Temporal property and reference frame of somatosensory active attention genesis

注意是大脑选择感觉信息并促进信息加工的重要机制之一。但其神经机制尚不清楚。最近使用功能磁共振成像和脑磁图的研究报告了与皮层活动的注意调节相关的神经元底物。我之前使用脑磁图进行的研究也报告说，在受试者开始将注意力转向手指约400毫秒后，施加刺激时，次级体感区的皮质活动增加。在预设研究中，我研究了手处于不同位置时体感觉皮层活动的注意调节的时间特性。实验对象被要求尽快将注意力转移到有箭头方向提示的手上。在提示提前时间200、300、400或500ms后，在受试者食指上施加电流。采用160通道全头脑磁图测量电流刺激引起的体感磁场。比较了平行手位和交叉手位的等效电流偶极矩。当提示发生后400和500 ms施加刺激时，整个受试者的次级体感激活的平均ECD时刻有增加的趋势。其中一名被试的结果显示，两种手部位置条件下的注意调制时间特性存在显著差异。在交叉手药水条件下，注意调制出现的延迟约为100毫秒。这种延迟可以用计算手的位置的时间来解释。计算后，将注意力引导到一个空间点，即手所在的位置。虽然体感注意力可能以空间框架而不是身体坐标为参照，但这一结果需要进一步分析。

Attention is one of important mechanism in the brain to select sensory information and to facilitate the information processing. However its neuronal mechanism has not been clearly elucidated. Recent studies using fMRI and MEG have reported neuronal substrates correlated to attentional modulation of cortical activities. My previous studies using MEG also reported that cortical activities in the secondary somatosensory area were increased when the stimuli were applied approximately 400ms after subjects started directing their attention to the finger. In the preset study, I investigated temporal properties of attentional modulation of the somatosensory cortical activities when the hands were in the different positions. The subjects were instructed to direct their attention to a hand indicated by a cue, arrow direction, as soon as possible. After the cue lead time, 200, 300, 400 or 500ms, the electrical current was delivered on the attended index finger. Somatosensory magnetic fields evoked by the current stimuli were measured by using a 160 channel whole head type MEG. Equivalent current dipole (ECDs) moments calculated from the measured fields were compared between the parallel and crossed hand position. The mean ECD moment for the secondary somatosensory activations across the subject tended to increase when the stimuli were applied 400 and 500 ms after the cue onset. The result from one of the subjects showed remarkable difference in the temporal property of the attentional modulation between the two hand position conditions. The attentional modulation appeared with delay of approximately 100 ms in the crossed hand potion condition. This delay might be explained by time for calculation of the hand position. After calculation, the attention was directed a spatial point, at which the hand was located. Although somatosensory attention might be directed with reference of spatial frame rather than body coordinates, further analysis is necessary for this consequence.