EFFECTS OF RHINAL CORTEX LESIONS COMBINED WITH HIPPOCAMPECTOMY ON VISUAL
RECOGNITION MEMORY IN RHESUS MONKEYS.
MEUNIER, M., W. HADFIELD, J. BACHEVALIER, E. A. MURRAY.
Laboratory of Neuropsychology, National Institute of Mental Health,
Bethesda, MD.
APStracts 2:0298N, 1995.
SUMMARY AND CONCLUSIONS
1. We assessed the visual recognition abilities, as measured by delayed
nonmatching-to-sample with trial-unique objects, of rhesus monkeys with
hippocampectomy (i.e. removal of the hippocampal formation plus
parahippocampal gyrus) combined with ablations of the rhinal cortex (i.e.
entorhinal cortex plus perirhinal cortex). 2. Relative to unoperated controls,
monkeys with combined hippocampectomy and rhinal cortex (H+Rh) ablation were
significantly impaired in visual recognition. 3. Comparison of the scores of
the monkeys in the present group H+Rh, which sustained near complete rhinal
cortex damage, to the scores of monkeys in an earlier group H+Rh in which the
rostral part of the rhinal cortex had been spared (Murray and Mishkin 1986)
indicates that the magnitude of the impairment is greater in the group with
the more complete rhinal cortex damage. This finding is consistent with the
idea that the rhinal cortex is critical for visual recognition. 4. Comparison
of the present results with those from an earlier study on visual recognition
that employed lesions limited to the rhinal cortex (group Rh; Meunier et al.
1993a) shows, paradoxically, that adding removal of the hippocampal formation
and parahippocampal gyrus to a rhinal cortex lesion significantly reduces the
recognition impairment produced by rhinal cortex lesions alone. 5. Our
findings do not fit the view that the hippocampal formation, parahippocampal
gyrus, and rhinal cortex constitute parts of a single functional system, such
that the greater the damage to the entire system, the more severe the
impairment. Instead, the results are consistent with the view that there are
multiple functional subdivisions within the medial temporal lobe.
Received 24 July 1995; accepted in final form 12 October 1995.
APS Manuscript Number J477-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95