The role of the thalamus and basal ganglia in human cognition

Cerebral lesions involving the thalamus or the basal ganglia can impair cognitive functions (e.g. language, memory, or attention) that were previously believed to be linked almost exclusively to cortical structures. These impairments are mostly evident when, in addition to nuclear lesions, there is an involvement of the subcortical white matter that includes bundles of fibres for cortico-cortical and cortico-subcortical connections. Based on this result, it has been hypothesized that cognitive deficits after subcortical lesions are due entirely to remote effects on select cortical targets. Thus, the notion of subcortical cognition has been questioned. However, since cortical lesions can have remote effects on their subcortical targets, the notion of cortical cognition can be challenged as well. The present article deals with the concept of subcortical cognition and reviews lesion studies hinting at a role for thalamus and basal ganglia in complex human behaviour. A proposal is made that the notion of large neural networks with both cortical and subcortical nodes may give a plausible interpretation of cognitive deficits. (C) 1997 Elsevier Science Ltd. All rights reserved.