Dysexecutive behaviour following deep brain lesions--a different type of disconnection syndrome?

The suppression of automatic prepotent behaviour in favour of more successful, more 'appropriate' behaviour is the primary function of the frontal lobe. Five frontal-subcortical circuits connect the frontal lobe to the basal ganglia and the thalamus. We report 17 patients with small lesions in the downstream structures of the frontal-subcortical circuits displaying severe dysexecutive behaviour. Positron emission tomography (PET) demonstrated hypometabolism of the frontal lobe in some of these patients. The literature on frontal lobe dysfunction after lesions in the basal ganglia and thalamus is discussed and the semiology of frontal lobe dysfunction in relation to the frontal-subcortical circuits is highlighted. Derived from our findings we suggest a disconnection syndrome of the frontal lobe caused by lesions in the downstream structures of the frontal-subcortical circuits.