Dear Science,

Why does the mere thought of sour foods make one's mouth fill with saliva? What are the connections between memory and our sense of taste?

Pucker Up, Buttercup

What you're describing—the memory of a previous experience inducing a physiological response to match that past experience—is precisely what Pavlov found when he rang a bell every time he fed his dogs. Soon, the dogs would start to salivate to the sounds of bells alone. For most of us, the thought of a Sour Patch Kid is no different.

Why does this happen? Homeostasis, Buttercup. Science completed a little experiment—to confirm his own conditioning—the morning after receiving your letter. Normal blood-sugar levels should range from no less than 60 mg/dL to no more than about 130 mg/dL. Upon waking up, Science's fasting blood sugar was a delightfully normal 68 mg/dL. Then Science took out his cereal bowl and filled it (as is the pattern each morning). Spoon in hand, but before one bite, the blood-sugar measurement was repeated: 43 mg/dL. The mere vision of the morning routine, the mind and body's anticipation of a load of sugar from breakfast cereal, was enough to drop the blood-sugar in preparation.

This ability to connect experiences on a conscious level—like a memory of a sour candy or putting together breakfast—to a deep, almost mechanical, response in the basic mechanisms of the body helps keep our insides within the narrow limits we need to live.

Let's stick with sugar, to understand this better. The middle of the normal range we should live in—about 100 mg/dL—works out to about five grams of sugar in all of our blood (five liters or so). Five grams is the same as a single packet of sugar. A can of soda, a bowl of cereal, a slice of cake, and a doughnut all contain tens of times this amount of sugar. Despite this challenge—this need to rapidly clear sugar from our blood to make room for the massive loads of it we're dumping in by eating—most of us manage to keep our sugar levels within these narrow limits even during the most vigorous of meals. These connections between our minds and our viscera make it possible. I sit to eat breakfast and my pancreas starts releasing insulin, my muscle cells start drawing sugar from my blood, and my mouth starts to water even before the first spoonful hits my lips.

For fun, take a moment to think how drinking a diet soda musses this all up. The insulin still releases, the sugar leaves the blood, but no sugar comes from the food. This is why some of us get so damn hungry after chowing down on diet soda. Our fake food fusses our flexible physiology.

Feeding Forwardly Yours,

Science

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