Speaking, singing, coughing, laughing, yelling, yawning, chewing-;we use our jaws for many purposes. Each action requires a complex coordination of muscles whose activity is managed by neurons in the brain. But it turns out that the neural circuit behind the jaw movement most essential to survival-;eating-;is surprisingly simple, as researchers from Rockefeller University recently described in a new paper in Nature .
Christin Kosse and other scientists from the Laboratory of Molecular Genetics, headed by Jeffrey M. Friedman, have identified a three-neuron circuit that connects a hunger-signaling hormone to the jaw movements of chewing. The intermediary between these two is a cluster of neurons in a specific area of the hypothalamus that, when damaged, has long been known to cause obesity.
Strikingly, inhibiting these so-called BDNF neurons not only leads animals to consume more food but also triggers the jaw to make chewing motions even in the absence of food or other sensory input that would indicate it was time to eat. And stimulating them reduces food intake and puts a halt to the chewing motions, acting as an effective curb against hunger. The simple architecture of this circuit suggests that the impulse to eat may be more similar to a reflex than was previously considered-;and may provide a new clue about how the initiation of feeding is controlled.
"It's surprising that these neurons are so keyed to motor control," says study first author Christin Kosse, a research asso.