Emergence of population bursts from simultaneous activation of small subsets of preBötzinger complex inspiratory neurons.

During rhythmic movements, central pattern generators (CPGs) trigger bursts of motor activity with precise timing. However, the number of neurons that must be activated within CPGs to generate motor output is unknown. In the mammalian breathing rhythm, a fundamentally important motor behavior, the preBötzinger Complex (preBötC) produces synchronous population-wide bursts of activity to control inspiratory movements. We probed mechanisms underlying inspiratory burst generation in the preBötC using holographic photolysis of caged glutamate in medullary slices from neonatal mice. With stimulation parameters determined to confine photoactivation to targeted neurons, simultaneous excitation of 4-9 targeted neurons could initiate ectopic, endogenous-like bursts with delays averaging 255 ms, placing a critical and novel boundary condition on the microcircuit underlying respiratory rhythmogenesis.