Disinhibition of sequential actions following right frontal lobe damage

Action disorganization syndrome (ADS) is a frontal lobe neuropsychological syndrome characterized by deficits in the performance of familiar sequential tasks such as making a cup of tea. In this study, we examined the performance of familiar sequential tasks by 3 patients with right frontal brain tumours and no other areas of brain damage. When task-irrelevant objects were presented as distractors in addition to the target objects, all patients used the distractors in accordance with the target task. These patients showed few of the sequential and omission errors that had been previously reported in patients with ADS. Although normal participants could suppress the activation of task-irrelevant objects, these patients had difficulty with this process, which would normally be carried out by the right frontal lobe to determine the most suitable action behaviour. The intact left frontal lobe may receive bottom-up activation from the distractors and modify this schema to match the behavioural context. Our findings suggest that patients with only right frontal lobe damage may be characterized more by action disinhibition than by disorganization.