Figure 3.

Licking-induced synchronization and phase-locked distribution across the four brain areas recorded. A, A schematic representation that illustrates the phase of the lick cycle. A phase (Φ) of 0 radians represents the tongue's contact with the sipper. Thus, neurons with a positive phase-relation (0 to π) tend to fire in the first half of the licking cycle (green), whereas coherent neurons with a negative phase (−π < 0) tend to fire in the second half (red) of the lick cycle. B, A histogram showing the percentage of neurons with significant coherence for each brain area: percentage of neurons with positive (0 to π; red) and negative (−π < 0; green) phase coherence. In the amygdala, the proportion of neurons with positive phase was larger than neurons with negative phase coherence. **Significant value of p < 0.05, χ² test. C, Distribution of phase-locked neurons sorted by brain region. In each histogram, the gray shaded rectangle indicates the percentage of neurons that were phase-locked with the tongue's contact with the sipper (−0.5 to 0.5 radians). In the OFC, NAcc, and IC, we found that the average firing phase (average phase across all licks in the cue epoch) was equally distributed over the entire lick cycle (Kuiper's test of uniformity, OFC, V′₁₅₃ = 1.37; NAcc, V′₂₀ = 1.25; IC, V′₁₇₃ = 1.69; nonsignificant). In contrast, the distribution of the phases of AMY was not uniform (V′₆₈ = 3.7; p < 0.05) in that they showed a marked preference to fire in the positive phase relative to the lick cycle. Thus, AMY neurons predominantly synchronize with neurons from the other three areas that also fire in a positive phase relative to the lick cycle (see D, green PSTH). D, Population PSTH of neurons with significant coherence (OFC, IC, NAcc, and AMY, n = 414) sorted by their phase relationship with licking. Gray, The population PSTH of neurons that fired in phase −0.5 to 0.5 radians relative to the lick (gray shaded rectangle in C). Green, The population PSTH of neurons that fired from 0.5 to π. Red, The population PSTH of neurons that fired from −π to −0.5 radians. Activity is aligned to cue delivery (time 0 s). The interval from the solid vertical line to the right dotted line indicates the first lick cycle after cue delivery. Note that the neuronal activity from these three PSTHs reset in each lick cycle.