? Also what deficits can occur if there is damage to the left cortex? I think that this is aphasia but I'm not sure. Can you help?

A. Just to back up a minute, the term "extrapyramidal system" is a bit hard to define--literally, it means "outside the pyramidal system". The latter includes neural pathways mediating voluntary movement, such as the corticospinal tract. Conventionally, the extrapyramidal system is usually identified with the basal ganglia (e.g., caudate, putamen, globus pallidus).

These subcortical structures appear to mediate involuntary movements, such as tremor or dyskinesia. Diseases that affect the extrapyramidal system include, e.g., Parkinson's Disease (PD) and Huntington's Disease (HD). So, in answering your question, I'd begin with these disorders.

In PD, there are well-known problems with speech function, due to the disease's effects on respiration, phonation, articulation, resonance, and prosody (Goberman & Coelho, NeuroRehabilitation 2002;17(3):237-46). In addition, PD patients may show abnormalities of communication when dealing with emotional recollections; e.g., one study found that individuals with PD showed a relative increase in the number of words spoken and in discourse duration when talking about emotional experiences associated with high levels of arousal and motor activation. (Crucian et al, Neurology 2001 Jan 23;56(2):159-65).

Communication processing deficits may depend on whether individuals with PD or HD also show evidence of dementia; e.g., one study found attentional deficits in PD and HD patients with dementia, but not in non-demented PD patients (Claus & Mohr, Acta Neurol Scand 1996 May;93(5):346-51).

Your other question regarding damage to the left cortex covers a very broad territory! Depending on the particular region of the left cerebral cortex affected, the person may wind up with anything from "pure word deafness" without aphasia (Takahashi et al, Cortex 1992 Jun;28(2):295-303) to constructive agraphia as seen in Gerstmann's syndrome(C. Lang, Fortschr Neurol Psychiatr 1994 May;62(5):155-63). I hope these references get you started!

June 2003

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