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Opposite relationship of hippocampal and rhinal cortex damage to delayed nonmatching-to-sample deficits in monkeys
1Department of Psychology, Harvard University, Cambridge, Massachusetts 02138, USA. mbaxter@wjh.harvard.edu
Abstract:
Three recent studies in macaque monkeys that examined the effects on memory of restricted hippocampal lesions (Murray and Mishkin, J Neurosci 1998;18:6568-6582; Beason-Held et al., Hippocampus 1999;9:562-574; Zola et al., J Neurosci 2000;20:451-463) differed in their conclusions about the involvement of the hippocampus in recognition memory. Because these experiments used a common behavioral procedure, trial-unique visual delayed nonmatching-to-sample (DNMS), a quantitative synthesis ("meta-analysis") was performed to determine whether hippocampal lesions produced a reliable net impairment in DNMS performance, and whether this impairment was related to the magnitude of hippocampal damage. A similar analysis was performed on data from monkeys with perirhinal or rhinal cortex damage (Meunier et al., J Neurosci 1993;13:5418-5432; Buffalo et al., Learn Mem 1999;6:572-599). DNMS performance scores were transformed to d' values to permit comparisons across studies, and a loss in d' score, a measure of the magnitude of the recognition deficit relative to the control group, was calculated for each operated monkey. Two main findings emerged. First, the loss in d' following hippocampal damage was reliably larger than zero, but was smaller than that found after lesions limited to the perirhinal cortex. Second, the correlation of loss in d' with extent of hippocampal damage was large and negative, indicating that greater impairments were associated with smaller hippocampal lesions. This relationship was opposite to that between loss in d' and rhinal cortex damage, for which larger lesions were associated with greater impairment. These findings indicate that damage to the hippocampus and to the rhinal cortex affects recognition memory in different ways. Furthermore, they provide a framework for understanding the seemingly disparate effects of hippocampal damage on recognition memory in monkeys, and by extension, for interpreting the conflicting reports on the effects of such damage on recognition memory abilities in amnesic humans.
Insights
A meta-analysis of monkey studies reveals hippocampal lesions impair recognition memory, but less so than perirhinal cortex damage. Greater memory impairment correlated with smaller hippocampal lesions, unlike rhinal cortex damage.
Area of Science:
- Neuroscience
- Cognitive Psychology
- Comparative Cognition
Background:
- Conflicting conclusions exist regarding the hippocampus's role in recognition memory based on macaque monkey studies.
- Previous research utilized the trial-unique visual delayed nonmatching-to-sample (DNMS) task to assess recognition memory deficits.
- The precise contribution of hippocampal versus rhinal cortex damage to recognition memory remains debated.
Purpose of the Study:
- To quantitatively synthesize data from multiple studies on hippocampal lesions and recognition memory in macaque monkeys.
- To determine if hippocampal lesions cause a reliable impairment in DNMS performance.
- To investigate the relationship between the extent of hippocampal damage and the magnitude of recognition memory impairment.
Main Methods:
- Performed a meta-analysis on data from three studies involving hippocampal lesions in macaque monkeys using the DNMS task.
- Analyzed data from studies with perirhinal or rhinal cortex damage for comparative purposes.
- Transformed DNMS performance scores to d' values and calculated the loss in d' (recognition deficit) for each operated monkey.
Main Results:
- Hippocampal lesions resulted in a significant loss in d' (recognition impairment), but this deficit was smaller than that observed with perirhinal cortex lesions.
- A strong negative correlation was found between the extent of hippocampal damage and the loss in d', indicating smaller lesions caused greater impairment.
- Conversely, larger rhinal cortex lesions were associated with greater impairment, suggesting differential effects of hippocampal and rhinal cortex damage on recognition memory.
Conclusions:
- Damage to the hippocampus and rhinal cortex affects recognition memory through distinct mechanisms.
- The findings provide a framework for reconciling disparate results on hippocampal damage effects in monkeys.
- This meta-analysis offers insights into human amnesia research by clarifying the role of the hippocampus in recognition memory.