The Default Mode Network and Ego Dissolution: Not So Cut and Dry

Written by Justin Belko

If you follow neuroscience, psychology, or psychedelic science, you’ve likely heard of the brain’s Default Mode Network (DMN) in the context of ego dissolution, a state wherein one’s sense of self is compromised. The total loss of one's sense of self, sometimes referred to as ego death, has been linked to inhibition of the DMN. Dramatized headlines and broad strokes have oversimplified the relationship between the DMN and ego dissolution. When examining research from psychedelic studies, it is clear there's more to the story.

The DMN -What Is It and Where Is It? 

The DMN is just one of the brain's multiple resting state networks. The DMN is not a single tangible brain structure. Instead, it is a set of functionally related regions throughout the entire brain, which have a wide variety of roles. The DMN can be broken down anatomically into its functional hubs, the dorsal medial subsystem and the medial temporal subsystem. 

The functional hubs, active when one is thinking of the self, include the medial prefrontal cortex (mPFC), posterior cingulate cortex (PCC) and angular gyrus. [1,2,5]

When one considers the headspace of others, the dorsal medial subsystem is at play. Activity in this region may influence our ability to socialize. [1-5] The dorsal medial subsystem includes the dorsal medial prefrontal cortex (dmPFC), the temporoparietal junction (TPJ), the lateral temporal cortex and the anterior temporal pole. [1-5]

Finally, the medial temporal subsystem, which plays a large role in memory storage and retrieval, includes the hippocampus, parahippocampus (PH), retrosplenial cortex (RSC) and the posterior inferior parietal lobe. [1,2,5]  

With all its collective components, the DMN acts as a resting state engaged in any thoughts that pertain to our memories or our conceptual knowledge. This includes any time we consider the headspace of others, our place in relationships and the world around us, contemplate our place in future events, and even when we dream or let our minds wander. [5,6]

Misconceptions

Many of the misconceptions surrounding the DMN revolve around the effects of psychedelics, a major misconception being that psychedelics shut off or reset the DMN, thereby causing ego dissolution. Again, ego dissolution is commonly understood as the complete loss or partial breakdown of one's sense of self. [7]

The boundaries one experiences through day to day life separating them from others dissolves, resulting in a temporary loss of self identity. This experience, often called “ego death” can bring immense peace, instilling a sense of collective unity with the world.

While scientific evidence supports the DMN-disintegrating effects of psychedelics , characterized by a temporary decrease in functional connectivity, the relationship between psychedelics and ego dissolution is much more nuanced. [8-12] 

When studied, LSD, psilocybin, ayahuasca, and salvia were all found to reduce DMN activity and promote disintegration. Yet, alcohol, THC and amphetamine all had effects on the DMNs connectivity similar to that of psychedelics, further suggesting that it is not the disintegration of the DMN alone that causes ego dissolution. [13-15]

Psychedelics and the DMN

Given the legally restricted nature of psychedelic research, empirical data on psychedelic drugs and ego dissolution remains somewhat limited. What is known about the relationship between psychedelics and ego dissolution comes from a handful of studies done with various psychedelic compounds. From these studies, a pattern seems to emerge. Psilocybin, LSD, ayahuasca and Salvia divinorum all seem to modify inter-network connectivity, while also decreasing connectivity within the DMN itself. However, subtle differences emerge between the effects of each compound on the brain. 

Psilocybin

With regards to inter-network connectivity, psilocybin was found to increase communication between most of the brain's resting state networks (RSNs), except visual and sensorimotor networks, which experienced decreased connectivity. [16,17]

Considering the DMN alone, a decrease in connectivity, between the mPFC and PCC, as well as a decrease between the cortical regions of the dorsal medial subsystem and the medial temporal lobe of the medial temporal subsystem were observed. [8-10]

LSD

LSD was found to have inter-network connectivity boosting effects similar to that of psilocybin, with the DMN, salience network (SN) and bilateral frontoparietal network all increasing in functional connectivity. [18]  This is quite interesting because the DMN and salience network are slightly competitive in nature, with the SN being utilized for tasks relating to our external environment, engaging our senses to process input. [19]

Within the DMN itself, LSD was found to cause a disconnect between the PH and RSC and a decrease in PCC alpha power. [20] Alpha power being a measure of oscillations speculated to suppress non-task related brain operations. [21-23]

Ayahuasca

The effects ayahuasca exert on the inter-network connectivity of the mind are somewhat consistent with the effects of psilocybin and LSD. Ayahuasca administration was found to boost connectivity between the DMN and the SN, but not affect connectivity within the visual and sensorimotor network. [24-25]

Within the DMN itself, ayahuasca was found to substantially decrease the connectivity of the PCC to the precuneus but leave the mPFC/PCC as well as the PH/RSC connectivity unchanged. [26] 

Salvia divinorum

Similar to that of psilocybin, LSD and ayahuasca, vaporized salvia administration was found to increase inter-network connectivity while also decreasing intra-network connectivity, especially in the DMN.

Other Considerations 

Looking at the nuanced results of these studies makes it clear that while the DMN is implicated in ego dissolution, its disintegration is not solely causative. Based on the current research, it seems that the integrity of one's sense of self rests on a handful of factors other than DMN connectivity, including but not limited to, salience network integrity, the brains oscillatory rhythms, glutamate and GABA activity, and communication between brain hemispheres. In light of this, one should expect future investigation into psychedelics and their interaction with the aforementioned systems.

Furthermore, the patterns that seem to emerge between psychedelics and the DMN cannot be generalized to all circumstances, as contrary results have been found based on the time in which the fMRI data was recorded and whether the subject was clinically depressed. To clarify, in clinically depressed patients, it was found that psilocybin decreased DMN integrity in the short term, but increased DMN activity was observed multiple days later [28]. It is currently unknown whether similar results can be found with other psychedelic compounds and mechanistically why this occurs. 

What is certain however, is that as decriminalization movements work their way across the United States and stigma dissolves, ease of access will allow researchers to develop a deeper understanding of how psychedelic compounds affect the human brain.

References  

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