The Photoparoxysmal Response Reflects Abnormal Early Visuomotor Integration in the Human Motor Cortex

• Main Authors: A. Suppa, L. Rocchi, P. Li Voti, O. Papazachariadis, S. Casciato, C. Di Bonaventura, A.T. Giallonardo, A. Berardelli
• Format: Article
• Language: English
• Published: Elsevier 2015-11-01
• Series: Brain Stimulation
• Subjects: Photoparoxysmal response; Epilepsy; Visuomotor integration; Primary motor cortex; Paired associative stimulation
• Online Access: http://www.sciencedirect.com/science/article/pii/S1935861X15009687

Background: Visual-paired associative stimulation (V-PAS) is a transcranial magnetic stimulation (TMS) technique able to investigate long-term potentiation (LTP) and depression (LTD)-like plasticity in the primary motor cortex (M1) arising through early visuomotor integration. Objective/hypothesis: Abnormal early visuomotor integration might contribute to the pathophysiology of intermittent photic stimulation (IPS)-induced photoparoxysmal response (PPR). Methods: We applied V-PAS in 25 healthy subjects (HS), 25 PPR-positive patients, with and without idiopathic generalized epilepsy (IGE), and 8 PPR-negative patients with IGE. V-PAS consisted of primary visual area activation achieved by visual evoked potentials coupled with TMS-induced M1 activation at 100 ms interstimulus interval (ISI) (V-PAS100). Before and after V-PAS, we measured changes in motor evoked potentials (MEPs). We compared MEPs after 1 Hz repetitive TMS (rTMS) and 0.25 Hz-V-PAS100. To examine possible V-PAS-induced after-effects at other ISIs, we delivered V-PAS at 40 (V-PAS40) and 140 ms ISIs (V-PAS140). To clarify whether V-PAS100 increases parieto-/premotor-to-M1 connectivity, before and after V-PAS100, we examined MEPs evoked by paired-pulse techniques. Results: V-PAS100 increased MEPs more in PPR-positive patients than in HS. PPR-negative patients had normal response to V-PAS100. 1 Hz-rTMS, 0.25 Hz-V-PAS100 and V-PAS40 elicited similar responses in HS and PPR-positive patients, whereas V-PAS140 induced stronger after-effects in PPR-positive patients than HS. After V-PAS, MEPs elicited by facilitatory paired-pulse protocols decreased similarly in HS and PPR-positive patients. Conversely, MEPs elicited by inhibitory protocols decreased in HS, whereas in PPR-positive patients, they turned from inhibition to facilitation. Conclusion: We suggest that abnormal early visuomotor integration contributes to the pathophysiology of PPR.