Temporal property and reference frame of somatosensory active attention genesis

注意是大脑中选择感觉信息、促进信息加工的重要机制之一。然而，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已经报道了与注意调节皮质活动相关的神经元底物。我之前使用脑磁图的研究也报告了，当受试者开始将注意力转向手指大约400ms后，施加刺激后，次级体感区域的皮质活动增加。在预先设定的研究中，我考察了手处于不同位置时，躯体感觉皮层活动注意调制的时间特性。受试者被指示尽快将他们的注意力引导到由箭头方向指示的手上。在提示引导时间200、300、400或500ms之后，电流被传递到被关注的食指上。用160通道全头型脑磁图测量电流刺激诱发的体感磁场。比较了平行手和交叉手两种姿势下的等效电流偶极子矩(ECDS)。当在线索开始后400和500ms施加刺激时，受试者的第二次躯体感觉激活的平均ECD时刻趋于增加。其中一名被试的实验结果显示，两种手位条件下注意调节的时间特性存在显著差异。在交叉药水条件下，注意调制出现了大约100ms的延迟。这种延迟可以用计算手部位置的时间来解释。经过计算，注意力指向一个空间点，即手所在的空间点。虽然躯体感觉注意可能是参照空间框架而不是身体坐标来引导的，但这一结果需要进一步的分析。

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.