Frequency selectivity is related to temporal processing in parallel thalamocortical auditory pathways

Lemniscal and non-lemniscal parallel thalamocortical auditory pathways have been identified with the ventral medial geniculate body (MGB) vs. the dorsal and medial MGB, respectively. Lemniscal neurons have narrow frequency tuning and provide highly specific frequency information to the auditory cortex whereas non-lemniscal neurons generally have broader tuning and greater response lability, including plasticity of frequency receptive fields during learning. To determine if frequency selectivity is related to temporal fidelity of response, we measured both the breadth of tuning and neuronal excitability in a paired tone paradigm for single neurons throughout the MGB. Excitability to the second tone of a pair was directly correlated with frequency selectivity: the narrower the frequency tuning, the greater the excitability. Cells with broad tuning based on multiple-peak response areas also were less excitable than cells with single-peak RAs. Cells in the ventral MGB showed greater temporal fidelity of response (greater excitability) than cells in the dorsal and medial MGB. These findings show that high degrees of both frequency selectivity and temporal response fidelity are characteristic of the lemniscal, but not the non-lemniscal, thalamocortical auditory system.