Cocaine boosts learning and decision-making circuits in the brain – but not in a good way, a study has shown.
Using a new technique to peer into the brains of living mice, US scientists witnessed the rapid growth of structures linking memory, drug experience and behaviour.
They say the findings shed new light on the way drug dependency can take over people's lives. Within two hours of being injected with cocaine, the brains of the mice started sprouting dendritic spines, twig-like structures that connect neurons.
The "fast and robust" growth occurred in the frontal cortex, which controls higher functions such as planning and decision-making.
It coincided with a dramatic change in the rodents' behaviour. Given the choice of two environments, mice switched preferences to the one where they had received the cocaine shot.
"It's been observed that long-term drug users show decreased function in the frontal cortex in connection with mundane cues or tasks, and increased function in response to drug-related activity or information.
"This research suggests how the brains of drug users might shift towards those drug-related associations," she added.
To conduct the study, the scientists used a hi-tech laser scanning microscope to look directly into nerve cells through a small window in the skulls of the mice.
Initially the mice were given access to two adjoining "conditioning" chambers, one smelling of cinnamon and the other vanilla. Individual mice settled on one they preferred.
Each mouse was then placed in the chamber they had rejected after being injected with cocaine.
From then on, they gravitated to the compartment associated with the drug.
The findings are published in the journal 'Nature Neuroscience'.