OPTICAL RECORDING OF SOUND-INDUCED DYNAMIC ACTIVITIES IN THE AUDITORY CORTEX

采用12×12通道光电二极管阵列和电压敏感染料(RH795)的光学记录方法，在麻醉条件下(Nembutal 30 mg/kg、多效唑0.3 mg/kg/h和喷妥英1.1 mg/kg/h)记录豚鼠听皮层前野(A：初级)和背尾野(DC)神经元的动态活动。对于声音刺激，纯音、调频(FM)音、频率阶跃变化(SF)的声音和连续的两个音被呈现在记录侧的对侧。对纯音的反应在A区和DC区都表现为一个频带(等频带)。反应是动态的：激活点沿等频带腹向或背向移动。对SF音的反应是与SF音中各成分的频率对应的等频段的顺序激活。每个反应都与对纯音的反应相似。对调频声音作出反应的激活点在等频段内倾斜移动。当频率扫描方向改变时，活动光点朝相反的方向移动。对连续两声的反应表明，兴奋反应后，同频频段之间和同频范围内的抑制发生。当GABA_A拮抗剂荷包牡丹碱应用于听觉皮质时，对纯音的兴奋反应被广泛地扩展到等频段之外。这些结果表明，声音是由听觉皮质中的动态神经活动表示的，这些活动是由等频带之间的兴奋性和抑制性相互作用产生的。提出了一个网络模型来模拟这些结果。

Using an optical recording method with a 12 x 12-channel photodiode array and a voltage-sensitive dye (RH795), dynamic activities of neurons in anterior (A : primary) and dorsocaudal (DC) fields of the guinea pig auditory cortex were recorded under anesthetized condition (Nembutal 30 mg/kg, doroperidol 0.3 mg/kg/h and pentazocine 1.1 mg/kg/h). For sound stimulation, pure tones, frequency-modulated (FM) sounds, sounds with step-wise frequency changes (SF) and sequential two tones were presented to the ear contralateral to the recording side.The response to a pure-tone appeared as a band (isofrequency band) in both fields A and DC.The response was dynamic : the active spot moved ventrally or dorsally along the isofrequency band. The responses to SF sounds were the sequential activation of the isofrequency bands corresponding to the frequencies of the components in the SF sounds. Each response was similar to those to pure tones. The active spot in response to FM sounds moved obliquely crossing the isofrequency bands. When the direction of the frequency sweep was changed, the active spot moved in the opposite direction. No cortical area specifically responding to the FM sounds was found.The responses to sequenial two tones showed that inhibition between and within isofrequency bands occurs after the excitatory responses. When bicuculline, a GABA_A antagonist, was applied to the auditory cortex, the excitatory response to a pure tone was spread widely beyond the isofrequency band. This spread was prevented by further application of an NMDA antaonist.These results indicate that sounds were represented by dynamic neural acivities in the auditory cortex and these activities were created by excitatory and inhibitory interactions between isofrequency bands. A network model to simulate these results was proposed.