As a culture, we have reached — and exceeded — peak pumpkin spice . We're tired of hearing about pumpkin spice lattes and tired of reading thinky-thought pieces about them. But there's one thing no one seems to be tiring of: actually drinking the darn things. At first, we were happy to blame our addiction on the Spirit of Fall imbuing our entire selves, but, in fact, there's actual science behind our love of these Starbucks-branded cups of hot squash. Finally, we're getting some answers!As even the most amateur PSL enthusiast knows, real pumpkin has finally been added to the PSL's list of ingredients — but an infographic designed by the Institute of Food Technologists (IFT) for Business Insider reveals that there isn't enough pumpkin puree to change the drink's nutritional value at all. In fact, only about 10% of the ingredients in the pumpkin-spice flavoring are natural spices. The remaining 90% is — you guessed it — a blend of synthetic (and sneaky) chemicals.Concocted to mimic the taste of cinnamon, nutmeg, and other autumnal spices, these chemicals trick our brains into thinking we're tasting the real thing. IFT food scientist Kantha Shelke, PhD, explains that pumpkin spice's flavor profile needs only five to 10% natural ingredients for our brains to be able to "fill in the blanks" and associate what we're tasting with the flavors of pumpkin pie. So even though we may understand that we're ordering a piping-hot chemical cocktail, our brains would like to connect those flavors with something real from our memories anyway.Also, remember that pumpkin puree we were so psyched about just a few months ago? It's not exactly a vegetable: The puree is a blend of pumpkin, condensed milk, and sugar. The latter ingredient is likely one reason why we keep coming back to the PSL, season after season; sugar activates the pleasure centers of brains even more than fat does, and it's been found to (temporarily) manage stress in the same way that alcohol can.So that's your brain on pumpkin spice. We never said it'd be pretty. In fact, we're suddenly looking forward to peppermint-mocha season.Click over to Business Insider for the full infographic and more about how pumpkin spice gets into our heads.