Previous research has shown that children who started using marijuana before the age of 16 are at greater risk of permanent brain damage, and have a significantly higher incidence of psychiatric disorders.
‘Adolescence is the critical period during which marijuana use can be damaging,’ said the study’s lead author, Sylvina Mullins Raver, a PhD candidate at the University of Maryland School of Medicine.
‘We wanted to identify the biological underpinnings and determine whether there is a real, permanent health risk to marijuana use.’
The scientists began by examining cortical oscillations in mice. Cortical oscillations are patterns of the activity of neurons in the brain and are believed to underlie the brain’s various functions.
These oscillations are very abnormal in schizophrenia and in other psychiatric disorders.
The scientists exposed young mice to very low doses of the active ingredient in marijuana for 20 days, and then allowed them to return to their siblings and develop normally.
‘In the adult mice exposed to marijuana ingredients in adolescence, we found that cortical oscillations were grossly altered, and they exhibited impaired cognitive abilities,’ said Raver.
‘We also found impaired cognitive behavioural performance in those mice. The striking finding is that, even though the mice were exposed to very low drug doses, and only for a brief period during adolescence, their brain abnormalities persisted into adulthood.’
The scientists repeated the experiment, this time giving marijuana to adult mice that had never been exposed to the drug before.
Their cortical oscillations and ability to perform cognitive tasks remained normal, indicating that it was only drug exposure during the critical teenage years that impaired brain activity.
‘We found that the frontal cortex is much more affected by the drugs during adolescence,’ said Keller.”
‘This is the area of the brain controls executive functions such as planning and impulse control. It is also the area most affected in schizophrenia.’
Keller now wants to know whether the effects can be reversed. ‘We are hoping we will learn more about schizophrenia and other psychiatric disorders, which are complicated conditions,’ he said.
‘These cognitive symptoms are not affected by medication, but they might be affected by controlling these cortical oscillations.’
