Monaural and Binaural Inhibition Underlying Duration-Tuned Neurons in the Inferior Colliculus

Abstract

Duration-tuned neurons (DTNs) in the mammalian inferior colliculus (IC) arise from a combination of excitatory and inhibitory synaptic inputs. Previous research has shown that the inhibition responsible for creating DTNs has a shorter latency than that of excitation and lasts longer than the stimulus duration. We used monotic and dichotic paired tone stimulation and recorded responses of DTNs from the IC of the bat to assess the relative contributions of each ear in forming duration-tuned circuits. The stimulus consisted of a short best duration (BD) excitatory tone and a longer duration nonexcitatory (NE) tone. In the monotic condition, when the BD and NE tones were presented to the contralateral ear and were sufficiently close in time, the NE tone always suppressed spikes evoked by the BD tone. In the dichotic condition, when the BD tone was presented to the contralateral ear and the NE tone to the ipsilateral ear, half of DTNs no longer showed spike suppression to the NE tone. Of those DTNs with suppression in both conditions, the latency of the inhibition was shorter and the duration of the inhibition was longer in the monotic condition. Therefore, in the monotic condition, DTNs received a contralaterally evoked inhibitory input that preceded the excitatory input to the same neuron. In the dichotic condition, DTNs received an ipsilaterally evoked inhibitory input that was weaker, longer in latency, and shorter in duration than the inputs from the contralateral ear. These findings indicate that the neural mechanisms that create DTNs in the IC are monaural.

Diverse cortical codes for scene segmentation in primate auditory cortex

“…D: the scatterplot is analogous to that in A, but the analysis interval is limited to the first 100 ms of the response, and only durations of 100 ms or greater (n ϭ 4) are discriminated, which shifts both chance and the statistical criterion to larger values, as indicated by the gray boxes. E and F obey the same conventions as B and C. 2011; Mora and Kössl 2004;Pinheiro et al 1991;Pollak and Schuller 1981;Sayegh et al 2011Sayegh et al , 2014. However, only a handful of studies focused on duration coding involved mammalian species that are not bioacoustically specialized for echolocation.…”

Organization and trade-off of spectro-temporal tuning properties of duration-tuned neurons in the mammalian inferior colliculus

“…To date, research on auditory DTNs has focused primarily on the neural mechanisms that create their temporally selective responses Ehrlich et al 1997;Fuzessery and Hall 1999;Hooper et al 2002;Faure et al 2003;Jen and Wu 2006;Aubie et al 2009Aubie et al , 2012Sayegh et al 2012Sayegh et al , 2014 and on the stability (tolerance) of duration tuning with changes in signal amplitude (Zhou and Jen 2001;Mora and Kössl 2004;Fremouw et al 2005). We know that duration tuning is disrupted or abolished by blocking neural inhibition in the IC, which also suggests that duration tuning originates there Faure et al 2003;Leary et al 2008).…”

Frequency tuning of synaptic inhibition underlying duration-tuned neurons in the mammalian inferior colliculus

“…Measuring onset and offset of inhibition with spike counts and latencies. We measured the duration and latency of the inhibition evoked by the NE tone by observing the time points when the BD tone-evoked spike count became suppressed and/or altered in latency, using the same criteria as Sayegh et al (2014). To measure the time course of the inhibition evoked by the NE tone, we first quantified the .…”

“…Using three criteria, we compared baseline responses with those obtained at each ISI to determine when spike counts or latencies were altered by NE toneevoked inhibition. As in our previous studies with paired-tone stimulation, we used a combination of detection criteria to measure the time course of inhibition evoked by the NE tone (Faure et al 2003;Sayegh et al 2012Sayegh et al , 2014. We used a 50% change in the evoked spike count as the initial criterion to delineate the time points for the onset and offset of spike suppression.…”

“…The final values of T 1 and T 2 were chosen to be those that were most sensitive in capturing the time course of the suppressed response evoked by the NE tone with a spike count and/or spike latency criterion. The use of spike counts or spike latencies (or both) to quantify changes in a neuron's responsiveness has previously been validated (Faure et al 2003;Sayegh et al 2012Sayegh et al , 2014. In cases in which cells responded with only a single spike per stimulus [i.e., baseline first spike latency (L first ) ϭ baseline last spike latency (L last )], a change in spike count was typically used for selecting T 1 and T 2 because this criterion was more accurate in reflecting the time course of the evoked inhibition.…”