In 1974, two months after having a portion of his brain removed due to an accident at the sawmill where worked, Cecil Clayton checked himself into a mental hospital, frightened by his suddenly uncontrollable temper.

Previously, Clayton had been an intelligent, guitar-playing family man, relatives said. He abstained from alcohol, worked part time as a pastor and paid weekly visits to a local nursing home.

But after the accident, which necessitated the removal of 20 percent of his frontal lobe, everything changed.

“He broke up with his wife, began drinking alcohol and became impatient, unable to work and more prone to violent outbursts,” Clayton’s brother Marvin testified at trial.

In 1979, he visited William Clary, a doctor who examined him for extreme anxiety, depression and paranoia.

“I can’t get ahold of myself, I’m all tore up,” Clayton told the doctor, according to court filings from his attorneys.

Clayton’s spiraling mental state and increasingly violent behavior came to a head in 1996, when he shot and killed Christopher Castetter, a sheriff’s deputy responding to a domestic disturbance between Clayton and his girlfriend. Clayton was eventually convicted of murder, and executed via lethal injection in Bonne Terre, Mo., Tuesday night.

His death brought to an end to nearly two decades of litigation during which it seemed that Clayton’s brain, rather than the man himself, was on trial.


“The effects of his 1972 accident left him blameless for the 1996 murder,” read a petition filed by his defense, asking for a stay of execution from the U.S. Supreme Court. It was accompanied by an image of his brain scan, which shows a sizeable chunk of his brain missing from the right-hand side.

Clayton’s attorney, Elizabeth Unger Carlyle, reiterated the defense’s stance in a statement released shortly after he was executed: “Mr. Clayton was not a ‘criminal’ before the sawmill accident that lodged part of his skull into his brain and required 20 percent of his frontal lobe to be removed,” she said.

In other words, Cecil Clayton wasn’t responsible for the shooting of a police officer — not fully. Instead, attorneys claimed the root of the killing was in that missing piece of his frontal lobe.

That argument — that a person’s brain anatomy ought to change the way we assign guilt — has become an increasingly common one, according to Duke law professor Nita Farahany.

“The more we understand about neuroscience we see that even subtle abnormalities can affect human behavior,” she said in a phone interview. “People are using neuroscience to argue, ‘It’s not my bad character, it’s my bad brain,'” she said.

Farhany is a member of the Presidential Commission for the Study of Bioethical Issues and an expert in the growing field of neurolaw, which examines how brain science is and ought to used in the legal system. She monitors cases where neuroscientific data has been brought as evidence and found a marked upswing in the past few years.

But as MRI scans and electroencephalogram recordings of brain activity are brought out of the examination room and into the courtroom, the focus of a trial shifts from assigning guilt to assessing mental and moral blame.

“As we develop better technologies for probing the brain, we detect more problems, and link them more easily to aberrant behavior,” neuroscientist David Eagleman wrote in an essay for the Atlantic. “… When a criminal stands in front of the jury’s bench today, the legal system wants to know whether he is blameworthy. Was it his fault, or his biology’s fault?”

Neuroscience has revealed that humans have a lot less control over their actions than they like to think, Eagleman said. Brain injuries — particularly ones to the frontal lobe, like Clayton’s — can radically reduce the ability to make decisions and check impulses.

And though it didn’t work for Clayton, that understanding has helped others avoid the death penalty in recent cases. In 2013, prison escapee and convicted murder John McCluskey was sentenced to life without parole rather than the death penalty after his defense presented MRI evidence showing significant abnormalities in his frontal lobe. The headline in Wired read “Did brain scans just save a convicted murderer from the death penalty?” Two years earlier, a juror at the trial of a Florida man who stabbed his wife and step-daughter said brain scans convinced him not to vote for the death penalty.

“It turned my decision all the way around,” juror John Howard told the Miami Herald.

Though there aren’t enough of these cases for a large enough sample size for serious study, research has shown that scientific evidence about a hypothetical defendant’s brain function is likely to limit a sentence’s severity. A 2012 study in Science found that, on average, judges subtracted a year from an imaginary convict’s sentence after being told he was genetically predisposed to violence.

“Those who read about the biological mechanism subtracted a year, as if to say, ‘This guy is really dangerous and scary, and we should treat him as such, but the biological evidence suggests that we can’t hold him as responsible for the behavior,” James Tabey, a co-author of the study, told the New York Times.

Even though neuroscientific evidence has been shown to be increasingly compelling in recent years, Farahany isn’t surprised that it wasn’t helpful in Clayton’s case. The more than 20-year gap between Clayton’s accident and his crime weaken the argument that he was unable to control his behavior. And though Clayton’s brain was clearly abnormal, there is not enough research to definitively say the missing part of his frontal lobe caused him to commit murder.

“That piece is missing literally and figuratively,” she said. “… Once neuroscience gets to the point of causal explanations, in retrospect we might look back at it and say, ‘Here’s why he did what he did.'”

It’s an exciting — but also worrying — possibility for neurolaw researchers. On one hand, neuroscience may help judges figure out when treatment rather than imprisonment is the more helpful option for someone who, for biological reasons, can’t control his or her behavior.

On the other hand, neuroscience has increasingly shown that none of us can really control our behavior.

“Saying, ‘My brain made me do it’ can be problematic because our brains make us do everything,” Farahany said. “Your preferences, your desires, your will power — a lot of that you have no control over.”

Eagleman, in his essay, agrees.

“The choices we make are inseparably yoked to our neural circuitry, and therefore we have no meaningful way to tease the two apart,” he wrote. “The more we learn, the more the seemingly simple concept of blameworthiness becomes complicated, and the more the foundations of our legal system are strained.”

Then the inclusion of MRI and EEG scans as trial evidence is not just a scientific or legal question, Eagleman and Farahany believe, but a philosophical one. In a justice system predicated on the idea that people act with free will, what does it mean to recognize that so much of behavior is biological rather than rational?

“Criminal law is going to have to grapple much more seriously with why people do what they do,” Farahany said.