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The basic phase precession phenomenon is apparent when you look at the timing of place cell spikes relative to the hippocampal theta rhythm: | The basic phase precession phenomenon is apparent when you look at the timing of place cell spikes relative to the hippocampal theta rhythm: | ||
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+ | (Figure from Malhotra et al. 2012) Each spike is assigned a color based on the /phase/ of the theta rhythm (a component of the LFP or "local field potential") at which it occurs. Note the smooth color change as the animal runs through the place field. | ||
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+ | Thus, when looking at a typical place cell like the above, phase precession manifests as (1) a relationship between *location* on the maze and the theta phase of a place cell's spikes, as shown when plotting spikes "in space" and (2) a relationship between *time* and the theta phase of a place cell's spikes, as shown when plotting spikes "in time" aligned to the LFP. | ||
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+ | When a rat runs through a place field, space and time will be correlated, so it is not a priori clear if either one is somehow "primary". There are numerous papers that explore this issue. | ||
An important conceptual step is to extend this idea to what happens in a population of place cells which are all phase precessing: | An important conceptual step is to extend this idea to what happens in a population of place cells which are all phase precessing: | ||
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(Figure from Skaggs & McNaughton 1996, which is well worth reading) | (Figure from Skaggs & McNaughton 1996, which is well worth reading) | ||
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+ | Note how in each theta cycle, there is now a *sequence* of place cells occurring! |