The convoluted path leading to neuronal circuit formation.

A limiting step of neuronal circuit formation is the extensive migration of interneurons from their birthplace to populate territories formed by excitatory neurons. Interneuron dynamics in the developing brain culminates with the organization of interneuron subtypes in specific configurations within layers of brain tissue. Decoding the logic behind these configurations is still matter of passionate debate. Do interneurons follow a sketched program from the progenitor state or is this organization sculpted from intricate cellular interactions? How do interneurons select interacting partners? How does interneuron diversity emerge? New technologies and access to brain tissue from different species are allowing us to reconstruct stone by stone, the convoluted path leading to the formation of neuronal cell assemblies made of excitatory and inhibitory neurons. The most recent research highlights that interneuron subtype circuit integration needs to be assessed case by case. Here, I highlight the need to keep delving into the complexities of interneuron interaction with their environment during development to accomplish this Herculean task.