title: Nonlinear Connectivity in the Human Stretch Reflex Assessed by Cross-Frequency Phase Coupling.
abstract: Communication between neuronal populations is facilitated by synchronization of their oscillatory activity. Although nonlinearity has been observed in the sensorimotor system, its nonlinear connectivity has not been widely investigated yet. This study investigates nonlinear connectivity during the human stretch reflex based on neuronal synchronization. Healthy participants generated isotonic wrist flexion while receiving a periodic mechanical perturbation to the wrist. Using a novel cross-frequency phase coupling metric, we estimate directional nonlinear connectivity, including time delay, from the perturbation to brain and to muscle, as well as from brain to muscle. Nonlinear phase coupling is significantly stronger from the perturbation to the muscle than to the brain, with a shorter time delay. The time delay from the perturbation to the muscle is 33 ms, similar to the reported latency of the spinal stretch reflex at the wrist. Source localization of nonlinear phase coupling from the brain to the muscle suggests activity originating from the motor cortex, although its effect on the stretch reflex is weak. As such nonlinear phase coupling between the perturbation and muscle activity is dominated by the spinal reflex loop. This study provides new evidence of nonlinear neuronal synchronization in the stretch reflex at the wrist joint with respect to spinal and transcortical loops.
authors.affiliation: * Department of Biomechanical Engineering, Delft University of Technology, Delft 2628 CD, The Netherlands.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Yang
authors.affiliation: * Department of Biomechanical Engineering, Delft University of Technology, Delft 2628 CD, The Netherlands.
authors.forename: Teodoro
authors.initials: T
authors.lastname: Solis-Escalante
authors.affiliation: † Department of Physical Therapy and Human Movement Sciences, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Yao
authors.affiliation: * Department of Biomechanical Engineering, Delft University of Technology, Delft 2628 CD, The Netherlands.|† Department of Physical Therapy and Human Movement Sciences, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA.
authors.forename: Frans C T
authors.initials: FC
authors.lastname: van der Helm
authors.affiliation: * Department of Biomechanical Engineering, Delft University of Technology, Delft 2628 CD, The Netherlands.|† Department of Physical Therapy and Human Movement Sciences, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA.|‡ Department of Biomedical Engineering, McCormick School of Engineering, Northwestern University, Evanston, IL 60208, USA.
authors.forename: Julius P A
authors.initials: JP
authors.lastname: Dewald
authors.affiliation: * Department of Biomechanical Engineering, Delft University of Technology, Delft 2628 CD, The Netherlands.|† Department of Physical Therapy and Human Movement Sciences, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA.|§ MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, 7500 AE, The Netherlands.
authors.forename: Alfred C
authors.initials: AC
authors.lastname: Schouten
mesh_terms: D016477:Artifacts; D004569:Electroencephalography; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008959:Models, Neurological; D009043:Motor Activity / Q000502:physiology; D009044:Motor Cortex / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology; D017711:Nonlinear Dynamics; D010507:Periodicity; D012026:Reflex, Stretch / Q000502:physiology*; D012815:Signal Processing, Computer-Assisted; D009435:Synaptic Transmission / Q000502:physiology*; D013997:Time Factors; D014955:Wrist Joint / Q000502:physiology; D055815:Young Adult
keywords: EEG; EMG; Stretch reflex; nonlinear connectivity; sensorimotor system; time delay