Vestibular processing

My (new, good) sensory integration therapist’s current hypothesis is that the areas of the brain that coordinate between senses aren’t working properly in me.  In particular, she thinks my vestibulo-ocular reflex (the system that automatically adjusts your eyes to compensate for movement) is weak.  This seems plausible.  I get motion sick easily and am constantly running into things, which indicates a proprioception/kinesthesia problem.  But those are not the symptoms that drove me to seek treatment; my inability to filter out sound and especially conversation has a much larger impact on my life.

My first thought was “well, those are right next to each other and develop from similar precursors, it would make sense they’d fail together.”  But she’s not suggesting physical damage*, but miswired connections in the processing apparatus.  I say processing apparatus and not brain because the vestibular system has some extra-brain communication with the eyes, which is why the vestibulo-ocular reflex is so fast.  Some of the neurons that listen to the vestibular (motion/spatial) system run alongside the neurons that listen to the cochlear (hearing) system, which is why they’re grouped to together as the vestibulocochlear nerve, but that wiki article suggested and everything else I read confirmed that the vestibular and cochlear nerves reported to different areas of the brain.  It’s like having two roads run parallel to each other, but it’s impossible to jump from one to another and eventually branch to different locations.  Both will be affected by a snowstorm in their shared area, but a traffic jam at the destination for one won’t affect the other.

My neurology is weak, so I’m not sure what snow storm could be an analogy for.  “Pinched nerve” is a phrase that exists, or perhaps something in the fluid they both float in?  Except the whole point of neurons is to be heavily insulated against outside effects.  What about the destinations?  Were they really so separate?  That is a good question.  The brain does not break down into discrete little units.  It’s not quite true that everything connects to everything else, but it is true that tracking down everything affected by two particular sensory inputs and cross-referencing them is unlikely to be a good use of time.

Now, a digression. After writing down all the reasons The Fabric of Autism was stupid, I find myself reading it again.  Even though it is wrong, it is bringing up facts in the right area, which spurs me to do more research.  Faced with a dense, correct text it’s easy for my eyes to glaze over.  DNBHelp seems to have a pretty good grasp on otology without my help.  But given a light, fuzzy text with an occasional fact that I’m pretty sure is wrong or at least misleading but am unable to explain why, I will do lots of research so I can more accurately explain to it why it is wrong.  This probably won’t scale for the amount of reading I’ll have to do for nursing school, but it’s helpful for now.

I read another two chapters last night.  Mostly it was some nice, fuzzy work about the relationship between sensory input and safety, but there was a throwaway reference to the superior and inferior colliculus as the parts of the brain that process sensory input.  I looked that up, and what do you know:  the inferior colliculus is a processing center for integrating sensory input.  It handles auditory and somatic senses.  Somatic is a broad term, but it includes both proprioception and touch.  It’s involved in both the startle reflex, which means assessing stimulus for danger potential, and that vestibulo-ocular reflex thing we’ve spent so much time on**.  There is some evidence it’s responsible for filtering auditory signals, which is certainly weak in me.

The superior colliculus is just neat.  Say some part of your brain wants to interact with a specific object in the world.  E.g. you want to pick up that glass of water on the table.  How do you translate your sensory input into something your motor system can use to calculate what movements are necessary?  I don’t know, but apparently the superior colliculus does it.  In humans the primary input is visual, but it also handles echolocation and magnetolocation in animals that have them.

After all that, I have a non-exhaustive list of sections of the brain that do sensory integration, one which I find awesome and others of which I glare at with suspicion.  I still don’t have a good sense of what distinguishes a functioning system from a non-functioning one, and that is something I really want.

*Although it seems like something we should maybe check for</divp

**Interesting note:  vestibulo-ocular reflex appears on the inferior colliculus wiki page, but the reverse is not true.  This is probably because a lot of brain structures have their finger in the vestibulo-ocular pot, and we just don’t have time to list them all.