猫听皮层调频诱发反应及其区域特性

利用平均技术在猫记录了听皮层纯音调频诱发电位,并测定了对不同载波频率F的调频反应阈△F_m。调频诱发电位的波形与短纯音诱发电位的相似,也有“给”、“撤”、“给-撤”等几种类型。△F_m因载波频率及皮层记录点的不同而异,最佳者中、高频可以在0.01F以下,低频在10赫以下,与文献上用条件反射方法测得的结果大致相当。高、中、低频纯音调频反应灵敏点在AI区的分布互相交错,不像调谐反应那样有排列整齐的频率区域特性。

FM-EVOKED RESPONSES AND FM-TONOTOPIC CHARACTERISTICS OF THE CAT AUDITORY CORTEX

Averaged responses evoked by frequency modulation (FM) of tones were recorded from different points on the surface of AI zone of the cat auditory cortex and response thresholds in terms of modulation depth (△ f_m) for different carrier frequencies (f) were determined. FM-evoked potentials were similar in wave form to those evoked by tone bursts. They appeared either as on-, or as off- (in correspondency to the beginning or termination of the rectangular modulating wave), or as on-off-type of response. △ f_m varied greatly with f and with the site of recording. The majority of the △ f_m-versus-f curves were marked by the presence of deep valley or valleys, where the location of the nadirs, which represented the characteristic f's of PM-responses f's of best △ f_m), differed with recording points in the auditory cortex. High, middle and low characteristic f points of PM-responses intermingled in the AI zone, a distribution entirely different from the tonotopic mapping of the auditory cortex in tuning responses. Comparison of △ f_m with the tuning threshold for the same f and for the same recording point revealed that best △ f_m were obtained mostly for those f's whose tuning sensitivity was in the middle range (threshold-40-60 dB).
The smallest △ f_m obtained in cats with the FM-response method were less than 0.01 f for f> 1000 Hz, and below 10 Hz for f< 1000 Hz, quite comparable to the smallest frequency differential thresholds of cats determined by some authors in conditioning avoidance experiments.
The divergence in topographic distribution,of characteristic f's of both FM- and tuning responses in the cat auditory cortex is discussed in the view that there is fine neuro-struc-tural differentiation at the cortex level for these two kinds of functions.