A conceptional framework for combining brain mapping and brain stimulation

Here, we introduce a conceptual framework for studies that combine non-invasive transcranial brain stimulation (NTBS) with neuroimaging. We outline the type of neuroscientific questions that can be addressed with a combined NTBS-neuroimaging approach and describe important experimental considerations. Neuroimaging methods differ with respect to their spatiotemporal resolution and reflect different neurobiological aspects of brain function, structure or metabolism. These characteristics need to be carefully considered in order to select the most appropriate neuroimaging modality. NTBS and neuroimaging can be combined concurrently (online) or sequentially (offline). The “online” approach applies neuroimaging while NTBS is delivered to the brain and thus, can reveal the immediate functional effects of NTBS on the targeted brain networks, but one has to deal with interfering effects of NTBS on brain mapping. The “offline” approach applies neuroimaging and NTBS in sequence: Offline neuroimaging can be performed BEFORE the stimulation session to inform NTBS parameter setting or AFTER the stimulation session to provide functional, metabolic or structural readouts of NTBS-effects. Since NTBS and neuroimaging can be separated in space and time, NTBS does not interfere with offline brain mapping. Finally, we discuss how NTBS and neuroimaging are gaining importance in clinical NTBS applications and how both techniques can be iteratively combined to create open-loop setups.