Programming and Execution of Movement in Parkinson's Disease

Abstract

Programming and execution of arm movements in Parkinson's disease were investigated in choice and simple reaction time (RT) situations in which subjects made aimed movements at a target. A no-aiming condition was also studied. Reaction time was fractionated using surface EMG recording into premotor (central) and motor (peripheral) components. Premotor RT was found to be greater for parkinsonian patients than normal age-matched controls in the simple RT condition, but not in the choice condition. This effect did not depend on the parameters of the impending movement. Thus, paradoxically, parkinsonian patients were not inherently slower at initiating aiming movements from the starting position, but seemed unable to use advance information concerning motor task demands to speed up movement initiation. For both groups, low velocity movements took longer to initiate than high velocity ones. In the no-aiming condition parkinsonian RTs were markedly shorter than when aiming, but were still significantly longer than control RTs. Motor RT was constant across all conditions and was not different for patient and control subjects. In all conditions, parkinsonian movements were around 37% slower than control movements, and their movement times were more variable, the differences showing up early on in the movement, that is, during the initial ballistic phase. The within-subject variability of movement endpoints was also greater in patients. The motor dysfunction displayed in Parkinson's disease involves a number of components: (1) a basic central problem with simply initiating movements, even when minimal programming is required (no-aiming condition); (2) difficulty in maintaining computed forces for motor programs over time (simple RT condition); (3) a basic slowness of movement (bradykinesia) in all conditions; and (4) increased variability of movement in both time and space, presumably caused by inherent variability in force production.

Bradykinesia Induced by Dopamine D2 Receptor Blockade Is Associated with Reduced Motor Cortex Activity in the Rat

“…Conversely, they produced some slow reaches before haloperidol injections. This trial-to-trial variability is similar to that seen in human Parkinson's disease, in which movement speed shows considerable within-session variability (Sheridan et al, 1987). Therefore, we were able to compare the movement-related firing rate in prehaloperidol and posthaloperidol sessions for trials matched for movement speed (see Materials and Methods).…”

Basal ganglia network mediates the control of movement amplitude

“…Consequently, the existence of a temporal de®cit for SRT but not for CRT would support the idea that PD patients are impaired at using advance information. This prediction was corroborated in several studies (Bloxham et al, 1984;Evarts et al, 1981;Sheridan et al, 1987;Pullman et al, 1990) but not in others (Girotti et al, 1986;Stelmach et al, 1986;Lichter et al, 1988;Jahanshahi et al, 1992), thus leaving the issue unresolved.…”

“…A point of interest is that most previous studies involved very simple manual responses such as depressing a key with a ®nger or moving a lever (Bloxham et al, 1984;Evarts et al, 1981;Sheridan et al, 1987;Lichter et al, 1988;Jahanshahi et al, 1992). These simple tasks may not be challenging enough to cause obvious variations in RT measurements in patients, leading to inconsistent results.…”

Correlates of movement initiation and velocity in Parkinson's disease: A longitudinal PET study

“…PD patients show longer simple reaction times (Bloxham et al, 1984;Hallett, 1990;Jahanshahi et al, 1992Jahanshahi et al, , 1993Rafal et al, 1989) even if no motor requirements were imposed (Sheridan et al, 1987). Interestingly, rather than performing eye movements and limb movements in parallel, PD patients tend to finish necessary fixation movements prior to limb movement onset (Warabi et al, 1988).…”