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    Excitatory and inhibitory mechanisms of photosensitivity

    Siniatchkin, M. and Groppa, S. and Jerosch, B. and Muhle, H. and Shepherd, Alex J. and Stephani, U. and Siebner, H. (2006) Excitatory and inhibitory mechanisms of photosensitivity. In: 7th European Congress on Epileptology, 2006, Helsinki, Finland. (Unpublished)

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    Purpose: Photosensitivity or photoparoxysmal response (PPR) is a highly heritable electroencephalographic trait characterised by an abnormal EEG reaction to intermittent photic stimulation (IPS), consisting of spikes, spike‐waves, and intermittent slow waves. The knowledge concerning the pathophysiology of human photosensitivity is still limited. Method: Threshold of phosphenes induced by a paired‐pulse transcranial magnetic stimulation (TMS, Magstim 200), stimulus‐response curves for phosphenes, suppression of visual perception by a single‐pulse TMS (40–180 stimulus onset asynchrony, 75% of stimulator output, perception of letter trigrams), visual evoked potentials (2 Hz stimulation rate, 8 c.p.d., N135, habituation paradigm), and duration of the motion aftereffect were studied in healthy subjects with (N = 17, age 25.2 ± 12.2 years) and without (N = 18, age 26.5 ± 7.3 years) PPR. Results: Subjects with PPR propagation were characterised by a lower phosphene threshold than subjects without PPR and with occipital spikes (F(2.32) = 3.73; p = 0.035). Stimulus‐response curves of subjects with PPR propagation were steeper than those of other groups (intensity x group F(9.297) = 4.58; p < 0.001). Amplitudes of VEP were significantly larger in the group with PPR propagation and showed a more pronounced habituation (block of recording x group F(28.406) = 2.01; p = 0.02). The PPR group demonstrated a shorter motion aftereffect (F(1.26) = 5.1; p = 0.03) and (5) a more pronounced visual suppression by a single‐pulse TMS (interaction SOA x group: F(14.224) = 2.34; p = 0.005). Conclusion: This study provides evidence for both increased cortical excitability and intracortical inhibition in the occipital cortex in subjects with PPR propagation. PPR with propagation and with only occipital spikes seem to represent different phenotypic expressions.


    Item Type: Conference or Workshop Item (Paper)
    School: Birkbeck Faculties and Schools > Faculty of Science > School of Psychological Sciences
    Depositing User: Sarah Hall
    Date Deposited: 18 Feb 2020 15:25
    Last Modified: 02 Aug 2023 17:57


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