Relationship between magnitude of damage to the hippocampus and impaired recognition memory in monkeys

Two recent meta-analyses, drawing on data from many of the same studies wit h monkeys, reached different conclusions about the relationship between hip pocampal damage and recognition memory performance. Both studies found evid ence of recognition memory impairment following hippocampal damage. However , Zola et al. (J Neurosci 2000;20:451-463) found no significant correlation between extent of hippocampal damage and recognition memory performance, w hereas Baxter and Murray (Hippocampus 2001;11:61-71) concluded that the ext ent of hippocampal damage in monkeys was inversely correlated with impaired performance. Here, we first consider the requirements for carrying out a v alid meta-analysis, and point out that the analysis carried out by Baxter a nd Murray (Hippocampus 2001;11:61-71) is invalid on simple statistical grou nds. We then adopt the appropriate statistical procedures (multiple regress ion analyses rather than simple correlational analysis) to assess the relat ionship between extent of hippocampal damage and recognition performance ac ross different studies. None of these analyses, including a reanalysis of t he data of Baxter and Murray (Hippocampus 2001;11:61-71), revealed a signif icant inverse relationship between lesion size and behavioral impairment. M ost of the variance was explained by differences between the studies that c ontributed to the meta-analysis, not by lesion size itself. Indeed, analysi s of covariance indicated that there were differences among the studies bey ond lesion size that significantly affected performance. Finally, we consid er what relationship might hold between lesion size and memory performance in the monkey. Hippocampus 2001;11:92-98. (C) 2001 Wiley-Liss, Inc.(dagger) .