Phase Precession

Phase precession is the phenomenon in which the spike phase of a hippocampal place cell advances relative to the ongoing theta oscillation as an animal traverses the cell's place field. Rather than firing at a fixed phase of the theta cycle, the cell fires at progressively earlier phases as the animal approaches the center of the field, then at progressively later phases as it departs. This phase shift encodes not just spatial position but trajectory and direction — doubling the information carried by the same spikes.

Phase precession is the canonical example of temporal coding in the mammalian brain. It demonstrates that the brain does not merely count spikes (rate coding) but uses the phase relationship between spikes and a global oscillation to encode additional variables. The mechanism is thought to involve interference between two oscillatory inputs — one at the baseline theta frequency and one at a slightly faster frequency — that produces a traveling wave of phase. This interference model connects phase precession to the phase-locked loop framework of neural oscillation and suggests that the hippocampus operates as a temporal interference detector.\n\n