Spatial Memory - Plasticity

Plasticity

Spatial memories are formed after an animal gathers and processes sensory information about its surroundings (especially vision and proprioception). In general, mammals require a functioning hippocampus (particularly area CA1) in order to form and process memories about space. There is some evidence that human spatial memory is strongly tied to the right hemisphere of the brain.

Spatial learning requires both NMDA and AMPA receptors, consolidation requires NMDA receptors, and the retrieval of spatial memories requires AMPA receptors. In rodents, spatial memory has been shown to covary with the size of a part of the hippocampal mossy fiber projection.

The function of NMDA receptors varies according to the subregion of the hippocampus. NMDA receptors are required in the CA3 of the hippocampus when spatial information needs to be reorganized, while NMDA receptors in the CA1 are required in the acquisition and retrieval of memory after a delay, as well as in the formation of CA1 place fields. Blockade of the NMDA receptors prevents induction of long-term potentiation and impairs spatial learning.

The CA3 of the hippocampus plays an especially important role in the encoding and retrieval of spatial memories. The CA3 is innervated by two afferent paths known as the perforant path (PPCA3) and the dentate gyrus (DG)-mediated mossy fibers (MFs). The first path is regarded as the retrieval index path while the second is concerned with encoding.