Effects of electrode angle-orientation on the impact of transcranial direct current stimulation on motor cortex excitability.

BACKGROUND

For effects of transcranial direct current stimulation (tDCS), electrical field distribution and coverage of the target areas play a decisive role.

METHODS

We explored the effect of different angle-orientations of tDCS electrodes applied over the upper limb motor cortex (M1) on motor cortex excitability in healthy volunteers. Sixteen individuals received 1 mA anodal or cathodal tDCS through 35 cm2 electrodes over M1 for 15 min. Transcranial magnetic stimulation was used to examine tDCS-generated cortical excitability effects. The M1 electrode-orientation was following the right-left longitudinal plane, or positioned with 45° deviation from the midsagittal plane. Coverage of underlying brain and electrical field orientation were also investigated.

RESULTS

Cortical excitability modulation was observed only when the electrode was aligned with 45° angle, which covered a larger area of the motor cortex.

CONCLUSION

an electrode angle-orientation of 45° induces superior neuroplastic effects of M1 due to a better alignment with the motor cortex.