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Objective There is a long interest in using EEG measurements to inform transcranial Electrical Stimulation (tES) but adoption is lacking. The conventional approach is to use anatomical head-models for both source localization (the EEG inverse problem) and current flow modeling (the tES forward model), but this approach is computationally demanding, requires an anatomical MRI, and strict assumptions about the target brain regions. We evaluate techniques whereby tES dose is derived from EEG without the need for an anatomical head model or assumptions. Approach The approaches are verified using a Finite Element Method (FEM) simulation of the EEG generated by a dipole, oriented either tangential or radial to the surface, and then simulating brain current flow produced by various model-free techniques including: (1) Voltage-to-voltage, (2) Voltage-to-Current; (3) Laplacian; and two Ad-Hoc techniques (4) Dipole sink-to-sink; and (5) Sink to Concentric Ring. These model-free approaches are compared to a numerically optimized dose that assumes perfect understanding of the dipole location and head anatomy. We vary the number of electrodes from a few to over three hundred, with focality or intensity as optimization criterion. Main results Our results demonstrate how simple Ad-Hoc approaches can achieve reasonable targeting for the case of a cortical dipole with 2–8 electrodes and no need for a model of the head. Significance For its simplicity and linearity, model-free EEG guided lends itself to broad adoption and can be applied to a static (tDCS), time-variant (e.g. tACS, tRNS, tPCS), or closed-loop tES. Figure options Download full-size image Download high-quality image (1118 K) Download as PowerPoint slide Figure options Download full-size image Download high-quality image (1499 K) Download as PowerPoint slide

Purpose Transcranial electric stimulations (tES) with amplitude-modulated currents are promising tools to enhance neuromodulation effects. It is essential to select the correct cortical targets and inhibitory/excitatory protocols to reverse changes in specific networks. We aimed at assessing the dependence of cortical excitability changes on the current amplitude of 20 Hz transcranial alternating current stimulation (tACS) over the bilateral primary motor cortex. Methods We chose two amplitude ranges of the stimulations, around 25 μ A/cm2 and 63 μ A/cm2 from peak to peak, with three values (at steps of about 2.5%) around each, to generate, respectively, inhibitory and excitatory effects of the primary motor cortex. We checked such changes online through transcranial magnetic stimulation (TMS)-induced motor evoked potentials (MEPs). Results Cortical excitability changes depended upon current density (p=.001). Low current densities decreased MEP amplitudes (inhibition) while high current densities increased them (excitation). Conclusions tACS targeting bilateral homologous cortical areas can induce online inhibition or excitation as a function of the current density.

Brodmann’s pioneering work resulted in the classification of the cortical areas based on their cyto-architecture and topology. Here, we aim at documenting that cortical areas can be also classified by neuronal activities specific to well identifiable structures and to the latter’s networking within the whole brain. We investigated this notion in the primary somatosensory area (S1) and in the primary motor area (M1) in both hemispheres. Our results show that S1 and M1 are topologically differentiated by their respective neuronal activities, which are specific, independent of hemisphere and of subject’s state (i.e., at rest, performing movements or receiving external stimulations). S1 displays higher power than M1 (p = .001) in the beta frequency band, while the opposite occurs in the gamma2 band (p = .034). We also show that the fractal dimensions (FD) emerged from our study as a strong index capable of differentiating the two brain areas in all subject’s states, with S1’s FD smaller than M1’s (p .00001). The present work intends to be a first step toward the identification and classification of brain cortical areas via the dynamics of their neuronal activity, which we believe will advance our knowledge of the brain’s intimate structural–functional unity.

Introduction Recently we developed a new procedure to personalize the electrode to selectively stimulate specific cortical regions by transcranial electric stimulations (tES).This study aims to assess by computational approach the distribution of the intra-cerebral electric field induced by tES through the personalized in comparison with a non-personalized electrode in human models. Methods We used two realistic human models and 40 tissue conductivities.We targeted bilateral primary motor (M1) and somatosensory cortex (S1) alternatively with the personalized and non-personalized electrode, with the reference on the occipital area. We estimated the distribution of the electric field across the brain structures. Results The personalized electrode was able to modulate more deeply and strongly the area of the central sulcus than the non-personalized one. This trend was more evident in the regions along the central sulcus more far away from Cz, where the two electrodes are less overlapped and for both targets (M1 and S1). Moreover, the personalized electrode used to target S1 more selectively modulated the postcentral gyrus, whereas the personalized electrode used to target M1 broadened its effects over both the pre and postcentral gyrus. Discussions This work strengthens the notion that tES can be focused by properly shaping and positioning the stimulating electrodes according to the target regions.

The large majority (80%) of people with multiple sclerosis (MS) complain of fatigue, which is the most disabling symptom in half of them. While the few drugs used to treat MS fatigue are limitedly useful, it was recently observed the efficacy of a personalized neuromodulation treatment, supporting the concept that interventions modifying the sensorimotor network activity balances could be suitable non-pharmacological treatments for MS fatigue. Aim of the present study is to strengthen knowledge of the brain unbalances, which proper neuromodulations should target to compensate. We collected electroencephalographic (EEG) data in 18 people with mild MS, while they were in resting state with open eyes. To ensure a wide range of fatigue, we enrolled patients to have Higher- or Lower-Fatigue based on scores of the modified Fatigue Impact Scale (mFIS). We selected the graph theory small-world index, calculated on networks of cortical nodes estimated by eLORETA, to evaluate the characteristics of left and right frontal (Motor) and parieto-occipital-temporal (Sensory) brain networks separately. Fatigue symptoms increased together with the small-world index in the Sensory network of the left dominant hemisphere. This finding hones understanding of the targets of neuromodulation interventions, indicating the sensory network of the dominant left hemisphere as a specific target.

Objective To test the need for the electrode personalization to induce neuromodulation effects on the bilateral primary motor cortex (M1) devoted to upper and lower limb representation. Methods We shaped the personalized electrode and positioned it matching the projection on the scalp of the individual central sulcus by a 2 cm strip. The non personalized electrode,equal for all subjects, was a 2 cm wide strip size-matched with the personalized electrode but shaped on a standard model fitting the curve passing through C3-CZ-C4 sites.To test neuromodulation electrode-dependent efficacy, we induced a 20 Hz sinusoidal modulated current (transcranial Alternating Current Stimulation, tACS) because it produces online effects.We simultaneously collected left and right hand and leg motor potentials (MEP) that were evoked by a rounded transcranial magneticstimulation (TMS) coil. Through each electrode we delivered both real and sham stimulations. Results While cortical excitability during tACS increased during both the non-personalized and the personalized electrodes for the leg, the hand representation excitability enhancement was induced selectively when using the personalized electrode. The results were consistent bilaterally. Conclusions Personalized electrode can induce the neuromodulation of a predetermined extended cortical target, which is impossible with a non-personalized electrode. Our findings can help in building neuromodulations that compensate for alterations across specific brain networks.