O-20 Epileptiform and non-epileptiform EEG abnormalities in Autism Spectrum Disorder relate to opposite excitation-inhibition balance disturbances

Background Autism spectrum disorder (ASD) has been associated to balance alterations between neuronal excitation and inhibition (E/I). Part of this association is built upon the frequent concurrence of ASD with epilepsy and epileptiform abnormalities. Non-epileptiform EEG abnormalities are also frequent, yet their clinical relevance remains unclear. We hypothesize that subjects with EEG abnormalities – epileptiform and non-epileptiform – represent different physiological subgroups within the autism spectrum and have different effects on E/I balance. Using a novel algorithm involving critical-state dynamics we show that fluctuations in neuronal oscillations can be used to estimate E/I balance of neuronal networks. Here, we use this method to test the relationship between epileptiform and non-epileptiform abnormalities and E/I balance disturbance in ASD. Methods We investigated 64-channel EEG recordings of 100 unmedicated children with ASD and 29 typically developing children (age range 7–15 years). We assessed for EEG abnormalities according to Luders and Noachtar’s atlas and classification of electroencephalography and estimated the E/I ratio based on alpha oscillations. Results ASD subjects with EEG abnormalities (ASDabn, 46%) had lower E/I ratios than the group without abnormalities ( p  = 0.00035). From the ASDabn group, subjects with slowing of activity showed the lowest global E/I ratios ( p  = 0.0001), while epileptiform abnormalities were related to localized high E/I ( p  = 0.0063). Conclusions Epileptiform and non-epileptiform EEG abnormalities showed opposite excitation-inhibition balance disturbances identifying two subgroups within ASD – one with global increase of inhibition and one with locally increased excitation. This neurophysiological distinction may be determinant for targeting future treatment decisions.