Figure 2. Representation of sensorimotor associations in the spiking activity in early auditory cortex.

(A–B) Spike rates of an example multiunit in auditory cortex to S1 and S2 in Task 1 (A) and Task 2 (B). Orange and blue traces represent spike rates to tones of 3 kHz and of 1 kHz, respectively. Each trace shows the spike rate averaged across trials from 250 ms before tone onset to 50 ms after tone offset. The open bars on the abscissae mark the timing and the 200 ms duration of the tones. The horizontal lines represent a spike rate of 20 spikes/s. Note that the ordinates have logarithmic scaling. The sensorimotor associations of S1s and S2s are also provided. (C) Larger spike responses to S1-no-go than to S1-uncertain when the frequency of the tones was 3 kHz. (i) Cumulative distribution of during-S1 (green) and before-S1 (black) spike ratios for all 298 multiunits recorded from the two monkeys. During-S1 spike ratios were the ratios of the mean spike rates during S1-no-go in Task 2 to the mean spike rates during S1-uncertain in Task 1. Before-S1 spike ratios were the ratios computed from the mean spike rates during the corresponding periods directly before the S1s. Ratios significantly different from 1 are marked by dots, and the proportions of multiunits with such ratios are provided. The horizontal dashed line marks the cumulative probability of 0.5 and the vertical dashed line the ratio of 1. (ii) Larger during-S1 spike ratios than before-S1 spike ratios. The analysis was limited to the 124 multiunits having significant during-S1 spike ratios (green dots in panel i). The open dots mark multiunits with significant during-S1 ratios only and the filled dots mark multiunits with significant during-S1 and before-S1 ratios. The proportion of multiunits with significant during-S1 and before-S1 ratios is provided. The diagonal marks cases where the two ratios were equal. Note that the axes have logarithmic scaling. (iii) Larger during-S1 spike ratios during task performance than in the passive condition. This comparison was limited to the 63 multiunits that exhibited significant during-S1 spike ratios during task performance and that were tested also in the passive condition. The open dots mark multiunits with significant ratios during task performance only and the filled dots mark those with significant ratios both during task performance and in the passive condition. Other conventions are equivalent to those of panel Cii. (D) Larger spike responses to S2-no-go than to S2-go when the frequency of the tones was 3 kHz. The organization of the panel and other conventions are equivalent to those of panel C. During-S2 spike ratios were the ratios of the mean spike rates during S2-no-go in Task 2 to the mean spike rates during S2-go in Task 1. Before-S2 spike ratios were the ratios computed from the mean spike rates during the corresponding periods directly before the S2s. (E) The average normalized spike rates to S1-no-go (orange trace) and S1-uncertain (purple trace) of the 124 multiunits with significant during-S1 spike ratios for the 3 kHz tone, shown from 50 ms before S1 onset to 800 ms after S1 offset. They were obtained by geometrically averaging the spike rates after normalizing each rate to baseline (the mean spike rate during the 250 ms period directly before S1). Note the logarithmic scaling of the ordinate. The stars above the traces mark a significant difference (p<0.05) between the two traces. (F) The average normalized spike rates to S2-no-go (orange trace) and to S2-go (purple trace) of the 108 multiunits with significant during-S2 spike ratios for the 3 kHz tone. Other conventions are equivalent to those of panel E.

Figure 2—figure supplement 1. Representation of sensorimotor associations in early auditory cortex revealed by comparing the spike responses to the tones with a frequency of 1 kHz.

The organization of the figure and all other conventions are identical to those of Figure 2. Note that the spike ratio was the ratio of the mean spike rate in Task 1 to that in Task 2.

Figure 2—figure supplement 2. Distributions of the spike ratios of single units in early auditory cortex.

Conventions in panels A and B are equivalent to those of Figure 2Ci and 2Di, respectively.

Figure 2—figure supplement 3. No consistent effects of tone probability on the differences in the neuronal responses between Task 1 and Task 2.

Each panel shows the proportion of multiunits or sites with significant during-S1 ratios >1 or during-S2 ratios >1 in experimental sessions with small or large ratios of tone probability between the two tasks (small ratios: range ~2–2.7, geometric mean ~2.4; large ratios: range ~2.7–5, geometric mean ~3.1). Results are shown separately for the spiking activity (A) and the local field potentials (B) and separately for the 3 kHz and 1 kHz tone.

Figure 2—figure supplement 4. Spiking activity related to bar release in early auditory cortex.

The average normalized spike rates with reference to the time of bar release after S2-go, shown separately for the 3 kHz (A) and 1 kHz tone (B).

Figure 2—figure supplement 5. Comparison of spike rates to S2 when S2 was needed to signal a motor response or not.

Cumulative distributions of spike ratios during S2 presentation for all multiunits recorded from the auditory cortex of the two monkeys. A spike ratio was the ratio of the mean spike rate during S2-no-go to that during S2-nil (S2-no-go/S2-nil) or the ratio of the mean spike rate during S2-go to that during S2-nil (S2-go/S2-nil). Data are shown separately for the 3 kHz (A) and 1 kHz tone (B).