Long-term use of heroin appears to change how genes are activated in the brain, a new study suggests. This leads to changes in brain function, HealthDay reports.

The findings come from a study of the brains of deceased heroin users. Researchers examined an area of the brain called the striatum, which plays an important role in drug abuse. They discovered major changes in how DNA was being used in the brain. The more years a person had been addicted to heroin, the greater the changes in the brain.

The researchers also found changes that suggest behaviors that lead to overdose have a different basis in the brain than those leading to long-term abuse, the article notes. The findings were presented at the Society for Neuroscience annual meeting on Sunday.

“Our study addresses a critical gap in our knowledge about heroin addiction because we cannot often directly study the brains of addicted humans,” said senior author Yasmin Hurd of the Icahn School of Medicine at Mount Sinai, in New York City. “Our results provide important insights into how human brains change in response to long-term heroin use, and give us the knowledge to help treat this dangerous disease.”