Precursor cells develop into neurons in the brain’s medial amygdala, which is involved in emotion, motivation and memory, and also helps to program reproductive and aggressive behaviors into the brain’s circuitry. Researchers at Children’s National Health System, centered in Washington, D.C., carried out tests involving three instinctual male and female behaviors – aggression, mating and avoiding predator odor. In one test of males, researchers gauged territorial aggression by placing an intruder into the cage. One test of females removed offspring from a nursing female followed by either introducing or not introducing a male intruder into the cage. Their research showed that events occuring when the fetal brain is developing may program instinctual behaviors such as avoiding predators, mating and protecting their territory. Two precursor cell types were involved. One, a protein known as Dbx1, expresses a developmentally regulated transcription factor. The other cell type expresses Foxp2, a transcription factor previously identified in humans as required for appropriate production of speech. When cells derived from these distinct cell subpopulations were activated during certain encounters, they showed differing patterns of activation in male, versus female brains. These experiments helped the research team to indentify specific neurons of interest in understanding how the brain regulates behavior.