[Isolated involvement of motivated behavior and basal ganglia diseases]

Focal brain lesions involving bilaterally either the globus pallidus, the corpus striatum or the deep frontal white matter, may result in a distinctive syndrome whereby patients become totally inert, with massive decrease in spontaneous behaviour, despite lack of obvious cognitive and mood disturbances. This syndrome has been variously labelled as "loss of psychic autoactivation" (Laplane et al.), "loss of action initiation and maintaining" (Ali Chérif et al.), "athymhormic syndrome" (Habib & Poncet). The most salient feature of this syndrome lies in the dissociation found between dramatic decrease in spontaneous mental (gestural, linguistic, emotional) productions, on the one hand, and almost normal productions given in response to external orders or stimulations, on the other hand. Patients are totally aware of these behavioural changes. According to their own reports, they do not suffer from these changes, they are not depressed or anxious, they do not make any plans or projects. Finally, a striking feature of their subjective experience is that they very often report an absence of spontaneous thought ("mental emptiness"). It is all though psychophysiological processes responsible for releasing and maintaining self-initiated behaviours or behaviours occurring in response to appetitive or aversive environmental stimulations, were impaired; this impairment may thus be termed a "motivational" disorder. Observations of the brain lesional substrate of this syndrome have focused on several sub-cortical neural structures, whose common feature is to be tightly connected with elements of the dopaminergic meso-limbic system, known from abundant experimental evidence to be chiefly involved in the regulation of motivated behaviour.