Long lasting attenuation by prior sounds in auditory cortex of awake primates

How the brain responds to sequences of sounds is a question of great relevance to a variety of auditory perceptual phenomena. We investigated how long the responses of neurons in the primary auditory cortex of awake monkeys are influenced by the previous sound. We found that responses to the second sound of a two-sound sequence were generally attenuated compared to the response that sound evoked when it was presented first. The attenuation remained evident at the population level even out to inter-stimulus intervals (ISIs) of 5 s, although it was of modest size for ISIs >2 s. Behavioral context (performance versus non-performance of a visual fixation task during sound presentation) did not influence the results. The long time course of the first sound's influence suggests that, under natural conditions, neural responses in auditory cortex are rarely governed solely by the current sound.