Cerebellar electric field intensity after tDCS predicts social cognition performance in neurotypical young adults
DOI: Pending DOI
Synopsis
We aimed to determine if individual electric field (EF) intensity predicts behavioral change after transcranial direct current stimulation (tDCS). T1-weighted MRI images from 28 neurotypical young adults (Mage=21.70 +/- 3.42, 17 females) were used to model EF intensity. Each participant completed three sessions in which 20min of 1.5mA tDCS (anodal, cathodal, or sham) was combined with functional MRI and behavioral assessments. Individual EF intensity was used as a predictor of post-tDCS behavioral change on the Reading the Mind in the Eyes (RME) test. Preliminary analyses suggest that individuals with higher cerebellar EF intensity after cathodal tDCS had higher RME accuracy (p=0.030) and efficiency scores (p=0.049). Results indicate that an EF intensity of ~0.3V/m can induce behavioral changes compared to sham tDCS.
Background
Transcranial direct current stimulation (tDCS) is a safe, non-invasive method for modulating neural tissue. tDCS has the potential to be a therapeutic option for a wide range of neurological and neurodevelopmental conditions1, though behavioral outcomes are often mixed and the large parameter space makes comparisons across studies challenging2. Additionally, most tDCS-related outcomes are assessed at the group level, whereas individual responses to tDCS are more clinically relevant. We aimed to better understand the predictors of individual responses to tDCS. It has been suggested that reaching certain electric field (EF) intensities at the surface of the neural tissue is a more important metric than the electric current at the scalp when predicting behavioral response to tDCS (e.g.,3, 4, 5). Inter-individual variability in neuroanatomy may influence the amount of current that reaches the neural tissue6, therefore EF modeling with individual patient neuroimaging data may result in more accurate EF intensity prediction rather than relying on a standard head model like the MNI152. In the current study, previously collected tDCS, neuroimaging, and behavioral data were leveraged to determine if EF intensities modeled at the neural target were a predictor of behavioral change following active tDCS compared to sham.
Methods
The study included 28 neurotypical young adults (Mage = 21.70 years, SDage = 3.42 years, range = 18-31 years, 17 females). Each participant completed three sessions scheduled approximately one week apart in which 1.5 mA of tDCS (anodal, cathodal, sham) was delivered for 20 minutes and immediately followed by tasks performed during functional MRI (fMRI). tDCS targeted either the posterior vermis (n = 17) or the right posterolateral cerebellum (n = 11) using two 5 cm2 saline-soaked sponge electrodes with the reference electrode on the right clavicle. The task of interest was the Reading the Mind in the Eyes (RME) task, a theory of mind task commonly used as a metric of social cognition and previously correlated with cerebellar activity. Individual EF modeling using a customized pipeline created by author JHK was completed using each participant’s T1-weighted MRI image; maximum EF intensity (V/m) within the cerebellum was extracted and used as a predictor of RME accuracy, reaction time (RT), and efficiency (combination of accuracy and RT) in linear mixed effects models, controlling for session number and the random effect of participant. Statistical significance was assessed at p(uncorrected) < 0.05.
Results
Linear mixed effects models indicated better RME accuracy was associated with higher EF intensities in the cerebellum after cathodal tDCS compared to sham tDCS (p = 0.030). The same relationship was found for RME efficiency scores after cathodal tDCS compared to sham tDCS (p = 0.049). There were no significant predictors associated with RME RT and no statistically significant effects of anodal tDCS compared to sham tDCS.
Discussion
We provide evidence of a relationship between the amount of current estimated to reach the neural tissue (EF) and behavioral change. Specifically, we found that participants with higher EF intensities in the cerebellum also had better RME accuracy and efficiency scores after cathodal tDCS. Further evaluation of performance after cathodal tDCS compared to sham indicated that these changes relative to baseline behavior emerge when the EF is around 0.3 V/m. This suggests that an individualized modeling approach could aid in predicting behavioral response to tDCS. Additionally, these findings could be used to optimize tDCS application and inform tDCS dosing: if behavioral changes are observed when the EF exceeds 0.3 V/m, then modeling can determine the appropriate montage and parameters to reach similar EF intensities at desired neural targets, hence potentially optimizing tDCS as a future treatment option. Future work will increase the sample size and explore additional behavioral tasks to assess the generalizability of these outcomes.
Disclosures
The work reported here is funded by the Raynor Cerebellum Project and R21MH140296
References
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