Reproducibility of evoked and induced MEG responses to proprioceptive stimulation of the ankle joint

Cortical processing of proprioceptive afference can be investigated by examining phase locked evoked and induced responses in cortical signals to passive movement stimuli. Reproducibility of evoked and induced responses has been studied using electroencephalography (EEG), but proprioceptive domain has received little attention. It is unclear whether evoked and induced responses to proprioceptive stimulation arising from the lower limbs are reproducible using magnetoencephalography (MEG). Nineteen healthy volunteers (18 right-foot dominant, 36.1 ± 6.6 yr, 7 females) were measured in two MEG sessions separated by 9 ± 5 days in which their right ankle was rotated intermittently using a pneumatic movement actuator (160 stimuli, 3000 ± 250 ms interstimulus interval) to elicit evoked fields and induced responses. The peak evoked field amplitude used in the final analysis was calculated from the gradiometer pair yielding the peak vector sum over vertex (i.e., the primary sensorimotor cortex for the lower limb). Peak induced response amplitudes were analyzed from the peak gradiometer demonstrating the most robust beta suppression and beta rebound. The between session reproducibility was estimated using intra-class correlation coefficient (ICC). Evoked field amplitudes, beta suppression and beta rebound amplitudes all demonstrated a large inter-individual variation but excellent between session reproducibility (ICC >0.81). Kinematics of the proprioceptive stimuli were stable and did not correlate with MEG response strengths. The results indicate that evoked and induced responses to proprioceptive stimuli from the lower limbs are reproducible and provide a valid tool for longitudinal experiments investigating the processing of proprioceptive afference in e.g., different clinical populations, but caution is advised when comparing individuals using these measures.