Event:

Cortical circuit development can be impacted by both environmental and genetic factors and both have been postulated as causes for neurodevelopmental disorders. However, our current understanding of the development of neuronal circuits is incomplete and insufficient to explain how neurodevelopmental disorders arise. This is in part because neuronal circuit development begins in the embryo, and until recently, it was not possible to visualize details of neuronal circuit formation during embryonic brain development in vivo. Here, we developed a method with sufficient mechanical stability to perform both two-photon imaging from individual neurites and two-photon targeted patch clamp recordings, in healthy living mouse embryos connected to the dam, to investigate circuit development of cortical pyramidal neurons. We found that embryonic cortical pyramidal neurons form two distinct active circuit motifs during embryonic development that switch after embryonic day 15.5. The first motif constitutes a new multi-layered circuit motif at the inception of the neocortex. Further, the perturbation of autism-associated genes interferes with the switch.