In vivo Measurements of Electric Fields During Cranial Electrical Stimulation in the Human Brain

Abstract

Cranial electrical stimulation (CES) has been applied at various current levels in both adults and children with neurological conditions with seemingly promising but somewhat inconsistent results. Stimulation-induced spatial electric fields (EFs) within a specific brain region are likely a significant contributing factor for the biological effects. Although several simulation models have been used to predict EF distributions in the brain, these models actually have not been validated by in vivo CES-induced EF measurements in the live human brain. This study directly measured the CES-induced voltage changes with implanted stereotactic-electroencephalographic (sEEG) electrodes in twenty-one epilepsy participants (16 adults and 5 children) and then compared these measured values with the simulated ones obtained from the personalized models. In addition, we further investigated the influence of stimulation frequency, intensity, electrode montage and age on EFs in parts of participants. We found both measured voltages and EFs obtained in vivo are highly correlated with the predicted ones in our cohort (Voltages: r = 0.93, p < 0.001; EFs: r = 0.73, p < 0.001). In white matter and gray matter, the measured voltages linearly increased when the stimulation intensity increased from 5 to 500 μA but showed no significant changes (averaged coefficient of variation <4.10%) with changing stimulation frequency from 0.5 to 200 Hz. Electrode montage, but not age, significantly affects the distribution of the EFs (n = 5, p < 0.01). Our in vivo measurements demonstrate that the individualized simulation model can reliably predict the CES-induced EFs in both adults and children. It also confirms that the CES-induced EFs highly depend on the electrode montages and individual anatomical features.

In Vivo Measurements of Transcranial Electrical Stimulation in Lesioned Human Brain: A Case Report

“…As displayed in Figure 4 B, we also found a moderate correlation between the measured and simulated values in the EF distributions ( r = 0.58, p < 0.001; s = 0.44). In line with several previous studies [ 16 , 27 ], we found a lower correlation between measured and simulated EF, in contrast to voltage values.…”

“…In this case report, our results show that the EF modeling can effectively predict EF distribution during tES in the lesioned brain under various electrical stimulation montages. The simulation model is also validated via in vivo measurement in previous studies of the non-lesioned brain [ 16 , 27 ]; they found a higher correlation between the simulated and predicted EF (Huang et al: r = 0.89; Wang et al: r = 0.73). These results indicated the influence of brain lesions on model performance.…”

Differences in electric field strength between clinical and non-clinical populations induced by prefrontal tDCS: A cross-diagnostic, individual MRI-based modeling study

“…First, the calculated e-field in this study is based on the individual anatomical features, meaning that it is only a proxy for the real e-field and stimulation. A kind of e-field validation can be obtained through in-vivo invasive electrophysiological recordings ( Opitz et al, 2018 , Wang et al, 2022 ). Second, in the present study, e-field modeling was based on the T1-weighted anatomical scans.…”

Multiple functions of the angular gyrus at high temporal resolution

“…The induced field distribution by transcranial stimulation might depend on multiple stimulation parameters such as time, intensity and duration of stimulation (Lerner et al, 2021;Sandrini et al, 2011;Westwood and Romani, 2017;Yeh and Rose, 2019), which makes the location and size of the stimulated cortical areas difficult to define accurately (Karabanov et al, 2019;Laakso et al, 2018;Weise et al, 2020). TES has a low spatial resolution, rendering selective stimulation of the AG without concomitant stimulation of nearby areas extremely difficult, as evidenced by simulations and in vivo measurements (Saturnino et al, 2019;Wang et al, 2022). The spatial resolution of TMS (Deng et al, 2013) is generally higher than that of TES, but TMS over the AG can also often induce relatively high stimulation intensities in other nearby areas (Kuhnke et al, 2020a), as mentioned above.…”