title: Defective interhemispheric inhibition in drug-treated focal epilepsies.
abstract: Focal epilepsies (FEs) arise from a lateralized network, while in generalized epilepsies (GEs) there is a bilateral involvement from the outset. Intuitively, the corpus callosum is the anatomical substrate for interhemispheric spread.
  
  
  
  We used transcranial magnetic stimulation (TMS) to explore whether there are any physiological differences in the corpus callosum of drug-treated patients with FE and those with genetic GE (GGE), compared to healthy subjects (HS).
  
  
  
  TMS was used to measure the interhemispheric inhibition (IHI) from right-to-left primary motor cortex (M1) and viceversa in 16 patients with FE, 17 patients with GGE and 17 HS. A conditioning stimulus (CS) was given to one M1 10 and 50 ms before a test stimulus delivered to the contralateral M1. Motor evoked potentials (MEPs) were analysed both as a function of the side of stimulation and of the epileptic focus (left-right).
  
  
  
  In HS, IHI was reproducible with suppression of MEPs at ISIs of 10 and 50 ms. Similar effects occurred in GGE patients. FE patients behaved differently, since IHI was significantly reduced bilaterally. When FE patients were stratified according to the side of their epileptic focus, the long-ISI IHI (=50 ms) appeared to be defective only when the CS was applied over the "focal" hemisphere.
  
  
  
  FE patients had a defective inhibitory response of contralateral M1 to inputs travelling from the "focal" hemisphere that was residual to the drug action. Whilst IHI changes would not be crucial for the GGE pathophysiology, they may represent one key factor for the contralateral spread of focal discharges, and seizure generalization.
authors.affiliation: Department of Translational Medicine, Section of Neurology, University of Piemonte Orientale, Novara, Italy; CRRF Mons. L. Novarese, Moncrivello, VC, Italy. Electronic address: gionata.strigaro@med.uniupo.it.
authors.forename: Gionata
authors.initials: G
authors.lastname: Strigaro
authors.affiliation: Department of Translational Medicine, Section of Neurology, University of Piemonte Orientale, Novara, Italy.
authors.forename: Erica
authors.initials: E
authors.lastname: Matino
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: Chiara
authors.initials: C
authors.lastname: Pizzamiglio
authors.affiliation: Department of Translational Medicine, Section of Neurology, University of Piemonte Orientale, Novara, Italy.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Tondo
authors.affiliation: Department of Medicine, Melbourne University, Victoria, Australia; Tamayoz Clinic, Cairo, Egypt.
authors.forename: Radwa
authors.initials: R
authors.lastname: Badawy
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; D000927:Anticonvulsants / Q000009:adverse effects / Q000627:therapeutic use; D016022:Case-Control Studies; D003337:Corpus Callosum / Q000503:physiopathology; D004828:Epilepsies, Partial / Q000188:drug therapy / Q000503:physiopathology*; D019054:Evoked Potentials, Motor; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000503:physiopathology; D009433:Neural Inhibition; D011897:Random Allocation; D050781:Transcranial Magnetic Stimulation
chemical_list: D000927:Anticonvulsants
keywords: Focal epilepsy; Functional connectivity; Generalized epilepsy; Motor cortex; Transcranial magnetic stimulation