Ioannides A A, Singh K D, Hasson R, Baumann S B, Rogers R L, Guinto F C, Papanicolaou A C
Open University, Department of Physics, Milton Keynes, UK.
Brain Topogr. 1993 Fall;6(1):27-34. doi: 10.1007/BF01234124.
Measurements of the magnetic field elicited by a 50 ms long auditory stimulus, from three normal subjects and one head injured subject, are used to estimate the three dimensional distribution of generators in the brain. The resulting images are compared with point source solutions obtained with the usual single current dipole fitting procedures, over a latency range which includes the extrema in the (average) measured signal. In all cases considered, 100 or so epochs time-locked to the stimulus were magnetically recorded. These were averaged, and then analyzed using two techniques; a new distributed current model known as Magnetic Field Tomography (MFT), and the standard single current dipole (SCD) model. Both methods provide estimates of the current generators in the brain. In two of the normal subjects, the MFT solutions are super-imposed onto Magnetic Resonance Images (MRI) of the relevant cortical area. The results show that when the SCD model provides a reasonable description of the data, the MFT estimate shows one dominant localized region in agreement with the current dipole position. In the MFT sequence of solutions the activity evolves smoothly; multiple areas of activity often arise as the focal activity in one region declines while focal activity in another region grows. In contrast the SCD solutions during these intermediate periods fit the data poorly, and may move erratically from one locale to another. We conclude that MFT seems to provide a reasonable description of the activity through cortical and subcortical regions. The evolution of activity, as derived from the average signal, can be traced continuously from the onset of the stimulus, not just at the peaks.(ABSTRACT TRUNCATED AT 250 WORDS)
对三名正常受试者和一名头部受伤受试者施加时长50毫秒的听觉刺激所引发的磁场进行测量，以估计大脑中信号源的三维分布。将所得图像与通过常规单电流偶极子拟合程序获得的点源解进行比较，比较的潜伏期范围包括（平均）测量信号中的极值。在所有考虑的情况下，对100个左右与刺激锁时的时段进行了磁记录。对这些记录进行平均，然后使用两种技术进行分析：一种是称为磁场断层扫描（MFT）的新分布式电流模型，另一种是标准单电流偶极子（SCD）模型。两种方法都能提供对大脑中电流源的估计。在两名正常受试者中，将MFT解叠加到相关皮质区域的磁共振图像（MRI）上。结果表明，当SCD模型能合理描述数据时，MFT估计显示出一个与电流偶极子位置一致的主要局部区域。在MFT解的序列中，活动平稳演变；随着一个区域的局部活动下降而另一个区域的局部活动增加，常常会出现多个活动区域。相比之下，在这些中间时段，SCD解对数据的拟合较差，并且可能会从一个位置不规则地移动到另一个位置。我们得出结论，MFT似乎能合理描述皮质和皮质下区域的活动。从平均信号得出的活动演变可以从刺激开始就连续追踪，而不仅仅是在峰值处。（摘要截短于250字）
