What’s happening in your brain while you’re watching a movie?

“Our work is the first attempt to map different brain regions and networks in vivo,” says first author and neuroscientist Reza Rajimer of the Massachusetts Institute of Technology (MIT).

Different regions of the brain are highly interconnected, and these connections form functional networks that influence how we perceive stimuli and behave. Most studies of functional brain networks have been based on resting-state fMRI scans of people, but many parts of the brain or cortex are not fully active in the absence of external stimulation.

In this study, the researchers wanted to find out whether watching movies during an fMRI scan could provide insight into how functional brain networks respond to complex audio and visual stimuli.

“With resting-state fMRI, there’s no stimulus—people are just thinking internally, so you don’t know what activated these networks,” says Rajimer. “But with our movie stimulus, we can go back and figure out how different brain networks respond to different aspects of the movie.”

To map the brain while watching movies, the researchers used a previously collected fMRI dataset from the Human Connectome Project, consisting of whole-brain scans of 176 young adults acquired while participants watched 60-minute short videos from a range of independent sources. and Hollywood films.

The researchers averaged the brain activity of all participants and used machine learning techniques to identify brain networks, particularly in the cerebral cortex. They then examined how activity on these various networks related to the film’s content, scene by scene, which included people, animals, objects, music, speech and narration.

Their analysis identified 24 different brain networks that were associated with specific aspects of sensory or cognitive processing, such as recognizing human faces or bodies, movements, places and landmarks, interactions between people and inanimate objects, speech and social interactions.

They also showed an inverse relationship between “executive control areas” – areas of the brain that allow people to plan, solve problems and prioritize information – and areas of the brain with more specific functions. When movie content was difficult to understand or ambiguous, there was increased activity in parts of the brain involved in executive control, but during more comprehensible scenes, areas of the brain with specific functions, such as language processing, predominated.

“Executive control areas tend to be active during complex tasks when cognitive load is high,” says Rajimer. “It appears that when movie scenes are fairly easy to understand, for example if there is a clear conversation, language areas are active, but in situations where there is a complex scene involving context, semantics and ambiguity in meaning in the scene, more cognitive effort is required and so the brain switches gears to the use of common executive control areas.”

Because the analysis in this paper was based on average brain activity, the researchers say future studies could explore how brain network function varies between people, between people of different ages, or between people with developmental or psychiatric disorders.

“In future studies, we will be able to look at the maps of individual subjects, which will allow us to relate each subject’s individual map to that subject’s behavioral profile,” says Rajimer. “We are now looking more deeply into how the specific content of each frame of a film drives these networks—for example, semantic and social context, or the relationship between people and the background scene.”