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Watching the Brain Get “High” on Cannabis in “Real Time”

A recent neuroimaging study discovered the effects of THC during euphoria.

Key points

  • Many different brain regions are involved in the production of the subjective feelings of euphoria.
  • Human neuroimaging studies suggest that there is a common neural circuitry that is shared by diverse types of pleasures.
  • Subjects who received THC demonstrated greater resting-state functional connectivity between the right NAcc and the medial prefrontal cortex.
  • The findings suggest that THC induces two of the brain’s principal reward centers to start talking to each other.

Scientists do not have a complete understanding of what happens in the brain when we experience drug-induced euphoria. Most probably, it is similar to, or at least overlapping with, what happens when we experience general, everyday type happiness. Many different neurotransmitters are known to be involved with the production of feelings of euphoria, including dopamine, serotonin, oxytocin, most of the endorphins, and probably all of the seven known endogenous cannabinoids that are produced in the brain. Similarly, many different brain regions are involved in the production of the subjective feelings of euphoria, including the medial prefrontal cortex, anterior cingulate gyrus, nucleus accumbens (NAcc), and insular cortex.

Human neuroimaging studies suggest that there is a common neural circuitry that is shared by quite diverse types of pleasures. The NAcc is probably the most intensively studied pleasure center of the brain; however, it is now thought that the role of the NAcc extends beyond reward and desire to the negative emotions of fear and disgust. Neuroimaging studies of the effects of euphorigenic drugs in humans may provide insight into the precise role of the other pleasure-related regions of the brain.

Do all of the pleasure-related neurotransmitters in all of the pleasure-related brain regions turn on, or off, in some complex fashion when we are high? No one knows. Yet.

The Brain's Reward Centers on THC

One recent neuroimaging study examined the effects of an acute dose of THC in healthy young adults with a limited history of cannabis use. The study was double-blinded and randomized with a between-subject design. About two hours after being administered THC, the subjects underwent a resting-state functional connectivity MRI (rsfMRI) scan. A resting-state functional connectivity scan measures the temporal correlation of brain activity between different brain regions. The assumption of this type of scan is that brain regions that are active at the same time might be talking to each other. There’s good reason to believe that this assumption is accurate.

The subjects who received THC demonstrated greater resting-state functional connectivity between the right NAcc and the medial prefrontal cortex. The “higher” the subjects rated themselves, the greater was the connectivity between the NAcc and medial prefrontal cortex.

What’s going on in the brain to explain this? The most common feature of all euphoria-inducing drugs is that they either stimulate dopamine receptors or induce the release of dopamine from terminals in the NAcc. The dopamine cells that project to the NAcc are continuously inhibited by the neurotransmitter GABA. That’s why you are not constantly euphoric!

Those GABA neurons have cannabinoid receptors on them that when stimulated prevent the release of GABA. The THC in cannabis stimulates cannabinoid receptors on the GABA neurons, thus turning off the continuous inhibition of dopamine neurons. Voila—you are now euphoric.

Overall, the results of this study suggest THC alone is capable of producing the subjective and neural responses that contribute to the rewarding properties of cannabis by inducing two of the brain’s principal reward centers to start talking to each other.

Facebook/LinkedIn image: AnnaTamila/Shutterstock

References

Wenk GL (2019) Your Brain on Food: How chemicals control your thoughts and feelings, Oxford University Press, U.K., 3rd Edition.

Crane NA, Luan PK (2021) Effect of delta 9-Tetrahydrocannabinol on frontostriatal resting state functional connectivity and subjective euphoric response in healthy young adults. Drug and Alcohol Dependence, Vol 221, Article Number: 108565, Published: ‏ APR 1

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