DYSSYNCHRONOUS APRAXIA: FAILURE TO COMBINE SIMULTANEOUS PREPROGRAMMED MOVEMENTS
Limb apraxia, a defect in skilled, learned purposive movement, may be related to impairment of either representational or innervatory components of praxis processing. Innervatory motor patterns, in turn,
may involve on-line motor programs (visual feedback-controlled) or prepared movement programs (independent of continuous visual feedback). We evaluated movement abilities ofthe innervatory pattern system
in TB,a 26-year-old patient with apraxia from a left dorsolateral frontal stroke. TB and four controls performed nonmeaningful single and multi-joint movements to command, with multi-joint movements combined
sequentially (e.g. "open and close your hand and then bend your elbow") or simultaneously (e.g. "open and close your hand; keep doing that while bending your elbow"). TB showed no difference
between single-joint (71.5% correct) and multi-joint movements in sequential combinations (68% correct), but she was significantly worse at simultaneous movement combinations (28.6% correct; P < .02).
Controls performed consistently at > 90% mean accuracy. TB and four normals also performed the Fitts (1954) task, in which they alternately tapped with a pen between two target circles of varying size.
TB was proportionately slower than controls on the larger Fitts circles, which call predominantly on prepared movement programs; her performance on the smaller circles (involving more on-line programs)
was comparable to normals. We conclude that functional synchrony of one innervatory pattern subtype, prepared movement programs, may require late-level frontal processing, and that failure at this level
can result in both apraxia and defective programming of nonmeaningful movements.
Document Type: Research Article
Publication date: 01 September 1998
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