“The brain on marijuana will never deviate from its destined disposition, nor be driven by madness.” - Charles Baudelaire

Already in 1860, the famous poet Charles Baudelaire was writing about the possible effects of marijuana on the brain. However, the custom of smoking marijuana is very ancient, dated a thousand years ago, with traces dating back to the Neolithic era. In all these years of “getting high”, have we really understood how cannabis alters the brain activity?

Nowadays, by means of neuroimaging techniques such as functional magnetic resonance imaging (fMRI), we are able to measure brain activity by detecting the changes associated with blood flow and connectivity between brain regions. This is a very powerful method to uncover alterations in brain activity when people take drugs, such as cannabis.

While working on my bachelor thesis, I have run a meta-analysis aimed at understanding which brain regions are specifically affected as a consequence of chronic cannabis use.

This lead to multiple results:

Chronic cannabis users present an increased connectivity in anterior cingulate cortex (ACC) and in the amygdala.

A greater connectivity in those areas indicates an alteration of the emotional side, and everything related to the affective part of one’s personality. Is this a good thing? Such an increased connectivity doesn’t always match with an improvement. Thus, frequent cannabis users could show problems in controlling their feelings, for example in stressful or emotionally rich situations (Lassen et al.,2007).

Cannabis usage enlarges the functional connection between nucleus accumbens (NAc) and orbitofrontal cortex (OFC).

These areas are, instead, involved in the decisional spheres one’s brain. What does this mean exactly? We can interpret this as proof that cannabis can alter the answers in decisional processing, making it possible for a cannabis user to evaluate and decide on things in the wrong way.

“it’s hard to be mean when you’re stoned” - Bill Lee

Cannabis alters the activity within the areas controlling attention, like the middle temporal gyrus and the subcallosal cingulate gyrus.

This suggests that you can’t be very focused when you’re high.

But at the end of the day, what’s the point of all such research?

The data from this meta-analysis suggest that usage of cannabis affects the brain in the areas related to attention, perception and emotion handling, changing brain connectivity and its activity.

Nevertheless, despite the advancements of scientific research, more work is needed on this topic before we can fully grasp and comprehend the way cannabis affects the human brain.

Why is research so important in this field?

In 2009, it has been estimated that 25% of young Americans, between 13 and 19 years old, used marijuana in the month prior to the investigation, and about 5% were daily users (Partnership for a Drug-Free America, 2010).

This survey shows how much important it is to acknowledge the increasing popularity of cannabis. This necessarily means that we should strive to provide consumers, especially the young ones, with a global and accurate overview of the effects.

Future research should then evaluate how much of the mentioned changes in one’s brain are reversible, and how much they relate to emotional, cognitive and behavioural alterations.

Do you want to know more? Please read:

• Yezhuvath (2013). Functional connectivity in inhibitory control networks and severity of cannabis use disorder.
• Harding IH, e. (2016). Functional connectivity in brain networks underlying cognitive control in chronic cannabis users.
• J, F. (2014). Differential reward network functional connectivity in cannabis dependent and non-dependent users.
• Jacobus J, e. (2012). Altered cerebral blood flow and neurocognitive correlates in adolescent cannabis users