对比度与照度对正常成人图形翻转视觉诱发磁场的影响

Magnetoencephalography Research on Effects of Contrast or Luminance on Pattern Reversal Visual Evoked Magnetic Field

目的：用MEG来描述人脑视皮质对不同对比度和照度条件下黑白棋盘格翻转刺激所产生的视觉诱发磁场，并研究对比度和照度对VEF成分之一的M100的影响。方法：测定11例健康志愿者对对比度分别为31％、62％、82％、90％和94％的5种对比度和白格照度分别为143．5、166．5和196．5Lux的3种照度条件下的左半视野棋盘格刺激的诱发磁场反应。结果：采用单因素方差分析进行数据分析。开始时，随着对比度增大，M100偶极强度迅速增大(P＜0．05)，M100峰值潜伏期迅速缩短(P＞0．05)，对比度增至82％时，M100偶极强度上升明显减慢，峰值潜伏期缩短减少；3种照度所引起的M100峰值潜伏期随照度增加而逐渐缩短(P＜0．05)，所引起的M100偶极强度随照度增加而逐渐增高(P＞0．05)。对不同对比度棋盘格刺激的M100反应均位于刺激野对侧半球枕区的距状沟后肢底部上唇或下唇，即楔下回、楔舌后回和舌上回；对不同照度的棋盘格刺激的M100反应起源均位于刺激野对侧半球枕区的距状沟后肢底部的下唇，即舌上回和楔舌后回，虽然个体间M100偶极位置有一定程度的差异，但在统计学上无明显差异(P＞0．05)。结论：棋盘格刺激是一种对比度刺激，对比度变化是影响视皮质对棋盘格刺激反应的敏感因素。尽管不同对比度和照度条件下的棋盘格刺激对源位置无显著影响，但在日常工作当中，应选择不低于82％的对比度和尽量高的照度方能获得较好的皮质反应波。

Objective：To describe the visual evoked field （VEF） of different contrast or luminance on white and black pattern reversal stimuli by using magnetoeneephalography, and to evaluate the effects of contrast or luminance on the M100. Methods ： Left half-field pattern reversal stimuli with contrast between black and white cheeks of 31%, 62%, 82%, 90% and 94% were given to 11 healthy subjects, and 5 of them were also accepted the different luminance stimuli which the luminance of white cheeks were 143.5, 166.5, and 196.5Lux. Results： One-way ANOVA was used in statistics. At the beginning, the M100 dipole strength increased rapidly according with the increase of contrast between black and white cheeks （P〈0.05）. When the contrast reached 82%, the increase of the wave altitude became slower obviously and retained stable. At the same time, sharp decrease of M100 peak latency was also detected with the increase of the contrast （P〈0.05）, when the contrast reached 82%, the peak latency became small and the change became flat. M100 peak latency shortened gradually with the increase of luminance of the white cheeks （P〈0.05）, and the relevant dipole strength increased with it（P〉0.05）. The equivalent current dipoles were located around the upper and lower leaves of the posterior of ealearine cortex eontralateral to the stimulated visual field in contrast condition and around the bottom of the posterior of ealearine cortex eontralateral to the stimulated visual field in luminance condition. Although the dipole position of M100 among individuals has difference to some extent, there is no significant difference on statistics. Conclusions.. The eherkerboard is a kind of stimuli based on contrast. The change of the contrast between black and white checks could make a large influence on the activity of visual cortex. Although there is no significant difference among various contrast or luminance on dipole position, a contrast higher than 82% and a luminance as bright as possible should be chosen to acquire excellent cortex activity.