title: Is motor inhibition during laughter due to emotional or respiratory influences?
abstract: We compared the effects of laughter and several respiratory movements on spinal motor excitability to unravel their respective influences. We measured H-reflexes in 13 healthy volunteers during 10 different tasks (including laughter, simulated laughter, and various respiratory movements). We compared the percentage that remained of the initial H-reflex during each task with that during a neutral task. H-reflex percentage differed between the neutral task (79.4 +/- 16.1%), true laughter (43.7 +/- 17.9%), and simulated laughter (66.6 +/- 24.3%), and between the two latter tasks. Coughing also resulted in H-reflex suppression, but not as deeply as true laughter. During the other respiratory maneuvers, the H-reflex increased compared to the neutral task. Our finding that true laughter evoked more H-reflex depression than simulated laughter suggests that mirth on its own depresses the H-reflex. This mechanism may also be involved in the pathophysiology of cataplexy, the main symptom of narcolepsy.
authors.affiliation: Department of Neurology and Clinical Neurophysiology, Leiden University Medical Centre, Leiden, The Netherlands. S.Overeem@lumc.nl
authors.forename: Sebastiaan
authors.initials: S
authors.lastname: Overeem
authors.forename: Walter
authors.initials: W
authors.lastname: Taal
authors.forename: E
authors.initials: E
authors.lastname: Ocal Gezici
authors.forename: Gert Jan
authors.initials: GJ
authors.lastname: Lammers
authors.forename: J Gert
authors.initials: JG
authors.lastname: Van Dijk
mesh_terms: D000293:Adolescent; D000328:Adult; D004558:Electric Stimulation; D004576:Electromyography; D004644:Emotions / Q000502:physiology*; D005260:Female; D006181:H-Reflex / Q000502:physiology; D006801:Humans; D007845:Laughter / Q000502:physiology*; D008297:Male; D009068:Movement / Q000502:physiology*; D015656:Respiratory Mechanics / Q000502:physiology*