θάλαμος

Greek thalamos meant the innermost room of a house — specifically the bedroom, the chamber farthest from the public rooms, the space of greatest privacy and intimacy. In Homer, the thalamos is where Penelope keeps Odysseus's secret bow; where lovers meet; where precious things are stored. It was the innermost, most protected space.

Ancient anatomists naming the structures of the brain reached for the word thalamos because the thalamic region sits deep inside the brain, protected by layers of tissue, enclosed in the center of the cerebral hemispheres. Like the bedroom of a Greek house, the thalamus is as far from the surface as it is possible to be.

The thalamus is the brain's relay station — a walnut-sized mass of gray matter that processes nearly all sensory information (except smell) before passing it to the cerebral cortex. Every sight, sound, touch, and taste passes through the thalamus on its way to conscious awareness. The ancient metaphor of the inner chamber is anatomically apt: everything enters through the outer rooms first.

Galen named the thalamus in the 2nd century CE, and the Greek word has been in anatomical use ever since. The thalamus is also involved in sleep regulation, alertness, and consciousness — which makes the bedroom metaphor accidentally profound. The structure named for a bedroom governs sleep.