Impact of Vestibular Stimulation at Powerline Frequency on Human Pointing Accuracy

Background: Electric vestibular stimulations (EVS) up to 300 Hz trigger vestibular myogenic responses. Interestingly, 300 Hz is the upper limit of the so called extremely low-frequency magnetic fields (ELF-MF) range found within the 2010 guidelines written by the International Commission for Non-Ionizing Radiation Protection. Such guidelines are used to protect the workers and the public from neurostimulation triggered by induced electric fields. Since EVS is known to bias reaching and pointing tasks, vestibular-specific electric fields at power-line frequency are likely to impact the safety and performance of workers in high ELF-MF environments. Objectives: This research aimed to investigate the impact of vestibular-specific electric-fields on manual pointing accuracy. Methods: Pointing accuracy of twenty healthy participants was analyzed with both direct current (2 mA) and sinusoidal (peak +/- 2 mA at 50 Hz) EVS. Spatial orientation and quantity of movement variables were used to investigate pointing modulations. Results: Despite a pre-trial conclusive positive control effect, no significant effects of both direct current and 50 Hz stimulation exposures were found. Conclusions: Although high vestibular-specific electric fields were used; no pointing accuracy modulation was found. These results suggest that ELF exposure even at high levels are not able to modulate hand pointing performance in humans. Even though this could be explained by context-specific habituation mechanisms rapidly decreasing EVS impact over time, these results represent useful knowledge for the safety and the performance of workers evolving in high ELF-MF environments.