Results
I mentioned neuronal capturing rates and you may LFP gamma power and level frequency into the V1 of 5 anesthetized macaque monkeys, getting drifting sinusoidal gratings various models, contrasts, orientations and you may disguised with assorted quantities of looks.
Round the personal web sites, stabilized gamma electricity decrease twofold when gratings was indeed disguised having 80% appears, and average height regularity managed to move on of 42
We analyzed a common set of sites across conditions-those that were activated by the smallest grating. The average LFP spectra showed nearly a twofold increase in gamma power with larger gratings (Fig. 2A, left), with a more apparent bump in the gamma range. We quantified the change in gamma power (25–55 Hz) by normalizing to its maximum across stimulus sizes at each site, and then averaging across sites (n = 209 sites). This normalized gamma power increased monotonically from 0.67 ± 0.02 for the smallest grating to 0.93 ± 0.01 for the largest (p < 0.0001, Wilcoxon signed-rank test; Fig. 2A, middle, black). Similar effects were seen in each individual animal (faint black lines, indicating average effect in each animal). Over the same range of sizes, the gamma peak frequency at individual recording sites decreased from 50.5 ± 0.2 to 37.9 ± 0.1 Hz (p < 0.0001, t test; Fig. 2A, middle, red; data from each animal in faint red). Thus, gamma power and peak frequency were modulated in opposite ways by stimulus size: an increase in gamma power was associated with a decrease in peak frequency. The simultaneously recorded neuronal responses showed strong suppression for large gratings, with the normalized spike rate decreasing from 0.86 ± 0.02 to 0.41 ± 0.02 (p < 0.0001, Wilcoxon signed-rank test; Fig. 2A, right).
Gamma power, top volume, and neuronal shooting rates for several stimulus modifications within the V1. An excellent, Left, Power spectra off LFP having gratings of different systems (n = 209 websites). Dashed range implies brand new gamma energy to own spontaneous interest. Middle, Top regularity regarding gamma assortment (dense reddish range) and you can normalized gamma fuel (thicker black line). The new light outlines indicate the average studies away from for every creature. Dashed line means brand new gamma energy to possess spontaneous activity. Proper, Normalized neuronal solutions (heavy black line). Light contours suggest an average data away from per animal. B, Leftover, Power spectra out of LFP for various quantities of sounds-hiding (n = 228 web sites). Middle, Peak volume and you can normalized gamma electricity. Best, Normalized neuronal firing speed. C, Remaining, Strength spectra off LFP for different stimulus contrasts (letter = ninety internet). sugar daddy St Louis MO Center, Top frequency and stabilized gamma strength. Best, Stabilized neuronal solutions. D, Kept, Fuel spectra of LFP to have gratings various orientations (n = 209 internet sites). Middle, Height regularity and normalized gamma power. Correct, Normalized neuronal answers. All mistake bars indicate SEM.
We next measured gamma induced by large gratings (10°) masked with different levels of noise. Noise was generated by replacing different proportions of the gratings with random large pixels of the same mean luminance (see Materials and Methods). We used large gratings because these induced the most gamma power, for which the peak frequency was most clearly defined. Masking noise reduced gamma power (see also Jia et al., 2011), and caused the peak frequency of the average spectrum to shift lower (Fig. 2B, left; n = 228 sites). 2 ± 0.1 Hz to 30.1 ± 0.4 Hz (p < 0.0001, t test; Fig. 2B, middle). Thus, for masking noise, gamma power and peak frequency were positively correlated across stimulus conditions: a ma power was associated with a decrease in peak frequency. Despite prominent changes in gamma, population neuronal firing rates were not affected by noise masking (ANOVA: F = 1.18, p = 0.14; Fig. 2B, right). The normalized spike rate for the unperturbed gratings was indistinguishable from the 80% noise condition (0.79 ± 0.02 vs 0.78 ± 0.01; p = 0.04, Wilcoxon signed-rank test).