Griskova Inga, Morup Morten, Parnas Josef, Ruksenas Osvaldas, Arnfred Sidse M
Department of Psychiatry, Hvidovre Hospital, University Hospital of Copenhagen, Copenhagen, Denmark.
Exp Brain Res. 2007 Oct;183(1):133-8. doi: 10.1007/s00221-007-1111-0. Epub 2007 Sep 9.
The aim of this study was to investigate, in healthy subjects, the modulation of amplitude and phase precision of the auditory steady-state response (ASSR) to 40 Hz stimulation in two resting conditions varying in the level of arousal. Previously, ASSR measures have shown to be affected by the level of arousal, but the findings are somewhat controversial. Generally, ASSR is diminished in sleep but it may be increased in drowsiness. Besides, ASSR reduction has been observed in schizophrenia. However, schizophrenic patients are known to have a disturbance of arousal level, what makes it pertinent to know the effects of fluctuations in arousal on passive response to gamma-range stimulation. In nine healthy volunteers trains of 40 Hz click stimuli were applied during two conditions: in the "high arousal" condition subjects were sitting upright silently reading a book of interest; in the "low arousal" condition subjects were sitting in a reclined position with eyes closed and the lights turned off. The 64-channel EEG data was wavelet transformed and the amplitude and phase precision of the wavelet transformed evoked potential were decomposed by the recently proposed multi-subject non-negative multi-way factorization (NMWF) (Morup et al. in J Neurosci Methods 161:361-368, 2007). The estimates of these measures were subjected to statistical analysis. The amplitude and phase precision of the ASSR were significantly larger during the low arousal state compared to the high arousal condition. The modulation of ASSR amplitude and phase precision by differences in the arousal level during recording warrants caution when investigating oscillatory brain activity and interpreting the findings of reduced ASSR in schizophrenia. It also emphasizes the necessity of standardized recording procedures and monitoring the level of arousal during ASSR testing.
本研究的目的是在健康受试者中，调查在两种不同觉醒水平的静息状态下，40赫兹刺激诱发的听觉稳态反应（ASSR）的幅度和相位精度的调制情况。此前，ASSR测量结果已显示受觉醒水平影响，但研究结果存在一定争议。一般来说，ASSR在睡眠中会减弱，但在困倦时可能增强。此外，在精神分裂症患者中也观察到ASSR降低。然而，已知精神分裂症患者存在觉醒水平紊乱，这使得了解觉醒波动对γ频段刺激被动反应的影响变得很有必要。在九名健康志愿者中，在两种状态下施加40赫兹的短声刺激序列：在“高觉醒”状态下，受试者笔直坐着，安静地阅读一本感兴趣的书；在“低觉醒”状态下，受试者斜躺着，闭上眼睛，灯也关掉。对64通道脑电图数据进行小波变换，并采用最近提出的多受试者非负多向分解（NMWF）（Morup等人，《神经科学方法杂志》，161:361 - 368，2007）对小波变换诱发电位的幅度和相位精度进行分解。对这些测量结果的估计进行统计分析。与高觉醒状态相比，低觉醒状态下ASSR的幅度和相位精度明显更大。在研究振荡性脑活动以及解释精神分裂症中ASSR降低的研究结果时，记录过程中觉醒水平差异对ASSR幅度和相位精度的调制值得谨慎对待。这也强调了标准化记录程序以及在ASSR测试期间监测觉醒水平的必要性。
