10/24/2012 10:52 am ET Updated Dec 24, 2012

50 Shades of Grey Matter: Your Mind on Smut

I recently awoke aboard a flight from Chicago to San Diego to notice that the young woman on my left was absorbed in an ereader. As soon as she saw me glancing over, she switched it off and slid it anxiously into her seat pocket, hoping perhaps that I didn't have time to see what she was reading.

But I did have time. And I did see what she was reading. It was smut.

This young woman was one of the more than 40 million people who have read the blockbuster erotic book 50 Shades of Grey, with its graphic descriptions of sexual acts and BDSM (that's Bondage, Discipline, Dominance, Submission, Sadism, and Masochism to you, gentle reader). And I was one of millions of observers who have inadvertently caught them in the act.

50 Shades of Grey is a paradox. Clearly, people experience anxiety when they're caught reading it, because that's how erotic fiction affects people. But at the same time, they don't seem to be able to help themselves. What is it that compels people to devour this book -- to the point where it's already sold more copies than Gone With the Wind?

Fortunately, cognitive scientists like myself have been researching exactly what's going on inside people's brains and bodies while they're reading and listening to language. When you read (whether it's smut or not), you project yourself into the world that the story describes. Language leads you to virtually feel, see and smell the content of language. When you read 50 Shades of Grey, even the parts that don't involve whips and chains, you experience being Anastasia Steele, swooning over the dashing Christian Grey (I'm not making these names up):

I surreptitiously gaze at him from beneath my lashes as he stands in line waiting to be served. I could watch him all day... he's tall, broad shouldered and slim, and the way those pants hang from his hips... Oh my. Once or twice he runs his long, graceful fingers through his now dry but still disorderly hair. Hmm... I'd like to do that. The thought comes unbidden into my mind, and my face flames. I bite my lip and stare down at my hands again, not liking where my wayward thoughts are headed.

Using varied methods -- brain imaging, carefully tracking people's reaction times, and so on -- our research shows that when you read language like this, your brain acts as though you were actually there. The vision system in your brain becomes active, allowing you to simulate what it would be like to see the dashing Mr. Grey, hips and all. And so does your brain's system for motor control, as you simulate biting down on your lip.

Just like any narrative language, erotic fiction is transporting. It just happens to transport you into experiencing sights and sounds that are emotionally charged and sexually arousing. If you were Anastasia Steele in flagrante delicto, your pulse would race, you'd start sweating and blood would flush your sexual organs. Reading about Anastasia Steele in such a state leads you to actually experience a little of the same.

Consequently, reading smut is arousing. We know this from research that measures the physiological effects of sexual arousal directly. These studies use instruments like the penile plethysmograph or the vaginal photoplethysmograph, which measure blood flow to and expansion or contraction of the relevant organs. And the evidence is very clear; people in general become sexually aroused when they read smut , and -- although there's a history in the field of thinking otherwise -- women become just as aroused when they read hard-core pornography, like 50 Shades of Grey, as when they read romantic fiction. Reading sexual narratives even increases people's sex drive and frequency of sexual activity. And here's the kicker -- it increases libido more in women than in men.

So perhaps there's a massive yet previously untapped female readership for erotica. But for it to work, readers have to identify with the characters. Not coincidentally, 50 Shades appears to be extremely accessible, especially to the female reader. Intentional or not, the author's choices are particularly well suited to make the reader identify with the protagonist. Anastasia is a recent college graduate, naïve but bright and spunky, who falls for an older, mysterious, powerful man. There's certainly a decent-sized readership who can identify directly with a character like that. What's more, Anastasia narrates the book in the first person, and according to recent research, readers are more likely to adopt the perspective of a narrative character when the writing uses the first person (I) than, for example, the third person (she).

So 50 Shades appears to have hit a sweet spot -- it has an accessible protagonist, it's stylistically suited to have people empathize with her and it's intrinsically arousing to the point of increasing libido.

Ironically, the very same things that make 50 Shades so compelling are also the things that give the reader a jolt of anxiety when caught reading it in public. To the extent that the young lady next to me on the plane was transported into the narrated body and experiences of Anastasia Steele, she was actually experiencing arousal; she was actually, in a limited way, feeling as though she were carrying on with Christian Grey. That might be an embarrassing experience to have an airplane next to a stranger.

Your mind on smut is very much like your mind on any other type of narrative. Language has a remarkable effect on us -- it takes us out of this world and drives us to simulate ourselves in different places, positions and bodies. In the case of 50 Shades of Grey, the narrative transports the reader's mind into positions that might be inappropriate where her body actually is.

Benjamin K. Bergen is the author of Louder Than Words: The New Science of How the Mind Makes Meaning (Basic Books, 2012).