听觉和视觉系统在皮层下和皮层水平的交互作用

In one of our projects, we found that the there was an interaction between the auditory and visual modalities in the thalamus level (Yu et al. 2009a, Nat Neurosci 12:1165). We would expect that there will be interactions between the auditory and visual cortices. The present study is designed to investigate the neuronal interaction between auditory and visual systems in subcortical and cortical levels. The first objective is to examine how the visual stimulus could affect the auditory responses in the auditory cortex. The visual modulatory effect on the auditory responses in cortical neurons will be examined by presenting a light stimulus immediately before the auditory stimulus. The second objective is to investigate the contributions of the visual modulatory effect in the auditory cortex via cortical visual pathway and via the subcortical pathway. Change in the visual modulatory effect in the auditory responses is examined by temporally inactivating the visual cortex. The third objective is to investigate the role of the thalamic reticular nucleus (TRN) in the visual modulatory effect via the subcortical pathway. The entire visual cortex will be removed at the beginning of the experiment to minimize the contribution from the visual cortex. We would then implant a glass pipette with glutamate antagonists into the auditory sector of the TRN. The visual modulatory effect would be examined while we manipulating the activities of the TRN, in order to see the involvement of the TRN in the modulatory process. Neuronal responses in the medial geniculate body (MGB) to the electrical activation of the lateral geniculate nucleus (LGN) would tell the interaction of the two thalamic nuclei. The involvement of the TRN would be further examined by manipulation of the activities of the TRN and/or manipulation of its action on the MGB. It can be achieved by 1) comparing the results on slices between that TRN is maintained and that the TRN is removed and 2) comparing the results before and after the administration of GABAA and GABAB antagonists into the MGB. The study would unveil the mechanism of the neuronal interactions between the auditory and visual systems in the ascending pathway at cortical and subcortical levels.

我们的前期研究发现视觉刺激可以影响听觉丘脑神经元的听觉反应。我们推测视觉系统和听觉系统在丘脑水平是有交互作用，预期这种交互作用在也发生在大脑皮质。本研究旨在探索视听系统在皮质和皮质下水平的交互作用。本研究旨在（1）通过在体麻醉动物的细胞外记录，搞清楚在皮层下通路内视觉系统是怎样影响听觉系统的，即视听双模态的交互作用是否在丘脑水平上就存在，且是通过什么样的机制实现的。（2）通过在体实验来检测丘脑网状核通过皮层下通路在视觉调制中所起的作用。（3）探讨视觉通过视皮层和皮层下通路对于听皮层反应调制的贡献程度。分两部分：一在麻醉动物上，另一在清醒动物上。通过注射利多卡因使视皮层失活，记录听皮层神经元的细胞外反应活动在视皮层失活前后的变化，以探讨视觉通过视皮层和皮层下通路对于听皮层反应调制的贡献。

视觉和听觉两种最重要的感觉信息在大脑中不同层面和不同区域进行整合。在我们的实验室先前的研究中发现，听觉皮层电刺激激活和视觉刺激配对呈现，再加上清醒大鼠足底电击或麻醉大鼠听皮层注射CCK，可以使先前对视觉刺激不反应的神经元产生反应。我们也知道，在丘脑水平的听觉和视觉形式之间存在相互作用。在本研究中，我们具体研究了皮层下和皮层跨模态神经回路如何参与上述视听联合记忆中。.我们发现从视觉丘脑到听觉皮层没有直接的投射。因为听觉皮层的主要投射来自MGB和视觉皮层，所以我们否定了视觉丘脑直接参与到视听觉联合记忆的这种可能性。解剖学结果告诉我们上述视听联合记忆的生理学基础可能来自于如下两条通路：1.视觉皮层到听觉皮层的直接投射;2.或来自皮质下如视觉丘脑或上丘的视觉信息间接通过听觉丘脑再传入到听皮层。接下来的生理结果表明，在没有听觉丘脑参与的情况下，仍然可以形成视听跨模态联系，这意味着听觉丘脑也不参与建立联接。同时，视觉听觉两个皮层的电刺激可以经过配对联系在一起，这种直接联系也不依赖于丘脑。此外，在CCK的作用下，两个皮层之间建立的联系可以转移到第三个皮层。最后，我们发现将视觉刺激和听觉刺激配对呈现并同时注射CCK之后，在听皮层激光刺激视觉皮层投射到听觉皮层的神经末梢所产生的反应会变强，而且听觉皮层接受从视觉皮层接受直接投射的神经元的钙信号响应增加，这个结果直接证实了视听跨模态联合记忆的生理学基础是视觉皮层到听觉皮层的直接投射。