FIG. 10.

Laminar dependence of 1st-spike latency, limiting modulation frequency, and group delay. Cortical depths are stated relative to the depth of the shortest-latency current sink evident in current-source density analysis. Shading in Fig. 10, A and B, indicates the interquartile ranges, and continuous lines in A–C represent medians. Those ranges and medians were computed by values within a 21-point sliding window. A: symbols represent 1st-spike latencies of individual single- or multiunit recordings. Latencies varied significantly with cortical depth (P < 0.0001, ANOVA; depths grouped in steps of 300 μm). B: the area of each circle is proportional to the number of recordings showing a particular limiting modulation frequency (rounded to the nearest 20 Hz) at a particular cortical depth (rounded to the nearest 50 μm). Limiting modulation frequency varied significantly with cortical depth (P < 0.01, Kruskal-Wallis nonparametric ANOVA). NPL, for “no phase locking,” indicates units for which no significant phase locking was observed at any tested modulation frequency or depth. A nonparametric test was selected because of those NPL points and because of the coarse sampling of modulation frequencies. Limiting modulation frequencies were assigned at the modulation depth that gave the highest value. C: symbols represent group delays of individual single- or multiunit recordings. O and X represent units for which the limiting modulation frequency was <60 or ≥60 Hz, respectively, and thick and thin lines represent the median values of those respective populations.