Paired-pulse protocols can also be used to assess dynamic changes in functional connectivity between brain regions. For example, in an elegant experiment Davere et al (2008) showed that a conditioning stimulus applied to the ventral premotor cortex in the resting state inhibited the subsequent MEP produced by a test stimulus to the primary motor cortex. In contrast, if the conditioning stimulus was applied during a precision grasping task, the subsequent TMS-evoked MEP was facilitated, suggesting that the influence of ventral premotor cortex on motor cortex varied as a function of the task state. Thus, paired-pulse TMS can be used to not only elucidate the task-related dynamics of interhemispheric functional connectivity, but also to explore how that connectivity is altered by disease.
