Psychedelics and Brain Imaging is an interesting video of a recent talk by Dr Robin Carhart-Harris who recently published a paper on "Neural correlates of the psychedelic state as determined by fMRI studies with psilocybin."
Basically, psilocybin decreases activity and connectivity in the Default Mode Network (DMN) that has to do with internal activities, daydreaming, and the narrative sense of self. This would be in contrast to the Task Positive Network that involves focused attention.
The decrease in connectivity and competition among networks ("profound decoupling") that was seen with psilocybin is similar to that seen in deep meditation as well as early schizophrenia or pre-psychosis. These are all states that reflect a disturbance in ego boundaries.
Mindfulness does similar things in terms of the DMN, and interestingly, so do a number of treatments for depression that reduce medial prefrontal cortex activity, including SSRIs, ketamine, cognitive behavior therapy and psychotherapy, and sleep deprivation. He described upcoming research to investigate the use of psilocybin for depression.
The connectivity in the DMN was described as being something along the lines of "constraints," and there are relationships between increased connectivity and neuroticism on the one hand, and conversely decreased connectivity with agreeableness and extroversion. High connectivity predicts rumination and depression.
From the Q&A there was a comment about the constraints, if you will, and the filters that were proposed by early consciousness explorers such as Blake:
Also the observation that the reduced connectivity seen with psilocybin or meditation might have something in common with the undeveloped brain of a child, or perhaps like our distant evolutionary ancestors.If the doors of perception were cleansed every thing would appear to man as it is, infinite.
A few minutes were devoted to a study on MDMA which noted a distinct positive shift, with bad memories having less activation and good memories having increased activation.
... I hate watching these things on my computer, and as Vimeo currently doesn't make it easy to download video, I found a freeware app that did the trick at Freemake.com.