A simple method for EEG guided transcranial electrical stimulation without models

Abstract

Our approach is verified directly only for a theoretically localized source, but may be potentially applied to an arbitrary EEG topography. For its simplicity and linearity, our recipe for model-free EEG guided tES lends itself to broad adoption and can be applied to static (tDCS), time-variant (e.g., tACS, tRNS, tPCS), or closed-loop tES.

Optimal use of EEG recordings to target active brain areas with transcranial electrical stimulation

“…This solution is in contrast to a “naive” reciprocity approach, which simply applies currents with the same spatial pattern as the recorded voltage distribution: I * ∝ V (Cancelli et al, 2016) and does not decorrelate the recorded voltages. Note that the ability of optimal reciprocity (4) to account for volume conduction is predicated on the availability of the lead field matrix R , which conveys the set of possible source locations (e.g., all cortical locations).…”

“…It differs therefore fundamentally from other forms of TES targeting that are based purely on anatomical information (Dmochowski et al, 2011). A previous attempt to leverage EEG for targeting (Cancelli et al, 2016) is based on the intuition that the injected currents should match the recorded voltages ( I ∝ V ), which we referred to here as the “naive” reciprocity approach (Figure 1B) as it does not recognize the importance of inverting the blurring introduced by volume conduction. Fernández-Corazza et al (2016) suggest the use of the traditional reciprocity principle, but fail to recognize the multi-dimensional reciprocity relationship (3).…”

“…Intuition suggests that reciprocity should allow one to leverage the information carried by EEG signals to guide the parameters of the TES. Indeed, recent work has proposed ad hoc rules for distilling EEG measurements to TES configurations (“montages”) (Fernández-Corazza et al, 2016; Cancelli et al, 2016). However, these initial efforts have not realized the multi-dimensional nature of the reciprocity principle, and thus have failed to overcome the spatial blurring that results from naive implementations of reciprocal stimulation.…”

Focal Hemodynamic Responses in the Stimulated Hemisphere During High-Definition Transcranial Direct Current Stimulation

“…Furthermore, there are safety concerns of fMRI causing heating in wires and electrodes on the scalp of subjects that may not be properly insulated, and in the case of PET, there are concerns of radiation and invasiveness of the method to inject radiolabels . Although portable and noninvasive electroencephalography approaches using scalp‐based electrodes can be used to determine neurophysiological correlates of electric field propagation within the brain during HD‐tDCS in natural settings, this method faces the fundamental biophysical limits imposed by the scalp, skull and brain as volume conductors that limit spatial resolution, and the need to remove artifacts imposed by the tDCS‐induced currents limits its application for in vivo online monitoring.…”

Letter: Electric Beats Open New Frontiers for Deep Brain Stimulation

“…15 Using the topography of electroencephalography, others have attempted to select locations for transcranial electrical stimulation using cortical dipoles for targeting and the needed current applied to each electrode. 16,17 An additional consideration for Grossman and colleagues is that the targeted "deep" structure was the murine hippocampus, less than 1.5 mm deep from the mouse brain surface. While the overlying cortex did not exhibit activation, what does remain to be tested and/or demonstrated is whether TI can selectively and accurately target deep structures like the subthalamic nucleus or nucleus accumbens; in a mouse brain they are approximately 4 mm deeper than the hippocampus, and in a human brain they can be as much as 6 to 8 cm from the brain surface.…”