Table 2.

Comparison of cell discharge during place cell activity and event-related activity

PropertyLocation-specific dischargeEvent-related discharge
Stability of correlateYesYes
Sparsity: fraction of participating cells40%25%
SpecificityOne firing field per cell; rarely twoDrop or jump; rarely both
DirectionalityOne way on linear trackUp or down
Clustering of similar cells in hippocampusNoNo
Peak firing rate5–50 spikes/s5–50 spikes/s
Firing modulation by thetaYesYes
Precession with thetaYesYes
Rate decreased by scopolamineYesYes
Precision reduced by scopolamineYesYes
Interneuron correlatesMultiple high-rate zonesMost fire at drop and jump
  • Stability describes the constancy of cell-specific discharge pattern seen when the rat is returned to the same circumstances. Sparsity refers to the fraction of pyramidal cells in the active subset. Specificity is confinement of discharge to a small number of regions or events. Directionality is the tendency of cells to fire only when the rat walks in one direction on a one-dimensional path; it is not distinguishable from specificity for event-related activity. The lack of clustering implies that cells with different discharge correlates occur independent of distance within the pyramidal cell layer. Modulation and precession with the theta rhythm indicate that discharge covaries with theta phase. Scopolamine rate effect is as described; scopolamine effect on precision is measured by coherence or its one-dimensional analog used here. The multiple high rate zone of interneurons during spatial tasks and the tendency for interneurons to fire at drop and jump may reflect their property of receiving convergent input from multiple pyramidal cells.