Fig. 2
Recording configuration and representative data showing dynamic transition in layer specificity of the inter-areal signal. a Spiking activities were recorded from A36, while local field potentials (LFPs) were recorded from TE by using a multi-contact linear array electrode. Inter-areal interaction was examined by coherence between these two signals. Cortical depths of the recording sites in A36 and TE were determined by histology and current source density of the LFP (see also Supplementary Fig. 13). IG infragranular layer, SG supragranular layer. b–f Representative data. b Top, spike density functions for the trials in which the presented cue stimulus exerted the largest response during the cue period (gray) and its paired associate was presented as a cue stimulus (black). We analyzed the latter trial (shown in black) for inter-areal coherence. Bottom, polar plots of mean firing rates during the cue and delay periods, shown for each cue stimulus. The responses to a stimulus and its paired-associate are indicated by radial lines. c Stimulus coding indices. CHI cue-holding index, PRI pair-recall index, PCI pair-coding index. *, P < 0.05. d Dynamics of coherence (coherogram) between A36 spikes and TE LFPs at the infragranular layer (top) and at the supragranular layer (bottom). The subtraction of trial-shifted control from raw coherence is shown. e Layer specificity of coherence as a function of frequency. The amplitude of coherence is color-coded. Black and white arrowheads depict coherograms shown in d. Left, corresponding histological section. f Laminar dynamics of coherence at 10−25 (black solid line) and 25−40 (gray dotted line) Hz during the cue (left) and delay (right) periods. g Temporal dynamics of coherence in IG and SG Hz at 10−25 to 25−40 Hz. P < 0.0001 for interaction between layer and frequency, between period and layer, and between period and frequency; F = 0.15, P = 0.69 for interaction among three effects, by three-way ANOVA for the effects of period, layer and frequency. *, P < 0.05; t-test against zero, corrected for multiple comparisons. †, P < 0.05; paired t-test, corrected for multiple comparisons. Error bars, mean ± s.e.m.
