HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: iovs.07-1462v1 50/3/1470    most recent Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Shepherd, A. J. Articles by Siniatchkin, M. Search for Related Content PubMed PubMed Citation Articles by Shepherd, A. J. Articles by Siniatchkin, M.

Visual Pattern Adaptation in Subjects with Photoparoxysmal EEG Response: Evidence for Increased Visual Cortical Excitability

¹From the School of Psychology, Birkbeck College, University of London, London, United Kingdom; and the ²Neuropediatric Department, Christian-Albrechts-University, Kiel, Germany.

PURPOSE. Photosensitivity, or photoparoxysmal response (PPR), is an abnormal EEG reaction to intermittent photic stimulation (IPS), consisting of spikes, spike-waves, and intermittent slow waves. Depending on the spread of the abnormal activity, PPR subgroups have been defined as having either propagating PPR or localized, occipital spikes (OS) only. Recent research suggests an enhanced excitability in the occipital cortex may underlie this reaction during IPS, but it remains unclear whether changes in excitability affect the function of the occipital cortex to other, less provocative visual stimuli. In this study, cortical function in photosensitivity was assessed using two visual aftereffects that occur after prolonged adaptation.

METHODS. Motion and tilt aftereffects were compared in healthy subjects with (n = 14, seven with propagating PPR, seven with OS) or without (n = 14) PPR.

RESULTS. The duration of the motion aftereffect was shorter in the PPR group than in the control group. The size of the tilt aftereffect did not differ between the groups. Thirteen from each group had participated in an earlier study in which occipital transcranial magnetic stimulation (TMS) was used to elicit phosphenes and to suppress the perception of briefly presented letters. The TMS intensity required to elicit phosphenes correlated with the size of the tilt aftereffect (TAE) in the PPR group only.

CONCLUSIONS. This study provides further evidence of enhanced cortical excitability in subjects with photosensitivity, which is likely to reflect changes in excitatory neurotransmission.