Rett syndrome (RTT) is a neurodevelopmental disorder primarily caused by mutations in the X chromosome-linked gene Methyl-CpG Binding Protein 2 (MECP2). Restoring MeCP2 expression after disease onset in a mouse model of RTT reverses phenotypes, providing hope for development of treatments for RTT. Translatable biomarkers of improvement and treatment responses have the potential to accelerate both preclinical and clinical evaluation of targeted therapies in RTT. Studies in people with and mouse models of RTT have identified neurophysiological features, such as auditory event-related potentials, that correlate with disease severity, suggesting that they could be useful as biomarkers of disease improvement or early treatment response. We recently demonstrated that treatment of RTT mice with a positive allosteric modulator (PAM) of muscarinic acetylcholine subtype 1 receptor (M