Classification of responders versus non-responders to tDCS by analyzing voltage between anode and cathode during treatment session

Abstract

Abstract-Transcranial direct current stimulation (tDCS) has been shown to be beneficial as a potential treatment of several disorders such as depression, addiction and chronic pain. Despite promising results reported in research, there is variability in responsiveness to tDCS among subjects. However, the source of this variability is still unknown. Creating a mechanism of determining non-responders (vs. responders) is a crucial step in order to either understand the physiology behind tDCS or increase the effectiveness of treatment. This work proposes a versatile method to predict whether a subject responds to tDCS by analyzing the voltage measured between anode and cathode during a tDCS session. Two groups of subjects are determined as responders and non-responders by assessing the effect of tDCS on their motor potential evoked by transcranial magnetic stimulation (TMS). Voltage measurements are modeled by a double Debye model and two relaxation times are extracted for each measurement. A quadratic classifier is trained to recognize responders and nonresponders based on these relaxation times. Our classification results show that there is a significant correlation between relaxation times extracted from voltage and responsiveness to tDCS determined through motor evoked potentials. These results suggest that the relative speed of polarization processes occurring in electrodes and tissue may be associated the amount of current delivered to the brain.

Functional Effects of Bilateral Dorsolateral Prefrontal Cortex Modulation During Sequential Decision-Making: A Functional Near-Infrared Spectroscopy Study With Offline Transcranial Direct Current Stimulation

“…This negative neural–behavioral correlation only in the tDCS group suggests that participants seem to differ in their response to tDCS as discussed above. More specifically, participants with a higher upregulation effect also seem to perform faster in the delayed reward condition of this task (i.e., positive tDCS responders), whereas a lower upregulation seems to be associated with slower task performance (i.e., negative or tDCS non-responders), similar to findings reported by earlier studies (Nejadgholi et al, 2015 ; Russo et al, 2017 ; Di Rosa et al, 2019 ; Lefebvre et al, 2019 ). The neural–behavioral associations based on optimal choice performance did not reach significance, indicating that the observed tDCS-induced hemodynamic upregulation was not accompanied by more successful learning to predict future reward.…”

“…For instance, Horne et al ( 2020 ) reported a transfer effect in visual episodic memory in Val/Val carriers of aforementioned genes after tDCS coupled with decision-making training, whereas no beneficial training or transfer effect was observed in carriers of other genotypes. The aforementioned aspects may lead to distinct responsiveness to tDCS across individuals resulting in a set of responders and non-responders and an overall null effect (López-Alonso et al, 2014 ; Wiethoff et al, 2014 ; Nejadgholi et al, 2015 ). Therefore, individualized and adjusted stimulation protocols (Berker et al, 2013 ; Edwards et al, 2013 ; Li et al, 2015 ; Nejadgholi et al, 2015 ; Laakso et al, 2016 ; Stephens et al, 2017 ) should be considered for future research to ensure the efficacy of tDCS interventions.…”

“…The aforementioned aspects may lead to distinct responsiveness to tDCS across individuals resulting in a set of responders and non-responders and an overall null effect (López-Alonso et al, 2014 ; Wiethoff et al, 2014 ; Nejadgholi et al, 2015 ). Therefore, individualized and adjusted stimulation protocols (Berker et al, 2013 ; Edwards et al, 2013 ; Li et al, 2015 ; Nejadgholi et al, 2015 ; Laakso et al, 2016 ; Stephens et al, 2017 ) should be considered for future research to ensure the efficacy of tDCS interventions. Moreover, more precise electrode montages (e.g., high-definition tDCS, multi-array electrodes) should be applied (Laakso et al, 2016 ), as it was shown that current density and focality of the tDCS effect improved with the smaller size of the electrodes (Faria et al, 2011 ).…”

The Tolerability and Efficacy of 4 mA Transcranial Direct Current Stimulation on Leg Muscle Fatigability

“…Certainly, there are other possible explanations that require further investigation. For example, some subjects respond to tDCS, while some do not [55][56][57] and some subjects may have brain connectivity that allows the current to flow in the preferential direction [58], which may not be the case for others. Furthermore, M1 to supraorbital montages do not, in general, stimulate the motor system in a consistent way [6] and two supraorbital active electrodes may allow a great amount of current to pass through the orbit; in either of these montages, it is also possible that some structures located behind the eye (e.g., lower surface of the frontal cortex) are also affected by the stimulation.…”