Functional Neuroimaging and Neuromodulation: Effects of Transcranial Magnetic Stimulation on Cortical Networks in Healthy Subjects and Patients

stimulation approaches off er great potential to modulate cerebral networks, thereby modifying behaviour. An interesting non-invasive approach to focally interfere with cortical networks is provided by transcranial magnetic stimulation (TMS). Functional neuroimaging techniques such as positron emission tomography (PET) or functional magnetic resonance imaging (fMRI) allow us to gain insights into the effects of TMS on neuronal circuits. Here we review recent papers on PET and fMRI studies investigating the neural effects of TMS under physiological and pathological conditions. We discuss data showing that focally applied TMS does not only regionally interfere with the cortex directly stimulated but also with remote and interconnected areas. The network effects of TMS are dependent on the stimulation frequency and location. Repetitive TMS protocols enable a distinct interference with pathological states of cerebral networks. Functional neuroimaging may serve as a surrogate marker to predict responses to a specific TMS-intervention protocol depending on neural activity levels in the affected or unaffected hemisphere. In the future such a combined approach may enable individualised treatment regimes to support recovery of function in patients suffering from neurological deficits.