STIMULUS-BOUND PERSEVERATION AFTER FRONTAL ABLATIONS IN MARMOSETS

Marmosets with bilateral ablations of either the lateral or ventral surface of the frontal lobes were found to perseverate on object but not spatial serial reversal. They also perseverated on reversal of a visuospatial task where different stimuli required different spatial responses. No differences were found between the two lesion groups. Since the control animals showed mild perseveration on spatial but not object serial reversal it is argued that frontal ablations do not lead to perseveration of a natural tendency but rather that object and visuospatial perseveration are forms of stimulus-bound behaviour which do not occur when the animal is performing a spatial task in which stimulus position is irrelevant. Perseveration was reduced by pretreatment with a dopamine-blocking drug (haloperidol). It is suggested that information from temporal lobe mechanisms, involved in long-term memory, and from frontal lobe mechanisms, which exert shorter acting influences on behaviour, compete within the basal ganglia to determine stimulus choice. The ascending dopaminergic pathway may modulate the balance between these competing factors.