Photosensitive epilepsy: spectral and coherence analyses of EEG using 14Hz intermittent photic stimulation.
OBJECTIVE
To evaluate the EEG recorded in photosensitive idiopathic generalised epilepsy (IGE) patients at rest and during 14Hz IPS, frequency capable of inducing photoparoxysmal responses (PPRs).


METHODS
Power spectrum density and coherence profiles were estimated using a block autoregressive parametric model (AR) in 28 patients and 22 controls.


RESULTS
At rest, the intra- and inter-hemispheric coherence spectra showed a significantly larger number of coherence peaks in the gamma band in patients with respect to controls. During intermittent photic stimulation (IPS), coherent gamma activity is mainly presented as IPS frequency harmonics; moreover, the patients' mean coherence values significantly increased. In six patients re-evaluated with IPS after putting on glasses with Z1 blue lens (which counteracts PPR) the spectral and coherence profiles tended to return to the resting ones.


CONCLUSIONS
Patients are endowed with inherited EEG hyper-synchrony as shown by the large number of coherence peaks detectable under resting conditions, whereas IPS enhances intra- and inter-hemispheric mean coherence values in the gamma band. The persistence of alpha activity peaks during IPS in most controls but not in patients suggests that the alpha generating network plays a significant role in counteracting PPR.


CONCLUSIONS
Both gamma and alpha EEG generators are involved in the PPR generation and in the widespread synchronisation characterising the IGE-associated photosensitivity.
Visani
E
E
Unit of Neurophysiopathology - Epilepsy Centre, Fondazione IRCCS Istituto Neurologico Carlo Besta, Via Celoria 11, Milano, Italy.
Varotto
G
G
Binelli
S
S
Fratello
L
L
Franceschetti
S
S
Avanzini
G
G
Panzica
F
F
D000293:Adolescent; D000328:Adult; D000513:Alpha Rhythm; D001683:Biological Clocks / Q000502:physiology / Q000528:radiation effects; D001931:Brain Mapping / Q000379:methods*; D002540:Cerebral Cortex / Q000503:physiopathology; D003198:Computer Simulation; D004569:Electroencephalography / Q000379:methods*; D020195:Epilepsy, Reflex / Q000175:diagnosis* / Q000503:physiopathology*; D005071:Evoked Potentials / Q000502:physiology* / Q000528:radiation effects; D005260:Female; D006801:Humans; D008297:Male; D010775:Photic Stimulation / Q000009:adverse effects / Q000379:methods*; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D014795:Visual Pathways / Q000503:physiopathology / Q000528:radiation effects; D055815:Young Adult