Two-dimensional neural processing of auditory information in mammalian auditory cortex

采用4×4通道微电极阵列技术和12×12通道光电二极管阵列光学记录方法，研究了豚鼠和大鼠听皮层的二维活动。这项研究的目的是研究听觉皮质如何沿皮质以二维方式处理听觉信息。分别给予硝丁胺30 mg/kg和氟哌利多16.7 mg/kg/h、戊唑西林5 mg/kg/h麻醉。对于光学记录，用电压敏感染料RH795(苯乙烯基染料，分子探针公司)对听觉皮质进行染色。彩色编码的时空响应模式显示在监视器屏幕上。所使用的声音刺激是纯音突发、调频(FM)声音和动物的发声。它们被呈现在记录侧的对侧耳朵。本研究利用这些二维记录证实了豚鼠和大鼠听皮质的体视学表征S…更多的系统。我们新近发现，这种通过大脑皮层功能组织的张力表征只是暂时的，而且随着时间的推移而变化。豚鼠听皮层的神经活动通常起始于腹侧，并沿皮质表面向背侧扩散。运动方向与等频段平行。对于调频声音刺激，神经活动在等频段内斜向传播。当调频扫描方向颠倒时，传播方向在频率轴上是颠倒的，但在背尾轴上不是。通过将GABA_A拮抗剂荷包牡丹碱应用于听觉皮质，我们发现在同频段之间有很强的GABA能抑制。然而，微电极阵列记录的神经元对动作电位之间的交叉相关分析表明，沿皮质表面间隔约0.5 mm的神经元很少显示出神经相关性。在本研究中没有发现发声特异性反应。这些结果表明，声音的参数沿着听觉皮质以二维的方式呈现，并且听觉信息被转换到听觉皮质内的位置。较少

We studied 2-dimensional activities of auditory cortex in guinea pigs and rats using a 4x 4 channel microelectrode-array technique and an optical recording method with a 12 x 12 channel photodiode array. The aim of this study was to examine how the auditory cortex processes auditory information in a two-dimensional way along the cortex. The animals were anesthetized with Nembutal (30 mg/kg) and neuroleptanalgesia (droperidole 16.7 mg/kg/h and pentazocine 5 mg/kg/h). For optical recording, the auditory cortex was stained with a voltage sensitive dye RH795 (styryl dye, Molecular Probes, Inc.). Color-coded spatiotemporal response patterns were displayd on a monitor screen. Sound stimuli used were pure tone bursts, frequency modulated (FM) sounds and vocalizations of the animals. They were presented to the ear contralateral to the recording side.Tonotopical representation of the auditory cortex in guinea pigs and rats was confirmed by the present study using these 2-dimensional recording s … More ystems. We found newly that this tonotopical representation through the functional organization of the cortex is only transient and it varies with time. The neural activity in the guinea pig auditory cortex usually initiates ventrally and it propagates toward dorsally along the cortical surface. The moving direction is parallel to the isofrequency band. For FM sound stimulation, the neural activity propagates obliquely across the isofrequency bands. When a direction of FM sweep is reversed, the direction of propagation is reversed in the frequency axis, but not in the dorsocaudal axis. By applying bicuculline, a GABA_A antagonist, to the auditory cortex, we found strong GABAergic inhibition between isofrequency bands. However, cross-correlation analysis between action potentials of neuron pairs recorded by the microelectrode-array revealed that neurons located in about 0.5 mm separation along the cortical surface rarely showed neural correlations. Vocalization-specific responses were not found in the present study. These results indicate that parameters of sounds are represented in a 2-dimensional way along the auditory cortex, and that the auditory information was transformed into places within the auditory cortex. Less