Résumé : Using electroencephalography (EEG) in combination with functional magnetic resonance imaging (fMRI), we studied a 9.5-year-old girl who developed cognitive and behavioral regression in association with intense interictal bilaterally synchronous epileptic discharges (IBSEDs) both during the awake state and during sleep. During runs of IBSEDs, EEG-fMRI demonstrated deactivations in the lateral and medial frontoparietal cortices, posterior cingulate gyrus, and cerebellum together with focal relative activations in the right frontal, parietal, and temporal cortices. The deactivations probably reflect the repercussion of the interictal epileptic activity on normal brain function which might cause the neuropsychological regression by inducing repetitive interruptions of neurophysiological function resulting in a chronic state of specific psychomotor impairment. The relative activations could possibly indicate the source of epileptic activity rapidly spreading to other brain regions.