COGNITIVE INFLEXIBILITY AFTER ARCHICORTICAL AND PALEOCORTICAL PREFRONTAL LESIONS IN MARMOSETS

The behaviour and cognitive abilities of marmosets with bilateral abla tions of either the archicortex on the mediodorsal surface or the pale ocortex on the ventrolateral surface of the frontal lobes were assesse d in terms of the types of information being handled, the mode of acti on (inhibitory versus productive mechanisms), and the level of functio ning of these frontal areas. Although there was a tendency for the ven trolateral ablation to produce a greater impairment on object than on spatial discrimination in comparison to the mediodorsal ablation, the differences between the two groups was not marked in this respect. The effect of ablations of either of these areas was more marked on tasks which required the inhibition of prepotent responses than on tasks wh ere novel or arbitrary responses were appropriate. The major effect of both lesions was the production of perseverative behaviour which occu rred at the level of motor output in the first few days after surgery but was then observed at the level of choice behaviour and attentional set in formal cognitive tests. Impairments were also seen on postoper ative retention of tasks learnt prior to surgery. It is suggested that all these impairments arise from an inability to use or modify stored information.