AUDITORY CORTICAL EFFERENT ACTIONS UPON INFERIOR COLLICULUS UNITARY ACTIVITY IN THE GUINEA-PIG

Differential actions on inferior colliculus central nucleus (ICc) sing le cells spontaneous activity were observed with both ipsilateral and contralateral auditory cortical electrical stimulation (ACx stimulatio n). Following ACx stimulation, a firing depression of the spontaneous activity was obtained using contralateral or ipsilateral cortical stim ulation, although a greater effect was elicited by the contralateral c ortex. In contrast, ipsilateral ACx stimulation elicited more excitati on with a shorter latency than contralateral stimulation. In units tha t failed to show spontaneous firing, the sound-evoked responses and AC x stimulation were studied; similar to 50% of them demonstrated firing depression to ACx stimulation on either side with either clicks or to ne-bursts. Thirty percent of the units failed to show changes in respo nse to any cortical stimulation. A temporary disruption of ICc-evoked neuronal discharge was elicited during contralateral cortex stimulatio n, as previously reported to occur during sleep. The demonstration tha t auditory cortices may differentially affect the same ICc unit activi ty, i.e, spontaneous and evoked, suggests that auditory processing may depend on the ongoing spontaneous activity plus the effects exerted f rom each auditory cortex activation. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.