Neurophysiological studies of auditory processing have led us to expect certain neural response properties during the presentation of simple sustained sounds. An interesting question raised by these studies is whether central auditory computations are altered by a period of acoustic stimulation. That is, can the same sound stimulus produce two different neural responses? We have found that auditory response properties of gerbil inferior colliculus (IC) neurons can be altered by preceding acoustic events. For example, IC neurons can respond to specific interaural level difference stimuli with a consistent discharge rate. However, this response can be enhanced if preceded immediately by a binaural `conditioning' stimulus. Furthermore, the greater-than expected discharge persists for several seconds (J Neurosci 18: 794). The most effective conditioning stimuli appear to be those with strong acoustically-evoked synaptic inhibition. In fact, this phenomenon can be reproduced when a brief pulse of the inhibitory neurotransmitter, GABA, is applied to the IC neuron being recorded from. Immediately after the pulse of GABA, there is a dramatic increase in the acoustically driven discharge rate. Finally, pharmacological blockade of the inhibitory (GABA and glycine) receptors can disrupt conditioned enhancement in some IC neurons. Taken together, our results suggest that a novel inhibitory-coupled mechanism modulates stimulus processing in the central auditory system over a time scale of seconds.
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