World's first brain scanner made for two

Two heads are better than one - particularly if you're studying the brain activity underlying social interaction. The problem is that imaging technologies such as MRI have only been able to handle one brain at a time - until now. Ray Lee at Princeton University has developed the world's first dual-headed fMRI scanner. The innovation allows the simultaneous imaging of the brain activity of two people lying in the same scanner.

Usually, a lone person lies inside a scanner's narrow tunnel, cocooned by powerful magnets and radio-frequency coils which detect how hydrogen atoms in the body respond to magnetic fields, or how the flow of oxygenated blood changes as a result of brain activity. Although it is possible to squeeze two adults into most MRI machines - Willibrord Weijmar Schultz at the University of Groningen in the Netherlands famously scanned the bodies of couples as they copulated inside an MRIMovie Camera - attempting to scan both their brains at once would produce too fuzzy an image.

So Lee designed a pair of coils that fits into a scanner, providing two distinct loops in which to place each participant's head. He also fitted a window between the coils so participants can see one another. "This opens up a new area of MRI," says Lucien Levy, head of neuro-radiology at George Washington University Medical Center in Washington DC. "I haven't seen anything like this."

To test the scanner, Lee asked couples to lie facing one another and blink in unison. Brain activity in the fusiform gyrus - involved in facial recognition - was tightly correlated. Lee also asked couples to repeatedly embrace and release one another, and observed similarly synchronised brain activity. He announced his results in November 2010 at the Society for Neuroscience conference in San Diego, California.

"In close proximity, people tend to mimic each other in all kinds of ways, especially through non-verbal signals," says Marco Iacoboni at the University of California, Los Angeles. "Now we can examine brain activity of an intimate pair copying each other in real time. That hasn't been done before."

James Coan at the University of Virginia in Charlottesville is also eager to test the device: "People distribute neural processing across multiple brains when solving problems," he says. "You essentially contract out part of a given problem to someone else's mind. Lee's work would give us the opportunity to see two brains reacting to a problem simultaneously."

Jesse Rissman at Stanford University in California says it remains unclear just how advantageous scanning people in the same machine will be compared with scanning people in different machines who are linked by video. He points out that if people move around too much inside a scanner, they disrupt the signal, so interactions may be limited to small gestures.

But Coan stresses the potency of even minor actions: "Couples could hold each other or rub each other's back," he says, "and simply having another human face inches from their own is a very powerful stimulus. With a little creativity, the sky's the limit for figuring out how brains respond to each other."