eLife assessment
This valuable study combines electrophysiology and neuroanatomy with pharmacological and optogenetic manipulation in the Drosophila genetic model system to pinpoint the neural substrate that is influenced by altered activity during a critical period (CP) of larval locomotor circuit development. Increasing activity during the CP causes permanent network changes, manifesting in increased recovery times from seizures and altered intersegmental coordination during locomotion, thus indicating that a setpoint of network excitability is determined during the CP. Next, compelling experiments demonstrate that this goes along with increased excitation/inhibition ratios to single identified motoneurons and most importantly, for excitability setpoint determination during the CP excitatory and inhibitory inputs are integrated such that the effect of CP hyperexcitation is rescued by the stimulation of endogenous inhibitory inputs to the motoneurons. This provides novel insight into how developing neural network excitability is tuned and how it can be entrained during the CP.