CORTICAL AND BEHAVIORAL RESPONSES TO COCHLEAR IMPLANTS

描述（由申请人提供）：本研究探讨了与语音相关的时间信息处理的大脑机制。声刺激和电刺激（耳蜗植入）的反应比较将有助于隔离“耳”从“脑”的时间处理组件，并将为临床人工耳蜗语音处理器的设计提供一个基本的科学基础。豚鼠的急性和慢性皮层实验将采用声刺激和电刺激。在豚鼠和人工耳蜗使用者身上进行的心理物理学实验将检验皮层研究的预测。特定目标1将表征用于幅度调制的代码的皮层变换。皮层输入层中的神经元相位锁定到频率>60 Hz的调制电脉冲串。前馈到其他皮层的时间信息必须以不需要强直相位锁定的形式重新编码。我们将测试的假设，即高频调制信息从强直锁相代码转换为速率代码或相位时间代码内的皮层列的A1区。该目的还测试了2个临床相关假设：（1）通过单极电极配置和足够低的载波脉冲速率优化电脉冲串调制的灵敏度，以允许在听神经或下脑干中夹带;（2）通过允许通道间时间间隔至少为500 μ s的脉冲速率最小化通道间干扰。具体目标2将区分周边和中央机制的时间敏锐度，并将确定影响前掩蔽的因素。我们将测试的假设，即前掩蔽反映了中央听觉系统内的机制，这是从幅度调制灵敏度的机制有很大的不同。我们的试点结果导致我们的假设，即前掩蔽在电听力最小化的脉冲率，超过最大率夹带的脑干听觉结构的使用。具体目标3将量化由耳聋和慢性刺激引起的时间信息传输的可塑性。我们将检验这一假设，即耳蜗植入刺激的前30天内，中央结构的颞部敏锐度得到改善。本研究的目的是直接应用于使用人工耳蜗的耳聋患者，特别是通过影响语音处理器的设计。目标1将确定最大化传输非冗余时间信息的假体通道数量的因素。目标2将确定可以将前掩蔽恢复到正常听力水平的因素。目标3将识别由耳聋和慢性电刺激引起的中枢听觉通路的变化，从而为植入年龄和慢性刺激模式的决策提供信息。

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.