Figure 6.
Spike Phases Relative to the Stimulus (but Not to Low-Frequency LFPs) Are Affected by the Envelope's Rate
(A) Spike phases obtained from an exemplary tracking unit (same shown in Figure 1) relative to the AM envelope, for modulation frequencies to which the unit's spiking was significantly synchronized (i.e., 2–8.57 Hz). Red arrows indicate the mean vector of the phase distribution.
(B) Spike phases relative to low-frequency (4–12 Hz) LFPs. Note that the spikes here are the same spikes as in (A).
(C) Top: distribution of spike-phase differences between two consecutive modulation frequencies, when phases were calculated relative to the AM envelope. The observed distribution is shown in blue, whereas a surrogate (randomized differences across not-ordered modulation frequencies) distribution is shown in gray. There was a significant difference between the randomized and observed distribution (Fisher's circular mean test, p < 1.78 × 10−8). Bottom: Same conventions as data shown on top, but spike phases were calculated relative to low-frequency (8–12 Hz) LFPs. No significant differences occurred between the observed and the surrogate phase difference distributions (Fisher's circular mean test, p = 0.19).
(D) Histogram (left) and circular histogram (right) for the distribution of preferred spike phases (relative to low-frequency LFPs) in tracking units (n = 31), across all modulation frequencies tested (i.e., all preferred phases of trackers with a cutoff frequency ≤ 22.63 Hz are represented). The red trace in the left histogram illustrates the phase convention relative to the LFP; the red line in the circular histogram shows the mean vector of the phase distribution. Statistics showed that there was a significant directionality in the spike phases (Rayleigh test for non-uniformity, p = 5.48 × 10−64).