CORTICAL AND BEHAVIORAL RESPONSES TO COCHLEAR IMPLANTS

描述（由申请人提供）：本研究探讨大脑处理与言语相关的时间信息的机制。比较声刺激和电刺激（人工耳蜗）的反应将有助于分离“耳”和“脑”的时间处理成分，并将为临床人工耳蜗语音处理器的设计提供基础科学依据。豚鼠的急性和慢性听觉皮层实验将采用声学和电刺激。在豚鼠和人类耳蜗植入者身上进行的心理物理实验将检验皮层研究的预测。具体目标1将描述调幅编码的皮层转换。皮层输入层的神经元锁相于频率为bbb60hz的调制电脉冲序列。传递给其他皮层层的时间信息必须以一种不需要强直相位锁定的形式重新编码。我们将测试假设，即高频调制信息从强音锁相码转换为A1区皮质柱内的速率码或相位时间码。这一目的也检验了两个临床相关的假设：(1)对电脉冲序列调制的敏感性通过单极电极配置和载波脉冲率低到足以允许在听神经或脑干下部携带来优化；(2)通过允许至少500 jis的信道间时间间隔的脉冲速率使信道间干扰最小化。具体目标2将区分外周和中枢的颞敏锐度机制，并将确定影响前向掩蔽的因素。我们将测试前向掩蔽反映了中枢听觉系统内与调幅敏感性机制本质上不同的机制的假设。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的最大携带率的脉冲速率，将电听力中的正向掩蔽最小化。具体目标3将量化由耳聋和慢性刺激引起的时间信息传递的可塑性。我们将测试中枢结构的颞敏锐度在人工耳蜗刺激的前30天改善的假设。本研究的目的直接应用于使用人工耳蜗的失聪患者，特别是通过影响语音处理器的设计。目的1将确定的因素，最大限度地增加假体通道的数量，传输非冗余的时间信息。目标2将确定能够将前向掩蔽恢复到正常听力水平的因素。目的3将确定耳聋和慢性电刺激导致的中枢听觉通路的变化，从而为有关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.