Squishy, wrinkled, weighing about as much as a cantaloupe, the brain may not be much to look at from the outside. Yet with a network of roughly 86 billion neurons, it generates more impulses daily than all the smartphones on the planet combined.

Scientists can track all that activity with scans. But what does a well-balanced brain actually look like?

Spoiler alert: New research says there’s no universal signature of mental health—or illness.