The firing of hippocampal place cells predicts the future position of freely moving rats

Abstract

Direct observation and automatic, video-based methods reveal that a large fraction of hippocampal pyramidal neurons recorded from freely moving rats behave as "place cells"; the firing of each place cell occurs almost exclusively when the rat is in a restricted part of its current environment. In earlier work, 2-dimensional firing distributions for place cells over the apparatus area were made under the assumption that the correct location for each spike was the animal's position at the instant that the spike was fired. Spatial firing distributions generated in this way often have a very simple structure, in which the single region of intense activity has a just one maximum, and where the rate decreases monotonically in all directions away from the maximum. We will refer to patterns of this sort as "ideal." We describe how the spatial firing pattern is altered by assigning spikes to positions earlier or later than the instant at which they were fired. Spatial firing distributions were generated for a range of constant displacements of the spike time-series against the position time series. Three quantitative measures were used to estimate the extent to which the spatial firing pattern at different "spike/position shifts" approximated the ideal pattern. The 3 measures are in agreement that spikes must precede the animal's position by about 120 msec for the spatial firing pattern to be closest to the ideal. These results suggest that hippocampal unit activity predicts the animal's future location on a short time scale.

Conjoint Control of Hippocampal Place Cell Firing by Two Visual Stimuli

“…(6) Coherence is a nearest-neighbor 2-D autocorrelation of firing rate (Muller and Kubie 1989) and is calculated in three steps. First, parallel lists are constructed for the firing rate in each pixel and the average firing rate in the eight nearest neighbors; the average is the sum of the number of spikes in the neighbors divided by the sum of the time spent in the neighbors.…”

Understanding hippocampal activity by using purposeful behavior: Place navigation induces place cell discharge in both task-relevant and task-irrelevant spatial reference frames

“…Only firing rate distributions with z info Ͼ 1.65 (less than 5% likely to come from the chance distribution) were considered to be location specific. Patchiness measures the global smoothness of a firing rate pattern (20). It is calculated as the number of contiguous regions (patches) in the highest firing rate category (purple) of the firing rate map.…”

“…It is calculated as the number of contiguous regions (patches) in the highest firing rate category (purple) of the firing rate map. Spatial coherence measures the local smoothness of a firing rate pattern (20) and is calculated as the z-transform of the correlation between the rate in a pixel and the mean rate in the immediately neighboring pixels.…”

Hippocampal and neocortical interactions during context discrimination: Electrophysiological evidence from the rat

“…Moreover, it has been suggested that the backward expansion phenomenon may contribute to the transformation of a rate code to a temporal code such as that illustrated in phase precession (Mehta et al, 2002). Perhaps, the backward expansion phenomenon could help to explain other place field phenomenon such as the tendency for place cells to fire in anticipation of entering a specified location within a familiar environment (Muller and Kubie, 1989).…”

“…earlier example of prospective coding by place cells was the demonstration that place fields seemed to anticipate the future location of an animal by some 90 ms (Muller and Kubie, 1989). The time scales for the latter two studies are very different so it remains to be determined if they are derived from the same or different mechanism.…”