Rotman Research Institute, Baycrest Centre, Toronto, Ontario, Canada M6A 2E1; Department of Medical Biophysics, University of Toronto, Canada M5G 2M9.
Exp Neurol. 2013 Jul;245:40-51. doi: 10.1016/j.expneurol.2012.08.019. Epub 2012 Aug 27.
The sensory evoked neuromagnetic response consists of superimposition of an immediately stimulus-driven component and induced changes in the autonomous brain activity, each having distinct functional relevance. Commonly, the strength of phase locking in neural activities has been used to differentiate the different responses. The steady-state response is a strong oscillatory neural activity, which is evoked with rhythmic stimulation, and provides an effective tool to investigate oscillatory brain networks. In this case, both the sensory response and intrinsic activity, representing higher order processes, are highly synchronized to the stimulus. In this study we hypothesized that temporal dynamics of oscillatory activities would characterize the differences between the two types of activities and that beta and gamma oscillations are differently involved in this distinction. We used magnetoencephalography (MEG) for studying how ongoing steady-state responses elicited by a 20-Hz vibro-tactile stimulus to the right index finger were affected by a concurrent isolated touch stimulus to the same hand ring finger. SI source activity showed oscillations at multiples of 20 Hz with characteristic differences in the beta band and the gamma band. The response amplitudes were largest at 20 Hz (beta) and significantly reduced at 40 Hz and 60 Hz (gamma), although synchronization strength, indicated by inter-trial coherence (ITC), did not substantially differ between 20 Hz and 40 Hz. Moreover, the beta oscillations showed a fast onset, whereas the amplitude of gamma oscillations increased slowly and reached the steady state 400 ms after onset of the vibration stimulus. Most importantly, the pulse stimuli interacted only with gamma oscillations in a way that gamma oscillations decreased immediately after the concurrent stimulus onset and recovered slowly, resembling the initial slope. Such time course of gamma oscillations is similar to our previous observations in the auditory system. The time constant is in line with the time required for conscious perception of the sensory stimulus. Based on the observed different spectro-temporal dynamics, we propose that while beta activities likely relate to independent representation of the sensory input, gamma oscillation likely relates to binding of sensory information for higher order processing.
感觉诱发神经磁响应由即时刺激驱动的成分和自主脑活动的诱导变化叠加而成，每种成分都具有不同的功能相关性。通常，神经活动的相位锁定强度用于区分不同的反应。稳态响应是一种强烈的振荡神经活动，它是由节律刺激引起的，为研究振荡脑网络提供了有效的工具。在这种情况下，感觉反应和内在活动，代表更高阶的过程，都与刺激高度同步。在这项研究中，我们假设振荡活动的时间动态将表征这两种活动之间的差异，并且β和γ振荡在这种区分中不同地参与。我们使用脑磁图（MEG）研究了由右手食指的 20Hz 振动触觉刺激引起的持续稳态响应如何受到同一手无名指的同时孤立触摸刺激的影响。SI 源活动显示出以 20Hz 为倍数的振荡，在β带和γ带中具有特征性差异。响应幅度在 20Hz（β）时最大，并在 40Hz 和 60Hz（γ）时显著降低，尽管由试验间相干性（ITC）表示的同步强度在 20Hz 和 40Hz 之间没有实质性差异。此外，β振荡具有快速的起始，而γ振荡的幅度缓慢增加，并在振动刺激开始后 400ms 达到稳态。最重要的是，脉冲刺激仅与γ振荡相互作用，方式是γ振荡在同时刺激开始后立即减少，并缓慢恢复，类似于初始斜率。这种γ振荡的时程类似于我们在听觉系统中的先前观察结果。时间常数与对感觉刺激的意识感知所需的时间一致。基于观察到的不同光谱-时间动态，我们提出，虽然β活动可能与感觉输入的独立表示有关，但是γ振荡可能与更高阶处理的感觉信息绑定有关。
