Cyclic time course of motor excitability modulation during the observation of a cyclic hand movement

• Published in: Brain research Vol. 1065; no. 1; pp. 115 - 124
• Main Authors: Borroni, Paola, Montagna, Marcella, Cerri, Gabriella, Baldissera, Fausto
• Format: Journal Article
• Language: English
• Published: London Elsevier B.V 14.12.2005; Amsterdam Elsevier; New York, NY
• Subjects: Adult; Biological and medical sciences; Efferent Pathways - physiology; Electric Stimulation; Evoked Potentials, Motor - physiology; Excitability modulation; Female; Forearm - innervation; Forearm - physiology; Fundamental and applied biological sciences. Psychology; H-reflex; H-Reflex - physiology; Hand - physiology; Humans; Male; Middle Aged; Mirror neuron; Motor control and motor pathways. Reflexes. Control centers of vegetative functions. Vestibular system and equilibration; Motor resonance; Motor-evoked potential; Movement - physiology; Muscle, Skeletal - innervation; Muscle, Skeletal - physiology; Prone Position - physiology; Supine Position - physiology; TMS; Vertebrates: nervous system and sense organs; Wrist - innervation; Wrist - physiology; Mirror neuron; Motor resonance; Excitability modulation; H-reflex; Motor systems and sensimotor integration; TMS; Motor-evoked potential; Human; Electrophysiology; Excitability; H-Reflex; Hand; Neuron; Cyclic; Body movement; Electromyography; Motor evoked potential
• ISSN: 0006-8993; 1872-6240
• DOI: 10.1016/j.brainres.2005.10.034

The observation of a sinusoidal flexion–extension of the wrist was utilized to determine the continuous time course and phase relation between observed movement and its effects on the observer's motor pathways. While observing movements performed by others, the observers' cortical motor areas and spinal circuits were activated, reflecting the specific temporal and muscular pattern of the actual movement (motor resonance). H-reflexes and motor-evoked potentials (MEPs) were elicited, respectively, by electrical stimulation of the median nerve and magnetic stimulation of the appropriate cortical area, in the right forearm muscle Flexor Carpi Radialis (FCR) of subjects who were observing a 1-Hz cyclic oscillation of the right prone hand executed by a different person. Observation elicited a parallel cyclic excitability modulation of the observer's H-reflex and MEP responses with identical period as the observed movement. Modulation was phase advanced, as is muscle activation with respect to the real movement. The same results were obtained when the observed hand oscillation was executed with different frequency (1.6 Hz) and when the hands of mover and observer were supine. No motor resonance was elicited by observing the oscillation of a metal platform. The excitability modulation of MEPs simultaneously monitored in both antagonists of the observer's forearm (FCR and Extensor Carpi Radialis, ECR) was in almost perfect phase opposition, reflecting their natural reciprocal activation during the execution of a hand oscillation. These findings suggest that during observation, motor pathways are modulated subliminally reproducing with high temporal fidelity the motor commands needed to execute the observed movement.