Cooke James E, Zhang Huiming, Kelly Jack B
Laboratory of Sensory Neuroscience, Department of Psychology, Carleton University, Ottawa, Ontario, Canada.
Hear Res. 2007 Sep;231(1-2):90-9. doi: 10.1016/j.heares.2007.06.002. Epub 2007 Jun 9.
The ability of rats to detect the presence of sinusoidal amplitude modulation (AM) of a broadband noise carrier was determined before and after bilateral ablation of auditory cortex. The rats were trained to withdraw from a drinking spout to avoid a shock when they detected a modulation of the sound. Sensitivity was evaluated by testing the rats at progressively smaller depths of modulation. Psychophysical curves were produced to describe the limits of detection at modulation rates of 10, 100 and 1000Hz. Performance scores were based on the probability of withdrawal from the spout during AM (warning periods) relative to withdrawal during the un-modulated noise (safe periods). A threshold was defined as the depth of modulation that produced a score halfway between perfect avoidance and no avoidance (performance score=0.5). Bilateral auditory cortical lesions resulted in significant elevations in threshold for detection of AM at rates of 100 and 1000Hz. No significant shift was found at a modulation rate of 10Hz. The magnitude of the deficit for AM rates of 100 and 1000Hz was positively correlated with the size of the cortical lesion. Substantial deficits were found only in animals with lesions that included secondary as well as primary auditory cortical areas. The results show that the rat's auditory cortex is important for processing sinusoidal AM and that its contribution is most apparent at high modulation rates. The data suggest that the auditory cortex is a crucial structure for maintaining normal sensitivity to temporal modulation of an auditory stimulus.
在双侧听觉皮层切除前后，测定了大鼠检测宽带噪声载波正弦调幅（AM）的能力。训练大鼠在检测到声音调制时从饮水口撤离以避免电击。通过在逐渐减小的调制深度下测试大鼠来评估灵敏度。绘制了心理物理学曲线，以描述在10、100和1000Hz调制率下的检测极限。性能分数基于在调幅期间（警告期）相对于未调制噪声期间（安全期）从饮水口撤离的概率。阈值定义为产生的分数介于完全避免和不避免之间（性能分数=0.5）的调制深度。双侧听觉皮层损伤导致在100和1000Hz调制率下检测调幅的阈值显著升高。在10Hz调制率下未发现明显变化。100和1000Hz调幅率的缺陷程度与皮层损伤的大小呈正相关。仅在损伤包括次级和初级听觉皮层区域的动物中发现了显著缺陷。结果表明，大鼠的听觉皮层对处理正弦调幅很重要，并且其贡献在高调制率下最为明显。数据表明，听觉皮层是维持对听觉刺激时间调制正常敏感性的关键结构。
