Transcranial direct current stimulation (tDCS) is used to modulate cortical excitability, but many animal studies apply intensities that exceed clinical levels. The off-line behavioral effects of weak electric fields in rodents remain unclear. This study tested whether repeated anodal tDCS, calibrated by electric-field simulation to match human-equivalent weak fields, can accelerate motor recovery after a focal cortical ischemic injury in rats.
The investigators used electric-field simulation to identify a stimulation current that produces cortical field strengths comparable to those applied clinically. Simulation results indicated that a scalp current of 50 μA yields a maximum electric field of approximately 1.96 V/m in the targeted motor cortex. This value was taken as the clinically relevant low-current condition for the in vivo experiments. Higher currents (250 μA and 1 mA) were also included to compare dose effects against the simulation-informed low-current setting.
Focal cortical ischemia was induced using a photothrombotic ischemic stroke (PIT) model targeted to motor cortex. Under isoflurane anesthesia, animals were assigned to receive anodal tDCS at one of three currents (50 μA, 250 μA, or 1 mA) or sham stimulation. Stimulation was delivered for 5 minutes per day, 5 days per week, for 2 weeks. The protocol therefore emphasized repeated short sessions of anodal stimulation beginning after stroke induction.
Motor recovery was evaluated using a beam-walking task conducted weekly for 4 weeks after stroke. The authors analyzed longitudinal behavioral data using a linear mixed-effects model, testing for main effects of time and group as well as the time × group interaction. This approach accounts for repeated measures within subjects and permitted assessment of whether stimulation condition altered the time course of recovery.
The statistical model revealed significant effects of time, group, and the interaction between time and group on beam-walking performance across the 4-week follow-up. Key comparisons reported in the abstract were:
The 50 μA group (simulation-informed low-current) showed better motor performance than the PIT (stroke) control at 1 week after stroke.
The 1 mA group demonstrated superior motor performance relative to the PIT control at 2 weeks after stroke.
No persistent between-group differences were detected beyond these early time points; performance converged across groups after the initial advantages.
These findings indicate that the lowest current, matched by simulation to produce ~1.96 V/m in cortex, produced the earliest measurable behavioral benefit, while a higher suprathreshold current (1 mA) showed a delayed benefit. The mid-level (250 μA) group's comparative outcomes were not specified in the abstract.
The authors interpret their results to mean that low-current anodal tDCS, when informed by electric-field simulation to approximate clinical weak-field intensities, can accelerate early motor recovery after focal cortical ischemia in rats. The temporal pattern of benefit—earliest improvement with the simulation-informed 50 μA condition and a later effect with 1 mA—supports the notion that weak-field neuromodulation can produce meaningful behavioral effects in the early post-stroke period. The data are presented as proof-of-concept that dosing guided by electric-field simulation may improve translational relevance of animal tDCS studies.
This report is a preprint and has not been peer reviewed. The abstract does not provide certain experimental details that would be needed to fully evaluate the study, including sample sizes per group, lesion characterization (e.g., volume or location metrics), full statistical values (effect sizes, confidence intervals, p values for each comparison), and whether investigators were blinded to treatment during behavioral scoring. These details are not reported in the abstract and would require consulting the full preprint for complete appraisal.
The authors declared no competing interests. Funding was provided by JSPS KAKENHI (grant numbers listed in the source). The manuscript is available on bioRxiv as a preprint under a CC-BY-NC-ND 4.0 International license.