Department of Physiology, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Chuo, Yamanashi 409-3898, Japan.
J Neurosci. 2009 Dec 16;29(50):15650-9. doi: 10.1523/JNEUROSCI.2442-09.2009.
Sound duration is important for distinguishing auditory object. Previous studies on the neural representation of duration have usually lacked psychophysical data obtained from the same species; hence, the correspondence between neural and behavioral discrimination of duration remains obscure. We addressed this issue in cats by using the signal detection theory to investigate both neural activities in the primary auditory cortex (A1) and the cat's behavioral performance. We found that 320 ms duration can be well discriminated from 10 ms duration by some A1 neurons with specific response patterns: sustained response extended proportionally with the increase of stimulus duration and the On-Off response synchronizing stimulus onset and offset. Neurons with only On response cannot discriminate duration. The discrimination performance of both sustained and On-Off responses deteriorated as the target duration decreased from 320 to 20 ms and the percentage of discriminative neurons (correct rate >0.75) decreased from 40 to 2%. Compared with the psychophysical results, we found that the psychometric functions of cats well matched the neurometric functions of most sustained-response neurons and a small number of On-Off-response neurons. Pooling the spikes of multiple units improved neural discrimination, which may be attributable to the salience (noise reduction) of the responses in pooled data. Our results suggest that the sustained and Off responses of A1 neurons underlie the duration discrimination behavior of cats.
声音的时长对于听觉对象的区分很重要。之前关于时长的神经表现的研究通常缺乏来自同一物种的心理物理数据；因此，神经和行为时长辨别之间的对应关系还不清楚。我们在猫身上通过使用信号检测理论来研究初级听觉皮层 (A1) 的神经活动和猫的行为表现，从而解决了这个问题。我们发现，一些具有特定反应模式的 A1 神经元可以很好地区分 320ms 的时长和 10ms 的时长：持续反应与刺激时长的增加成比例地延长，而 On-Off 反应则与刺激的起始和结束同步。只有 On 反应的神经元不能区分时长。持续反应和 On-Off 反应的辨别性能随着目标时长从 320ms 降低到 20ms 而恶化，具有辨别能力的神经元比例（正确率>0.75）从 40%降低到 2%。与心理物理结果相比，我们发现猫的心理物理函数与大多数持续反应神经元和少数 On-Off 反应神经元的神经物理函数很好地匹配。多个单位的尖峰的汇集提高了神经辨别，这可能归因于汇集数据中响应的显著性（降噪）。我们的结果表明，A1 神经元的持续和 Off 反应是猫时长辨别行为的基础。
