Analysis of the neural circuit related to auditory discrimination based on multi-dipole estimation with high temporal resolution.

虽然用于测量局部脑血流和代谢的新成像方法（例如PET和fMRI）提供了在感觉辨别过程期间活跃的脑区域的详细解剖图片，但是这些方法未能以足够高的时间分辨率揭示活跃区域的时间过程。另一方面，大脑活动模式的时间过程可以通过记录由活跃的神经细胞群体产生的神经磁场以毫秒级的分辨率测量。此外，最近开发的全皮层MEG系统使我们能够一次测量所有的大脑区域，而无需重新定位以记录每个区域。本研究的目的是构建一个系统，用于半自动估计多个偶极子具有足够高的时间分辨率。多偶极子估计算法基于以下三个基本点：1）在选择向内最大值和向外最大值对时，首先选择同侧半球内最邻近的一对偶极子进行估计; 2)对于4个、3个和2个偶极子，估计误差分别小于10%、15%和20%。3)利用神经元活动的时空连续性和稳定性进行多偶极子估计，观察到与听觉（感觉）辨别相关的神经元活动：1）模态特异区的活动。2)与注意有关的脑区如前额叶、扣带回等; 3）与记忆有关的脑区如背外侧前额叶、海马、顶叶联合皮层和颞叶联合皮层。这些活动在开始时按照上述顺序进行估计，之后平行进行。

Although new imaging methods for measuring regional cerebral blood flow and metabolism such as PET and fMRI provide a detailed anatomical picture of the brain regions that are active during an sensory discrimination process, these methods fail to reveal the time course of the active regions with sufficiently high temporal resolution. On the other hand, the time course of brain activity patterns can be measured at the millisecond level of resolution through recordings of the neuromagnetic fields that are generated by active populations of nerve cells. Furthermore, recently developed whole-cortex MEG systems enabled us to measure all the brain areas at a time, without repositioning to record each area. The purpose of the present study was to construct the system for semi-automatically estimating multiple dipoles with sufficiently high temporal resolution. Furthermore, the temporal structure of the neural activity related to auditory (sensory) discrimination was investigated by using the analyzing system.The algorithm for multi-dipole estimation is based on the following three basic points : 1) In selection of the pair of the inward maximum and the outward maximum, the most neighboring pair in one hemisphere is to be selected as the first step for estimation. 2) Estimation errors are less than 10%, 15% and 20% for 4, 3 and 2 dipoles respectively. 3) Multi-dipole estimation is carried out based on spatio-temporal continuity and stability of the neuronal activities.By using the system, the following neuronal activities were observed related to auditory (sensory) discrimination : 1) activity in its modality-specific area. 2) the areas related to attention such as prefrontal area, cingulate gyrus, and so on. 3) the areas related to memory such as dorsolateral prefrontal cortex, hippocampus, parietal association cortex and temporal association cortex. These activities were estimated following the above order during the beginning, and in parallel after.