A NEUROPHYSIOLOGICAL STUDY ON COCHLEAR IMPLANTATION BY OPTICAL IMAGING

应用光学成像技术观察耳蜗电刺激在豚鼠听皮层的时空表征。用12 × 12光电二极管阵列和电压敏感染料记录声刺激和耳蜗电刺激引起的皮层活动。对于电刺激，将导线电极插入耳蜗的鼓阶和前庭阶中。双极刺激与单电脉冲耳蜗诱导两个活跃点分离的听觉皮层领域，前和背尾侧，这是tonotopically组织。这种活性点在声刺激下也短暂地定位在皮层中。然而，由电刺激引起的活动点横向移动跨越听觉皮层的等距轮廓，并随着时间的推移广泛分布在整个皮层。作为电强度的函数的响应幅度显示出非常窄的动态范围。此外，对不同刺激强度的反应潜伏期几乎是恒定的。这些结果与正常声音刺激的结果有显著差异。这表明电刺激绕过感觉换能器机制，直接激活耳蜗中的神经末梢。

To observe the spatio-temporal representation of cochlear electrical stimulation in the auditory cortex, we applied the optical imaging technique in the guinea pig. The cortical activity induced by acoustic and cochlear electrical stimulation were recorded with a 12*12 photodiode array and a voltage-sensitive dye. For electrical stimulation wire electrodes were inserted into the scala tympani and the scala vestibuli of the cochlea. Bipolar stimulation with single electrical pulses to the cochlea induced two active spots separated in the auditory cortical fields, anterior and dorsocaudal, which are tonotopically organized. Such active spots were transiently localized in the cortex also in acoustic stimulation. However, the active spots induced by electrical stimulation moved transversally across isofrequency contours in the auditory cortex and spread broadly throughout the cortex with time. The magnitude of responses as a function of electrical intensity showed a very narrow dynamic range. In addition, the response latencies were almost constant for various stimulus intensities. These results were significantly different from those for normal sound stimulation. This suggests that electrical stimulation bypasses the sensory transducer mechanism, and activates directly the nerve terminals in the cochlea.