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, 1986), 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 temporal lobe.