Unilateral lesions of the medial agranular cortex impair responding on a lateralised reaction time task

The present study assessed the behavioural sequalae of unilateral excitotox ic cortical lesions made either in the medial agranular cortex (AGm) or in the medial prefrontal cortex (mPFC) using a visual reaction time task. The task required animals to sustain a nose-poke in a central hole, until a bri ef light stimulus was presented in either of two holes which were located o n the same side of the box: this enabled performance on each side of the ra t's body to be assessed independently. Lesions of the AGm impaired performa nce on the contralateral side, with rats biasing their responding to the ne arer of the two response locations. Analysis of the deficit revealed that r ats were able to discriminate between the two stimuli and suggested that AG m lesions disrupted the control of contralateral responding. Lesions of the mPFC produced similar response-related deficits, but these were more trans ient in nature. Neither AGm lesions nor mPFC lesions impaired performance o n the ipsilateral side, consistent with the concept of an egocentrically co ded deficit. (C) 2000 Elsevier Science B.V. All rights reserved.