Scientists map brain-wide signals that spark emotions

What Happened

Scientists led by Karl Deisseroth at Stanford University reported the first brain‑wide map of activity patterns that generate emotions, publishing the findings in Science. The team used an eye‑puff assay where a tonometer delivered 60 ms puffs of air to the left eye at intervals of 3‑8 seconds for a five‑minute session. Healthy volunteers and a separate group of epileptic in‑patients with implanted brain electrodes both described the sensation as "unpleasant" and "annoying".

Findings

Each puff triggered an immediate burst of neural firing that spread across the brain, followed by a slower, lingering signal that persisted after the stimulus ended. The fast phase lit up the thalamus and periaqueductal grey; the slower phase activated limbic regions and the frontal cortex. When participants were given a low dose of ketamine—an FDA‑approved anaesthetic that also works as an antidepressant—the initial burst and reflexive blinking stayed the same, but the lingering signal faded much faster. Volunteers then called the feeling a "tickling of the eyeball" and stopped blinking between puffs, keeping their eyes open. In mice subjected to the same assay, ketamine produced identical changes, affecting only neurons that drove the second, slower phase.

Context

The study shows that emotions are built on a two‑stage brain response: a rapid sensory alert followed by a prolonged emotional wave. The thalamus acts as a bridge, relaying the first alert and helping hand off signals to higher‑order areas. Understanding how the timing of these signals shapes feeling could help design treatments for mood disorders that target specific brain phases.