title: Dyssynchronous apraxia: failure to combine simultaneous preprogrammed movements.
abstract: 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.
authors.forename: A M
authors.initials: AM
authors.lastname: Barrett
authors.forename: R L
authors.initials: RL
authors.lastname: Schwartz
authors.forename: A L
authors.initials: AL
authors.lastname: Raymer
authors.forename: G P
authors.initials: GP
authors.lastname: Crucian
authors.forename: L G
authors.initials: LG
authors.lastname: Rothi
authors.forename: K M
authors.initials: KM
authors.lastname: Heilman