Encoding of natural sounds by variance of the cortical local field potential

Neural encoding of sensory stimuli is typically studied by averaging neural signals across repetitions of the same stimulus. However, recent work has suggested that the variance of neural activity across repeated trials can also depend on sensory inputs. Here, we characterize how inter-trial variance of the local field potential (LFP) in primary auditory cortex (A1) of awake ferrets is affected by continuous natural sound stimuli. We find that natural sounds often suppress the inter-trial variance of low-frequency LFP (< 16 Hz). However, the amount of the variance reduction is not significantly correlated with the amplitude of the mean response at the same recording site. Moreover, the variance changes occur with longer latency than the mean response. Although the dynamics of the mean response and inter-trial variance differ, spectro-temporal receptive field (STRF) analysis reveals that changes in LFP variance have similar frequency tuning to multi-unit activity at the same recording site, suggesting a local origin for changes in LFP variance. In summary, the spectral tuning of LFP inter-trial variance and the absence of a correlation with the amplitude of the mean evoked LFP suggest substantial heterogeneity in the interaction between spontaneous and stimulus-driven activity across local neural populations in auditory cortex.

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