Annie is lying down when she answers the phone; she is trying to recover from a rare trip out of the house. Moving around for an extended period leaves the 56-year-old exhausted and with excruciating pain shooting up her back to her shoulders. “It’s really awful,” she says. “You never get comfortable.”

In 2011, Annie, whose name has been changed at the request of her lawyer, slipped and fell on a wet floor in a restaurant, injuring her back and head. The pain has never eased, and forced her to leave her job in retail.

Annie sued the restaurant, which has denied liability, for several hundred thousand dollars to cover medical bills and lost income. To bolster her case that she is in pain and not just malingering, Annie’s lawyer suggested that she enlist the services of Millennium Magnetic Technologies (MMT), a Connecticut-based neuroimaging company that has a centre in Birmingham, Alabama, where Annie lives. MMT says that it can detect pain’s signature using functional magnetic resonance imaging (fMRI), which measures and maps blood flow in the brain as a proxy for neural activity.

The scan is not cheap — about US$4,500 — but Steven Levy, MMT’s chief executive, says that it is a worthwhile investment: the company has had ten or so customers since it began offering the service in 2013, and all have settled out of court, he says. If the scans are admitted to Annie’s trial, which is expected to take place early this year, it could establish a legal precedent in Alabama.

Most personal-injury cases settle out of court, so it is impossible to document how often brain scans for pain are being used in civil law. But the practice seems to be getting more common, at least in the United States, where health care is not covered by the government and personal-injury cases are frequent. Several companies have cropped up, and at least one university has offered the service.

The approach is based on burgeoning research that uses fMRI to understand the nature of pain — a very subjective experience. Scientists hope that the scans can provide an objective measure of that experience, and they see potential applications, such as in testing painkillers. But many neuroscientists say that the techniques are still far from being accurate enough for the courtroom. Critics say that the companies using them have not validated their tests or proved that they are impervious to deception or bias. And whereas some think the technologies will have a place in legal settings, others worry that the practice will lead to misuse of the scans.

“There’s a real desire to come up with some more-objective proxy for pain,” says Karen Davis, a neuroscientist at the University of Toronto in Canada. But such measures must be extremely accurate, she says. “The outcome of having a wrong answer can be quite catastrophic.”

Neural origins

The methods that doctors commonly use to assess pain can seem crude. People are asked to rate their pain on a scale from one to ten, or choose from a row of cartoon faces that go from happy to anguished. These measures can help to chart changes in pain, as someone recovers from surgery, for example. But each person will experience and rate their pain differently, so one person’s five could be worse than another’s seven, and a nine might or might not be bad enough to keep someone from working.

An objective answer should lie in the brain, where the experience of pain is ultimately constructed. And although every experience is different, pain should share some common elements. Neuroscientist Tor Wager at the University of Colorado Boulder has been trying to decipher pain’s signature in the brain by placing people in an fMRI scanner while they touch a hot plate. As the researchers turn the plate’s temperature up and down, they record the activity across different parts of the brain, including the sensory regions associated with the hand. From these patterns, Wager says, they can predict with better than 90% accuracy whether the plate is just warm or painfully hot1.

“There’s a real desire to come up with some more-objective proxy for pain.”

But this measures acute pain — the immediate response to an obvious stimulus. Chronic pain, like Annie’s, affects hundreds of millions of people worldwide. And although its cause can be obvious, that is not always the case. Vania Apkarian of Northwestern University in Chicago, Illinois has scanned dozens of individuals soon after a back injury and then again over the course of a year or more. The pain went on to become chronic in roughly half of those people, and even though they described the pain the same way throughout, Apkarian could detect a shift in the pain signature in their brains2. It changed from a signal of activity in the insula, which is associated with acute pain, to one of activity in the medial prefrontal cortex, which processes cognitive behaviour, and the amygdala, which controls emotion. “Our interpretation is that the pain is becoming more internalized,” Apkarian says.

This and other work suggests that there is an emotional component to chronic pain that is not necessarily involved in acute pain. Chronic pain and depression often coexist and reinforce one another. And some chronic pain can be eased with antidepressant drugs. But Wager cautions that focusing on these links can be treacherous. Suggesting that pain is all in the head — even if that is technically the case — does not mean that it is imagined or faked. “People will always go to that black and white line,” he says.

That line is a particular challenge in legal settings. “A person cannot be found disabled based on pain unless they can point to a specific cause,” says Amanda Pustilnik, a legal expert at Harvard Law School in Cambridge, Massachusetts.

Isolated instances

The United States sees tens of thousands of injury lawsuits every year, most of which involve claims of unresolved pain. But that might be unusually high — countries with national health systems, such as Canada, see fewer lawsuits, says Davis. So far, the only pain case involving brain-imaging techniques known to have progressed to trial involved a truck driver named Carl Koch, whose wrist was burned by a glob of molten asphalt in 2005. A year later, he said he was still in pain and sued his former employer, Western Emulsions in Tucson, Arizona, for damages.

Koch had had his brain scanned by Joy Hirsch, a neuroscientist who was running the fMRI Research Center at Columbia University in New York City. Hirsch had developed a method that she says can “tap into” chronic pain. Lightly touching the affected wrist provoked a signal in sensory regions and other brain areas associated with pain; touching the other wrist did not. The test, she says, is a well-characterized way to distinguish allodynia — a pain response to a stimulus that does not normally cause pain — from imagined pain.

At the trial, Western Emulsions called Sean Mackey, a neurologist at Stanford University in Redwood City, California, as an expert witness. Mackey maintained that pain is too subjective to measure in this way and that the signature Hirsch was detecting could have been produced if Koch had expected to feel pain in the affected wrist or was unduly concentrating on it — deliberately or not. Hirsch argued that there are known signals for imagined pain that were not apparent in the scans.

Ultimately, the judge admitted the scan, and the case settled for $800,000 — more than ten times the company’s initial offering, according to Koch’s lawyer, Roger Strassburg.

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