The combination of TMS with other technologies also permits more sophisticated analysis of the dynamics of interactions between different cortical regions. For example, in one novel study, the TMS-evoked response was studied using functional connectivity analysis of EEG data in the awake and sleeping state (Massimini et al., 2005). The authors hypothesized that consciousness is based on the brain’s ability to integrate information from disparate sources, which in turn is contingent on effective connectivity between different specialized regions of the thalamocortical system. As a consequence of this hypothesis, the authors predicted that effective connectivity decreases during sleep. To test this hypothesis, they applied single-pulse TMS to the frontal cortex of subjects in either wakefulness or different sleep stages, and studied the resulting TMS-evoked potential using EEG. The authors found that during wakefulness TMS induced a sustained response of recurrent waves of activity, with the underlying cortical currents shifting over time to different regions across the cortex. In contrast, during non-REM sleep, TMS induced a much larger immediate local response that then terminated rapidly. Furthermore, the TMS-evoked potential was confined to
