The brain’s reward circuit – properly known as the mesolimbic reward pathway – is affected by the habitual stimulation of dopamine receptors from alcohol or drugs including marijuana. These changes can be permanent, so it’s important to make sure you understand how the brain’s reward pathway operates so you can avoid doing permanent damage to it.

How Does The Brain’s Reward Circuit Work?

The mesolimbic reward pathway is a dopaminergic pathway that connects several vital areas of the brain. The reward pathway releases dopamine after something deemed to be exciting or pleasurable is experienced. This controlled release of dopamine means that the mesolimbic path regulates things like motivation and addiction.

If the mesolimbic pathway is depleted of dopamine, the person or animal will go to much less of an extent to receive a reward. For example, animals will dedicate less time and energy to finding a favourite food or receiving a dose of nicotine when they’re deficient in their reward pathway.

The reward pathway can produce less dopamine when it begins to perceive natural rewards as being less pleasurable. This can occur when the system is bombarded with drugs that cause an unnatural release of dopamine.

How Does Marijuana Affect The Reward Pathway?

The mesolimbic pathway has a huge role in regard to any sort of addiction or habit.

The excessive use of any pleasurable act can dysregulate the mesolimbic pathway. As we’ve learned, a lack of dopamine in the reward pathway leads to decreased motivation. Conversely, dopaminergic drugs can flood the pathway, increasing motivation – and increasing the chance of addiction.

One study aimed to put a solid link between marijuana and diminished mesolimbic function. It compared a group of 59 daily marijuana smokers who had been regular users for over a decade with 70 non-users. Both study groups were shown visual stimuli related to marijuana – joints, smoking devices, etc. – and their favourite fruits. Fruit is generally considered to be a good example of a natural reward.

The two groups were shown the images while their brains were observed with MRI scans. The chronic pot smokers showed a significantly higher level of activity in their mesolimbic pathways than when they were shown pictures related to marijuana. The non-using group showed positive activity when shown the pictures of fruit, but displayed no significant response to the other pictures.

In short, this shows that consistent use of marijuana disrupts the ability of the reward system to find pleasure in things that non-users enjoy.

Another study, published in JAMA Psychiatry, did a similar experiment. They involved 108 people, all in their early twenties. Instead of using natural reward stimuli like pictures of fruit, they used the power of suggestion. The subjects would play a game which asked them to click a button when they saw a target on the screen, which, when successful, would tell them they might win a financial reward.

Again, marijuana users showed a diminished response in terms of how active their reward pathways became when presented with the suggestion of winning money. There was also a direct correlation between the amount and the length of time the user has reported smoking marijuana, and the blunted response of the mesolimbic pathway.

  • This study goes into some detail about the specifics of mesolimbic deterioration. The reward pathway is connected an area of the brain known as the nucleus accumbens.
  • At the moment of anticipation – right when the subjects knew they had a solid chance to win money – the nucleus accumbens would begin to fire out dopamine. This is the typical reward sensation that we experience.
  • The more intense of an anticipatory response – say, users who were flagged for winning $5 instead of $1 – the more dopamine was released and the more likely the user is to repeat the activity (this also explains why gambling is such a popular addiction.)

Addiction and the Mesolimbic Pathway

This research adds to the already growing amount of information that suggests the mesolimbic pathway has a huge role in addiction. As a user begins to associate the substance or activity of their addiction – be it food, drugs, sex – with pleasure, the mesolimbic pathway begins to respond more actively when stimulated by things related to that particular addiction and less to other pleasurable things.

In short, normal activities become physically and biochemically less enjoyable as a person continues to use drugs. This makes them much more likely to fall into a pattern of addiction the longer they use.

In Conclusion

While marijuana certainly has an effect on the reward pathway, it’s important to remember that this effect isn’t as significant as that caused by cocaine, alcohol, or amphetamines. These drugs cause much larger influxes of neurotransmitters and can saturate entire receptor bodies, leading to much more severe dependencies and cravings.

Marijuana users also seem to generate normal amounts of dopamine, when compared to those affected by addictions to cocaine or alcohol. The brain just doesn’t know what to do with it.

That’s not to say that you should neglect this information. Excessive use of anything pleasurable, including marijuana, can negatively impact your ability to enjoy life.

  • If you begin to think about a particular activity, substance, or habit very often, consider avoiding it. If you can’t, then seek professional help. It might only be a matter of time before these thoughts become actions and you begin losing the ability to find pleasure outside of that activity. Balance is key!
  • If you’ve noticed that you experience some of the symptoms we’ve talked about, you’re not out of luck. Certain nootropics can help restore plasticity to damaged systems in your brain.
  • Surrounding yourself with the following is the healthiest hope to restoring a damaged reward system. These activities all promote enhanced neuroplasticity, allowing neurons to more effectively communicate.
    • Meditation
    • Exercise
    • Positive social interaction; laughter
    • Stress and anxiety management
    • A diet regimen that includes all necessary amino acids

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