O'Keefe and Recce, in 1993, discovered that as a rat moves through the spatial firing field of a hippocampal pyramidal cell, spikes from the cell shift gradually to earlier and earlier phases of the theta cycle. Further research has shown that this "phase precession" reflects a population-wide phenomenon, in which the hippocampus plays in compressed form brief portions of the trajectory on which the animal is traveling. Several computational models of this effect have been proposed over the past few years: they can be divided roughly into "individual neuron" models, based on mechanisms operating within a single cell, and "network" models, based on interactions between groups of cells. The functional significance of the effect remains speculative. An interesting possibility is that, by compressing the temporal structure of the spike sequence, phase precession increases the influence of temporal structure on the synaptic enhancement produced by long term potentiation in the hippocampus.

Back to Workshop Schedule