One of the primary effects of psilocybin (and meditation) is to decrease the activity of the Default Mode Network (DMN), an area of the brain that usually receives about 40% more blood than other areas. The DMN, something like the wandering mind, involves activities such as:
- complex mental imagery
- mental time travel
- theory of mind (thinking about other's thoughts)
- metacognition (thinking about thinking)
In addition to decreasing DMN activity, the integrity of DMN and other networks is decreased. This may be related to feelings of being "fragmented" or a disintegration of self, and may explain distortions in time perception.
EEG amplitudes are decreased, particularly alpha, in part because of a decrease in overall coherence and synchrony. There is more instability, more chaos or entropy. Since the waves aren't aligned, they can't get reach the same amplitudes.
However at a network level, say between the DMN and TPN (task) networks that are usually more anti-correlated, these actually become more similar in activity. The integration of the mind at this level might relate to feelings of oneness.
The decreases in the DMN are correlated with intensity of effects, ego disintegration, decrease in alpha power, as well as an increase in "magical thinking" and speculative ("impetuous") inference.