Furtak Sharon C, Allen Timothy A, Brown Thomas H
Department ofPsychology, Yale University, New Haven, Connecticut 06520, USA.
J Neurosci. 2007 Nov 7;27(45):12277-91. doi: 10.1523/JNEUROSCI.1653-07.2007.
Pretraining lesions of rat perirhinal cortex (PR) severely impair pavlovian fear conditioning to a 22 kHz ultrasonic vocalization (USV) cue. However, PR lesions are without significant effect when the cue is a continuous tone at the same or a lower frequency. Here we examined fear-conditioning-produced changes in single-unit firing elicited in rat PR by a 22 kHz tone cue or a 22 kHz USV cue. Chronic recording electrodes were introduced from the lateral surface of the skull. Altogether, 200 well isolated units were studied in 28 rats. Overall, 73% of the recorded single units (145 of 200 units) evidenced statistically significant firing changes in response to the tone or USV conditional stimulus (CS) after it had been paired several times with an aversive unconditional stimulus (US). Interestingly, 33% of units (66 of 200 units) that were initially CS-unresponsive became CS-responsive after conditioning. After conditioning, there were two notable differences between single-unit responses elicited by the USV cue and those elicited by the tone cue. First, 11% of the units (14 of 123 units) recorded from the USV-conditioned group displayed a precisely timed increase in firing rate during the 260 ms interval in which the US had previously occurred. This US-timed response was unique to the USV-conditioned group. Second, the mean latency of cue-elicited firing was approximately 30 ms longer in the USV-conditioned group than in the tone-conditioned group. These cue-specific differences in acquired firing latencies and acquired firing patterns suggest that spectrotemporal properties of a CS can control the essential circuitry or neurophysiological mechanisms underlying fear conditioning.
大鼠嗅周皮质（PR）的预训练损伤会严重损害对22千赫超声发声（USV）线索的巴甫洛夫恐惧条件反射。然而，当线索是相同频率或更低频率的连续音调时，PR损伤没有显著影响。在这里，我们研究了由22千赫音调线索或22千赫USV线索在大鼠PR中引发的恐惧条件反射所产生的单单位放电变化。慢性记录电极从颅骨外侧引入。总共在28只大鼠中研究了200个分离良好的单位。总体而言，在与厌恶非条件刺激（US）配对几次后，73%的记录单单位（200个单位中的145个）对音调或USV条件刺激（CS）表现出统计学上显著的放电变化。有趣的是，33%最初对CS无反应的单位（200个单位中的66个）在条件反射后变得对CS有反应。条件反射后，USV线索引发的单单位反应与音调线索引发的反应之间存在两个显著差异。首先，在USV条件刺激组记录的11%的单位（123个单位中的14个）在US先前出现的260毫秒间隔内显示出精确计时的放电率增加。这种与US时间相关的反应是USV条件刺激组独有的。其次，USV条件刺激组中线索引发放电的平均潜伏期比音调条件刺激组长约30毫秒。这些习得的放电潜伏期和习得的放电模式中的线索特异性差异表明，CS的频谱时间特性可以控制恐惧条件反射背后的基本神经回路或神经生理机制。
