February 2001

From Yale University

Cocaine use decreases ability to respond to stimulation, Yale researchers find

Using an innovative method called transcranial magnetic stimulation (TMS) to measure brain responsiveness, Yale researchers have found that a cocaine addict’s response to stimulation is decreased, indicating possible evidence that cocaine causes permanent brain damage.

"Contrary to what we expected, the results showed that cocaine-dependent individuals displayed increased resistance to brain stimulation," said Nashaat Boutros, associate professor of psychiatry at Yale and principal investigator on the study. "We expected them to be jumpy or more responsive because of the sensitizing effects of cocaine, but it took much stronger stimulation to get them to respond."

Boutros and his team examined 10 cocaine-dependent subjects (four men and six women) who had not used cocaine for at least three weeks and were addicted to no other drugs. A magnetic stimulus was delivered by TMS using a hand-held magnetic coil over the motor cortex, the part of the brain that moves the hands and fingers. The amount of magnetic stimulus needed to move the fingers is an indication of sensitivity in that part of the brain.

The results, published in the February 15 issue of Biological Psychiatry, showed that those without cocaine addiction need about 35 to 55 percent of the output to move their fingers. Boutros said cocaine-addicted individuals sometimes need as much as 80 percent. "Somehow addicts have increased their resistance to the effect of the stimulus," Boutros said.

Boutros and his team started out with the theory that the longer people use cocaine, the more it causes symptoms like paranoia, panic attacks and seizures. "People have thought that a process called kindling—over time, less stimulus is needed to elicit the same response—would apply to cocaine addicts," Boutros said. "But these results raise other possibilities."

Boutros believes there are two possible theories that could explain the findings. One is that the cocaine caused widespread damage that decreased the brain’s ability to respond to stimulation. "The other possibility," Boutros said, "is that the brain was indeed sensitized via the kindling response, and what we’re seeing is a normal response from the brain, like an overcompensation. The brain feels too sensitive from all the cocaine jitter and cools off the response."

A follow-up study, Boutros said, will confirm this initial finding by examining a different group of cocaine-addicted people using additional TMS techniques. TMS has been used to study neurological disorders for 10 years, but was first used in exploration of cortical function in psychiatric disorders about three years ago.












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