Abstracts

Rationale: We investigated the source generators of inter-ictal and ictal discharges, at different frequency bandwidths (1-200Hz) in patients with absence epilepsy using magnetoencephalography (MEG).  Methods: Twenty patients (M: F=10:10; age: 10.11±3.6 years; duration of illness: 2.52±1.56 years), with childhood (n=12) and juvenile (n=8) absence epilepsies underwent MEG recording. Continuous generalized spike-wave discharges (GSWD) lasting for >5s, was regarded as ‘electrographic seizures’ and GSWD of 1-30Hz (C), 30-80Hz (G) and 80-200Hz (R), for every subject. Early 300ms of each interictal and ictal GSWD were concatenated independently and subjected to source localization over a cortical grid using adaptive spatial filtering method. Subsequently, at each frequency band, group statistics was computed with t-test, corrected for multiple comparisons using cluster permutation approach (n=500 iterations; p Results: A total of 3988 (212.37±34.82) independent inter-ictal GSWD (Iic) and 123 (5.72±1.3) electrographic seizures (Ic) were recorded in 20 patients. Further, only 932Iic and 49Ic discharges were source reconstructed. The cortical regions localized during both inter-ictal and ictal period were comparable at all 3 frequency bands (C, G and R): superior, middle and inferior frontal gyri; frontal operculum; supplementary motor area; somatosensory cortex; angular gyrus; inferior parietal lobule and precuneus/ cuneus; middle temporal gyrus; calcarine/middle occipital cortices and anterior cingulate gyrus. There were no statistical differences in the source localization regions between C &G or G&R or C&R frequency bands or between the Ic or Iic states (p>0.05). However, there were variations in the generators between the Ic or Iic discharges and the 3 frequency bands.  Conclusions: In absence seizures manifesting with 3 Hz generalized discharges, the cortical regions recognized at 3 frequency bands suggested multiple focal brain regions and involved the dorsal attention network, sensori-motor network and prefrontal network. These observations suggest that loss of awareness in absence seizures might be related to disruption of these specific network nodes. These findings were noted regardless of the frequency (1-200Hz) indicating the existence of under modulation or exhaustion of intrinsic neuronal firing.  Funding: NIL