The potential of interleaved TMS-fMRI for linking stimulation-induced changes in task-related activity with behavioral modulations

The simultaneous combination of TMS with fMRI has emerged as a promising means to investigate the direct interaction between stimulation-induced changes at the behavioral and neural activity level. This enables the investigation of whole brain neurobehavioral interactions underlying cognitive disruption or facilitation. Yet to date, the literature on interleaved TMS-fMRI in cognitive neuroscience is sparse and neuromodulatory patterns of different TMS protocols are still poorly understood. Here, we synthesize interleaved TMS-fMRI studies on the relationship between direct stimulation-induced changes on task related neural activity and behavior. The following main findings are discussed. First, approximately half of the studies report a relationship between neural activity and behavioral changes as a marker for network excitation or inhibition. Secondly, task difficulty and stimulation timing are crucial factors that impact the interaction between neural activity changes and behavior. Third, stimulation-induced changes in remote, connected areas seem to be stronger associated with facilitation effects at the behavioral level. A better understanding of the relationship between stimulation-induced changes at the neural and behavioral level will increase the current understanding of the neuromodulatory potential of TMS at different levels and may help to develop more efficient stimulation protocols for basic and applied research.