EFFECTS ON VISUAL RECOGNITION OF COMBINED AND SEPARATE ABLATIONS OF THE ENTORHINAL AND PERIRHINAL CORTEX IN RHESUS-MONKEYS

Performance on visual delayed nonmatching-to-sample was assessed in rhesus monkeys with combined and separate ablations of the perirhinal and entorhinal cortex, as well as in unoperated controls. Combined (i.e., rhinal cortex) lesions yielded a striking impairment on this task, one almost as severe as that seen after combined amygdalohippocampal removals that included some of this subjacent cortex (Mishkin, 1978; Murray and Mishkin, 1984). Ablations of the perirhinal cortex alone produced a deficit nearly as severe as that found after rhinal cortex lesions, whereas ablations of the entorhinal cortex alone produced only a mild deficit. Contrary to the conclusion from an earlier study (Murray and Mishkin, 1 986), the present results demonstrate not only that damage limited to the rhinal cortex is sufficient to produce a severe loss in visual recognition, but also that such damage leads to a far greater loss than damage to any other single structure in the medial part of the tem oral lobe.