Entorhinal Cortex Lesions Disrupt the Relational Organization of Memory in Monkeys

By C. Buckmaster, Howard Eichenbaum, D. Amaral, Wendy A. Suzuki, P. Rapp. 2004

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Recent accounts suggest that the hippocampal system critically supports two central characteristics of episodic memory: the ability to establish and maintain representations for the salient relationships between experienced events (relational representation) and the capacity to flexibly manipulate memory (flexible memory expression). To test this proposal in monkeys, intact controls and subjects with bilateral aspiration lesions of the entorhinal cortex were trained postoperatively on two standard memory tasks, delayed nonmatchingto-sample (DNMS) and two-choice object discrimination (OD) learning, and three procedures intended to emphasize relational representation and flexible memory expression: a paired associate (PA) task, a transitive inference (TI) test of learning and memory for hierarchical stimulus relationships, and a spatial delayed recognition span (SDRS) procedure. The latter assessments each included critical “probe” tests that asked monkeys to evaluate the relationships among previously learned stimuli presented in novel combinations. Subjects with entorhinal cortex lesions scored as accurately as controls on all phases of DNMS and OD, procedures that can be solved on the basis of memory for individual stimuli. In contrast, experimental monkeys displayed deficits relative to controls on all phases of the PA, TI, and SDRS tasks that emphasized the flexible manipulation of memory for the relationships between familiar items. Together, the findings support the conclusion that the primate hippocampal system critically enables the relational organization of declarative memory.

Subfields: Behavioral Neuroscience, Cellular and Molecular Neuroscience, Cognitive Neuroscience

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Citations in the corpus

The hippocampus and inferential reasoning: building memories to navigate future decisions (2012, background): “Notably, both lesioned rats (Dusek and Eichenbaum, 1997) and lesioned monkeys (Buckmaster et al., 2004) performed perfectly on novel non-inferential test trials that probed knowledge about the relationship between end items of the hierarchy (e.g., A ?”
An investigation of learning strategy supporting transitive inference performance in humans compared to other species. (2006, background): “…in humans versus other species Previous work suggests that associative learning is sufficient for successful performance in non-human animals (Buckmaster et al., 2004; Rapp et al., 1996; Roberts & Phelps, 1994; Van Elzakker et al., 2003; Ferson et al., 1991; Wynne, 1995, 1997, 1998; Wynne et…”
Declarative Memory, Awareness, and Transitive Inference (2005, background): “Given that transitive inference performance is dependent on the hippocampal region in experimental animals (Dusek and Eichenbaum, 1997; Buckmaster et al., 2004), and given that conscious awareness for what is learned usually accompanies declarative (hippocampusdependent) learning in humans, it has s”
The medial temporal lobe and recognition memory. (2007, background): “In contrast, monkeys with selective damage to the hippocampus (Nemanic et al. 2004) (Figure 6) or entorhinal cortex (Buckmaster et al. 2004) can perform normally on DNMS even at substantial memory delays.”