Cortical activity emerges in region-specific patterns during early brain development.

The development of neural circuits in the brain is initiated by molecular signals and then sculpted by neural activity. In the rodent cerebral cortex patchwork and wave patterns of activity develop in somatosensory and visual regions, respectively, and are present at birth. However, whether such activity patterns occur in non-eutherian mammals, as well as when and how they arise during development remain open questions relevant to understand brain formation in health and disease. Since the onset of patterned cortical activity likely occurs prenatally in eutherians, here we offer a new approach to study these questions in a minimally invasive manner using marsupial dunnarts, whose cortex form postnatally. We discovered similar patchwork and travelling waves in the dunnart cortex at stage 27 (equivalent to newborn mice), and examined progressively earlier stages of development to determine their onset and how they first emerge. We observed that these patterns of neural activity emerge in a region-specific and sequential manner, becoming evident as early as stage 24 in somatosensory and stage 25 in visual cortices (equivalent to embryonic day 16 and 17, respectively, in mice) as upper neuron layers establish and thalamic axons innervate the cortex. In addition to sculpting synaptic connections of existing circuits, patterned activity could therefore help regulate early events in cortical development.