Phase de-synchronization effects auditory gating in the ventral striatum but not auditory cortex.

The underlying mechanisms and involved brain areas in sensory gating of repetitive auditory stimuli remain unclear. Especially, the influence of the auditory cortex and the role of temporal precision are under debate. Our first objective was to analyze gating dynamics of local field potentials in the primary auditory cortex and the ventral striatum in an animal experiment, particularly, assessing the influence of the cortex. The second aim was to follow the hypothesis that auditory gating results from phase de-synchronization of evoked potentials in response to the second auditory stimulus. Local field potentials were recorded simultaneously in the auditory cortex and ventral striatum of awake Mongolian gerbils (n=15) during stimulation with trains of frequency-modulated tones. Gating was analyzed by amplitude ratios of the auditory potentials evoked by the first two stimuli in a train, as well as by time-frequency analyses and between-area phase coupling. The strength of auditory gating in the striatum was found to exceed that in the primary auditory cortex by more than 50%. While total-signal-power was comparable between areas, energy in the striatum was primarily expressed in the non-phase-locked fraction. At the same time, energy in the auditory cortex remained phase-locked to the stimuli. Furthermore, we also observed a between-area phase unlocking during sound presentations. Phase de-synchronization appears to be the candidate mechanism behind attenuation of responses to identical repetitive stimuli in the ventral striatum. We conclude that a direct inhibitory response suppression by the auditory cortex plays a minor role in this process.