Computational models of temporal processing in the auditory thalamus.

Abstract

Previous work has shown that neurons in the medial geniculate body (MGB) of the echolocating bat, Myotis lucifugus, display response properties that are distinguishable from those of their afferents in the inferior colliculus (IC). Specifically, MGB neurons display phasic temporal discharge patterns, poor entrainment to trains of constant-amplitude sound pulses, and facilitated responses to amplitude-modulated trains of sound pulses (Llano and Feng 1999). In this study we used a modeling approach to examine the relative contributions of different known sources of inhibition on the temporal response properties of auditory thalamocortical neurons. We found that GABA(A)-mediated post-excitatory inhibition resulting from coactivation of thalamocortical neurons and local inhibitory interneurons (in a triadic arrangement) is sufficient to reproduce many of the temporal response properties of MGB neurons. Addition of long-duration GABA(B)-mediated inhibition gave the thalamocortical neuron temporal response characteristics that more closely resemble those seen in the experimental data. Neither recurrent inhibition from the thalamic reticular nucleus nor postsynaptic nonlinear mechanisms were necessary to reproduce the temporal transformations between the IC and MGB. This work suggests that feed-forward inhibitory circuitry, coupled with slow GABA(B)-mediated inhibition, can emulate temporal information processing at the MGB. The transformation taking place in the MGB can be used to extract salient features from complex, time-varying stimuli, such as echoes returning from moving prey.