Movement-related potentials in Huntington's disease: movement preparation and execution

Movement-related potentials (MRPs) reflect increasing cortical activity rel ated to the preparation and execution of voluntary movement. Execution and preparatory components may be separated by comparing MRPs recorded from act ual and imagined movement. Imagined movement initiates preparatory processe s, but not motor execution activity. MRPs are maximal over the supplementar y motor area (SMA), an area of the cortex involved in the planning and prep aration of movement. The SMA receives input from the basal ganglia, which a re affected in Huntington's disease (HD), a hyperkinetic movement disorder. In order to further elucidate the effects of the disorder upon the cortica l activity relating to movement, MRPs were recorded from ten HD patients, a nd ten age-matched controls, whilst they performed and imagined performing a sequential button-pressing task. HD patients produced MRPs of significant ly reduced size both for performed and imagined movement. The component rel ating to movement execution was obtained by subtracting the MRP for imagine d movement from the MRP for performed movement, and was found to be normal in HD. The movement preparation component was found by subtracting the MRP found for a control condition of watching the visual cues from the MRP for imagined movement. This preparation component in HD was reduced in early sl ope, peak amplitude, and post-peak slope. This study therefore reported abn ormal MRPs in HD. particularly in terms of the components relating to movem ent preparation, and this finding may further explain the movement deficits reported in the disease.