Place cells are the hippocampal pyramidal cells, and they derive their name from the fact that they only fire when an animal is in the cellÆs firing field, i.e. in a part of its environment that the cell responds to (Kentros et al, 1998, 2121). Place cells, which are found in hippocampal area CA1, receive positional information from two different areas: the intrahippocampal network in area CA3, and directly from the entorhinal cortex (Brun et al, 2002, 2243). It is thought that these cells are characterized by location-specific firing, and that the angular position of their firing fields suggests that visual cues may activate them (Save, Cressant, Thinus-Blanc and Poucet, 1998, 1818). However, these cells have also been found to be active during sleep, and in blind rats, which indicates that the true nature of these cells has not yet been elucidated (Wilson and McNaughton, 1994, 676; Save, Cressant, Thinus-Blanc and Poucet, 1998, 1818). This paper will look at some of the investigations that have been carried out to try and elucidate the true nature and role of hippocampal place cells in location mapping.
Kentros et al (1998) investigated the effects of N-methyl-D-aspartate (NMDA) blockade on the glutamate receptors, and how this affected the NMDA-based plasticity of synapses in the formation and maintenance of firing fields . Encoding occurring in place cells in the rat hippocampus is thought to map out new environments by the fact that each cell fires only when the animal is in its firing field. The cells then coordinate their information to produce a memory. Evidence for this comes from the fact that a particular cell has the same firing field every time it is introduced into the same environment; and the firing of a particular cell in one environment does not predict its firing in another environment. New maps are made in each cell in each new environment it is exposed to, and they do not interfere with previous maps...