What Cannabis Actually Does to Your Brain?

Scientists at Osaka University found out, that the body’s own cannabinoids, called endocannabinoids, play a very important role in regulating the formation of brain connections. Smoking marijuana whilst the brain is still developing, can interfere with this process. The study, published in the Journal of Neuroscience, analyzes potential dangers associated with the regular use of cannabis during brain development, and clarifies the long-term mystery of how neural circuits are created.

How the brain works?

Researchers have known for some time that when a brain is maturing, it undergoes major structural changes. During the formative period, the number and arrangement of brain connections, called synapses, are remodeled. The neural process occurs in two phases. The first includes the formation and strengthening of new synapses, while the other is characterized by synaptic pruning, which means the unnecessary brain connections are erased to streamline neural circuits.

The research

Scientists used fluorescent proteins to help them track the brain activity of newborn mice. They focused mainly on the development of thalamocortical axons(TCAs), which are the nerve fibers linking the neurons of the thalamus to those of the cortex.

The research showed that after the new-born TCAs developed to a certain point, new connections stopped occurring and many of them started to prune. Researchers found that the shift coincided with an increase in expression of a type of brain receptor known as type 1 cannabinoid receptors (CB1Rs). These findings suggest that endocannabinoids are involved in stimulating synaptic pruning.

As a control group, they chose mice that had been engineered to lack CB1Rs in this region of the brain. Then they injected their brains with THC — the psychoactive ingredient in cannabis. They discovered that when THC binds to CB1Rs it interferes with the proper formation of synapses.

In humans, synaptic pruning occurs during adolescence, therefore any disruption in the process can lead to cognitive impairment. In conclusion, the research suggests that cannabis abuse during adolescence could prevent the formation of healthy neural circuits.