SUBCORTICAL DEMENTIA - IS A REVISION OF T HE CONCEPT NECESSARY

The term subcortical dementia suggests that the cerebra lesions critic al for the occurrence of dementia are located in subcortical structure s. Accordingly, these dementias are usually observed in patients suffe ring from degenerative disorders affecting subcortical structures. The y are characterised by neuropsychological and behavioral disorders res embling those observed in lesion of the prefrontal cortex. Numerous re ports suggest that patients suffering from degenerative and focal lesi ons of the striatum exhibit an impairment of the so-called <<frontal f unctions>>. These results support the hypothesis that the striatum is involved in these functions and therefore, that its lesion might accou nt for the neuropsychological disorders. The interpretation of these r esults assumes that cerebral lesions are restricted to the striatum. H owever, recent studies have shown that lesions of degenerative and vas cular disorders of the striatum frequently extend into the cortex. Mor eover, assessment of patients with striatal infarct has shown that the occurrence of frontal lobe symptoms depended on the associated cortic al lesion and that patients with pure striatal lesion did not exhibit a full dysexecutive syndrome. The contribution of the striatum to fron tal lobe functions might thus have been overestimated. Despite the unc ertainty about the critical locus of lesions accounting for the emerge nce of dementia, the term subcortical dementia has the advantage to re fer 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 candate nucleus is mainly involved in response selection, at least in unusual or complex tasks.