TMS in combination with neuroimaging techniques can be used to study the dynamic mechanisms that the brain utilizes to compensate for focal disruptions in activity. In one elegant study, O’Shea et al (2007) used repetitive TMS to induce mild, transient disruptions to a focal cortical region, and then used fMRI to study compensatory changes in the brain. They focused on the left dorsal premotor region, which shows increased activation after motor stroke and is involved in action selection. Inhibitory rTMS applied to the left dorsal premotor cortex initially resulted in a disruption in performance on an action selection task. However, within a few minutes, performance returned to baseline. fMRI demonstrated that during task performance prior to rTMS, blood flow increased to a left-hemisphere dominant premotor-parietal network. fMRI several minutes after rTMS of the left premotor cortex, after behavioral performance had recovered to baseline, demonstrated increased activation in the right premotor cortex, left supplementary motor area, and bilateral cingulate motor areas (Figure 8). Thus, recovery of task performance was associated with increased activity in multiple other cortical regions. These compensatory increases
