An Investigation into the Role of Cortical Synaptic Depression in Auditory Processing

M. J. Denham and S. L. Denham

In comparison with the speed and precision associated with processing in the auditory periphery, the temporal response properties of neurons in primary auditory cortex can appear to be surprisingly sluggish. For example, much of the temporal free structure is lost, best modulation frequencies are generally low and the effects of forward masking can be detected for a surprisingly long time. What gives rise to these responses and can they be explained by some common mechanism? Intracortical inhibition has been suggested as a likely cause but inhibition does not provide an adequate account, at least in the case of forward masking, which is unaffected by the application of inhibitory antagonists. On the other hand, simple threshold neural models cannot replicate such behaviour without some form of inhibition. The purpose of this investigation was to explore whether depression at thalamocortical synapses could account for these observations. As far as we are aware, the experiments whichwe have replicated, many of them only recently published, have not previously been modelled, and certainly not all by the same model. Since synaptic depression depends on pre- and not postsynaptic activity, the model also provides a novel account of the effect of subthreshold stimuli.

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