Amerika

Giulio Tononi, a University of Wisconsin neuroscientist, suggests that the secret of anesthesia may not in fact lie in any single clump of neurons. It may lie instead in the conversations that take place between many clumps in the brain. Normally information from our senses races from one region of the cortex to another, getting processed in different ways in each place. Some regions help us recognize faces in a scene, for example, while other regions help us figure out what emotions those faces are expressing. The sensory signals travel through a mass transit system made up of long branches of neurons that crisscross the brain. This system has a few hubs through which many connections pass. One is the thalamus, but certain parts of the cortex also serve as hubs.

Although the brain may become less active under anesthesia, it usually doesn’t shut down completely (if it did, we would die). In fact, when scientists played a tone into the ears of an anesthetized cat, its cortex still produced strong bursts of electricity. But its responses were different from those of a waking cat. In an anesthetized cat, the brain responds the same way to any sound, with a noisy crackle of neurons. In a waking cat, the response is complex: One brain region after another responds as the animal processes the sound, and different sounds produce different responses. It’s as if the waking brain produces a unique melody, whereas the anesthetized brain can produce only a blast of sound or no sound at all.

Tononi suggests that this change happens because anesthesia interferes with the brain’s mass transit system. Individual parts of the cortex can still respond to a stimulus. But the brain can’t move these signals around to other parts to create a single unified experience.

Discover

Our scientists always start looking for a singular locus of anything.

A race gene. A consciousness center. A regulatory organ.

What they’re finding instead is that our most fascinating properties are emergent, not discrete.

There is no race gene; race arises from a compilation of genes, acting like computer code.

There is no consciousness center; consciousness arises from the interaction of parts of the brain.

There is no single regulatory organ; many organs work together like a drum circle, making other systems work at the right time.

The problem is in our heads. We look for the discrete, but our world doesn’t work that way.