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Cannabis Increases Cortical Activity in Users, Resulting in ‘Noisy Brain’

By Leo Bear-McGuinness
Published: Sep 27, 2018   
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According to recent research from the Center for BrainHealth® at The University of Texas at Dallas, cannabis users are more likely to experience increased cortical activation during the brain's resting state compared to non-users.

The study, which was published in the journal NeuroImage, showed that regular cannabis users had "noisier brains" compared to those of nonusers: a side effect which may impair brain activity and disrupt cognitive processes.

While further task-related research is needed for comparison, this increased cortical activity may indicate that cannabis use leads to a loss of neural refinement and efficiency.

Cannabis and brain impairment: a tale as old as time

If you were to ask the general public to name one side effect of cannabis use, you would most likely get a variation on the same answer: impaired brain activity.

Of course, for many recreational cannabis users, this often negatively perceived effect can be their main motive for taking the drug. But several scientific studies have shown the dangers of this slothful stereotype. Research into heavy cannabis use among adolescents showed that the drug can create persistent neurocognitive abnormalities, and another study demonstrated that compared with controls, cannabis users had significantly less bilateral orbitofrontal gyri volume - the area of the brain involved in decision-making.

To date, however, there has been precious little research into whether chronic cannabis use creates similar changes in the baseline resting state and functional organization of neural activity of users.

"This study is the first to characterize global cortical activation and both inter- and intra-hemispheric functional connectivity during resting state in cannabis users," explained Dr. Shikha Prashad, the study's lead author and a research scientist at the Center for BrainHealth.

Getting a brainwave

Traditionally, a brain’s baseline resting state or default mode network (DMN) is thought to be more active when an individual isn’t performing a task.

The researchers measured this form of baseline activity with an electrophysiological monitoring method to record the electrical activity of the brain. Typically noninvasive, this form of electroencephalography (EEG) involved placing electrodes along the base of the 38 participants’ scalps – 17 of which were cannabis users and 21 of which were non-users. The researchers then related any brain activations to the metrics of cannabis use.

To better understand the group’s results, it’s important to first understand the varying degrees of brain waves.

Brain signals, or brain waves, are grouped into five different types. In acceding order of frequency, the bands are delta (1–4Hz), theta (4–7 Hz), alpha (8–12 Hz), beta (13–30 Hz), and gamma (31–50 Hz). These five classifications are associated with different states of mental activity; the highest frequency band, gamma, communicates higher mental activity signals (problem-solving etc.), while the lowest frequency band, delta, is the form of signals sent during dreamless sleep.

The results

Compared to the control group, the cannabis users exhibited decreased delta activity and increased theta, beta, and gamma signals. This kind of high-frequency activity suggests increased cortical activation in the participants’ resting states and a disinhibition of inhibitory functions that may interrupt cognitive processes.

The cannabis users also exhibited an increased level of inter-hemispheric (communication between the two hemispheres of the brain) and intra-hemispheric (internal communication within one hemisphere) coherence relative to the control group.

This increase in activity could signify that participants who took cannabis had difficulty inhibiting their neural activity; an observation that has been made in one of the author’s previous studies. Such a problem of inhibiting one’s own brain activity means individuals find it harder to stop doing certain tasks and feel a sense of helplessness over their own cognition.

All these side effects indicate a great loss of neural refinement and efficiency that may have created, what the researchers term, a “noisy brain”.

Interestingly, this ‘noisy brain’ effect has also been observed in research studying the chronic effects of alcohol, heroin and cocaine, which indicates that ongoing use of any stimulating drug will overstimulate brain activity, even beyond the direct consumption.

What this means for regular users

The researchers’ findings were not entirely unexpected - increased cortical activation has long been understood to be par for the course for chronic alcohol and illicit drug users.

However, the study was the first to characterize both inter- and intra-hemispheric functional connectivity during the resting state of cannabis users. The changes in communication found between these two areas of the brain strongly indicate that cannabis users will suffer, to some degree, from cognitive impairments.

More importantly, though, this loss of neural refinement and efficiency doesn’t just occur during cannabis consumption but is a longer-lasting and more ongoing change to cognitive functions – something that wasn’t known until the publication of this study.

On a more positive note, one meaningful result of the study is an increased level of understanding of cortical activity levels of cannabis users at resting state – information that could one day inform effective intervention programs and treatments.

With regards to follow-up studies, the researchers have suggested that further task-related research is needed for a full comparison. These results would add to the growing literature on cannabis’ effects on the brain and could contribute to the development of electrophysiological patterns; in turn, this could help map and evaluate the success of interventions.


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