Your Brain: The Missing Manual

The Secret Gears of Appetite

You've now learned what the brain does with your dinner. However, you haven't considered how it gets what it wants—in other words, what neurological process underpins the hunger pangs that can drive you out of bed for a midnight snack or cripple your resolve when strolling past the vending machine.

In truth, the full appetite story is still shrouded in mystery. This isn't because the human appetite is a particularly strange phenomenon, but because there are many overlapping influences that come into play. At any given moment, your desire to eat (or ignore) food is shaped by the time of day, the current fullness of your stomach, your emotional state, and the amount of fat, sugar, and protein that's circulating in your body.

Although even the sharpest brain scientist can't discern the appetite's exact equation, we do know the brain center that evaluates these factors and triggers your hunger. It's the hypothalamus, the ancient control center that sits at the top of the brain stem. (You first met the hypothalamus in Chapter 1, where you learned how it controls the pituitary gland, the brain's 24-hour pharmacy shop.) In studies with unfortunate rats, scientists discovered that damage to one section of the hypothalamus causes rats to lose their appetite and willingly starve. Damage to another section causes rats to eat insatiably and balloon up to three times their normal size.

Figure 2-4. 

The appetite-controlling system of the hypothalamus is surprisingly complex. ...