MRI scans show that the brainwaves of close companions match when watching videos clips of a wide variety of subjects, including comedy, documentaries debates and music.
In fact, it is even possible to calculate just how close the friendship is, simply by measuring the synchronicity of neural activity.
Good friends were found to have the most similar neural patterns, followed by friends of friends, who in turn had closer brainwaves than friends of friends of friends.
"Neural responses to dynamic, naturalistic stimuli, like videos, can give us a window into people's unconstrained, spontaneous thought processes as they unfold," said lead author Carolyn Parkinson, who was a postdoctoral fellow in psychological and brain sciences at Dartmouth at the time of the study and is now at UCLA.
"Our results suggest that friends process the world around them in exceptionally similar ways."
The study analysed the friendships or social ties within a cohort of nearly 280 graduate students.
The researchers estimated the social distance between pairs of individuals based on mutually reported social ties.
Forty-two of the students were then asked to watch a range of videos while their neural activity was recorded in a functional magnetic resonance imaging (fMRI) scanner.
The findings revealed that neural response similarity was strongest among friends across brain regions involved in emotional response, directing one's attention and high-level reasoning.
The team also found that MRI response similarities could be used to predict not only if a pair were friends but also the social distance between the two.
"We are a social species and live our lives connected to everybody else," added senior author Thalia Wheatley, an associate professor of psychological and brain sciences at Dartmouth.
"If we want to understand how the human brain works, then we need to understand how brains work in combination-- how minds shape each other."
The research team now plans to explore if people naturally gravitate towards people who see the world the same way we do, or if we become more similar once we share experiences.
The research was published in the journal Nature Communications.