Corticofugal modulation of multi-parametric auditory selectivity in the midbrain of the big brown bat.

Corticofugal modulation of sub-cortical auditory selectivity has been shown previously in mammals for frequency, amplitude, time, and direction domains in separate studies. As such, these studies do not show if multi-parametric corticofugal modulation can be mediated through the same sub-cortical neuron. Here we specifically studied corticofugal modulation of best frequency (BF), best amplitude (BA), and best azimuth (BAZ) at the same neuron in the inferior colliculus of the big brown bat, Eptesicus fuscus, using focal electrical stimulation in the auditory cortex. Among 53 corticofugally inhibited collicular neurons examined, cortical electrical stimulation produced a shift of all three measurements (i.e., BF, BA, and BAZ) toward the value of stimulated cortical neuron in 13 (24.5%) neurons, two measurements (i.e., BF and BAZ or BA and BAZ) in 19 (36%) neurons, and one measurement in 16 (30%) neurons. Cortical electrical stimulation did not shift any of these measurements in the remaining five (9.5%) neurons. Corticofugally induced collicular BF shift was symmetrical, whereas the shift in collicular BA or BAZ was asymmetrical. The amount of shift in each measurement was significantly correlated with each measurement difference between recorded collicular and stimulated cortical neurons. However, shifts of three measurements were not correlated with each other. Furthermore, average measurement difference between collicular and cortical neurons was larger for collicular neurons with measurement shifts than for those without shifts. These data indicate that multi-parametric corticofugal modulation can be mediated through the same subcortical neuron based on the difference in auditory selectivity between subcortical and cortical neurons.