Quantifying connectivity via efferent and afferent pathways in motor control using coherence measures and joint position perturbations

Abstract

The applicability of corticomuscular coherence (CMC) as a connectivity measure is limited since only 40-50 % of the healthy population presents significant CMC. In this study, we applied continuous joint position perturbations to obtain a more reliable measure of connectivity in motor control. We evaluated the coherence between joint position perturbations and EEG (position-cortical coherence, PCC) and CMC. Healthy subjects performed two isotonic force tasks against the handle of a wrist manipulator. The baseline task was isometric; in the perturbed task, the handle moved continuously with small amplitude. The position perturbation signal covered frequencies between 5 and 29 Hz. In the perturbed task, all subjects had significant PCC and 86 % of the subjects had significant CMC, on both stimulus and non-stimulus frequencies. In the baseline task, CMC was present in only 45 % of the subjects, mostly on beta-band frequencies. The position perturbations during an isotonic force task elicited PCC in all subjects and elicited CMC in most subjects on both stimulus and non-stimulus frequencies. Perturbed CMC possibly arises by two separate processes: an intrinsic process, similar to the process in an unperturbed task, involving both efferent and afferent pathways; and a process related to the excitation of the afferent and efferent pathways by the perturbation. These processes cannot be separated. PCC, however, reflects connectivity via the afferent pathways only. As PCC was present in all healthy subjects, we propose this coherence as a reliable measure for connectivity in motor control via the afferent pathways.

A Generalized Coherence Framework for Detecting and Characterizing Nonlinear Interactions in the Nervous System

“…5 to 8 for an example subject (Subject 10, number of data segments: 942). In line with a previous study [36], the linear interaction (the first order harmonic coupling) was shown between the perturbation and EEG. High order (≥ 2) harmonic and intermodulation couplings were detected for this subject, as well as subharmonic coupling for 29 Hz (1:2).…”

“…visual flickering) has often been reported in the human visual system [3,7]. Most studies using somatosensory stimuli, mainly using tactile stimuli,) only reported harmonic and intermodulation coupling (see [8,10,14,36,41] for examples and a brief review is available in [42]). To the best of our knowledge, only Langdon and his colleagues has reported 2:3 subharmonic coupling between brain responses and tactile vibrations [11].…”

“…The perturbation signal consisted of a sum of three sine waves with the frequencies 7, 13, and 29 Hz and random phases. The magnitude of the sinusoids decreased with frequency to keep the same power per frequency in the velocity signal [36]. The period of the perturbation signal was 1 s, and the peak-to-peak amplitude was 0.06 rad.…”

Quantifying Nonlinear Contributions to Cortical Responses Evoked by Continuous Wrist Manipulation

“…Mechanical (i.e. joint angle and torque) and EMG recordings obtained from continuous mechanical TNSRE-2015-00235 stimulation also show a small response at non-stimulated frequencies [18][19][20]. Nonlinear responses in the sensorimotor system could result from sensors (e.g.…”

Identification of connectivity in human motor control: exciting the afferent pathways

“…When studying sensory and motor function after stroke with CMC, no information can be obtained from individuals without voluntary muscle control. Finally, a large downside for the potential clinical application of CMC is that it cannot be detected in all cases: even healthy subjects, with normal voluntary motor control, do not all present CMC (Ushiyama et al, 2011;Mendez-Balbuena et al, 2011;Campfens et al, 2013). The inter-individual difference in the presence of CMC reflect physiological inter-individual differences in the strength of the oscillatory corticomuscular coupling and are not the result of technical aspects such as the (mis-) placement of EEG electrodes (Ushiyama et al, 2011).…”