CharlieM wrote:Here is an interesting article:
Abstract
Psychedelic drugs have a long history of use in healing ceremonies, but despite renewed interest in their therapeutic potential, we continue to know very little about how they work in the brain. Here we used psilocybin, a classic psychedelic found in magic mushrooms, and a task-free functional MRI (fMRI) protocol designed to capture the transition from normal waking consciousness to the psychedelic state. Arterial spin labeling perfusion and blood-oxygen level-dependent (BOLD) fMRI were used to map cerebral blood flow and changes in venous oxygenation before and after intravenous infusions of placebo and psilocybin. Fifteen healthy volunteers were scanned with arterial spin labeling and a separate 15 with BOLD. As predicted, profound changes in consciousness were observed after psilocybin, but surprisingly, only decreases in cerebral blood flow and BOLD signal were seen, and these were maximal in hub regions, such as the thalamus and anterior and posterior cingulate cortex (ACC and PCC). Decreased activity in the ACC/medial prefrontal cortex (mPFC) was a consistent finding and the magnitude of this decrease predicted the intensity of the subjective effects. Based on these results, a seed-based pharmaco-physiological interaction/functional connectivity analysis was performed using a medial prefrontal seed. Psilocybin caused a significant decrease in the positive coupling between the mPFC and PCC. These results strongly imply that the subjective effects of psychedelic drugs are caused by decreased activity and connectivity in the brain's key connector hubs, enabling a state of unconstrained cognition.
This is the exact opposite of what would have been expected. According to
Wiki normal effects include euphoria, visual and mental hallucinations, changes in perception, a distorted sense of time, and spiritual experiences, and can include possible adverse reactions such as nausea and panic attacks. If this is the case why did they record such a decrease in brain activity?
From
Sam Wong, Imperial College, LondonProfessor David Nutt, from the Department of Medicine at Imperial College London, the senior author of both studies, said: "Psychedelics are thought of as 'mind-expanding' drugs so it has commonly been assumed that they work by increasing brain activity, but surprisingly, we found that psilocybin actually caused activity to decrease in areas that have the densest connections with other areas. These hubs constrain our experience of the world and keep it orderly. We now know that deactivating these regions leads to a state in which the world is experienced as strange."
The intensity of the effects reported by the participants, including visions of geometric patterns, unusual bodily sensations and altered sense of space and time, correlated with a decrease in oxygenation and blood flow in certain parts of the brain.
This is contradictory evidence for brain activity being the source of consciousness.
Actually, i think that finding hints at the opposite conclusion.
If the brain is making sense of the world, and it's own function, then we could suppose that some barin activity serves to model the extent of the body, measure the veracity of perception, determine what to include in 'model of attention (Graziano).
Neural activity has to deal with a lot of 'noise' from confusing stimuli, electro-chemical noise, cross-talk and inherent limits of the sensory systems. Suppose that part of the perceptual system is detecting and correcting errors, suppressing invalid
percepts. You could think of it as a conscillience detector. Inhibit such a function and the apprent error level drops. Even weird percets will not seem weird. A suppressed sense of unreality is the same as a heightened sense of reality. We should expect such supression of neiral activity to lead to perception of strange things that would normally be filtered out, and a sense that they are hyper-real.
Similar reasoning would apply to sense of personal extent. Normally brain function does a good job of mapping the boundaries of the body, but impair that faculty and it could result in body parts seem to not belong to you, or objects around you seeming to be you. It could give rise to sense of being one with everything because your sense of bodily self is suppressed.
It seems obvious to me that inhibiting a time-keeping function will result in distorted time perception with no 'extra work'.
We have a sense of what is known to us that is not identical to access to our knowledge. It seem likely that errors in estimation of what is known would lead to a sense of knowing more or less than one actually knows. In the extreme you might have a sense of omniscience, without any change in the information available to you, simply because your brain has made a poor estimation of it's own capability.
A case for more brain activity when hallucinating might be the idea that the brain is a transmitter of information, or a generator of a virtual world. In each case, if we assume that there is an increase in novel detail the transmitter or generator has more work to do. Both these assumptions suppose a sort of Cartesian Theatre, where there is a subjective entity that experiences a level of detail. Such assumptions are probably false.
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