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PZ'S DUNGEON
CHAMBER 2
If I were to take a stab at addressing these experiences, I'd have to bring up the reticular formation again.  It's a very cool part of the brain, and it is associated with activities that dovetail quite nicely with what is described by "OBE" experients.

The reticular formation is part of the brainstem that seems to be a central integrative core -- it takes in sensory input from all over the place and redistributes it all over the brain and spinal cord.  It has a complex but diffuse structure that baffled neuroanatomists for a long time.  It's not quite gray matter and not quite white, having elements of both.  Cytologically, it contains a huge number of fibers passing through it, and contains widely distributed cells that have broad dendritic arbors splayed out in the transverse plane, like nets sieving through all the information passing by.  Efferent axons just plain go everywhere.

This area has a lot of functions:

1) Regulating spinal motor activity. This is the function I'm most familiar with.  Descending fibers from this region enter the spinal motor column and inhibit or excite spinal output.  This is important in things like sleep paralysis, and also in prepping the body for fight or flight.  For example, if you are trembling in fear, part of that is caused by signals from the RF hypersensitizing motor neurons.

Q: So this might help account for cases that include seemingly uncontrollable, mindless fear?

Sure.  There's also the connection with the sensation of self; I wouldn't be surprised if a little coincidental scrambling of that couldn't lead to a complementary sensation of other.

2) Regulating sensory input. The RF can also gate sensory information to higher centers, either by feeding back on the sensory cells sending information to the brain, or by filtering the information before passing it on to higher centers.  This regulation can go either way, either suppressing information (as you might expect in sleep) or accentuating it, to highlight a particular modality.

Q: You once agreed that a certain hypothesis of OBE origins, according to which sensory input and motor output happen to be suppressed while higher cortical functions incongruously remain well supported during the transition to sleep, seemed plausible.  So the reticular formation has its metaphorical hands in all of these functions, and is thus the likely culprit?

Yes.  You could say that the RF is reaching out in 3 directions: towards motor centers, towards peripheral sensory structures, and towards higher cortical regions.  Maybe the order in which it shuts down those three in the transition to sleep is somewhat variable, and unfortunate individuals in whom the cortical activation is suppressed last experience the distressing symptoms sometimes described.

3) "Coloring" sensory input. Sensations have particular associations.  For example, imagine feeling a pebble in your shoe vs. getting a foot massage.  Both inputs may involve activation of the very same sensory cells, but one is pleasant and the other is unpleasant.  The RF is responsible for integrating the whole of the sensory stimulus and flagging it with additional biases, like "this is uncomfortable" or "this feels good."
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