Think about it. How many of your ancestors had easy access to tasty munchies that were ready-to-eat, available cheaply in endless variety, and carefully laced with fat, sugar and salt to keep them coming back for more? How many had computers on which they could click to an unending stream of superstimulating erotic videos, featuring real, novel mates, writhing with desire (perceived by a primitive part of the brain as genetic opportunities)—and, when appetite flagged, a cornucopia of ever kinkier videos?

Pornography? It's a new synaptic pathway. You wake up in the morning, open a thumbnail page, and it leads to a Pandora's box of visuals. There have probably been days when I saw 300 vaginas before I got out of bed.—John Mayer, musician

The extreme stimulation of today's enticements can hijack our brains. There's no way John Mayer would view the same vagina 300 times before rising if, say, he only had a porn magazine, or even a woman. Constant novelty-plus-erotica is riveting. His brain releases more dopamine with each new image, even as it shuts down key nerve cell receptors (to drive him to binge). He is tricked into valuing his pussy panorama even above 3-D stimuli.

PLAYBOY: You'd rather jerk off to an ex-girlfriend than meet someone new?

MAYER: Yeah.... Internet pornography has absolutely changed my generation's expectations. How could you be constantly synthesizing an orgasm based on dozens of shots? You're looking for the one ... out of 100 you swear is going to be the one you finish to, and you still don't finish. Twenty seconds ago you thought that photo was the hottest thing you ever saw, but you throw it back and continue your shot hunt and continue to make yourself late for work. How does that not affect the psychology of having a relationship with somebody? It's got to.

This is how food and sex, which throughout evolution have generally contributed to our well-being and led naturally to warm feelings of satiety, morph into drug-like and addictive superstimuli that don't. When we plunge in, we fall for enticements that are not especially valuable, and sometimes risky. Not only can they steal our attention from soothing connections with real people (and nutritional food), they can actually hook us.

Who's at risk for addiction to natural reinforcers?

Most addiction research focuses on substance abuse, not addiction to natural reinforcers. It reveals that only a minority of us ("novelty-seekers" and "impulsives") are genetically susceptible to substance abuse, due to low dopamine receptors in different regions of the brain's reward circuitry. (Dopamine is the "Gotta get it!" neurochemical, and the reward circuitry is the brain pathway that drives all appetites and motivation.)

So, are the rest of us safe from addiction? When it comes to substance abuse, perhaps yes. Yet when it comes to unrestricted access to superstimulating natural reinforcers, the answer may be no, although certainly not everyone gets hooked. The reason hyper-stimulating versions of food and sex can hook us—even if we're not otherwise susceptible to addiction—is that our reward circuitry evolved to drive us toward food and sex, not drugs.

Take food. If you binge on hyper-stimulating foods (say, concentrated fat and refined sugar) it can cause changes that resemble the brain changes seen in substance abusers. This happens in rats, too, and not just in the novelty-seeking, impulsive minority. Nearly all the animals that were offered unrestricted access to goodies like bacon, sausage, cheesecake, pound cake, Ding Dongs and frosting couldn't stop binging and became obese.

Almost immediately, dopamine receptors dropped in their brains, which drove the rats to binge, and ensured they would later experience less stimulation from normal chow. Other changes, such as a numbed pleasure response, worsened over time. Two weeks after scientists returned them to rat chow, the rats' brains still hadn't recovered. In fact, when confronted with a diet of normal chow, they chose to starve for a time rather than eat it. (Full study)

It makes sense for mammals to have a built-in mechanism that can override feelings of satiety. They must "get it while the getting is good": storing calories when fruit is ripe, gorging before hibernation, swallowing a kill before the competition shows up, and so forth.

"Not found in nature"

The binge-to-obesity phenomenon, however, doesn't show up unless mammals, including humans, shift to diets that don't exist in nature: unrestricted starches and sugars.

Although obesity has been increasing among all Americans in recent decades, it has skyrocketed on Indian reservations since the 1960's. The [starchy] commodity and fast food diet is the opposite of what Indians ate until recent generations: ... [In contrast,] high protein and saturated fat food [bison, elk, antelope, deer, with some berries, nuts and roots] seemed to serve the tribe well.

Native Americans aren't the only ones bulging, however. Nearly two-thirds of most Westerners are overweight, and 30+ percent of Americans obese. This is especially telling because, unlike rats, we care about our waistlines, which keeps some of us in check even in the face of severe temptation.

The regions of the brain that change in response to superstimulating food also govern sexual appetite. So, are today's sexual superstimuli, like today's junk food, causing drug-like changes in the brain's reward circuitry? They certainly constitute a sexual diet not found in nature.

So far, no one seems to be able to do the necessary (brain) research. However, the symptoms heavy porn users complain of could logically be explained by the same brain changes observed in rats with unrestricted access to super-goodies. (Incidentally, rats and humans are distant relatives, and share the same primitive brain mechanisms for appetite and addiction.)