A NEUROPHYSIOLOGICAL STUDY ON COCHLEAR IMPLANTATION BY OPTICAL IMAGING

为了观察耳蜗电刺激在听觉皮层的时空表征，我们在豚鼠身上应用了光学成像技术。用12*12光电二极管阵列和电压敏感染料记录声和耳蜗电刺激引起的皮层活动。为了电刺激，将导线电极插入耳蜗的中耳膜和前庭膜。单电脉冲双极刺激耳蜗，在听觉皮层区产生两个分离的活动点，即耳蜗前和耳蜗后，这两个活动点是局部组织的。这些活跃点在声刺激下也会短暂地定位于皮层。然而，电刺激引起的活动点在听觉皮层的等频线上横向移动，并随着时间的推移在整个皮层中广泛扩散。作为电强度函数的响应幅度显示出一个非常窄的动态范围。此外，在不同刺激强度下，反应潜伏期基本不变。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.