title: Tonic pain abolishes cortical habituation of visual evoked potentials in healthy subjects.
abstract: We investigated changes in visual cortex excitability by analyzing visual evoked potential (VEP) habituation in healthy subjects during tonic pain evoked by the cold-pressor test (CPT). We tested VEP amplitude habituation (slope of the linear regression line for N1-P1 amplitude from the 1st to 6th block of 100 sweeps) in 19 healthy volunteers during 4 experimental conditions: baseline; no-pain (hand held in warm water, 25 degrees C); pain (hand held in cold water, 2-4 degrees C); and the after-effects of tonic pain. During baseline and no-pain sessions, VEPs habituated normally across the 6 consecutive blocks (mean slope -.28 and -.18%), whereas during pain and its after-effects they failed to decrease (0%, and -.11%). Tonic pain induced by the CPT abolishes normal VEP habituation and the lack of habituation persists after the CPT is stopped. Tonic pain probably abolishes VEP habituation by acting on brainstem neural structures which modulate thalamo-cortical activation thereby changing visual cortex excitability.
  
  
  CONCLUSIONS
  This study shows that tonic pain alters visual cortex excitability, a brain region unrelated to pain processing. These changes probably reflect defensive strategies against pain. Extending the study from healthy volunteers to patients with migraine between attacks would offer the opportunity to investigate visual cortical excitability under conditions when baseline habituation is absent.
authors.affiliation: G.B. Bietti Eye Foundation-IRCCS, Dept of Neurophysiology of Vision and Neurophthalmology, Rome, Italy. gianluca.coppola@gmail.com
authors.forename: Gianluca
authors.initials: G
authors.lastname: Coppola
authors.forename: Mariano
authors.initials: M
authors.lastname: Serrao
authors.forename: Antonio
authors.initials: A
authors.lastname: Currà
authors.forename: Cherubino
authors.initials: C
authors.lastname: Di Lorenzo
authors.forename: Marianthi
authors.initials: M
authors.lastname: Vatrika
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Parisi
authors.forename: Francesco
authors.initials: F
authors.lastname: Pierelli
mesh_terms: D000328:Adult; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006185:Habituation, Psychophysiologic / Q000502:physiology*; D006801:Humans; D008297:Male; D009483:Neuropsychological Tests; D010147:Pain Measurement; D017288:Pain Threshold / Q000502:physiology; D010148:Intractable Pain / Q000150:complications / Q000503:physiopathology* / Q000523:psychology; D010468:Perceptual Disorders / Q000209:etiology / Q000503:physiopathology* / Q000523:psychology; D010775:Photic Stimulation; D010812:Physical Stimulation; D012684:Sensory Thresholds / Q000502:physiology; D013788:Thalamus / Q000503:physiopathology; D014793:Visual Cortex / Q000503:physiopathology*; D055815:Young Adult