A limited role for the hippocampus in the modulation of novel-object preference by contextual cues

Abstract

Recent evidence suggests that rats require an intact hippocampus in order to recognize familiar objects when they encounter them again in a different context. The two experiments reported here further examined how changes in context affect rats' performance on the novel-object preference (NOP) test of object-recognition memory, and how those effects interact with the effects of HPC damage. Rats with HPC lesions and control rats received NOP testing in either the same context in which they had previously encountered sample objects, or in a different but equally familiar context. In Experiment 1, the two contexts had very few overlapping cues within or outside the apparatus; thus, the differences between them were global. Consistent with previous results, control rats showed a novel-object preference in both the unchanged and (globally) changed contexts, whereas rats with HPC lesions displayed a preference only in the unchanged context. In Experiment 2, the context shift included only local features proximal to the test objects. The main results were the reverse of Experiment 1-rats with HPC lesions displayed a novel-object preference in both the unchanged and (locally) changed contexts, whereas control rats displayed a preference only in the unchanged context. The findings are consistent with the view that HPC damage does not cause a general inability to recognize objects, nor an inability to encode or store a representation of the context in which the objects are encountered. They suggest instead that HPC damage impairs the ability to remember specific locations of familiar objects within a particular context.The hippocampal formation (HPC) is thought to play a critical role in memory for contextual information. Much of the evidence for this role comes from studies in which rats with HPC lesions showed impaired fear conditioning to a test chamber in which an aversive event occurred (Sutherland and McDonald

Modulation of long-term memory for object recognition via HDAC inhibition

“…3B and the 24-h test a day later on the same mice shown in Fig. 3C) revealed a main effect of test [F (1,26) (Fig. 3B).…”

“…In our previous study, we only examined hippocampal LTP in the cbp KIX/KIX mutant mice (18). The object-recognition experiments we performed in this study may be hippocampus independent because we do not alter object location or the relationship between object and context, both of which have been shown to engage the hippocampus during object recognition (13,25,26). Thus, HDAC inhibition-dependent enhancement in hippocampal LTP may require CBP whereas HDAC inhibition-dependent modulation of long-term memory for object recognition may not.…”

“…A 2-way ANOVA yielded no significant difference because of genotype and no significant interaction between genotype and treatment [Main effect of genotype F (1,26) ϭ .016, P ϭ 0.90; Genotype ϫ Treatment interaction, F (1, 26) ϭ 1.27, P ϭ 0.268]. However, there was a significant difference among treatment [F (1,26) ϭ 27.32, P Ͻ 0.001]. One-way ANOVA revealed that neither Cbp KIX/KIX homozygous mice treated with vehicle (Fig.…”

The rat perirhinal cortex: A review of anatomy, physiology, plasticity, and function

“…Lesions of the hippocampus cause impairments in a similarly designed task in the monkey (Gaffan and Harrison, 1989) and also in the rat (Bussey et al, 2000(Bussey et al, , 2001. Hippocampal lesions in the rat have also shown that the hippocampus does not contribute to object recognition nor object context memories but only to the spatial location where an object has been previously encountered (Piterkin et al, 2008). An elegant study by Barker et al (2007) have shown that interaction between the perirhinal and medial prefrontal cortices is required in order to solve tasks where association between different forms of memory are required such as the object-in-place task.…”

On the Dynamic Nature of the Engram: Evidence for Circuit-Level Reorganization of Object Memory Traces following Reactivation

“…Indeed, studies with the spontaneous object recognition (SOR) task for rats have implicated PRh in object memory encoding, consolidation, and retrieval (Winters and Bussey, 2005a,b;Barker et al, 2006a,b). The hippocampus (HPC) may also play a role in object recognition, but the specific involvement of this structure remains unclear and may be related to processing of contextual information, rather than object representation per se (Gaffan, 1994;Cassaday and Rawlins, 1997;Bussey and Aggleton, 2002;Mumby et al, 2002;Aggleton and Brown, 2005;O'Brien et al, 2006;Piterkin et al, 2008).…”