CORTICAL AND BEHAVIORAL RESPONSES TO COCHLEAR IMPLANTS

描述(由申请者提供)：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出“耳”和“脑”的时间加工成分，并为临床人工耳蜗术中语音处理器的设计提供基础科学基础。豚鼠的急性和慢性听觉皮质实验将采用声学和电刺激。在豚鼠和人类人工耳蜗使用者身上进行的心理物理实验将检验皮质学研究的预测。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以60赫兹的频率锁定到调制的电脉冲序列。前馈到其他皮质层的时间信息必须以不需要紧张期锁定的形式重新编码。我们将测试这样的假设，即高频调制信息在A1区的皮质柱内从主音锁相码转换为速率码或相位时间码。这一目标还测试了两个临床上相关的假设：(1)通过单极电极配置和足够低的载波脉冲率来优化对电脉冲序列的调制的敏感性，以允许夹带在听神经或下部脑干中；(2)通过允许至少500jis的通道间时间间隔的脉冲率来最小化通道间干扰。具体目标2将区分时间敏锐度的外周和中枢机制，并将确定影响前向掩蔽的因素。我们将测试这一假设，即前向掩蔽反映了中枢听觉系统内的机制，这与幅度调制敏感性的机制有本质上的不同。我们的试验结果使我们得出这样的假设，即通过使用超过脑干听觉结构夹带的最大频率的脉搏频率，电听力中的前向掩蔽被最小化。具体目标3将量化耳聋和慢性刺激导致的时间信息传输的可塑性。我们将检验这一假设，即中央结构的时间敏锐度在人工耳蜗刺激的前30天内得到改善。本研究的目的是通过影响语音处理器的设计，直接应用于使用人工耳蜗术的聋人患者。目标1将确定使传输非冗余时间信息的假体通道数量最大化的因素。目标2将确定可以将前向掩蔽恢复到正常听力的典型水平的因素。目标3将确定耳聋和慢性电刺激引起的中枢听觉通路的变化，从而为关于植入年龄和慢性刺激模式的决定提供信息。

DESCRIPTION (provided by applicant): 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 1 will 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.