Is Short-Term Memory for Discrete Arm Movements Impaired in Huntingtonʹs Disease?

Explicit memory for arm movements was investigated in patients with Huntingtonʹs disease (HD) and normal controls (NC). Participants recalled the end-position of arm movements determined by the examiner following an immediate or a 30-second delay that was either unfilled or filled with a motor distractor task. Movement error was measured in absolute (AE), variable (VE), and constant (CE) error. When performance was measured in AE, HD patients were impaired equally across delays compared to controls, regardless of whether the delay was filled or unfilled. HD patients did not demonstrate a directional bias (i.e., CE), but they were more inconsistent in their reproduction of arm movements (i.e., VE). Both groups were more variable in their reproduction of the movements following the delay, and were most variable when the delay was filled with motor distraction. Results preliminarily suggest that the caudate is specifically involved in the encoding, or temporary storage, of explicit motor information and may be less involved in the short-term retention of newly learned motor information. Results should be viewed somewhat cautiously, however, as the relative contributions of proprioceptive sense and primary motor functioning on task performance were not fully explored.