Abstract
Objectives: Brain injury, including stroke, can cause a partial or total loss of movement of the body contralateral to the affected area. Movementexecution is dependent on movement preparation for optimal motor performance and studying advance movement preparation in those with hemiparesis will help elucidate whether this process is involved in the observed motor impairment. Motor control can be studied using response priming paradigms, in which prime stimuli give some degree of prior information that allows preparation of the forthcoming response. Dependent on the level of advance information, participant’s reaction times are modulated, with reaction time costs for incorrect prime information and reaction time benefits for correct information when compared with an uninformative prime. This reaction time pattern is termed the validity effect and is indicative of cognitive processing of the prime and subsequent movement preparation. The presence of such an effect in hemiparetic patients would reveal this ability to be intact, which would aid in the construction of therapeutic interventions. Method: Twenty-nine participants with hemiparesis (at least 1 year post-injury) and 16 age matched control (non-brain injured, non-hemiparetic) subjects were recruited. They performed a response priming task whereby they were expected to press buttons with their hands dependent on a left or right button cue. Priming stimuli presented before that were either informative (Valid) or uninformative (Neutral). Reaction times were recorded for the affected and unaffected arms. Results: Within-group means comparison revealed a significant validity effect in control and hemiparetic participants, with both groups taking longer to respond to the neutral prime trial than to the valid prime trial. For the affected arm this difference was 210 ms, for the unaffected arm this was 125 ms and for controls this was 58 ms. In addition, hemiparetic participants were significantly slower than control participants in both affected and unaffected arms. However, the affected arm reaction time differed from the controls to a greater extent (325 ms for valid prime) than the unaffected arm (179 ms for valid prime). Conclusions: Our study shows that hemiparetic participants are generally slower to respond to visual stimuli than a control group, as would be expected in a group with motor impairment. However, despite the deficit the validity effect is preserved for both their affected and unaffected arms. This suggests that the cognitive processes involved in advance motor preparation are still functioning despite the brain injury. Furthermore, reaction times for the unaffected hand were slower than controls, which may be explained by generalized slowing across modalities in brain injury.