I can already see the bright red steam locomotive in my mind’s eye. Platform 9¾ at King’s Cross station, in London, is bustling with activity. Young wizards and witches push huge carts laden with luggage, punctuated now and then by the screech of an owl. They are on their way back to Hogwarts, the famed school of witchcraft and wizardry, where the new school year is about to start. And I’m going along! Through my reading, I share in the adventures of Harry Potter and his friends Ron and Hermione as they move through the wizarding world, experiencing their fears and joys and joining with them in the struggle against evil.

I don’t realize that I am actually lying in bed, not having budged an inch, until I close the book again. Hours have passed by without my noticing. It’s a feeling that will be familiar to many Harry Potter fans. After all, it was no coincidence that the seven-volume series of novels penned by British author J. K. Rowling became a runaway global hit within just a short time. According to Rowling’s publisher, Bloomsbury, more than 450 million copies have been sold; the books have been translated into 78 languages, adapted for the big screen, and even continued onstage.

But how do readers become so immersed in a book, apparently forgetting everything around them? And what happens in our brains during this process?

Arthur M. Jacobs and his colleagues decided to find out. Jacobs, a neuropsychologist from the Department of Education and Psychology at Freie Universität, calls the state we experience during this kind of intense reading “immersion” – which, of course, comes from the Latin immersio, which just incidentally sounds like it could be a spell from the world of Harry Potter itself. Scholars in other disciplines also call the experience “transportation,” “absorption,” “presence,” or “flow.”

The Harry Potter Series as an Example

It is a phenomenon that has been known for a long time – “so it’s even more astonishing that apparently neither psychology nor neuroscience has worked on it so far,” Jacobs says. He and his former doctoral candidate Chun-Ting Hsu wanted to change that. The researchers initiated empirical studies of immersion, using the Harry Potter series as an example, since it is viewed by literary scholars as being “especially immersive.”

Finding out what is happening inside the head of someone who is utterly immersed in a book isn’t as easy as it sounds, Jacobs says. An online survey, for example, wouldn’t make sense; “after all, as soon as I ask readers whether they are immersed, they aren’t anymore.” And if Harry Potter fans were to report on their reading experiences and perceptions afterward, the only thing it would be possible to measure would be the memory of immersion, not the state itself. That meant the researchers needed to find a way to “look inside people’s heads” while they were reading.

To do so, Jacobs and his colleagues turned to magnetic resonance imaging (MRI) technology, which uses a powerful magnet to produce high-resolution images of how the blood circulation in various regions of the brain changes as a person thinks and experiences emotions. In this way, the MRI scanner offers detailed and precise information on brain activity. Together with other labs, it was installed at Freie Universität in 2009 with funding from the Languages of Emotion cluster of excellence, which received funding under the Excellence Initiative from 2007 until 2014. The labs, which occupy 800 square meters in all, are a feature not found at any other university psychology department anywhere in Germany, Jacobs says. “They offer doctoral candidates and other students a tremendous advantage, namely the ability to apply practically any neurocognitive measurement method right on site.”

The team of researchers performed a total of four Harry Potter studies on the subject of immersion, testing 20 to 24 subjects each time. All of them were familiar with the books, which was an important factor in ensuring that they would be able to connect with the short text passages easily. The texts were displayed to the test subjects on a screen inside the scanner. The specific passages had been selected through close cooperation with literary scholars. Some were neutral, some were highly suspenseful, and others were very emotional.

The description of the scene on Platform 9¾ was used as a neutral sample, while the depiction of the “dementors” – lifeless creatures that suck all the happiness out of a person – offered suspense, and a scene of Harry looking at a photo of his parents taken at their wedding – before they were murdered by the powerful evil wizard Voldemort, Harry’s adversary, when Harry was just a baby – evoked an emotional response.

For comparison purposes, another group of test subjects answered a questionnaire to indicate how immersive they thought the individual passages were. The researchers used this information to interpret the data collected from the scanner. “We found out that the central cingulate cortex of the brain reacts sensitively when people are immersed,” Jacobs says. This region of the brain is otherwise associated with perceptions of pain, sympathy and empathy.

Readers Identify with Characters in Books as if They Were Friends

When characters in the Harry Potter books experience something sad, for example, and their responses are described in the text, the reader’s brain responds much as it would if a person close to him or her were very sad. What the person has read evokes empathy – an important factor in immersion.

Another important thing is the physical focus, explains Jacobs, whose research focuses on various topics, including eye movements. “When a person reads, their eyes are focused on that page of the book, whether it is an e-book or an analog book with actual pages. The reader goes into the text and does not move around through space as one might when listening to music. This already contributes to the feeling of immersion in purely physical terms.”

Another factor that should not be underestimated when it comes to immersion is the suspense within the narrative, which is what causes the reader to want to keep going. “From the writer’s perspective, the craft is, ‘How do I create suspense in my text?’” Jacobs explains. Rowling, for example, is skilled at describing action vividly. “There is a high density of action,” he explains.

“In our labs, we can measure not just the responses taking place in the brain, but also other factors as well, such as elevated heart rate and perspiration,” Jacobs says. “We can see whether the ‘worry muscle’ between the eyes is wrinkled or the smile muscle at the corners of the mouth is activated.” All of this, he explains, takes place unconsciously, but it may be part of the reader’s immersion – and it can be measured using neuropsychological methods.

One question that was part of the studies generated particularly great interest internationally: Does it matter whether a person reads a book in their native language or in a second language? The people who participated in the study are native speakers of German who speak English fluently. The experience confirmed the researchers’ suspicions: “Feelings such as fear and happiness are experienced more intensely when a person reads the book in their native language. In a second language, the brain doesn’t draw as clear a distinction between basal feelings, such as fear and disgust. Which regions of the brain associated with feelings are activated during reading is not as clear, though,” Jacobs says. There are many reasons for this, but one thing is clear: There is a measurable connection between the language, the quality of the text, and the immersion experience.

The study’s results are not representative; because performing MRI scans is expensive, the researchers were unable to take as many samples as they would have liked, and not all of the test subjects found the conditions in the scanner conducive to reading.

Still, as Jacobs explains, “We put forward a hypothesis, and our results showed a tendency that other studies can build on.” There are many other questions waiting to be explored, such as whether reading is in fact the most immersive way of consuming media. “And what Ms. Rowling was thinking when she wrote Harry Potter,” Jacobs adds. “I’d love to look inside her brain while she is writing sometime!”

This text originally appeared in German on December 3, 2016 in the Tagesspiegel newspaper supplement published by Freie Universität.