Analysis and Measurement of Neuromagnetic Fields Elicited by Stimulations of Sensory Nerves

我们研究了周围神经和听觉刺激所引起的神经磁场。我们开发的测量系统包括一个测绘设备，其中包括一个二阶梯度仪和SQUID，一个体感和听觉刺激器，以及一个用于平均和幅度和相位检测的信号处理器。体感诱发场（SEF）的反应在刺激后80 ms和160 ms出现两个主峰，听觉诱发场（AEF）的反应在100 ms和180 ms出现主峰。基于最小二乘拟合的电流偶极子源参数估计表明，对于SEF和AEF，偶极子分别位于体感觉和听觉皮层。这些位置与MRI观察吻合良好。偶极矩为5-30 nAm。在稳态SEF对重复刺激的响应中，相位滞后与刺激的频率呈线性关系。线性关系给出了时滞的三个值，其中两个值与瞬态响应中主峰的延迟一致。最短的时间延迟归因于早期组件的延迟。在带有突音和/a/、/ka/等短言语的aef中，对言语的反应与对突音的反应有相似的峰值。音调和语音的电流偶极子源的估计矩在右半球与左半球几乎相同或更大。在左半球，声调和口头声音的偶极子的位置似乎略有不同。

We have studied the neuromagnetic fields which are evoked by peripheral nerve and auditory stimulations. The measurement system we have developed consists of a mapping apparatus which includes a 2nd-order gradiometer and SQUID, a somatosensory and auditory stimulator, and a signal processor for averaging and amplitude and phase detection.In the somatosensory evoked fields (SEF), responses have two main peaks at 80 and 160 ms after the stimulus, while responses of the auditory evoked fields (AEF) have main peaks at 100 and 180 ms latencies. Estimation of parameters of a current-dipole source based on a least-squares fit to the mapping measured data has indicated that the dipole is located at somatosensory and auditory cortexes for the SEF and AEF, respectively. These locations agree well with MRI observation. The dipole moments are 5-30 nAm.In the steady state SEF responses to repeated stimuli, phase lag exhibits a linear dependence on the frequency of the stimuli. The linear relation gives three values of the time lag, two of which agree with the latencies of the main peaks in the transient response. The shortest time lag is attributed to the latency of the early component.In the AEFs with tone burst and short verbal sounds like/a/and/ka/, responses to the verbal sounds have similar peaks to the tone burst response. Estimated moments of the current-dipole sources for the tones and verbal sounds are nearly the same or larger in the right hemisphere than in the left hemisphere. There seems a slight difference in the location of the dipoles of the tones and verbal sounds in the left hemisphere.