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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.

Proprioceptive perception is impaired with aging, but little is known about aging-related deterioration of proprioception at the cortical level. Corticokinematic coherence (CKC) between limb kinematic and magnetoencephalographic (MEG) signals reflects cortical processing of proprioceptive afference. We, thus, compared CKC strength to ankle movements between younger and older subjects, and examined whether CKC predicts postural stability. Fifteen younger (range 18–31 years) and eight older (66–73 years) sedentary volunteers were seated in MEG, while their right and left ankle joints were moved separately at 2 Hz (for 4 min each) using a novel MEG-compatible ankle-movement actuator. Coherence was computed between foot acceleration and MEG signals. CKC strength at the movement frequency (F0) and its first harmonic (F1) was quantified. In addition, postural sway was quantified during standing eyes-open and eyes-closed tasks to estimate motor performance. CKC peaked in the gradiometers over the vertex, and was significantly stronger (~76%) at F0 for the older than younger subjects. At F1, only the dominant-leg CKC was significantly stronger (~15%) for the older than younger subjects. In addition, CKC (at F1) was significantly stronger in the non-dominant than dominant leg, but only in the younger subjects. Postural sway was significantly (~64%) higher in the older than younger subjects when standing with eyes closed. Regression models indicated that CKC strength at F1 in the dominant leg and age were the only significant predictors for postural sway. Our results indicated that aging-related cortical-proprioceptive processing is altered by aging. Stronger CKC may reflect poorer cortical proprioceptive processing, and not solely the amount of proprioceptive afference as suggested earlier. In combination with ankle-movement actuator, CKC can be efficiently used to unravel proprioception-related-neuronal mechanisms and the related plastic changes in aging, rehabilitation, motor-skill acquisition, motor disorders etc.