CORTICAL AND BEHAVIORAL RESPONSES TO COCHLEAR IMPLANTS

这项研究考察了处理与语音相关的时间信息的大脑机制。 比较声刺激和电刺激(人工耳蜗)的反应将有助于分离“耳朵” 从“脑”成分的时间加工，并将提供基础科学基础的设计 用于临床人工耳蜗术的语音处理器。豚鼠急性和慢性听皮质实验 猪将采用声学和电刺激。在豚鼠和日本的心理物理实验 人类人工耳蜗使用者将测试皮质研究的预测。具体目标1将描述 用于幅度调制的代码的皮质变换。皮质输入层中的神经元相位锁定到 涉及频率为60赫兹的调制电脉冲序列。前馈到的时间信息 其他皮质层必须以不需要紧张期锁定的形式重新编码。我们将测试 假设高频调制信息从主音锁相码转换为 A1区皮质列内的费率代码或相位时间代码。这一目标也在临床上测试了2 相关假设：(1)电脉冲序列对调制的敏感度由单极子优化 电极配置和载波脉冲率低到足以允许夹带在听神经或 更低的脑干；以及(2)通过允许通道间的脉冲率来最小化通道间干扰 至少500 JI的时间间隔。具体目标2将区分外周机制和中枢机制 时间敏锐度，并将确定影响前向掩蔽的因素。我们将检验这一假设 前掩蔽反映了中枢听觉系统内的机制，这些机制与 调幅敏感性的机制。我们的试验结果使我们得出这样的假设： 通过使用超过最大频率的脉冲频率来最小化电听力中的掩蔽 脑干听觉结构的夹带。具体目标3将量化传播过程中的可塑性 由震耳欲聋和慢性刺激产生的时间信息。我们将检验这一假设 在人工耳蜗刺激的前30天，中央结构的时间敏锐度有所提高。 这项研究的目的是直接适用于使用人工耳蜗术的聋人患者，特别是 通过影响语音处理器的设计。目标1将确定使数量最大化的因素 传输非冗余时间信息的假体通道。目标2将确定能够 将前向掩蔽恢复到正常听力的典型水平。目标3将确定中枢听觉的变化 由耳聋和慢性电刺激引起的通路，因此将提供关于 植入年龄和慢性刺激方式。

This research examines brain mechanisms for processing of temporal information relevant to speech. Comparison of responses to acoustical and electrical (cochlear-implant) stimulation will help to isolate"ear" from "brain" components of temporal processing and will provide a basic-science foundation for design of speech processors for clinical cochlear prostheses. Acute and chronic auditory-cortex experiments in guinea pigs will employ acoustical and electrical stimulation. Psychophysical experiments in guinea pigs and in human cochlear-implant users will test predictions from the cortical studies. Specific Aim 1will characterize the cortical transformation of codes for amplitude modulation. Neurons in cortical input layers phase lock to to modulated electrical pulse trains at frequencies to >60 Hz. Temporal information that is fed forward to other cortical layers must be re-coded in a form that does not require tonic phase locking. We will test the hypothesis that high-frequency modulation information is transformed from a tonic phase-locking code to a rate code or phasic temporal code within the cortical columns of area A1. This aim also tests 2 clinically relevant hypotheses: (1) Sensitivity to modulation of electrical pulse trains is optimized by monopolar electrode configurations and by carrier pulse rates low enough to permit entrainment in the auditory nerve or lower brainstem; and (2) Inter-channel interference is minimized by a pulse rates that permit inter-channel temporal separation of at least 500 jis. Specific Aim 2 will distinguish peripheral and central mechanisms of temporal acuity and will identify factors that influence forward masking. We will test the hypothesis that forward masking reflects mechanisms within the central auditory system that are substantially distinct from the mechanisms of amplitude-modulation sensitivity. Our pilot results lead us to the hypothesis that forward masking in electrical hearing is minimized by the use of pulse rates that exceed maximum rates for entrainment of brainstem auditory structures. Specific Aim 3 will quantify plasticity in transmission of temporal information resulting from deafening and chronic stimulation. We will test the hypothesis that temporal acuity of central structures improves during the first 30 days of cochlear-implant stimulation. The aims of this study have direct application to deaf patients who use cochlear implants, particularly through influencing design of speech processors. Aim 1 will identify factors that maximize the number of prosthesis channels that transmit non-redundant temporal information. Aim 2 will identify factors that can restore forward masking to levels typical of normal hearing. Aim 3 will identify changes in the central auditory pathway that result from deafness and chronic electrical stimulation and,thus, will inform decisions regarding age of implantation and patterns of chronic stimulation.