Deep in the brainstem sits a small but important cluster of neurons known as the locus coeruleus (LC), Latin for "blue place." It makes up a tiny fraction of the brain's cells but plays an important role by releasing the chemical messenger norepinephrine (NE).

Neuroscientists have made a major advance in modeling the human brain in mice, offering a new way to study conditions like cerebral palsy. Ethicists ask if it changes how these mice should be treated.