Hippocampal synaptic plasticity, spatial memory and anxiety.

Bannerman DM
Sprengel R
Sanderson DJ
McHugh SB
Rawlins JN
Monyer H
Seeburg PH

It is widely believed that spatial learning and memory require long-term changes in a brain region called the hippocampus. This review challenges this received wisdom and uses recent evidence to argue that, rather than encoding or storing spatial memories, the hippocampus may use spatial information to resolve conflict and reduce uncertainty. This may explain its role in anxiety as well as memory.

Scientific Abstract

Recent studies using transgenic mice lacking NMDA receptors in the hippocampus challenge the long-standing hypothesis that hippocampal long-term potentiation-like mechanisms underlie the encoding and storage of associative long-term spatial memories. However, it may not be the synaptic plasticity-dependent memory hypothesis that is wrong; instead, it may be the role of the hippocampus that needs to be re-examined. We present an account of hippocampal function that explains its role in both memory and anxiety.

Hippocampal synaptic plasticity, spatial memory and anxiety.
(a) Grin1 mice with genetic ablation of NMDA receptors in the hippocampal CA1 region and dentate gyrus (DG) lack normal long-term synaptic plasticity and are impaired in a task that requires learning which of two identical beacons indicate the location of an escape platform, the other beacon being a ‘decoy’. (b) However, Grin1 mice are not impaired in remembering the correct platform location when the beacons are removed. This suggests that the spatial information is acquired and stored normally but cannot be used appropriately in the presence of ambiguous retrieval cues (i.e. the beacons). Activation in response to conflict and uncertainty may be a feature of hippocampal function that explains its role in anxiety as well as spatial memory.
2014.Nat. Rev. Neurosci., 15(3):181-92.
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