大鼠下丘神经元对重复刺激适应性的时频表征

自由声场下，通过给大鼠不同刺激呈现率（presentation rate，PR）的重复声刺激，用钨丝单电极记录神经元的放电信号，系统分析了下丘神经元对重复刺激的表征特性。作为发放率表征的刺激后脉冲发放数（spike count，SC）随着刺激重复不断减少，作为时间表征的首次发放潜伏期（first spike latency，FSL）逐渐延长，时间过程均呈指数形式变化。起始型神经元FSL 的时间常数大于SC，在FSL上呈现慢适应；持续性神经元FSL 的时间常数小于SC，在SC 上呈现慢适应。随着刺激呈现率PR 的增加，过渡过程的时间常数缩短，稳态SC减少，
稳态FSL延长。稳态SC 和FSL与PR呈对数线性关系，SC 的线性度更高。下丘神经元的适应性能够提高对新奇刺激的响应能力，为皮层下检测异常信息提供了可能。

Rate and Temporal Characteristics of Adaptation to Repetitive Stimulus of Rat Inferior Colliculus Neurons

Firing rate and timing information were characterized using single-unit data collected from inferior colliculus (IC) neurons in urethane-anesthetized rats responding to repetitive sound stimuli at different presentation rates (PR) in the free sound field. Results revealed that the spike count (SC) decreased and the first spike latency (FSL) increased when stimuli were repeatedly presented, which was referred to as adaptation. The time course of adaptation was fitted with a single-exponential model. Onset neurons showed slow adaptation in the FSL, due to the fact that the time constant of the FSL was found to be longer than that of the SC at the same PR. Meanwhile, tonic neurons showed slow adaptation in the SC. In the faster presentation rate, the time constant of both the SC and FSL decreased while the steady state value of the SC was reduced and the steady state value of the FSL became larger. Single linear regression analysis demonstrated that the steady state of responses for the SC and FSL were logarithmic linearly dependent on PR. However, the SC demonstrates a stronger linearity with a larger determination coefficient than that of FSL. Adaptation to repetitive stimuli could enhance subsequent detection of novel sound in the IC, which may serve as a sub-cortical neural mechanism for novelty detection.