Retrosplenial cortex: possible role in habituation of the orienting response.

A patient with a unilateral lesion that included the retrosplenial area had a propensity to attend to contralateral stimuli. To determine whether the retrosplenial-area lesion was inducing this defect, unilateral retrosplenial lesions were produced in rats by surgical aspiration. Animals were assessed preoperatively and postoperatively for orientation and habituation to bilateral simultaneous stimulation in 3 sensory modalities: visual, tactile, and auditory. At each session, the orientation test was terminated upon completion of 5 trials per modality, and the habituation test ended after 4 consecutive response failures or upon completion of 15 trials per modality. Postoperatively, contralateral orientation was not significantly different from ipsilateral orientation, suggesting that there was no neglect. However, there was a significant delay in habituation to contralateral stimulation in postoperative weeks 2 and 3-5. Our results suggest that rats with retrosplenial area lesions have normal orientation but fail to habituate to contralateral stimuli.