fuzzyfelt said:
OK, that is a relief! I had been confused by the words and run-ons and thought you were saying the OBE phenomenon or proprioception is specifically located at the TPJ, which seemed a big leap. Rather you only meant that electrodes in that spot caused something-‘failure’, ‘blocking’…- affecting something around the area which has something to do with proprioception. It took me a while to get that!
Sorry if my wording was confusing. Yes, all I meant to say was that the TPJ had been isolated as a critical spot where an OBE could be triggered. What that means is that it's neurological. The TPJ is some kind of important point of contact with the circuit, or circuits that are involved in the OBE, but "OBE activity" in these circuits may range far from that spot.
... but is there any reason to state that lack of sensation is sole cause?
The failure of one sensation, proprioception in this case, is all we need to start a multimodal hallucination in other senses. Removing one class of information, internal sense of body, is all we need to require the brain to reprocess everything else it has to work with into the new fictional picture of the body located floating in the room near the ceiling. If you don't feel located anywhere you confabulate something plausible to account for that and outright hallucinate a view of yourself lying in bed from a perspective near the ceiling.
You may wonder why I don't suppose the visual hallucination precedes the feeling of floating: Autoscopy can, and does, happen by itself with no "floating", as in the report from Ramachandran I quoted to Neodevin. The "double" seems perfectly subject to gravity. In other reports the person's visual perspective can shift from the real position to the perspective of the double and they can look at themselves from either perspective, but neither is floating. It's not a case of being
out of body, but more like suddenly having two separate bodies and one consciousnes that can shift back and forth. There is no automatic tendency for autoscopic experiences to take the form of "floating", therefore there must be some specific trigger for it when they do.
If we suppose that an unexpected failure of proprioception is the primary event, then we have good reason for the hallucinations that follow which are, in effect, answers to the question "Why don't I feel like I'm in my body?"
Interferring with some integrative process (test-for-fit) by the introduction of "noise" seems very unlikely to produce the relatively coherent (however erroneous) experience of the OBE. Failures of integration, agnosias, are incoherent, chaotic experiences. Here's what facial agnosia looks like to a migraine sufferer who has episodic experiences of it:
https://www.amazon.com/gp/product/037570406X/?tag=pfamazon01-20
Sacks describes an equally horrifying, Picasso-like, experience of his leg the first time he tried to stand on it after recuperating from having torn a major muscle loose: it's position seemed to change incoherently six times a second. Ascribing the cause of the OBE to a failure of a specific integration process doesn't fit with the much more chaotic and bewildering, choppy things that actually seem to happen when integration fails. I am more likely to suppose the integration process goes really well in an OBE. The problem with it is that it's based on incomplete data: with no internal information from the body the brain decides it is located floating in the room.
Messages from proprioceptors in the body, like all other sensory information, go first to the thalamus, and they are reworked and sent to the cortex from there. The cortex feeds info back to the thalamus, and the thalamus responds. The thalamus always controls the cortex and has the ability to put the cortex to "sleep": to slow or stop the information it feeds to the cortex and to send those neurons the instruction to stop processing. This is what happens when we go to sleep. This thalamo-cortical-thalamo circuit is where proprioceptive information could be blocked or disrupted. The TPJ may be a critical place to get into that circuit and mess with it.
And no, I didn’t think Ehrsson’s glove experiment that you linked to was more similar to anecdotally reported OBEs, and I think that answers some of your questions. Instead I meant Ehrsson’s OBE experiment that I had linked to.
To explain, I had originally linked to Ehrsson’s OBE experiment as good reason to question Blanke’s OBE experiment since it is a repeatable experiment and unlike Blanke’s, involves healthy people. Another reason was because it may not involve TPJ disturbance. Further, it also is more similar to anecdotal descriptions of OBEs than the experience in Blanke’s case. I raised it again here because it involves virtual sensations, suggesting involvement in this seemingly better OBE experiment of more, rather than less, sensation.
Blankes' is repeatable, in principle, though no one would allow such an invasive procedure under other circumstances. The Ehrrson demonstration is of gravity-bound autoscopy, not an OBE with floating near the ceiling. The Blanke OBE definitely sounds more like the average anecdotal report than the Ehrrson one. Also, I hope it is clear by now that I am not asserting the OBE consists exclusively of the lack of proprioception. The "more sensations" are obviously there, but they are supplied by hallucination: there are no cameras showing you a view of yourself from the outside, no one simultaneously touching you and your virtual image with a stick. That demonstration tells us that proprioception can be fooled: over-ridden by conflicting information from other senses. It doesn't begin to explain why someone should suddenly not feel located in their body or why they have a clear view of themselves from the outside in the absence of a camera set up.
I get the feeling you are attaching to the "healthy" part of the Ehrrson demonstration, as if it's a forgone conclusion that all spontaneous OBE experiencers are neurologically perfectly sound. The full body lab illusion in healthy people requires an elaborate technological set up to create autoscopy. What is creating the autoscopy in the spontaneous OBE? Clearly it is some kind of hallucination, and, as such, pathological: something isn't working right. The notion of a perfectly "healthy" spontaneous OBE doesn't really make sense.