[Subcortical dementia: is a revision of the concept necessary?]

The term subcortical dementia suggests that the cerebral lesions critical for the occurrence of dementia are located in subcortical structures. Accordingly, these dementias are usually observed in patients suffering from degenerative disorders affecting subcortical structures. They are characterised by neuropsychological and behavioral disorders resembling those observed in lesion of the prefrontal cortex. Numerous reports suggest that patients suffering from degenerative and focal lesions of the striatum exhibit an impairment of the so-called "frontal functions". These results support the hypothesis that the striatum is involved in these functions and therefore, that its lesion might account for the neuropsychological disorders. The interpretation of these results assumes that cerebral lesions are restricted to the striatum. However, recent studies have shown that lesions of degenerative and vascular disorders of the striatum frequently extend into the cortex. Moreover, assessment of patients with striatal infarct has shown that the occurrence of frontal lobe symptoms depended on the associated cortical lesion and that patients with pure striatal lesion did not exhibit a full dysexecutive syndrome. The contribution of the striatum to frontal lobe functions might thus have been overestimated. Despite the uncertainty about the critical locus of lesions accounting for the emergence of dementia, the term subcortical dementia has the advantage to refer to a group of dementias with a specific neuropsychological pattern. A much more relevant approach would be to evaluate the contribution of the striatum to the executive functions. In keeping with this view, recent studies suggest that the caudate nucleus is mainly involved in response selection, at least in unusual or complex tasks.