The same trend was observed across all recording sites (Fig. 3C). BF estimates were not significantly different between the 3 signals (Friedman's non-parametric repeated measures ANOVA, χγ2 (2, n=130) = 0.92, p = 0.2, Fig. S1). The tuning bandwidths of MUA, CSD and LFP differed significantly from one another (Friedman's non-parametric repeated measures ANOVA, χγ2 (2, n=130) = 85.2, p < 0.01), in an order of BWMUA < BWCSD < BWLFP (Tukey's HSD test, all comparisons p < 0.05, Fig. 3D). Similar results were found for the tuning of 3 signals in the supragranular layers (Fig. S2), where BWMUA did not differ significantly from layer 4 (Wilcoxon rank sum test, p = 0.34). Two physiological factors likely can account for these differences. First, due to reflection of subthreshold synaptic currents in the CSD measure, the tuning of CSD responses to tones is wider than that of MUA responses to the same tones. Second, due to volume conduction of electrical events in auditory cortical loci tonotopically not matched to the penetration sites, the tuning of LFP is wider than that of CSD measures.
