Daily oscillation of the excitation/inhibition ratio is disrupted in two mouse models of autism

Autism spectrum disorder (ASD) is a prevalent neurodevelopmental disorder involving sensory processing abnormalities. Alterations to the balance between excitation and inhibition (E/I ratio) are postulated to underlie behavioral phenotypes in ASD patients and mouse models. However, in primary visual cortex (V1) of wild type mice, the E/I ratio is not a fixed value, but rather oscillates across the 24h day. Therefore, we hypothesized that the E/I oscillation, rather than the overall E/I ratio, may be disrupted in ASD mouse models. To this end, we measured the E/I ratio in Fmr1 KO and BTBR mice, models of syndromic and idiopathic ASD, respectively. We found that the E/I ratio is dysregulated in both models, but in different ways: the oscillation is flattened in Fmr1 KO and phase-shifted in BTBR mice. These phenotypes cannot be explained by altered sleep timing, which was largely normal in both lines. Furthermore, we found that E/I dysregulation occurs due to alterations in both excitatory and inhibitory synaptic transmission in both models. These findings provide a crucial perspective on the E/I ratio in ASD, suggesting that ASD phenotypes may be produced by a mismatch of E/I to the appropriate behavioral state, rather than alterations to overall E/I levels per se.