Switching on to the basal ganglia and cognition

Abstract

In addition to the well-known contribution of the basal ganglia to motoric function, evidence is accumulating that suggests that these subcortical structures also play an important role in more cognitive operations. For example, neuropsychological, behavioural and functional neuroimaging evidence suggests that the basal ganglia is implicated in the cognitive processes that are required when a change or switch in the behavioural set that governs behaviour is required. Patients with Parkinson's disease, in which the functions of the basal ganglia are disrupted by dopamine deficiency, are impaired on tasks that measure the ability to switch attentional set in this manner. However, switching deficits have not been observed when a Posner spatial-cueing paradigm is used to examine switching time in Parkinson's disease. Hayes et al.[1xToward a functional analysis of the basal ganglia. Hayes, A.E. et al. J. Cog. Neurosci. 1998; 10: 178–198Crossref | PubMed | Scopus (156)See all References[1]present evidence that suggests that this apparent conflict can be resolved by a consideration of the precise form of the switch that is required. Thus, when subjects were asked to switch their response from one stimulus dimension (colour) to another (shape), or when the subjects were required to switch from one sequence of key presses (three key presses in one order) to another (same three key presses in a different order) the patients with Parkinson's disease were slower than the age-matched control subjects. Importantly, these differences were greater than those seen during non-switch trials. Subsequent experiments suggest that the switching impairment is related to the dopamine systems in the Parkinson's patients. The authors discuss the results in the context of `executive' switching and a conceptual framework that suggests that the switching deficits also underlie the motor disturbances observed in Parkinson's disease.