title: Three silent periods in the orbiculari oculi muscles of man: normal findings and some clinical vignettes.
abstract: OBJECTIVE
  To investigate how many true silent periods could be found in the orbiculari oculi muscles of man.
  
  
  METHODS
  10 subjects, clinically healthy (5 male, 5 female), with a mean age of 34 years-old (range: 23 to 48) were evaluated by mean of the blink reflex at resting and during contraction of the orbiculari oculi reflex according to protocols validated internationally.
  
  
  RESULTS
  Three responses called R1, R2 and R3 were obtained in the orbicular oculi muscle at resting state which had latencies and amplitudes within normal limits. What was new was to obtain three silent periods when the subjects were evaluated during muscle contraction. The duration of the first silent period was statistically longer than the second one (p < 0.004) and shorter than the third silent period (p < 0.0001). In addition, this test was found useful in detecting more specific findings in patients with hemifacial spasm and Meigge syndrome.
  
  
  CONCLUSIONS
  This is by the first time that three silent periods in the orbicular oculi muscles are consistently demonstrated. The refractoriness of the alpha motoneurons and the action of gamma-collateral activity seem to be the main conditions leasing to display the first two periods of muscle suppression. The modification of gamma motoneurons firing as well as a pause of muscle spindles in facial muscles due to the action of nociceptive stimuli traveling unmyelinated C fibers of the supraorbital nerve might be the most important mechanisms involved in the production of the third silent period. These results enables further clinical application of this test.
authors.affiliation: Unit of Neurology, Department of Internal Medicine & Basic Sciences, Faculty of Health, UIS-Santander University School of Medicine, Bucaramanga, Colombia, USA. leonf@ninds.nih.gov
authors.forename: F E
authors.initials: FE
authors.lastname: León-Sarmiento
authors.forename: K
authors.initials: K
authors.lastname: Arimura
authors.forename: M
authors.initials: M
authors.lastname: Osame
mesh_terms: D000328:Adult; D001767:Blinking / Q000502:physiology*; D004558:Electric Stimulation; D004576:Electromyography; D005143:Eyelids / Q000503:physiopathology*; D005260:Female; D019569:Hemifacial Spasm / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008538:Meige Syndrome / Q000503:physiopathology*; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D009801:Oculomotor Muscles / Q000503:physiopathology*; D011930:Reaction Time / Q000502:physiology; D012016:Reference Values; D013997:Time Factors