Figure 11.

CA3 population activity and subthreshold membrane potential dynamics during sequence generation. (A) Representative spectrogram of CA3 excitatory population rates, showing increased power in the 100–250 Hz ripple band. FFT spectra were computed with a Hanning window of size 1024, advanced in increments of 2 ms. (B) Time course of CA3 excitatory population rates during sequence generation before the first trial, after the first trial, and after the fourth trial. Population rates were smoothed with a Gaussian kernel of 2 ms width. (C) Time-average (mean ± s.e.m.) of population rates shown in (B) for early, middle, and late phases of each sequence. Before learning, firing rates remain approximately constant. After the first rewarded trial, higher population rates are observed in the middle and last third of a sequence relative to the first third. This effect becomes more pronounced after additional trials. (D) Representative membrane potential traces of CA3 place cells with place field locations near the start and end points of the sequence as well as a silent cell with a place field not overlapping with the sequence trajectory. Cells participating in the bump trajectory show ramp-like dynamics, with gradual ramping depolarization for cells firing late in the sequence, and gradual ramping hyperpolarization for cells firing early in the sequence. Silent cells show increasing hyperpolarization across a single sequence.