健康与遗传心理学研究室知识库

    对内侧膝状体(medial geniculate body, MGB)生理学性质和功能的探索一直是听觉中枢系统研究中的重点，已有研究发现，根据生理学性质和功能，听觉丘脑通路可能分为丘系核团与非丘系核团两大部分，但目前为止，缺乏对两类核团内单个神经元声音诱发反应及调谐性质的记录，也缺乏MGB神经元膜反应性质和解剖位置的直接对应关系，无法直接验证两类核团的假说。
    为阐明听觉丘脑内丘系核团与非丘系核团的膜反应性质及频率调谐特性，进一步探索丘系核团与非丘系核团的功能异同，本研究采用在体细胞内记录和标记技术，记录戊巴比妥钠麻醉状态下豚鼠MGB神经元对声音刺激的反应性质并标记其解剖位置。研究结果将MGB的神经元反应模式、频率调谐性质与具体解剖位置联系起来，发现:
    1)对重复的白噪声刺激呈现单一兴奋性突触后电位或峰电位反应的神经元均出现        在丘系核团内，持续性与连发性放电的神经元多位于非丘系核团。声音诱发抑制性反应的神经元位于非丘系核团内。ON, OFF/ON-OFF神经元分别位于丘系核团中心、丘系核团外或与非丘系核团的交界区域。
    2)丘系核团神经元的纯音调谐频率窄而特异，而非丘系核团神经元对纯音的反应        多样且不规则。
    基于以上发现，结合己有研究，我们的结果验证:丘系核团保留了从耳蜗基底膜就已呈拓扑排列的频率调谐信息，精确地保存了对声音信号的反应时和调谐特性;而非丘系神经元记录到的不同放电模式，提示在这一复杂的感觉中继核团内存在着对纯音刺激的多种编码机制。纯音刺激引发的调谐反应提示非丘系核团神经元可能选择性地抑制“次要”信息的影响，以更好地处理具有生物学意义的重要信息。
    本研究具有重要的理论意义和现实意义。在理论意义方面，对MGB生理学性质及功能的研究对听觉和其它高级感觉加工过程的研究都有着直接影响;在现实意义方面，对听觉核团反应机制的研究对我们理解和分析生物行为有着重要意义，在康复医疗和临床治疗中都有十分重要的应用价值。

    The physiological and functional organization of medial geniculate body (MGB) has been one of the key issues in the understanding of central auditory system. Recent studies have led to the theory that physiologically and functionally auditory thalamus can be subdivided into lemniscal (primary) and nonlemniscal (secondary) pathways. However, it has been lacked of direct recording of acoustic evoked responses in unit neuron and the corresponding relationship between MGB neuronal  memberane response patterns  and anatomical locations to approve the hypothesis.
    To demonstrate the membrane response patterns and frequency tuning properties in
MGB neurons and further investigate the functional contradistinction of lemniscal and nonlemniscal systems, we examined the’ neuronal auditory response features to noise and tonal stimuli and labelled the target MGB neurons by in vivo intracellular recordings in anaesthetized guinea' pigs. We correlated the response patterns, the tuning properties and the anatomical locations of MGB neurons. The main finds are showed below:
    1)Neurons with either a single EPSP or spike response pattern to repeated noise stimuli located in lemniscal MGB, while neurons with sustained or burst responses were mostly located in nonlemniscal MGB. Neurons with inhibitory response patterns to acoustic stimuli were located in nonlemniscal MGB. ON, OFF/ON-OFF firing     neurons were located in the central lemniscal, outside or around the border of     lemnical MGB.
    2)Frequency tuning curves in lemniscal neurons is sharp and specific while those in nonlemniscal neurons broad and irregular.
    Based on both the results of the present study and extensive studies, our result confirmed that the lemniscal MGB reserved the representation of frequency consistent with the tonotopic organization of the basilar membrane and precisely kept the response time and tuning property to acoustic signals. Multiple discharge patterns in nonlemniscal neurons indicated that diverse encoding mechanisms exist in the complex sensory information processing nuclei. Tuning characteristics to tonal stimuli suggested that nonlemniscal neurons may selectively switch off this pathway, avoid the influence of less important information and prepare for more biological significant information.
    The present study has both important theoretic and practical significance. For the theoretic significance; studies in the physiological property and function of MGB directly affect auditory and other high-level sensory processes; as to the practical significance,research in the response mechanisms of auditory nucleus helps us to understand and analyze biological behavior and has important application value in rehabilitation medication and clinical practice.