Department of Neurobiology, Kyoto University Graduate School of Medicine, Kyoto 606-8501, Japan.
Neurosci Res. 2012 Jul;73(3):224-37. doi: 10.1016/j.neures.2012.04.009. Epub 2012 May 1.
Offset neurons, which fire at the termination of sound, likely encode sound duration and serve to process temporal information. Offset neurons are found in most ascending auditory nuclei; however, the neural mechanisms that evoke offset responses are not well understood. In this study, we examined offset neural responses to tonal stimuli in the inferior colliculus (IC) in vivo with extracellular and intracellular recording techniques in mice. Based on peristimulus time histogram (PSTH) patterns, we classified extracellular offset responses into four types: Offset, Onset-Offset, Onset-Sustained-Offset and Inhibition-Offset types. Moreover, using in vivo whole-cell recording techniques, we found that offset responses were generated in most cells through the excitatory and inhibitory synaptic inputs. However, in a small number of cells, the offset responses were generated as a rebound to hyperpolarization during tonal stimulation. Many offset neurons fired robustly at a preferred duration of tonal stimulus, which corresponded with the timing of rich excitatory synaptic inputs. We concluded that most IC offset neurons encode the termination of the tone stimulus by responding to inherited ascending synaptic information, which is tuned to sound duration. The remainder generates offset spikes de novo through a post-inhibitory rebound mechanism.
起始神经元在声音结束时放电，可能对声音持续时间进行编码，并用于处理时间信息。起始神经元存在于大多数上行听觉核中；然而，引发起始神经元反应的神经机制尚不清楚。在这项研究中，我们使用细胞外和细胞内记录技术，在体内研究了下丘脑中（IC）对音调刺激的起始神经元反应。基于刺激后时间直方图（PSTH）模式，我们将细胞外起始神经元反应分为四种类型：起始、起始-起始、起始-持续-起始和抑制-起始类型。此外，我们发现使用体内全细胞记录技术，大多数细胞通过兴奋性和抑制性突触输入产生起始神经元反应。然而，在少数细胞中，起始神经元反应是在音调刺激期间的超极化时产生的反弹。许多起始神经元对音调刺激的优选持续时间表现出强烈的反应，这与丰富的兴奋性突触输入的时间相吻合。我们得出结论，大多数 IC 起始神经元通过响应固有上行突触信息来编码音调刺激的结束，该信息调谐到声音持续时间。其余的通过抑制后反弹机制新产生起始神经元反应。
