Defendants may soon have to face a witness that they never imagined would testify against them — their own brain.

Law School Prof. Hank Greely ‘74 is part of a nationwide group of researchers centered at UC-Santa Barbara that recently received a $10 million grant from the MacArthur Foundation to study the ways in which neuroscience can be applied to the justice system.

Greely’s research could alter the way we think about criminal and civil justice.

“Advances in neuroscience and our understanding of how the brain functions have both immediate and long term implications for the legal system,” Law School Dean Larry Kramer told The Daily in an email. “As advances in neuroscience teach us to understand this better, we cannot help but change the way law deals with a wide variety of problems.”

Neuroscience has a number of applications to the law, mainly involving lie detection and personal responsibility for criminal behavior, which could raise serious ethical questions for judges and juries in the future.

San Diego-based startup No Lie MRI has developed a lie detector that employs MRI technology to detect lies with 90 percent accuracy. The possibility of foolproof lie detection could have far-reaching effects on the justice system, but experts are careful not to get carried away before the new technology has established itself as legitimate.

“The more excited we get about what happens if it works,” Greely warned, “the more we must remember that we don’t know if it does work.”

If the new technology does prove to be reliable — and Greely puts the odds of this happening at below 50 percent — it will raise a number of constitutional issues, as defendants and witnesses may be obligated to take lie detector tests.

“A judge could conceivably issue a warrant on someone’s mind,” Greely said.

Current constitutional protections were not written in anticipation of advances in neuroscience and would not offer much defense against the aggressive use of neuroscience in trials. Greely argued that the First Amendment does not currently guarantee freedom of thought, and that the Fifth Amendment protection against self-incrimination only applies to testimony. MRI tests may be put under the same non-testimonial category as breathalyser tests, he said.

If neurological advances occur in the near future, Greely warned that the Bill of Rights may not be expanded to address neuroscience.

“Our current Supreme Court is not highly likely to extend rights,” he said.

The way in which courts hold people liable for their actions may change as a result of advances in neuroscience.

“Neuroscientists believe that behaviors are a function of brain function,” Greely said.

Even today, judges and juries take neuroscience into account when punishing criminals. In the 2005 case Roper v. Simmons, the Supreme Court ruled that the death penalty could not be applied to minors, in part because neurological analysis showed that minors do not have the same capacity for judgment that adults do.

If neuroscience continues to progress, it is conceivable that neuroscientists may one day argue that all criminal behavior is a result of biological defects. Greely argued that even if this day comes, we are so deeply wedded to the concept of free will that such findings will not dramatically alter the current criminal justice system.

“We will continue to believe we have free will no matter what neuroscientists say,” Greely said. “Criminal responsibility is not going to dry up and blow away.

According to Greely, the concept of preventative justice is one of the most exciting — and frightening — applications of neuroscience. Greely said it is possible that in the foreseeable future we will be able to identify patterns in MRIs that indicate psychopathy in children.

“Would we put these people in jail and throw away the key because of a scan? I don’t think so,” Greely said. “But other countries might.”

Today, some forms of preventive justice are common. College-age males are forced to pay higher car insurance premiums than middle-aged mothers. Repeat offenders are routinely given longer prison sentences than first-time offenders. It is not hard to imagine a time when law enforcement officials could closely monitor potential criminals based on brain scans.

“Preventive measures,” Greely postulated, “may not be as far away as you would think.”