Neuronal mechanisms of sensory binding

当脑电图（EEG）被发现时，一个早期的观察结果是大脑活动遵循有节奏的变化，称为振荡。无论我们是醒着还是睡着，眼睛是睁着还是闭着，无论我们是在运动还是在休息，缓慢和快速的振荡都会发生。最近，人们发现大脑振荡对于大脑远端区域之间的神经交流很重要。***我们用脑磁图（MEG）记录了志愿者在听40赫兹调幅声时的快速伽马振荡（40赫兹）。40赫兹的振荡告诉我们关于听觉和听觉感知是如何在大脑中组织的，比如当我们在空间中定位声音或在噪音中理解语音时。之前的动物研究帮助我们解释了MEG的结果，并建立了一个中枢听觉处理的模型。然而，以往的研究与我们的工作有很大的不同，并没有完全解释无创记录MEG的神经机制。因此，在当前的项目中，我们将进行一组研究，以帮助我们解释MEG和EEG的发现。首先，我们将测试我们的假设，即快速振荡的一个作用是，确定神经元在哪个确切的时间点放电。这是一个重要的机制，因为大脑的振荡将决定哪些神经元同时放电，从而连接并一起工作。我们将用40赫兹的声音刺激鼠的听觉皮层，用电极记录神经放电。***第二，我们将使用磁共振波谱法测量神经递质GABA的浓度，并将GABA水平与脑磁图中记录的伽马振荡幅度进行比较。结果将告诉我们伽马振荡是如何产生的，特别是皮层中的抑制性中间神经元是如何参与产生伽马振荡的。***第三，我们将研究40hz振荡对听觉感知的影响。我们将在听40-Hz AM声音时执行间隙检测任务，并测试我们的假设，即在40-Hz声音的某个阶段间隙检测会比其他阶段更好，根据假设，伽马振荡决定神经放电的时间点。此外，我们将把部分语音刺激分别呈现给左耳和右耳，并测试普通的40-Hz调制是否有助于将这些部分融合成可理解的语音。***我们将使用这项研究的结果来解释我们关于老年人听觉处理的变化和他们在噪音中理解语言的问题的MEG发现。此外，已经发现伽马振荡在大脑状况和疾病（如自闭症和精神分裂症）中是不同的。如果我们对伽马振荡的机制和功能意义有了更多的了解，我们可以利用脑电图或脑磁图记录的伽马振荡作为敏感的诊断工具。**

When the electroencephalogram (EEG) has been discovered, one early observations was that the brain activity follows rhythmic changes, termed oscillations. Slow and fast oscillations, occur whether we are awake or in sleep, our eyes are open or closed, or whether we are moving or at rest. Recently, it has been found that brain oscillations are important for neural communication between distant brain areas.***We recorded fast gamma oscillations (40 Hz) with magnetoencephalography (MEG) in human volunteers, who were listening to 40-Hz amplitude modulated sound. 40-Hz oscillations informed us about hearing and how auditory perception is organized in the brain, such as when we localize a sound in space or understand speech in noise. Previous animal research helped us interpreting our MEG results and to develop a model of central auditory processing. However, the previous studies were rather different from our MEG work and did not completely explain the neural mechanisms underlying the non-invasively recorded MEG. Therefore, in the current project we will perform a set of studies that will help us interpreting MEG and EEG findings. ***First, we will test our hypothesis, that one role of fast oscillations is, to determine at which exact time point a neuron fires. This is an important mechanism, because the brain oscillations would determine which neurons are firing at the same time and thus would be connected and work together. We will record neural firing with electrodes in the auditory cortex in chinchilla while stimulating with 40-Hz sound. ***Second, we will measure the concentration of the neurotransmitter GABA using magnetic resonance spectroscopy and compare the GABA level with the amplitude of gamma oscillations recorded in MEG. The results will inform us about how the gamma oscillations are generated, specifically how inhibitory interneurons in the cortex are involved in generating gamma oscillations.***Third, we will investigate how 40-Hz oscillations influence auditory perception. We will perform a gap detection task while listening to 40-Hz AM sounds and test our hypothesis, that gap detection will be better at a certain phase of the 40-Hz sound than on others, according to the hypothesis, that gamma oscillations determine the time point of neural firing. Moreover we will present parts of speech stimuli separately to the left and right ear and test, whether common 40-Hz modulation helps to fuse the parts into understandable speech.***We will use the results of this research for interpreting our MEG findings about changes in auditory processing in elderly people and their problem of understanding speech in noise. Moreover, it has been found that gamma oscillations are different in brain conditions and disorders such as in autism and in schizophrenia. If we know more about the mechanisms and functional meaning of gamma oscillations, we can use EEG or MEG recording of gamma oscillations as sensitive diagnostic tool. **