Comparison of the basal ganglia and cerebellum in shifting attention

The basal ganglia anti cerebellum have traditionally been associated with m otor performance. Recently, there has been considerable interest regarding the contributions of these subcortical structures to aspects of cognition. In particular, both the basal ganglia and cerebellum have been hypothesized to be involved in the control of attentional set. To date, no neuropsychol ogical studies have directly compared the effects of basal ganglia and cere bellar dysfunction on the same attention shifting tasks. To this end, we em ployed an alternating attention task that has been used to demonstrate puta tive attentional control deficits in children with cerebellar pathology, ei ther related to autism or neurological insult. When adult patients with eit her Parkinson's disease or cerebellar lesions were tested on this task, a s imilar pattern of deficits was observed for both groups. However, when the motor demands were reduced, cerebellar patients showed a significant improv ement on the alternating attention task, whereas the Parkinson patients con tinued to exhibit an impairment. This dissociation suggests that attentiona l deficits: reported previously as being due to cerebellar dysfunction may be, at least in part, secondary to problems related to coordinating success ive responses. In contrast, attention-shifting deficits associated with bas al ganglia impairment cannot be explained by recourse to the motor demands of the task.