Changes in the spatiotemporal pattern of spontaneous activity across a cortical column after noise trauma.

In the auditory modality, noise trauma has often been used to investigate cortical plasticity as it causes cochlear hearing loss. One limitation of these past studies, however, is that the effects of noise trauma have been mostly documented at the granular layer, which is the main cortical recipient of thalamic inputs. Importantly, the cortex is composed of six different layers each having its own pattern of connectivity and specific role in sensory processing. The present study aims at investigating the effects of acute and chronic noise trauma on the laminar pattern of spontaneous activity (SA) in primary auditory cortex (A1) of the anesthetized guinea pig. We show that spontaneous activity is dramatically altered across cortical layers after acute and chronic noise-induced hearing loss. First, spontaneous activity was globally enhanced across cortical layers, both in terms of firing rate and amplitude of spike-triggered average of local field potentials. Second, current source density on (spontaneous) spike-triggered average of local field potentials indicates that current sinks develop in the supra- and infragranular layers. These latter results suggest that supragranular layers become a major input recipient and the propagation of spontaneous activity over a cortical column is greatly enhanced after acute and chronic noise-induced hearing loss. We discuss the possible mechanisms and functional implications of these changes. The present study investigates the effects of acute and chronic noise trauma on the laminar pattern of spontaneous activity in the primary auditory cortex. Our study is first to report that noise trauma alters the sequence of cortical column activation during ongoing activity. In particular, we show that the supragranular layer becomes a major input recipient and the synaptic activity in the infragranular layers is enhanced.