along a straight path, place fields are activated one after another. When young rats repeatedly traverse the same straight path, connection between place fields are strengthened due to plasticity, causing subsequent place fields to fire more quickly and causing place field expansion, possibly aiding young rats in spatial memory and learning. However, this observed place field expansion and plasticity is decreased in aged rat subjects, possibly reducing their capacity for spatial learning and memory. This plasticity can be rescued in aged rats by giving them memantine, an antagonist that blocks the NMDA receptors which is known to improve spatial memory, and was therefore used in an attempt to restore place field plasticity in aged subjects. NMDA receptors, which are glutamate receptors, exhibit decreased activity in aged subjects. The application of memantine leads to in increase in place field plasticity in aged rat subjects. Although memantine aids in the encoding process of spatial information in aged rat subjects, it does not help with the retrieval of this information later in time. Aged rats further show a high instability in their place cells in the CA1 region. When introduced to the same environment several times, the hippocampal map of the environment changed about 30% of the time, suggesting that the place cells are remapping in response to the exact same environment. Contrarily, the CA3 place cells are show increased plasticity in aged subjects. The same place fields in the CA3 region to activate in similar environments, whereas different place fields in young rats would fire in similar environments because they would pick up on subtle differences in these environments. One possible cause of these changes in plasticity may be increased reliance on self-motion cues. See also Spatial view cells, primate hippocampal counterpart for visual field. Grid cells Head direction cells References External links Articles containing video clips Hippocampus (brain) Neurons Spatial cognition