Gauging the Effects of Head Injuries

Imagine a person who suffers a head injury serious enough to cause a coma. He emerges neurologically intact, or so it seems, until he--and those around him--realize that his personality has turned from a calm Dr. Jekyll to a sinister Mr. Hyde. His life may be spared, but his behavior now is aggressive, socially inappropriate and impulsive, and he can no longer hold down a job.

“It’s bizarre,” said Daniel Hommer, a senior scientist at the National Institute of Alcoholism and Alcohol Abuse. “These guys look very much like people with antisocial personality disorder, exhibiting bad behavior.”

He decided to study these patients to see if there was any undetected brain damage that could explain such a dramatic change in temperament. He worked with several rehabilitation hospitals throughout Maryland and Washington, D.C., and settled on 10 men, half of whom had suffered head injuries from car accidents.

All had been unconscious for at least three days and some as long as one month. They all seemed to have recovered, except their behavior had changed for the worse. Not only were they acting out, but as many as two-thirds of them became alcoholic or addicted to drugs.

It was a medical mystery that Hommer thought he could solve by peering deep into the brain to detect any subtle changes that may have slipped by a common neurological work-up. He gathered a control group of similarly aged men and began his studies using positron emission tomography, or PET, scans to study the brain’s ability to metabolize glucose during a specific learning test.

The men had no changes in intelligence or memory. Just behavior.

Hommer and his colleagues found significant decreases in glucose in regions of the brain that are thought to be important in social and emotional behavior. Specifically, limbic regions on the right side of the brain did not seem to be processing information properly, Hommer said. Another type of brain scan, magnetic resonance imaging, or MRI, showed the same reduction in volume in the right caudate nucleus and the right thalamus.

The findings were presented at the Society for Neuroscience annual meeting in New Orleans last month.

“We found a correlation between metabolism and ratings of aggressive behavior,” Hommer said.

“So many of the changes are found on the right side of the brain,” Hommer said. “These regions are very important for emotional control.” It is not yet clear whether neurons, or brain cells, in this region have been damaged, he said.

The team will do similar brain scans on men with a lifetime history of antisocial personality disorder to see if they have similar brain responses. The team will also do scans on men who abuse their wives.