Fig. 3

LFP and spike latency analysis for individual responses. a Exemplary unit recorded in the left hippocampus that responded to the picture of Stonehenge. The red curve corresponds to the instantaneous firing rate, whereas the vertical dashed line marks the spike response onset. The average LFP responses are shown in brown (raw LFP: 2 to 512 Hz) and black (theta LFP: 3 to 6 Hz), with the vertical dashed line marking the LFP response onset (Methods). The spike response latency was 221 ms and the LFP onset occurred 118 ms before. Due to copyright issues, the image presented here (cropped from “Stonehenge 02” by Bernard Gagnon, licensed under CC BY-SA 3.0) is similar to the one actually presented to the subject. b Latency corrected average of the 151 theta LFP responses. The LFP traces of the individual responses are aligned to the spike latency before computing the grand average. The blue dashed line marks 70 ms before the spike latency. c LFP and spike latencies for individual responses were significantly correlated (Pearson correlation, r = 0.35, p = 4 × 10⁻³). Points were projected into the orthogonal direction to y = x (black dashed line) and their distribution shows a clear peak. The blue dashed line represents y = x − 70. d Grand average of the instantaneous firing rate (red) and the theta LFP (black) for the “early” (light traces) and “late” (dark traces) subsets of responses, which were split with respect to the median spike latency (278 ms, blue dashed line). The peak LFP latency was significantly different for the early and late groups (one-sided rank-sum test, p = 3 × 10⁻³) and for both groups the LFP responses preceded the ones of the spikes