Urge for Drugs, Sex, and Food All Linked in the Lizard Brain

When someone hooked on cocaine tells you they "just can't help themselves," they may be right. The dinosaur living in our brains takes over when a cocaine user even catches a glimpse of something that reminds them of cocaine, according to a study released January 30 in the journal Public Library of science.

The limbic system is common in structure and function to that found in modern day reptiles and has probably existed since the time of the dinosaurs. It triggers many of the "unconscious" actions of virtually every land-dwelling animal, such as the fight-or-flight reflex, sexual desire, even controlling your heart rate and the reflex that keeps you breathing.

The research team at the University of Pennsylvania, led by Drs. Anna Rose Childress and Charles O'Brien were curious to see if the amygdala (part of the limbic system), which causes hair trigger reactions to both danger and pleasure cues, would react when cocaine users were presented with pictures that reminded them of their drug use. They hypothesized that the reaction would be "outside of awareness," much like the reaction seen in previous studies conducted by Sygmund Freud in the 19^th Century, later confirmed by modern neuroimaging.

The study was conducted under the auspices and with funding from the National Institute of Drug Abuse (NIDA), part of the National Institutes of Health (NIH). One of the areas NIDA is studying are what triggers the desire to abuse drugs. This breakthrough in understanding the desire to acquire illicit drugs may help formulate a treatment regimen.

"This is the first evidence that cues outside one's awareness can trigger rapid activation of the circuits driving drug-seeking behavior," said NIDA director Dr. Nora Volkow in a press release from the NIH. "Patients often can't pinpoint when or why they start craving drugs. Understanding how the brain initiates that overwhelming desire for drugs is essential to treating addiction."

Subjects in the study were shown images that reminded them of drug use for as short as 33 milliseconds, literally flashed before their eyes much faster than can be consciously perceived, while taking images of their brain activity using fast-reaction magnetic resonance imaging (fMRI).

Childress feels what is going on is that these reminders in the environment are either masking or overriding a drug abuser's natural cravings for normal activities, such as sex and seeking food, since the areas reacting to the drug images substantially overlapped those that respond to sexual images.

"We have a brain hard-wired to appreciate rewards, and cocaine and other drugs of abuse latch onto this system," Childress said. "We are looking at the potential for new medications that reduce the brain's sensitivity to these conditioned drug cues and would give patients a fighting chance to manage their urges."