Figure 6. L6 CT activation changes the frequency and resets the phase of local electric field oscillations in A1.

(A) The raw L6 CT-evoked CSD signal recorded across the A1 column from a single trial in an awake mouse. Optogenetic activation of L6 CT neurons induces a high-frequency oscillation while the laser is on, followed by a few cycles of a low-frequency rhythm following L6 CT deactivation. Scale bar = 0.2 s and 5 mV/mm². (B–C) Change in CSD frequency power spectrum during laser (blue) and 0–400 ms after the laser is turned off (black) relative to pre-laser baseline. B plots the full frequency range to highlight the high-gamma peak during laser activation, whereas C plots frequencies ≤ 30 Hz to emphasize the delta-theta power after laser offset. (D) Mean (±1 SEM) L2/3 unfiltered CSD amplitude for laser durations varying from 10–400 ms. The short- and long-delay periods following L6 CT deactivation are indicated by the purple and green arrows, respectively. (E) Phase histograms at the corresponding laser duration for the short- and long-delay period. L2/3 CSD phase is consistently near zero in the short-delay period and pi in the long-delay period. (F) Normalized spontaneous firing rate in each layer as a function of the spontaneous L2/3 delta-theta CSD phase (2–6 Hz). Spontaneous firing rate was modulated across L2/3 CSD phase for all layers (ANOVA, F > 3.6 and p < 0.001), with the lowest spike rate consistently occurring at the zero phase. (G) Tone-evoked frequency tuning functions at three phases of the spontaneously occurring L2/3 delta-theta CSD: zero, π and the average of the intermediate phases, ±π/2. Tuning shape was significantly modulated by phase in L4, L5 and L6, (ANOVA, F > 6.3, p < 0.005 for all), but not in L2/3 itself (F = 1.4, p = 0.28).