Research Institute MOVE, VU University Amsterdam, Amsterdam, The Netherlands.
Neuroimage. 2013 May 1;71:104-13. doi: 10.1016/j.neuroimage.2012.12.076. Epub 2013 Jan 11.
We demonstrate the capacity of dynamic causal modeling to characterize the nonlinear coupling among cortical sources that underlie time-frequency modulations in MEG data. Our experimental task involved the mental rotation of hand drawings that ten subjects used to decide if it was a right or left hand. Reaction times were shorter when the stimuli were presented with a small rotation angle (fast responses) compared to a large rotation angle (slow responses). The grand-averaged data showed that in both cases performance was accompanied by a marked increase in gamma activity in occipital areas and a concomitant decrease in alpha and beta power in occipital and motor regions. Modeling directed (cross) frequency interactions between the two regions revealed that after the stimulus induced a gamma increase and beta decrease in occipital regions, interactions with the motor area served to attenuate these modulations. The difference between fast and slow behavioral responses was manifest as an altered coupling strength in both forward and backward connections, which led to a less pronounced attenuation for more difficult (slow reaction time) trials. This was mediated by a (backwards) beta to gamma coupling from motor till occipital sources, whereas other interactions were mainly within the same frequency. Results are consistent with the theory of predictive coding and suggest that during motor imagery, the influence of motor areas on activity in occipital cortex co-determines performance. Our study illustrates the benefit of modeling experimental responses in terms of a generative model that can disentangle the contributions of intra-areal vis-à-vis inter-areal connections to time-frequency modulations during task performance.
我们展示了动态因果建模的能力，以刻画作为 MEG 数据时频调制基础的皮质源之间的非线性耦合。我们的实验任务涉及到用手绘制的心理旋转，十名被试者用它来判断它是左手还是右手。当刺激呈现小旋转角度（快速反应）时，反应时间比大旋转角度（缓慢反应）时更短。平均数据表明，在这两种情况下，表现都伴随着明显的伽马活动增加，以及枕部和运动区域的阿尔法和贝塔功率的相应降低。对两个区域之间的定向（交叉）频率相互作用的建模表明，刺激引起枕部区域伽马增加和贝塔减少后，与运动区域的相互作用有助于减弱这些调制。快速和缓慢行为反应之间的差异表现为前后连接中耦合强度的改变，这导致更困难（反应时间较慢）的试验衰减不那么明显。这是由来自运动源到枕部源的（向后）贝塔到伽马耦合介导的，而其他相互作用主要在同一频率内。结果与预测编码理论一致，并表明在运动想象期间，运动区域对枕叶皮层活动的影响共同决定了性能。我们的研究说明了根据生成模型对实验反应进行建模的好处，该模型可以分离任务表现期间区内相对于区际连接对时频调制的贡献。
