Hippocampal units maintain coupling precision to the local field potential during alternating network states.

A: Local field potential recordings and single unit activity (symbolized by vertical ticks) in CA1 and CA3 during the three experimental steps of the CCh experiments: baseline recording (SPW 1, left panel) followed by carbachol-induced gamma oscillations (Gamma, middle panel) and re-established SPW by wash-in of atropine (SPW 2, right panel). Two representative units are indicated by colored ticks in each region. Note that the individual units could be observed in all three phases of the experiment. B: Event cross-correlograms of field-potentials and firing time points of the units depicted in A. During SPW 1 and SPW 2, unit firing is correlated to the ripple-oscillation troughs in CA1 (peak intervals at ∼5 ms, corresponding to ripple cycle length); during the gamma episode they are correlated to the local gamma oscillation troughs (peak intervals at ∼30 ms). C: Mean firing rates of units remain constant during gamma oscillations. D: Firing phases of units to ripple troughs remain stable after an intermittent episode of gamma oscillations. The ripple cycle is described by a circular scale of 360° and the ripple trough is set to 0°. Each unit's preferred firing phase angle to the ripple contributes as one data point. Mean angle of the sum of all units is represented by the red arrow. The length of the red arrow is proportional to the length of the vector corresponding to the mean angle.