The effect of cytotoxic lesions of the hippocampus on recognition memory in the rat: Effects of stimulus size.

Abstract

Rats with excitotoxic hippocampal lesions were trained on delayed nonmatching-to-sample (DNMS) with small goal boxes, containing complex objects, presented on a pseudo trial-unique schedule. A series of experiments then tested performance on repeated presentation of either the small object or large empty goal boxes. All rats acquired the nonmatching rule, but hippocampal-lesioned rats performed less well than controls on choice accuracy for the final 2 blocks of acquisition. In the study's main phase, the lesions impaired choice accuracy when the large empty boxes were used as stimuli. This deficit was ameliorated when the rats were tested with the small object boxes, although the performance of the hippocampal-lesioned rats was still below that of controls. These results extend previous reports of box size-dependent effects of hippocampal aspiration lesions on DNMS and suggest that selective damage to the hippocampus, not neuronal loss in adjacent structures or fiber tracts, is critical for the effect.

Hippocampal CA1 Place Cells Encode Intended Destination on a Maze with Multiple Choice Points

“…They are also consistent with a study using delayed non-matching-to-sample task on a Y-maze (Higgs et al, 2001) in which the hippocampus-lesioned animals were significantly impaired in choosing the nonmatching box relative to the control animals but still performed at a 75% correct level. This agrees with the current findings that lesioned animals were impaired in acquiring the alternation task but ultimately learned the alternation rule.…”

Modulation of the Impairment of Hippocampectomized Rats on the Radial-Arm Maze Cue Task by Visual Characteristics and Subicular Damage.

“…These results were not consistent with the cognitive map theory (O'Keefe & Nadel, 1978) and suggested that the distance of the relevant stimuli and the nature of recurring information influence the performance of fornix-transected rats in the radial-arm maze. These results also implied that the hippocampal formation may play a role in working or episodic memory, depending on the type of stimuli to be remembered (Cassaday & Rawlins, 1995, 1997Higgs et al, 2001;Yee & Rawlins, 1994). Whether similar results would be obtained after selective lesions of the hippocampus (i.e., the dentate gyrus and the Ammon's horn) has yet to be verified.…”

“…Deficits have been observed after fimbria-fornix transections or hippocampal aspiration lesions in different tests that do not include spatial components (Cassaday & Rawlins, 1997;Hudon, Dore ´, & Goulet, 2003b;Olton & Feustle, 1981;Yee & Rawlins, 1994). Higgs, Bannerman, and Rawlins (2001) have recently proposed that damage limited to the hippocampus is sufficient to produce impairments in nonspatial memory tasks. However, other analyses have suggested that combined cell loss in the hippocampus and in the subiculum is essential in order to cause a long-lasting impairment on nonspatial working memory tasks (Jarrard, 1986(Jarrard, , 1993.…”