Figure 7.

Asymmetric ramp-like membrane potential depolarization inside place fields. (A) LFP as measured from within the soma of a CA pyramidal cell, outside (0–2 s) and within a place field (2–4 s); spike unit timing is indicated by dotted red lines. Cyan and magenta markers indicate auto-detection of 0 and 180° theta limits. (B) Corresponding intracellular Vm (green line), and superimposed 1–2 Hz filtering (dashed black line). Red dots indicate spike timing (truncated, n = 1 cell as an example). (C) Representative sample of mean 1–2 Hz filtered ramps from third place field; statistics were performed on all 30 control (unlesioned) runs (n = 472 cells with increasing mean). Black line, mean of all curves; black vertical dashed line, true center of place field; red vertical dashed line, mean timing of the peak of individual ramps. Asymmetric ramp depolarization is attributable to the propagation delay, or “momentum” of RAIN networks; perturbation of a RAIN network affects all other cells with delays ranging from 50 to 100 ms, because both excitatory and inhibitory cells are sparsely connected and tonically inhibited, resulting in widely spaced irregular bursting. In this case, the CA RAIN networks experience an average delay of about 70 ms.