[Dysexecutive syndromes and degenerative diseases]

A dysexecutive syndrome is observed not only in frontotemporal lobar degeneration, but also in subcortical degenerative diseases, and even in Alzheimer's disease whose lesions predominate in temporoparietal associative areas. The association between a dysexecutive syndrome and various cerebral localisations may be explained by the fact that cognitive and behavioral organisation recruits anatomofunctional frontostriatal and frontoparietal circuits. Both animal experimentation and human clinical observation argue in favour of a functional continuity and complementarity among these loops. The prefrontal cortex would be particularly needed in new situations, to inhibit old programs of action not adapted to the present context and to elaborate new ones; the basal ganglia would be rather required by the repetition of the situation to progressively transform the new program in routine. If we refer to Shallice model, we can hypothesize that optimal executive functions require the preservation not only of the Supervisory Attentional System, mainly dependent on the prefrontal cortex, but also of the Contention Scheduling, recruiting the basal ganglia, and of the Schemas of Action, represented in parietal and premotor areas. Therefore, the neuropsychological assessment of patients with degenerative diseases contributes to the understanding of the anatomofunctional architecture of executive functions.