Palva Satu, Linkenkaer-Hansen Klaus, Näätänen Risto, Palva J Matias
BioMag Laboratory, Engineering Centre, Helsinki University Central Hospital, FIN-00029 Helsinki, Finland.
J Neurosci. 2005 May 25;25(21):5248-58. doi: 10.1523/JNEUROSCI.0141-05.2005.
The cortical processing of consciously perceived and unperceived somatosensory stimuli is thought to be identical during the first 100-120 ms after stimulus onset. Thereafter, the electrophysiological correlates of conscious perception have been shown to be reflected in the N1 component of the evoked response as well as in later (>200 ms) nonstimulus-locked gamma-band (28-50 Hz) oscillatory activity. To evaluate more specifically the time course and correlation of neuronal oscillations with conscious perception, we recorded neuromagnetic responses to threshold-intensity somatosensory stimuli. We show here that cortical broadband activities phase locked to the subsequently perceived stimuli in somatosensory, frontal, and parietal regions as early as 30-70 ms from stimulus onset, whereas the phase locking to the unperceived stimuli was weak and primarily restricted to somatosensory regions. Such stimulus locking also preceded the perceived stimuli, indicating that the phase of ongoing cortical activities biases subsequent perception. Furthermore, the data show that the stimulus locking was present in the theta- (4-8 Hz), alpha- (8-14 Hz), beta- (14-28 Hz), and gamma- (28-40 Hz) frequency bands, of which the widespread alpha-band component was dominant for the consciously perceived stimuli but virtually unobservable for the unperceived stimuli. Our results show that the neural correlates of conscious perception are already found during the earliest stages of cortical processing from 30 to 150 ms after stimulus onset and suggest that alpha-frequency-band oscillations have a role in the neural mechanisms of sensory awareness.
在刺激开始后的最初100 - 120毫秒内，有意识感知和未被感知的体感刺激的皮层处理被认为是相同的。此后，有意识感知的电生理相关性已被证明反映在诱发反应的N1成分以及后期（>200毫秒）的非刺激锁定伽马波段（28 - 50赫兹）振荡活动中。为了更具体地评估神经元振荡与有意识感知的时间进程和相关性，我们记录了对阈强度体感刺激的神经磁反应。我们在此表明，早在刺激开始后30 - 70毫秒，体感、额叶和顶叶区域的皮层宽带活动就与随后被感知的刺激锁相，而与未被感知的刺激的锁相较弱，主要局限于体感区域。这种刺激锁相也先于被感知的刺激，表明正在进行的皮层活动的相位会影响随后的感知。此外，数据表明，刺激锁相存在于theta（4 - 8赫兹）、alpha（8 - 14赫兹）、beta（14 - 28赫兹）和gamma（28 - 40赫兹）频段，其中广泛存在的alpha频段成分在有意识感知的刺激中占主导，但在未被感知的刺激中几乎观察不到。我们的结果表明，在刺激开始后30至150毫秒的皮层处理最早阶段就已经发现了有意识感知的神经相关性，并表明alpha频段振荡在感觉意识的神经机制中起作用。
