For many, curling up on the couch with popcorn and a movie means shutting your brain off to relax after a long day. But unbeknownst to you, two dozen brain networks are lighting up as you watch different types of movies, a new study finds.
The new research, published Nov. 6 in the journal Neuron, shows that our brains are actually incredibly active when we watch movies. Researchers at MIT took advantage of this to create the most accurate functional brain map to date, charting specific circuits that activate to support different aspects of cognition.
They tracked where the brain becomes active during movie scenes — for instance, when Dom Cobb explores a dream world in "Inception," Kevin McCallister realizes he is "Home Alone," or Leia calls Han a "scruffy-looking nerf-herder" in "Star Wars: The Empire Strikes Back." From there, they were able to identify different brain networks needed to process different types of scenes.
"Our work is the first attempt to get a layout of different areas and networks of the brain during naturalistic conditions," study first author Reza Rajimehr, a neuroscientist at MIT, told Live Science. By comparison, many functional brain mapping studies have been performed when the brain is "at rest," not engaged in observing a specific scene.
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Snapshots of the resting brain are still informative, but the challenge is that some of the brain's networks are activated only with external stimulation.
In the new study, the researchers used a functional MRI (fMRI) dataset from the Human Connectome Project, which consisted of brain scans from 176 young adults who watched 60 minutes of short clips from several independent and Hollywood movies. An fMRI scan indirectly measures brain activity by tracking where blood flows to different regions of the brain. If a part of the brain is active, blood flow to that part increases.
"The movie stimulus is a rich stimulus, but on the other hand, it is not a very well-controlled stimulus," Rajimehr said. "And when you show a movie to a subject, you may get some idiosyncratic responses, which cannot be generalized to other subjects." Not everyone reacts to or processes movies in the same way.
So a trick Rajimehr and his team used was to average the brain activity across participants. This enabled them to map and study brain responses and networks that are common across all the people in the study. With this initial map in place, they could then identify which networks were active during different movie scenes.
Overall, 24 different brain networks were activated during movie watching. The researchers could then assign functions to each network by associating them with specific cognitive processes, such as recognizing human faces, watching people interact with one another, and observing familiar settings and landmarks.
This analysis resulted in the most comprehensive functional map of the brain to be presented so far, the researchers say.
From this map, the researchers discovered an inverse relationship between "executive control domains" — parts of the brain involved in planning and decision-making — and parts of the brain with other functions.
When a movie scene was complex and difficult to follow — like when Danny Ocean and his crew are planning a Las Vegas heist in "Ocean's 11" — the executive domains responsible for making plans, solving problems and prioritizing information were highly active. However, when a scene was relatively simple — like when Julia Roberts talks casually to a plaintiff in "Erin Brokovich" — more specialized brain regions including those involved in language processing dominated.
"One result that was quite surprising was that … whenever the clip ends, there is [also] a huge response in these executive control networks," Rajimehr added. During the study, the clips would end abruptly with a 20-second rest between each scene. Rajimehr proposed that this abrupt end might automatically activate specific memory circuits, as subjects attempted to recall the content of the clips.
A functional map of the brain with this level of detail could provide insights into how the organ's networks are organized in both healthy people and those with conditions, such as schizophrenia or autism. And in theory, understanding how the brain responds to movies could even teach Hollywood a thing or two, helping filmmakers create more engaging content, Rajimehr said.
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