RELIANCE ON ADVANCE INFORMATION AND MOVEMENT SEQUENCING IN HUNTINGTONS-DISEASE

To identify the focus of impairment in the performance of sequential m ovements in Huntington's disease (HD) patients, the extent of their re liance on external advance information was examined. Twelve patients w ith HD and their age-matched controls performed a series of button-pre sses at sequential choice points along a response board. A sequential pathway was designated, and with each successive button press, advance visual information was systematically reduced to various extents in a dvance of each move. HD patients, like previously studied parkinsonian patients, were particularly disadvantaged with high levels of reducti on in advance information, and as a consequence, both their initiation and execution of movements progressively slowed with each successive element in the response sequence. The pattern of results was not affec ted whether or not patients were taking neuroleptic medication, nor di d performance on a variety of cognitive measures correlate with motor performance. Control subjects' performance, on the other hand, remaine d constant in terms of both initiation and execution with each of the three levels of reduction in advance information. We conclude that HD patients, like parkinsonian patients, who also suffer from a basal gan glia (BG) disorder, require external visual cues to sequence motor pro grams effectively. Our findings suggest that with HD there may be abno rmalities in a central mechanism that controls switching between movem ent segments within an overall motor plan. The BG, which provide inter nal cues necessary for component sequencing, may be disrupted, thereby impairing the ability to use such internally generated cues to guide movement.