On Thursday, First Lady Michelle Obama implied that Donald Trump has the brain of a tween without mentioning his name once. Speaking at a Philadelphia rally, she reminded voters that the United States needs a president with a steady temperament or, as she phrased it, an “adult in the White House.”

But what does that actually mean?

There are implied meanings and technical meanings. Michelle Obama was likely suggesting that Trump lacks impulse control. Would someone with a mature brain encourage Russia to hack Hillary Clinton’s emails? Or tweet that global warming is a Chinese hoax? Presumably not. She was, in short, talking about restraint.

But she was also talking about the human prefrontal cortex and the neurological networks that allow humans to think critically. Though the brain finishes growing in size by age 10, it undergoes a series of gene and experience driven modifications during adolescence. These changes happen in the brain’s frontal lobes, which consists of gray matter made up of neuron cell bodies and nerve fibers, and increase in size while the number of synaptic connections between nerve cells skyrockets. As these changes settle, an adult brain emerges — one that has learned to control impulses. But all that churning during adolescent developments leaves immature cognitive control centers vulnerable for emotional impulses to break through and influence behavior. Researchers say that immature front lobes aren’t entirely to blame for the risk-taking behavior of teens (children have immature frontal lobes too and they demonstrate way less risky behavior). Still, their immature frontal lobes make teens more vulnerable to impulses. We know that even if we don’t know for sure exactly how this behavior emerges.

Trump has made his good health — he’s chunky but stable — a focus of his campaign while attempting to diagnose Clinton with various maladies. Perhaps the Democrats have finally settled on a medical talking point of their own: underdeveloped frontal lobes.

Photos via Getty Images / Spencer Platt, Giphy