Influence of layered skull modeling on the frequency sensitivity and target accuracy in simulations of transcranial current stimulation

Abstract

With the development of electrical stimulation technology, especially the emergence of temporally interfering (TI) stimulation, it is necessary to discuss the influence of current frequency on stimulation intensity. Accurate skull modeling is important for transcranial current stimulation (tCS) simulation prediction because of its large role in dispersing current. In this study, we simulated different frequencies of transcranial alternating current stimulation (tACS) and TI stimulation in single‐layer and layered skull model, compared the electric field via error parameters such as the relative difference measure and relative magnification factor. Pearson correlation analysis and t‐test were used to measure the differences in envelope amplitude. The results showed that the intensity of electric field in the brain generated by per unit of stimulation current will increase with current frequency, and the layered skull model had a better response to frequency. An obvious pattern difference was found between the electric fields of the layered and single‐layer skull individualized models. For TI stimulation, the Pearson correlation coefficient between the envelope distribution of the layered skull model and the single‐layer skull was only 0.746 in the individualized model, which is clearly lower than the correlation coefficient of 0.999 determined from the spherical model. Higher carrier frequencies seemed to be easier to generate a large enough brain electric field envelope in TI stimulation. In conclusion, we recommend using layered skull models instead of single‐layer skull models in tCS (particularly TI stimulation) simulation studies in order to improve the accuracy of the prediction of stimulus intensity and stimulus target.

Optimized APPS-tDCS electrode position, size, and distance doubles the on-target stimulation magnitude in 3000 electric field models

“…Important foundational research comparing E-field modeling estimates and actual intracranial recordings established a strong linear relationship between these values, mitigating some but not all of the concern that E-field modeling is an estimation of cortical stimulation 58 , 59 . Further improvements in E-field modeling methodology, such as taking different sub-layers of meninges 60 , skull composition 61 , or anisotropy 62 into consideration, may help to further refine the fidelity of E-field models. A further limitation is that we combined relative (i.e., 10–10 EEG-based electrode placements) and absolute measurements (i.e., 2 cm increments further apart), which resulted in slight disparities of up to a few millimeters between inter-electrode distances between participants.…”

Safety Evaluation of Employing Temporal Interference Transcranial Alternating Current Stimulation in Human Studies

“…Since 2017, Grossman et al brought TI-tACS into the field of brain stimulation [ 3 ], and many subsequent studies have shown evidence supporting its effectiveness [ 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. However, to the best of our knowledge, this is the first study to test the safety of TI-tACS in the human brain.…”

“…However, at the intersection of the two currents, there would form an envelope at a low-frequency equal to the difference of the two high-frequency currents (e.g., 20 Hz), which can modulate deep brain areas like conventional tACS ( Figure 1 ) [ 4 , 5 ]. Although the results of subsequent animal studies [ 6 , 7 , 8 ], simulation studies [ 9 , 10 , 11 , 12 , 13 , 14 ] and human studies [ 15 , 16 ] supported the effectiveness of TI-tACS in stimulating brain areas in a selective manner, its safety in stimulating human brains is still unclear. It is necessary to verify the safety of TI-tACS before we apply TI-tACS to human participants and patients.…”

Neuroinflammation mechanisms of neuromodulation therapies for anxiety and depression

“…Since its introduction in the 1980s, this method has been used to improve a variety of diseases, such as mood [ 89 ], cognitive [ 90 ], and motor disorders [ 91 ]. It is generally accepted that TES can alter cortical excitability, for example, anodal stimulation has an excitatory effect, cathodal stimulation has an inhibitory effect, and alternating current can modulate endogenous brain oscillations [ 92 , 93 ]. Accumulating evidence suggested that non-invasive TES could affect inflammatory response and microglial function.…”