title: Overactive visuomotor connections underlie the photoparoxysmal response. A TMS study.
abstract: OBJECTIVE
  The photoparoxysmal response (PPR) involves rapid spread of epileptic activity from visual to parietal and frontal areas. We used a transcranial magnetic stimulation (TMS) technique to assess the physiologic connections between primary visual (V1) and motor (M1) areas in patients with idiopathic generalized epilepsy (IGE). We hypothesized that in PPR-positive patients, M1 would respond excessively to inputs from V1.
  
  
  METHODS
  Eleven photosensitive patients with IGE who had a PPR at the time of the study were compared with 10 similar patients without a PPR, and with 11 healthy subjects of similar age and sex. The connection between V1 and M1 was assessed in resting participants by delivering a conditioning stimulus (CS) over the phosphene hotspot of the visual cortex (intensity 90% phosphene threshold, PT) followed at random interstimulus intervals (ISIs; 15, 18, 21, 24, 27, 30, 35 and 40 msec) by a test stimulus (TS) over the left motor cortex to elicit a motor evoked potential (MEP) of ~1 mV from the right first dorsal interosseous muscle.
  
  
  RESULTS
  In healthy subjects, a CS over V1 suppressed M1 at ISIs between 18 and 40 msec. Similar effects occurred in IGE patients without a PPR. This was not true in PPR-positive IGE patients, in whom this type of physiologic inhibition was significantly (p < 0.05) reduced.
  
  
  CONCLUSIONS
  IGE patients with a PPR have an overactive functional response of M1 to inputs traveling from V1. This may represent one core factor for the anterior spread of the PPR itself and for the origin of the abnormal epileptic motor phenomenon, such as myoclonus.
authors.affiliation: Department of Translational Medicine, Section of Neurology, University of Piemonte Orientale, Novara, Italy.
authors.forename: Gionata
authors.identifier: http://orcid.org/0000-0003-4115-3874
authors.initials: G
authors.lastname: Strigaro
authors.affiliation: Department of Translational Medicine, Section of Neurology, University of Piemonte Orientale, Novara, Italy.
authors.forename: Lina
authors.initials: L
authors.lastname: Falletta
authors.affiliation: Department of Translational Medicine, Section of Neurology, University of Piemonte Orientale, Novara, Italy.
authors.forename: Claudia
authors.initials: C
authors.lastname: Varrasi
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, University College London Institute of Neurology, London, United Kingdom.
authors.forename: John C
authors.initials: JC
authors.lastname: Rothwell
authors.affiliation: Department of Translational Medicine, Section of Neurology, University of Piemonte Orientale, Novara, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Cantello
mesh_terms: D000328:Adult; D000368:Aged; D004831:Epilepsies, Myoclonic / Q000175:diagnosis* / Q000503:physiopathology*; D004829:Epilepsy, Generalized / Q000175:diagnosis / Q000503:physiopathology; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000503:physiopathology*; D009434:Neural Pathways / Q000503:physiopathology; D010775:Photic Stimulation / Q000379:methods*; D010787:Photosensitivity Disorders / Q000175:diagnosis* / Q000503:physiopathology*; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D014793:Visual Cortex / Q000503:physiopathology*; D055815:Young Adult
keywords: Functional connectivity; Generalized epilepsy; Motor cortex; Photoparoxysmal response; Transcranial magnetic stimulation; Visual cortex