While there are many studies on this topic currently underway and more to come, research has thus far revealed that the power of psychedelic experiences to promote mental wellness and healing are the result of their ability to temporarily suspend the Default Mode Network (DMN) of the brain (Palhano-Fontes et al. 2015).
The DMN is a section of correlated parts of the brain, consisting primarily of the prefrontal cortex (PFC), posterior cingulate cortex (PCC) and the inferior parietal lobe (IPL). As the brain matures, the DMN starts to rely more consistently on certain pathways and algorithms that become habitual. This is our mind's way of optimizing energy consumption, by helping us to think quicker and more efficiently. This certainly has its benefits, but it also makes learning new behaviors or changing habits more challenging.
The DMN is also thought to be responsible for our ego (Carhart-Harris et al. 2014). According to Sigmund Freud’s Personality Theory (Freud 1923), the personality is composed of three elements: the id, the ego, and the superego. The id consists of our primal desires and urges, while the superego is the moral compass that operates from internalized rules we acquire from our parents and society. The ego is the mediator between the urges of the id, the idealistic standards of the superego, and the demands of reality. The ego, then, forms the identity that helps us best fit in the world—it defines who we are to ourselves and how we project ourselves to others. We need an ego to function productively and collaboratively, but when we begin to internalize it, when our ego becomes one and the same with “I”, our emotions get wrapped up in maintaining it. This leads to pain, fear, or shame when the ego is bruised and we form protective, often limiting, walls to avoid that sort of pain in the future.
During a trip, the DMN has been shown to temporarily shut down, thus creating an experience that's referred as "ego dissolution". This is why people often speak of returning from trips with a whole new perspective on themselves and their lives. Prior to the experience, their perspectives were likely shaded by their ego identity. The quieting or even fully dissolving of the ego during a trip allows one to see that the ego is an object just like thoughts are objects, they are things that live in our heads but they are not "I".
The "I" is the observer to it all in the dance that is life, but internalizing that truth is far easier said than done. Psychedelics are a powerful way to help us get out of our own way, so to speak, to detach from the shade of our ego and confront and take down the protective walls it has built.