Targeting brain functions from the scalp: Transcranial brain atlas based on largescale fMRI data synthesis. Abstract   Transcranial brain mapping techniques, such as functional nearinfrared spectroscopy (fNIRS) and transcranial magnetic stimulation (TMS), have been playing an increasingly important role in studies of human brain functions. Given a brain function of interest, fNIRS probes and TMS coils should be properly placed on the scalp to ensure that the function is effectively measured or modulated. However, since brain activity is inside the skull and invisible to the researcher during placement, this blind targeting may cause the device to partially or completely miss the functional target, resulting in inconsistent experimental results and divergent clinical outcomes, especially when participantsu0027 structural MRI data are not available. To address this issue, we propose here a framework for targeting a designated function directly from the scalp. First, a functional brain atlas for the targeted brain function is constructed via a metaanalysis of largescale functional magnetic resonance imaging datasets. Second, the functional brain atlas is presented on the scalp surface by using a transcranial mapping previously established from an structural MRI dataset (nxe2x80xafxe2x80xaf114), resulting in a novel functional transcranial brain atlas (fTBA). Finally, a lowcost, portable scalpnavigation system is used to localize the transcranial device on the individualu0027s scalp with the guidance of the fTBA. To demonstrate the feasibility of the targeting framework, both fNIRS and TMS mapping experiments were conducted. The results show that fTBAguided fNIRS positioning can detect functional activity with high sensitivity and specificity for working memory and motor systems; Moreover, compared with traditional TMS targeting approaches (e.g. the International 10xe2x80x9320 System and the conventional 5cm rule), the fTBA suggested motor stimulation site is closesr to both the motor hotspot and the center of gravity of motor evoked potentials (MEPCOG). In summary, the proposed method unblinds the transcranial function targeting process using prior information, providing an effective and straightforward approach to transcranial brain mapping studies, especially those without participantsu0027 structural MRI data.

A novel approach to localize cortical TMS effects Despite the widespread use of transcranial magnetic stimulation (TMS), its precise cortical location underlying the physiological and behavioral stimulation effects are still only coarsely known. So far, mapping strategies that systematically measure TMS effects rely on center of gravity approaches and therefore localize the stimulated cortical site only approximately and indirectly. Focusing on the motor cortex, we present a new method to reliably determine the stimulated cortical site at the individual subject level. The approach combines measurements of motor evoked potentials (MEPs) at different coil positions and orientations with numerical modeling of induced electric fields. We identify sharply bounded cortical areas around the gyral crowns and rims of the motor hand area as the origin of the MEPs and show that the tangential field component and the magnitude of the electric field is most relevant for the observed effect. The identification requires relatively few measurements at different coil positions and orientations. We use extensive uncertainty and sensitivity analyses to verify the robustness of the method and identify the most critical model parameters. Our approach improves the localization of the cortex area stimulated by TMS. It is generic and can potentially be applied to other modalities such as language mapping.