Department of Psychology, Neuroscience & Behaviour, McMaster University, Hamilton, Ontario L8S 4K1, Canada, and Department of Psychology, University of Washington, Seattle, Washington 98195-1525.
J Neurosci. 2014 Jan 8;34(2):481-92. doi: 10.1523/JNEUROSCI.3732-13.2014.
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.
哺乳动物下丘脑中的时长调谐神经元 (DTN) 是由兴奋性和抑制性突触输入共同产生的。先前的研究表明，产生 DTN 的抑制作用比兴奋作用具有更短的潜伏期，且持续时间长于刺激持续时间。我们使用单耳和双耳成对音调刺激，并记录蝙蝠下丘脑中 DTN 的反应，以评估每只耳朵在形成时长调谐回路中的相对贡献。刺激由一个短的最佳时长 (BD) 兴奋性音调以及一个较长的非兴奋性 (NE) 音调组成。在单耳条件下，当 BD 和 NE 音调被呈现给对侧耳朵，且时间足够接近时，NE 音调总是会抑制由 BD 音调引发的 spikes。在双耳条件下，当 BD 音调被呈现给对侧耳朵，而 NE 音调被呈现给同侧耳朵时，一半的 DTN 不再对 NE 音调表现出 spike 抑制。在这两种条件下都表现出抑制的 DTN 中，抑制的潜伏期更短，持续时间更长。因此，在单耳条件下，DTN 接收来自对侧的抑制性输入，该输入先于同一神经元的兴奋性输入。在双耳条件下，DTN 接收来自同侧的抑制性输入，其强度较弱，潜伏期较长，持续时间较短。这些发现表明，在 IC 中产生 DTN 的神经机制是单耳的。
