Lesions of the dorsomedial striatum impair formation of attentional set in rats.

Behavioural flexibility refers to the ability to rapidly adapt to novel situations and it has been suggested that the frontal lobe and basal ganglia are implicated in various components of adjusting to changes in environmental contingencies. Behavioural flexibility can be assessed using attentional set-shifting tasks, in which performance is impaired after damage to the prefrontal cortex. The present study explores the downstream contribution of the prefrontal projection zone in the dorsomedial striatum (DMS) to attentional set shifting. Rats were tested in two set-shifting tasks following quinolinic acid injections bilaterally into the DMS. When tested in a rodent version of the set-shifting task, rats with a DMS lesion displayed a greater number of errors during the reversal stages of the task than sham lesion controls but the nature of the errors did not differ between the two groups. Interestingly, when the rats were tested in a modified version of the set-shifting task, directly designed for measuring the formation of an attentional set, sham lesion controls displayed a pronounced shift-cost, evident of successful set-formation. In contrast, rats with DMS lesions failed to form an attentional set, showing no performance cost when a shift of attention was required. These results support previous reports of the importance of the DMS in behavioural flexibility but also suggest that this region is vital for the formation of set, possibly by extrapolating different perceptions into a unified representation of a dimension.