Timing and mechanism of a window of spontaneous activity in embryonic mouse hindbrain development

Spontaneous activity (SA) in the developing vertebrate brain is required for correct wiring of circuits and networks. In almost every brain region studied to date, SA is recorded during a period of synaptogenesis, and may deploy ionic mechanism(s) that are not expressed in the adult structure. Eventually the conditions in the immature neurons that allow SA are replaced with ion channels found in the mature neuron; this replacement may itself require SA. In the embryonic (E) 11.5 mouse hindbrain, SA is initiated by a subgroup of serotonergic neurons derived from former rhombomeres 2 and 3; SA events propagate rostrally and caudally along the midline, and into the lateral hindbrain. In this review, I describe the properties of mouse hindbrain SA and the developmental window during which it is expressed, summarize the known mechanisms by which SA arises, and describe other brain regions where this SA is similar (chick hindbrain) or influential (mouse midbrain).