How Imagining a Game of Tennis Can Reveal Consciousness

Jul 6, 2017


There are tens of thousands of people in the United States who have been diagnosed as being in a vegetative state – unresponsive and unaware of their surroundings. But as many as 15 to 20 percent of those people may actually be fully conscious and simply unable to make that known. Unless, of course, you put them in a high-end brain scanner and ask them to imagine playing tennis.

No joke.

Neuroscientist Adrian Owen began conducting brain scans of vegetative patients about twenty-five years ago. At the time, it was a PET scanner. Now, it’s a research-grade functional MRI. In both cases, the idea is simple: give the patient a mental task to perform, and look for areas of the brain where blood flow increases – a sign of increased activity.

At first, Owen showed patients photographs of familiar faces, or played recordings of speech and nonsense sounds. In both cases, Owen found vegetative patients whose brain scans looked just liked healthy individuals.

But there were questions about how conscious, or deliberate, those responses were. Owen needed some way to test whether patients could intentionally respond to instructions, and he found his inspiration in Wimbledon.

It turns out that imagining for thirty seconds that you’re playing a vigorous game of tennis evokes a strong response in an area of the brain, called the premotor cortex, which is involved in planning physical actions. Owen attributes the clear signal to the fact that tennis is familiar to most and involves (at the most basic level) just a few, large motions - running, and swinging a racket.

While the response is nearly universal in healthy patients, Owen says 15-20 percent of the vegetative patients he’s tested show a similar response. And, to pass Owen’s test, they have to do it not just once, but repeatedly. 

Owen and his colleagues have actually used the so-called tennis experiment to communicate with some vegetative patients. Instead of “blink once for yes, two for no,” patients are asked to imagine tennis for one answer or walking through their house (another task that produces a clear response, but in a different part of the brain) for the other.

It’s no mean feat. Owen put himself in a scanner several years ago and realized that maintaining focus on an imaginary game of tennis for thirty seconds is far harder than he’d imagined. That difficulty is key to the rigor of the test, but it also led Owen and his colleagues to wonder if there are more vegetative patients who are conscious but unable to pass the tennis test.

So, they designed the Hitchcock test. They show healthy individuals an Alfred Hitchcock movie while scanning their brains. Those scans can be synchronized to show common cognitive and emotional responses to the plot. And, while a gunshot elicits an automatic response from hearing centers in the brain, a child playing with a loaded gun only evokes a strong response if the viewer understands, consciously, the ramifications of the scene. Some vegetative patients do.

The idea that patients diagnosed as vegetative may actually be conscious has been controversial. For many, it’s just easier to think that these individuals are unaware, than to accept that they are conscious and completely locked in. But Owen says others have replicated his findings, and while there is still debate about what percentage of vegetative patients are conscious, the concept is almost universally accepted.

Adrian Owen's new book is "Gray Zone: A Neuroscientist Explores the Border Between Life and Death."