No one really knows how millions of microscopic brain cells can weigh objective legal notions of right and wrong. But last month, researchers at Vanderbilt University for the first time identified distinctive strands of neural tissue active when, like a judge or juror, we think about crime and punishment. In an experiment at the frontier of law and philosophy, the researchers used a brain scanner to examine the impartial judgments at the heart of our legal system, recording how brain cells behave when assessing criminal responsibility and meting out sentences.
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No one part of the brain stands in judgment of others, they found. Instead, at least two areas of the brain assess guilt and assign an appropriate penalty. An area associated with analytical reasoning, called the right dorsolateral prefrontal cortex, became very active, they reported. But the decision process also electrified emotional circuits.
Dr. Marois found so much emotional activity during an impartial legal decision surprising. "This reasoning may not be so detached. It shattered my preconceived ideas of the legal system," says Dr. Marois. "But for a lawyer, maybe it doesn't."
Further research will look at the brains of diagnosed psychopaths and of State and Federal judges. (No, they're not saying the two are the same -- they're trying to look at extreme ends of the spectrum: people who can't judge to save their lives, and people who judge for a living.)
Researchers caution people against reading too much into these early results:
So far, neuroscience has delivered few, if any, dependable courtroom insights into criminality. "This is baby science, first-step science, like genetics in the 1950s," says Dr. Gazzaniga, a member of the President's Council on Bioethics, which studied the impact of neuroscience evidence in criminal law. "This should be used cautiously in the courtroom -- if at all."
There have been some interesting findings, but we don't know how widely they can be applied.
Last spring, for example, an Indian court found a woman guilty of murder based, in part, on the evidence of guilty knowledge purportedly revealed by her brain wave oscillations, even though a government panel of scientists had recommended that the technique should be ignored.
Why? What we have is a brain wave pattern that was associated with "guilty knowledge" in a small number of people. What we don't have is any way of knowing that's the only thing that produces that brain wave pattern. It may turn out that "guilty knowledge" is one of a dozen mental states that produce the same kind of brain wave, and of that dozen, who knows how many even rise to conscious awareness. Maybe not, but the point is, we just don't know. Yet.
Another problem has to do with the technology used to create images. It's easy to be misled by the apparent precision of a computer display. Certainly, in my physics lab classes, one of the things we had to learn was when to ignore the last few digits of an electronic computer display. It's one thing when we're looking at a needle on a dial. We can watch the needle wobble and see for ourselves that we can't pin the number down past a certain point. But when a numeric display pops up with five digits of precision, we have to be careful not to read too much into any changes in the last digit. That may just be noise.
Even functional brain imaging -- invaluable as a medical research tool since its debut 15 years ago -- can't be trusted yet as courtroom evidence of an individual's personality traits, truthfulness, bias or criminal intent, experts say. Nonetheless, fMRI brain scans are showing up as evidence before the U.S Supreme Court.
Although such scans often look like a photograph of a brain at work, they actually are easily manipulated computer creations resulting from sophisticated signal processing.
"The image that can come out is very dependent on the statistics you use and the colors you pick and the tasks involved and the inferences you make," says Dartmouth College philosopher Adina Roskies, who is studying how such brain images may unduly influence legal judgment. "You can get very different images from the same test depending on what the experimenter does."
A brain image from fMRI has the same problem that we see with electronic displays, compounded millions of times. Each pixel in the image is the result of millions of calculations, subject to a certain amount of noise. Artifacts -- are a common problem. Errors in the calculation can result in images of things that aren't there, or they can hide things that are there.
Precision in the display does not equal precision in the input data.
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