Sensory neurons across sensory modalities and specific processing areas have diverse levels of spontaneous firing rates (SFRs) in the absence of sensory stimuli. However, the functional significance of this spontaneous activity is not well understood. Previous studies in the auditory system have demonstrated that different levels of spontaneous activity are correlated with a variety of physiological and anatomical properties, suggesting that neurons with differing SFRs make unique contributions to the encoding of auditory stimuli. Additionally, altered SFRs are a correlate of tinnitus, arising in several auditory areas after exposure to ototoxic substances and noise trauma. In this study we recorded single-unit activity from primary auditory cortex of awake marmoset monkeys while delivering wideband random-spectrum stimuli (RSS) and white Gaussian noise (WGN) in order to examine any divergences in stimulus encoding properties across SFR classes. We found that higher levels of spontaneous activity were associated with both higher levels of activation relative to suppression across a variety of wideband stimuli and higher driven rates in response to WGN. Moreover, response latencies to WGN were negatively correlated with the level of excitation in response to both stimulus types. These findings are consistent with a novel view of the role spontaneous spiking may play during normal stimulus processing in primary auditory cortex and how it may malfunction in cases of tinnitus.
- primary auditory cortex
- sparse coding
- spontaneous activity
- marmoset monkey
- Copyright © 2016, Journal of Neurophysiology