Optical recording studies on segmentation and induction of sounds in the auditory cortex

本研究旨在探讨声音的分组、分离和时间诱导的神经机制。用电压敏感染料RH 795的光学成像技术，记录了麻醉豚鼠初级听皮层（AI）的神经活动。复合音（CT，200毫秒长）组成的两个纯音（PT）与0-2.0倍频程的频率分离和0-100毫秒的时间延迟被用来研究分组和隔离。间隔插入（PGP）和白噪声（WN）插入纯音（PWP）与0-120-ms的间隙和WN长度被用来研究诱导。在0.2-0.7倍频程时，AI活动强度和反应区宽度增加，但在0.8倍频程以上时，AI活动强度和反应区宽度增加不明显。如果CT中的一个成分比另一个延迟超过5 ms，则对延迟成分的反应被前一个成分抑制。这些结果表明，豚鼠听觉诱发电位具有将频率相近的声音进行分组的机制（小于0.7倍频程）和短延迟当间隔小于5 ms的PGP出现时，AI反应仅出现在间隔前音的起始处，当差距大于5 ms时，在间隙前和间隙后均出现响应，当在差距中插入WN时，即使WN周期大于5 ms，也只在WN前音开始时出现响应。这些结果表明，WN的插入提高了AI的间隙检测阈值，这一现象可能与大脑中的听觉诱导机制有关。

This study was aimed to investigate neural mechanisms of grouping, segregation and temporal induction of sounds. Using an optical imaging technique with a voltage-sensitive dye RH795, neural activity was recorded in the primary auditory cortex (AI) of anesthetized guinea pigs. Complex tones (CT, 200-ms long) consisting of two pure-tones (PT) with 0-2.0-octave frequency separations and 0-100-ms time delays were used to study grouping and segregation. Gap-inserted (PGP) and white-noise (WN)-inserted pure tones (PWP) with 0-120-ms gap and WN lengths were used to study induction. They were presented to the ear contralateral to the recording cortex.In response to CT, strength of AI activity and widths of responding areas increased at 0.2-0.7 octave but did not at more than 0.8 octave. If one component in the CT was delayed more than 5ms from the other, the response to the delayed component was inhibited by the preceding one. These results suggest that AI of guinea pigs has a mechanism to group sounds with near frequencies (less than 0.7 octave) and short delays (less than 10 ms) and to separate those with far frequencies and long delays.When PGP with a gap shorter than 5 ms was presented, the AI response appeared only at the onset of the pre-gap tone, while it appeared at both the onsets of pre- and post-gap tones if the gap was longer than 5 ms. If WN was inserted into the gap, the response appeared only at the onset of the pre-WN tone, even if the WN period was longer than 5ms. These results suggest that the insertion of WN increases the threshold of gap detection in AI and this phenomenon may relate to auditory induction mechanism in the brain.