"I did it—but it's not my
fault." It's one of the more controversial strategies defendants can use: admitting
they committed a serious crime but arguing that, because of some mitigating factor
such as disease or depression, they should not be held responsible. As new and
improved imaging tools allow for more detailed images of the brain and as our
understanding of behavior and personality becomes more sophisticated,
neuroscientists are increasingly having to come to terms with how their
findings and expertise are being used—or misused—in the courtroom.
Experts in law, ethics, and brain
science highlighted the complexity of the issue by staging a mock trial
yesterday in San Diego, at the annual meeting of the American Association for
the Advancement of Science. As the two sides argued for and against the
introduction of MRI data in a murder trial, the complexities piled up: how to
reconcile previous case law dealing with neuroscientific evidence, how MRI data
might bias the jury for or against the defendant, whether brain scans
consistently reveal damage or disease, how closely brain scan results reflect
the psychological states of mind relevant in criminal cases, and so forth.
Neuroscience and law have had a rocky
relationship in recent years; in particular, many researchers have said that
functional MRI (fMRI), which looks at patterns of brain activity, has been
used prematurely in courtrooms as a form of lie detection service. The mock case,
however, revolved around structural MRI, which offers a detailed 3-D image of a
person's brain. Such a scan showed a severe frontal lobe lesion in a fictional
defendant who was tightly linked to a murder by both forensic evidence and
The scenario played out in two phases.
The judge first heard arguments and testimony over whether the MRI data should be
admitted into evidence; after he ruled in favor, the participants skipped
forward to near the end of the trial, when two expert witness, neuroscientists James Brewer and
of the University of California, San Diego, took the stand, respectively, for
the defense and prosecution.
Brewer cited studies that suggest that
frontal lobe damage can lead to poor impulse control, difficulty in formulating
plans, lack of concern for social conventions, and personality changes. His
testimony led the defense attorney, played by Robert Knaier, an associate in
the San Diego office of Latham and Watkins, to argue that the defendant
"could not have formed the requisite intent" to be held responsible
for his crime.
Rafii, on the other hand, pointed out
that the link between brain damage and personality change is extremely
tenuous—some people exhibit similar shifts in behavior without any sign of
brain lesions, and others with much greater levels of damage show no adverse
affects at all.
"Frankly, we have a naked
brain," said prosecuting attorney Hank Greely, a
professor of law at Stanford University, in his closing arguments. "The
law doesn't care about brains. It cares about minds." While brains
generate minds, he added, the relationship is "not simple and
straightforward" and cannot be used in this case to excuse the defendant's
Between the two phases and after the mock-trial, the players broke character to discuss the implications of their arguments and answer questions from the audience. Many of the concerns were similar. Both groups, for instance, worried about whether a series of successful defenses based on neuroscience would erode the concept of personal responsibility and what do about people declared not guilty because of a neurological disorder but who remained a danger to society. But most of the anxiety revolved over whether it was even appropriate to consider using cutting-edge neuroscience in the courtroom. With research findings being revised and refined on the basis of new data and very few solid causal links between features of the brain and any aspect of behavior, many people worried that the law was racing ahead of the science.
If the session's organizers didn't have
answers to those hard questions, and acknowledged that missteps are likely as
judges and scientists grapple with extremely difficult legal and ethical
issues, they did at least suggest that there is still time to change things.
Greely said that, despite its high profile, neuroimaging is still used
relatively rarely in criminal proceedings. In an ongoing survey of all
California criminal cases between July 2006 and July 2010, he has identified
only 40 candidate cases in which a brain image of a defendant was offered as
evidence; when the work is completed, he expects that number to end up
somewhere between 30 and 100, out of tens of thousands of total cases. Rather,
MRI scans of crime victims are used more often, he said, to detail the extent
of their injuries. When it comes to the more controversial fMRI, cases are even
more uncommon. Although employed with some regularity in civil proceedings,
Greely said he knows of only one criminal case in which fMRI was used—an
Illinois case in which a brain scan was unsuccessfully offered up to help
mitigate a capital sentence.