Dyssynchronous apraxia: Failure to combine simultaneous preprogrammed movements

Limb apraxia, a defect in skilled,learned purposive movement, may be relate d to impairment of either representational or innervatory components of pra xis processing. Innervatory motor patterns, in turn, may involve on-line mo tor programs (visual feedback-controlled) or prepared movement programs (in dependent of continuous visual feedback). We evaluated movement abilities o f the innervatory pattern system in TB, a 26-year-old patient with apraxia from a left dorsolateral frontal stroke. TB and four controls performed non meaningful single- and multi-joint movements to command, with multi-joint m ovements combined sequentially (e.g. "open and close your hand and then ben d your elbow") or simultaneously (e.g. "open and close your hand; keep doin g that while bending your elbow"). TB showed no difference between single-j oint (71.5% correct) and multi-joint movements in sequential combinations ( 68% correct), but she was significantly worse at simultaneous movement comb inations (28.6% correct; P < .02). Controls performed consistently at > 90% mean accuracy. TB and four normals also performed the Fitts (1954) task, i n which they alternately tapped with a pen between two target circles of va rying size. TB was proportionately slower than controls on the larger Fitts circles, which call predominantly on prepared movement programs; her perfo rmance on the smaller circles (involving more on-line programs) was compara ble to normals. We conclude that functional synchrony of one innervatory pa ttern subtype, prepared movement programs, may require late-level frontal p rocessing, and that failure at this level can result in both apraxia and de fective programming of nonmeaningful movements.