Figure 2.

Three distinct states of hippocampal field and unit activity during urethane anesthesia. A, Hippocampal field (top) and stratum oriens (SOr) single-unit (bottom) activity at three separate instances during a single recording episode. Representative traces are plotted for theta, LIA, and the SO. Each state was characterized by distinct patterns of field waveforms, spike trains, and field-unit correlations. B, Spike-triggered averages of field activity and spike train autocorrelation histograms (C) for the three respective hippocampal states shown in A. Gray lines in B and C represent 95% confidence intervals. Phase histograms for this unit during theta (D) and the SO (E) demonstrate significant state-dependent phase-related preferences, which changed across states. Both phase histograms were significantly nonuniform. F, Power spectra and autocorrelation functions of hippocampal field activity demonstrate the differences in frequency components and rhythmicity across all three states (gray shaded area represents 95% confidence interval). The SO was characterized by a dramatic increase in rhythmic power and a shift of peak frequency values to a lower range (∼1 Hz and below). G, Average firing rates of the same cell for a 60 s episode in each state showing significant differences between all three states. fiss, Fissure.