Abstract
Proprioceptive afference can be investigated using corticokinematic coherence (CKC), which indicates coupling between limb kinematics and cortical activity. CKC has been quantified using proprioceptive stimulation (movement actuators) with fixed interstimulus interval (ISI). However, it is unclear how regularity of the stimulus sequence (jitter) affects CKC strength. Eighteen healthy volunteers (16 right-handed, 27.8 ± 5.0 yr, 7 females) participated in magnetoencephalography (MEG) session in which their right index finger was continuously moved at ∼3 Hz with Constant 333 ms ISI or with 20% Jitter (ISI 333 ± 66 ms) using a pneumatic-movement actuator. Three minutes of data per condition were collected. Finger kinematics were recorded with a three-axis accelerometer. CKC strength was defined as the peak coherence value in the Rolandic MEG gradiometer pair contralateral to the movement at 3 Hz. Both conditions resulted in significant coherence peaking in the gradiometers over the primary sensorimotor cortex. Constant stimulation yielded stronger CKC at 3 Hz (0.78 ± 0.11 vs. 0.66 ± 0.13, P < 0.001) and its first harmonic (0.60 ± 0.19 vs. 0.27 ± 0.11, P < 0.001) than irregular stimulation. Similarly, the respective sustained-movement evoked field was also stronger for constant stimulation. The results emphasize the importance of temporal stability of the proprioceptive stimulation sequence when quantifying CKC strength. The weaker CKC during irregular stimulation can be explained with temporal and thus spectral scattering of the paired peripheral and cortical events beyond the mean stimulation frequency. This impairs the signal-to-noise ratio of respective MEG signal and thus CKC strength. When accurately estimating and following changes in CKC strength, we suggest using precise movement actuators with constant stimulation sequence.NEW & NOTEWORTHY Cortical proprioceptive processing can be investigated using corticokinematic coherence (CKC). The findings show that CKC method is sensitive to temporal stability in the stimulation sequence. Although both regular and irregular sequences resulted in robust coherence, the regular stimulation sequence with pneumatic movement actuator is recommended to maximize coherence strength and reproducibility to allow better comparability between groups or populations.
Highlights
Proprioceptive afference to the primary sensorimotor (SM1) cortex can be quantified in magnetoencephalography (MEG) or electroencephalography (EEG) either using cortical evoked responses to regular intermittent passive movements [1,2,3,4] or computing coupling between movement kinematics and cortical activity during continuous movements, i.e., corticokinematic coherence (CKC) [5, 6]
We examined how regularity of proprioceptive stimulation affects the strength of corticokinematic coherence (CKC)
Irregular stimulation most likely resulted in lower signal-to-noise ratio (SNR) of the stimulus-related cortical MEG signal in the 3-Hz frequency bin in which the CKC peaked
Summary
Proprioceptive afference to the primary sensorimotor (SM1) cortex can be quantified in magnetoencephalography (MEG) or electroencephalography (EEG) either using cortical evoked responses to regular intermittent passive movements [1,2,3,4] or computing coupling between movement kinematics and cortical activity (using MEG or EEG) during continuous movements, i.e., corticokinematic coherence (CKC) [5, 6]. Kinematics of limb movements have shown to be coherent with cortical activity during continuous voluntary [5, 7, 8] and passive [3, 7, 9, 10] movements. CKC can be used clinically to quantify deficits in proprioceptive processing in newborns using EEG [15] or motor impairments such as Friedreich ataxia using MEG [16]
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