title: Damage to the perirhinal cortex exacerbates memory impairment following lesions to the hippocampal formation.
abstract: Recent work has been directed at identifying the critical components of the medial temporal lobe that, when damaged, produce severe memory impairment. The H+A+ lesion includes the hippocampal formation, the amygdala, and the adjacent entorhinal, parahippocampal, and perirhinal cortices. A more restricted medial temporal lobe lesion that includes the hippocampal formation and parahippocampal cortex (the H+ lesion) produces less severe memory impairment. Previous work demonstrated that extending the H+ lesion forward to include the amygdala did not exacerbate the impairment. Here, we tested the hypothesis that extending the H+ lesion forward to include the perirhinal cortex (the H++ lesion), but sparing the amygdala, should produce a more severe memory impairment and one that would approximate the level of memory impairment associated with the H+A+ lesion. Monkeys with the H++ lesion were severely impaired on two of three amnesia-sensitive tasks (delayed nonmatching to sample and delayed retention of object discrimination). On the third amnesia-sensitive task (concurrent discrimination learning), two of the monkeys in the H++ group obtained poorer scores than all seven normal monkeys, although the overall group comparison was not significant. The memory impairment following H++ damage was more severe overall than the impairment associated with the H+ lesion and approached the level of impairment associated with the H+A+ lesions. Quantitative measurement of damage in each anatomical component of the lesion indicated that the perirhinal cortex was the only brain region that was more extensively damaged in the H++ group than in the H+ group. These findings emphasize the importance of the perirhinal cortex in the anatomy of the medial temporal lobe memory system.
authors.affiliation: Veterans Affairs Medical Center, San Diego, California 92161.
authors.forename: S
authors.initials: S
authors.lastname: Zola-Morgan
authors.forename: L R
authors.initials: LR
authors.lastname: Squire
authors.forename: R P
authors.initials: RP
authors.lastname: Clower
authors.forename: N L
authors.initials: NL
authors.lastname: Rempel
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D001931:Brain Mapping; D004192:Discrimination, Psychological / Q000502:physiology; D006624:Hippocampus / Q000502:physiology*; D008032:Limbic System / Q000502:physiology*; D008252:Macaca fascicularis; D008568:Memory / Q000502:physiology*; D009043:Motor Activity / Q000502:physiology; D012153:Retention, Psychology / Q000502:physiology; D013997:Time Factors