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Drugs and the Brain: Understanding the Default Mode Network

We are going to explore the underlying neuroscience of drugs: how different drugs affect the brain and which areas are activated or suppressed when we are high. The many benefits of drugs: psychedelics and cannabinoids are known when it comes to mental health and cognitive functioning. At CBD testers we have already reviewed lots of evidence for psychedelics and cannabis having positive effects on mood, creativity and the regulation of emotions.

Whilst understanding these positive effects from a distance can be useful as an introduction to these drugs, understanding the neural mechanisms underneath these benefits will help us to understand drugs even better. In today’s article I am going to introduce you to one of the most talked about networks of connected brain regions in neuroscience, the default mode network.

An intimidating name, but a very simple system that has been tied to so many psychological processes of late. The default mode network is a bit of a rockstar when it comes to modern cognitive neuroscience and in this article we will get to know exactly what it is and the many functions it may be linked to, as well as understanding how drugs may affect it.   

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What is the Default Mode Network?

The default mode network (DMN) in its simplest terms is a collection of brain regions that seem to be active when your brain is in its resting state: When you’re not thinking about anything, when your mind is wandering, when you’re using your inner monologue. The idea is that the brain is actually always active, even during states of rest and even when you are asleep. Though this theory itself isn’t exactly new (researches in the 30’s, such as Hans Berger believed this) the DMN was only really discovered after a huge leap forward in the technologies used to measure brain activity.

In the 80’s and early 90’s, much research done on brain regions and their functions was carried out using CT scanners or MRIs. Both produce pretty stationary images of the brain that give little information about the current activity of the brain being scanned. Then, a new method of brain imaging emerged, fmri (functional magnetic resonance imaging). fMRI allowed for real time brain activity to be examined, showing psychologists exactly which parts of the brain were active during an activity, or during rest when participants were doing nothing. Raichle et al were some of the first researchers to define a default network of brain regions active during this resting state. fMRI allowed researchers to look at how different areas of the brain worked together under certain conditions and allowed scientists to view the brain in a much more connected way.

The key areas that seemed to be active in this default mode network were: the posterior cingulate cortex, the medial prefrontal cortex and the angular gyrus. Crikey, those are some rather grim names, but let’s break down what they do. All of these areas in the brain are linked to the perception of the self, as well as predicting what other people are thinking. The posterior cingulate cortex, PCC (labelled on the diagram below) is linked to a variety of functions, including the remembrance of autobiographical memories and the orientation in time and space. The medial prefrontal (mPFC) cortex is linked to emotional processing and the retrieval of memories. Then, the angular gyrus (AG), seems to be linked to self-processing and mentalizing (imagining yourself doing something in the future) as well as putting oneself in another’s shoes (Theory of mind). 

All of these areas, when firing together make up this default mode network and create the resting brain state when our mind wanders off, or when we think about ourselves, or imagine what other people are thinking. So, it seems that the DMN is mostly active when we’re not doing anything, but less active when we are doing goal directed behaviour. Initially the discovery of the DMN was deemed interesting as it allowed for us to remove it from scans of the brain if we wanted to remove a control state, but with more research, the role of the DMN in a number of cognitive functions has come to light.

What does the DMN do?

Since its discovery, the DMN has been implicated in a whole host of functions. It has been linked to the ability to think about the future, imagining future events. It has been linked to theory of mind, experiencing how someone else thinks about the world. It also seems to have a role in dreaming, with the DMN seemingly active in REM sleep. Most notably though, the DMN has been theorised as a network linked to our conscious experience of the world. Recent studies have shown that people with disorders of consciousness (brain injury or a lack of consciousness) seem to have issues in the links between the DMN. Researchers have begun to hypothesise that our DMN is very important in the subjective experience of consciousness and it kind of makes sense given the links the DMN and its constituent areas have with autobiographical memory and daydreaming. 

Getting High & the DMN

With such an integral link to consciousness and perceptions of the self, it’s easy to see why researchers have wanted to investigate the effects of drugs on the activity of the DMN. What would you predict different drugs do to our DMN, an area that seems to be linked with thinking about the self? Well many researchers actually believe that drugs can act as a way to calm down and control the DMN. Overactivity in the DMN has been linked with some mental illnesses, such as depression and anxiety.

As you can imagine a network of brain areas linked to thinking about the self, if overactivated would lead to dangerous thought patterns and indeed that’s true. Studies have shown that the DMN is more active in depressed participants when thinking negatively. So how can specific drugs help?  Well, A recent study into schizophrenia and the DMN has suggested that there may be a rather incredible relationship between cannabis and DMN activity. The paper argues that schizophrenia is linked to a hyperactivity of the DMN, this means that there is too much activity between the different brain areas.

This hyperactivity then makes it harder for the brain to allocate attention to other functions, but also may result in problems with distinguishing between real events and internal thoughts. What the study found, rather incredibly, was that patients with hyperactive DMNs, when given a low dose of cannabis or THC, actually showed a reduction in this hyperactivity. Not only this, but a possible reduction in symptoms was also observed. Though further research is needed to exactly understand the relationship between THC and the default mode network, this study seems to suggest that THC actually decreases the activity in the Default Mode network.

Psychedelics & the DMN

Similar calming effects to the DMN have been observed from psychedelic drug research. Robin Cahart-Harris investigated what was happening to the brain on LSD by scanning participants’ brains using multiple imaging devices. He found that there was a significant decrease in DMN activity, particularly in the Posterior Cingulate Cortex (described above). What the study showed was that this decreased DMN activity was correlated with the experience of a dissolved ego, or ego death. Incredibly, it seems that LSD allows us to think in a less egotistical way because of the dissolution of our DMN. This dissolution, it also seems, allows for experiences of spirituality too. Perhaps, this decrease in DMN activity from psychedelics can explain the many benefits of the drugs on disorders such as depression and anxiety. If LSD and Psilocybin reduce an overactive DMN, this would make sense.

Addiction & the DMN

One other area of drug related psychology that seems to be tied with the DMN is addiction. It seems that an increased activity of specific parts of the DMN, linked to internal thoughts may be linked with drug addiction. Again, suggesting a possible reason as to why some psychedelic drugs which decrease the activity of the DMN may help with some forms of addiction. Of course, this research is still preliminary and there is always a risk when using drugs to treat an addiction, but still it is fascinating research to read. There is also contradictory evidence that suggests that the DMN in drug addicts brains is decreased in certain areas, particularly those linked to self control and the evaluation of reward, so again, caution is needed when reviewing how drugs may help with the treatment of addiction.

Conclusion

Hopefully this article has given an interesting insight into one of the most relevant areas of neuroscience at the moment. The DMN is a truly remarkable network of brain areas and there seems to be no limit to the functions of human psychology it has been linked to. The interaction between the DMN and drugs is also truly fascinating, with the research suggesting that some drugs seem to reduce activity in the DMN, perhaps leading to the calming state of being high and the loss of ego one gets from some psychedelic drugs. I really do recommend looking further into the DMN as it likely holds the answers to some of the biggest questions in psychology.

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Disclaimer: Hi, I’m a researcher and writer. I’m not a doctor, lawyer, or businessperson. All information in my articles is sourced and referenced, and all opinions stated are mine. I am not giving anyone advice, and though I am more than happy to discuss topics, should someone have a further question or concern, they should seek guidance from a relevant professional.

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