Hartmann R, Shepherd R K, Heid S, Klinke R
Physiologisches Institut III der J.W. Goethe-Universität, Frankfurt/M, Germany.
Hear Res. 1997 Oct;112(1-2):115-33. doi: 10.1016/s0378-5955(97)00114-7.
Neural activity plays an important role in the development and maintenance of sensory pathways. However, while there is considerable experience using cochlear implants in both congenitally deaf adults and children, little is known of the effects of a hearing loss on the development of the auditory cortex. In the present study, cortical evoked potentials, field potentials, and multi- and single-unit activity evoked by electrical stimulation of the auditory nerve were used to study the functional organisation of the auditory cortex in the adult congenitally deaf white cat. The absence of click-evoked auditory brainstem responses during the first weeks of life demonstrated that these animals had no auditory experience. Under barbiturate anaesthesia, cortical potentials could be recorded from the contralateral auditory cortex in response to bipolar electrical stimulation of the cochlea in spite of total auditory deprivation. Threshold, morphology and latency of the evoked potentials varied with the location of the recording electrode, with response latency varying from 10 to 20 ms. There was evidence of threshold shifts with site of the cochlear stimulation in accordance with the known cochleotopic organisation of AI. Thresholds also varied with the configuration of the stimulating electrodes in accordance with changes previously observed in normal hearing animals. Single-unit recordings exhibited properties similar to the evoked potentials. Increasing stimulus intensity resulted in an increase in spike rate and a decrease in latency to a minimum of approximately 8 ms, consistent with latencies recorded in AI of previously normal animals (Raggio and Schreiner, 1994). Single-unit thresholds also varied with the configuration of the stimulating electrodes. Strongly driven responses were followed by a suppression of spontaneous activity. Even at saturation intensities the degree of synchronisation was less than observed when recording from auditory brainstem nuclei. Taken together, in these auditory deprived animals basic response properties of the auditory cortex of the congenitally deaf white cat appear similar to those reported in normal hearing animals in response to electrical stimulation of the auditory nerve. In addition, it seems that the auditory cortex retains at least some rudimentary level of cochleotopic organisation.
神经活动在感觉通路的发育和维持中起着重要作用。然而，虽然在先天性耳聋的成人和儿童中使用人工耳蜗已有相当多的经验，但对于听力损失对听觉皮层发育的影响却知之甚少。在本研究中，通过电刺激听神经诱发的皮层诱发电位、场电位以及多单元和单单元活动，来研究成年先天性耳聋白猫听觉皮层的功能组织。出生后最初几周内缺乏短声诱发的听觉脑干反应，表明这些动物没有听觉经验。在巴比妥类麻醉下，尽管完全没有听觉经验，但对耳蜗进行双极电刺激时，仍可从对侧听觉皮层记录到皮层电位。诱发电位的阈值、形态和潜伏期随记录电极的位置而变化，反应潜伏期从10到20毫秒不等。有证据表明，根据AI已知的耳蜗拓扑组织，阈值随耳蜗刺激部位而变化。阈值也随刺激电极的配置而变化，这与之前在正常听力动物中观察到的变化一致。单单元记录显示出与诱发电位相似的特性。增加刺激强度会导致放电率增加，潜伏期缩短至最小值约8毫秒，这与之前正常动物AI中记录到的潜伏期一致（拉吉奥和施赖纳，1994年）。单单元阈值也随刺激电极的配置而变化。强烈驱动的反应之后是自发活动的抑制。即使在饱和强度下，同步程度也低于从听觉脑干核记录时观察到的程度。综上所述，在这些听觉剥夺的动物中，先天性耳聋白猫听觉皮层的基本反应特性似乎与正常听力动物在听神经电刺激时所报告的相似。此外，听觉皮层似乎至少保留了一些耳蜗拓扑组织的基本水平。
