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

The present study assessed the behavioural sequalae of unilateral excitotoxic 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 brief light stimulus was presented in either of two holes which were located on the same side of the box: this enabled performance on each side of the rat's body to be assessed independently. Lesions of the AGm impaired performance on the contralateral side, with rats biasing their responding to the nearer of the two response locations. Analysis of the deficit revealed that rats were able to discriminate between the two stimuli and suggested that AGm lesions disrupted the control of contralateral responding. Lesions of the mPFC produced similar response-related deficits, but these were more transient in nature. Neither AGm lesions nor mPFC lesions impaired performance on the ipsilateral side, consistent with the concept of an egocentrically coded deficit. (C) 2000 Elsevier Science B.V. All rights reserved.