Functional brain mapping by means of a dipole tracing method with a realistic 4-layr head model

为了定位脑电和诱发电位的电流源发生器(偶极子)，提出了一种基于头皮-头骨-液体-脑四层模型的偶极跟踪(DT)方法(SSLB/DT方法)。液晶快门的制作视觉诱发电位(VEP)的视觉刺激的持续时间由放置在投影仪前的液晶振荡器控制，并由运算放大器驱动。当运算放大器的驱动电压脉冲开启时，快门在0.5毫秒内从不透明变为透明。头部模型三维测量装置的研制研制了一种利用声波发生器和接收器的三维测量系统。利用该系统在工作站上重建了一个逼真的头部模型，并测量了头部电极的三维坐标。结合一个真实的四层头部模型的SSLB/DT方法的算法是…更发达。通过边界元方法，SSLB/DT方法可以将头皮上的表面电势分布等效为一个或两个相应的等效偶极子。对SSLB/DT方法的软件进行了优化调整，使其能够在并行计算机上运行。1)用SSLB/DT方法研究人VEP对视觉刺激的偶极子。结果表明，根据视野轨迹，距骨裂周围偶极子的位置有一定的定位。这与基于临床病理研究的人类枕叶视网膜手术类似。2)对发作期脑电进行SSLB/DT定位，以确定发作期的起始区。SSLB/DT法与皮层脑电图法的结果比较，证实SSLBDT法能准确定位偶极子，即使受试者因神经外科手术或脑萎缩导致硬膜下液体空间扩大。3)在3只猕猴的硬膜外电极上记录到刺激右侧胫后神经诱发的体感诱发电位(SEP)，并用DT法进行分析。这些SEP的偶极子位于顶前皮质内侧壁的左侧，并倾斜地朝向右半球。较少

To localize current source generators (dipoles) of EEGs and evoked potentials, a dipole tracing (DT) method with a realistic 4-layr (scalp-skull-liquor-brain : SSLB) head model (SSLB/DT method) was developed.1. Manufacturing of a liquid crystal shutterThe duration of the visual stimulus for visually evoked potentials (VEPs) was controlled by a liquid crystal shtter, which was positioned before the projector and driven by an operation amplifier. The shutter changed from opaque to transparent within a span of 0.5 msec when a driving voltage pulse from the operation amplifier was on.2. Manufacturing of 3-D measurement device for a head modelA3-D measurement system using a sonic generator and receiver was developed. A realistic head model was reconstructed on a workstation using this system, and 3-D coordinations of electrodes on a head were also measured by this system.3. Development of the SSLB/DT methodThe algorithm for the SSLB/DT method incorporating a realistic 4-layr head model was … More developed. The SSLB/DT method can, by a boundary element method, equate the surface potential distributions on a scalp to one or two corresponding equivalent dipoles. The software for the SSLB/DT method was adjusted optimally to run on a parallel computer.4. Neurophysiological studies1) Dipoles of the human VEPs to visual stimuli were investigated with the SSLB/DT method. The results indicated topographic localization of the dipoles around the calcarine fissure based on the loci of the visual fields. This was comparable to the retinotopy of the human occipital lobe based on clinicopathological studies. 2) To localize ictal onset zone, the SSLB/DT was applied to ictal EEGs. Comparison of the results by the SSLB/DT method and the electrocorticograms confirmed that the SSLB/DT method could accurately localize dipoles even when a subject has an enlarged subdural liquor space due to neurosurgical operation or brain atrophy. 3) Somatosensory evoked potentials (SEPs) elicited by right posterior tibial nerve stimulation were recorded from epidural electrodes in 3 monkeys, and analyzed by the DT method. Dipoles of these SEPs were located in the left side of the mesial wall of the anterior parietal cortex, and oriented obliquely toward the right hemisphere. Less