Nalcaci E, Basar-Eroglu C, Stadler M
Physiology Department of Medical Faculty, University of Ankara, Turkey.
Clin Neurophysiol. 1999 Jan;110(1):71-81. doi: 10.1016/s0168-5597(98)00049-5.
Visual evoked potentials (VEP) have been used to estimate interhemispheric transfer time (IHTT). However, the complex wave of VEP is most probably formed by different generators of neural populations that act through different frequency channels. If the main peaks of VEP are established by different types of generators, which can also be connected to each other by a different type of callosal fibres, we would be able to estimate a wide range of various IHTT by measuring the latency between time-locked peaks of narrow band-pass filtered VEP. This research aimed to test this hypothesis.
Nine right-handed men were presented with a reversal of a checkerboard pattern as stimuli at RVF or LVF, and EEG was recorded at O1, O2, P3, P4. The grand-averaged VEPs were transformed to the frequency domain by means of the fast Fourier transform to obtain the amplitude frequency characteristics. Band-pass filters were chosen adequately, according to tuning frequencies indicated by clear peaks in the amplitude frequency characteristics. The chosen band pass filters (4-8 Hz, 8-15 Hz, 15-20 Hz, 20-32 Hz) were applied to the VEP of the subjects, and 4 different components of VEPs for each VEP were obtained. The latency of P100 and N160 of unfiltered VEP was measured. In the band-pass digital filter applied VEPs, positive and negative peaks, which are consistent with P100 and N160, were measured for each subject. Latency differences between hemispheres for digitally unfiltered and filtered VEPs were computed to estimate IHTT.
In the different frequency bands, different IHTTs were estimated, ranging from 3 ms to 30 ms. Approximately 16 ms for theta band, 11 ms for alpha band, 6 ms for 15-20 Hz and 3 ms for 20-32 Hz bands were found.
Our findings support the hypothesis which states that unfiltered VEPs provide us with only a rough estimation of IHTT. Also, they are consistent with anatomical findings that describe callosal fibres of varying dimensions, predicting various velocities between hemispheres.
视觉诱发电位（VEP）已被用于估计半球间传递时间（IHTT）。然而，VEP的复合波很可能是由通过不同频率通道起作用的不同神经群体发生器形成的。如果VEP的主要峰值是由不同类型的发生器建立的，而这些发生器也可以通过不同类型的胼胝体纤维相互连接，那么我们就能够通过测量窄带通滤波VEP的锁时峰值之间的潜伏期来估计广泛的各种IHTT。本研究旨在验证这一假设。
对9名右利手男性，分别在右视野或左视野呈现棋盘格图案反转作为刺激，并在O1、O2、P3、P4记录脑电图。通过快速傅里叶变换将总体平均VEP转换到频域，以获得幅度频率特性。根据幅度频率特性中清晰峰值所指示的调谐频率，适当选择带通滤波器。将所选的带通滤波器（4 - 8Hz、8 - 15Hz、15 - 20Hz、20 - 32Hz）应用于受试者的VEP，每个VEP获得4种不同的VEP成分。测量未滤波VEP的P100和N160潜伏期。在应用带通数字滤波器的VEP中，测量每个受试者与P100和N160一致的正峰和负峰。计算未滤波和滤波VEP半球间的潜伏期差异以估计IHTT。
在不同频带中，估计出不同的IHTT，范围从3毫秒到30毫秒。发现θ频带约为16毫秒，α频带为11毫秒，15 - 20Hz频带为6毫秒，20 - 32Hz频带为3毫秒。
我们的研究结果支持这样的假设，即未滤波的VEP仅为我们提供IHTT的粗略估计。此外，它们与描述不同尺寸胼胝体纤维、预测半球间不同速度的解剖学发现一致。
