A Mind Damaged by Addiction

Stimulants may permanently stymie motivation.

By Colin Allen, published on September 1, 2003 - last reviewed on June 9, 2016

One downside of cocaine and amphetamines: Doing stimulants can cut
your motivation to do anything else. Researchers have found that stifled
ambition may be an enduring side effect of a stimulant addiction,
persisting long after the habit is gone. In addition, an area of the
brain involved in curiosity seems to be permanently damaged by the

The findings, published in the Proceedings of the National Academy
of Sciences, explain why stimulant abusers have a hard time kicking the
addiction and often relapse. In the brain, stimulants stunt the growth of
spiny neurons in the nucleus accumbens and pyramidal cells in the
parietal cortex. The former is involved in motivation and reward and the
latter helps with sensory and motor function.

In the experiment, a team led by Bryan Kolb, professor of
psychology and neuroscience at the University of Lethbridge in Alberta,
Canada, exposed one group of laboratory rats to amphetamine and cocaine
for twenty days. A similar group was treated with a sodium control
solution. After this time, both groups of rats were transferred to new
accommodations. Some were housed in normal laboratory cages, while others
stayed in more interesting pens, with multiple levels, ramps, bridges,
tunnels and even a climbing chain. These rats also got toys, which were
rearranged each week to encourage exploration.

After three months, the researchers inspected the condition of the
spiny neurons in each rat's brain. Non-drugged rats that were placed in
the complex cages had spiny neurons with increased dendritic branching,
reflecting new neuronal development. For the stimulant-treated rats, the
elaborate settings did nothing to improve or develop these neurons. Their
minds were the same as the rats left in the simple cages.

Kolb says these findings help explain the repetitive and compulsive
behavior of people addicted to stimulants. Further research may find
experiences that can counteract the long-term effects of stimulants on
the brain.