Mapping Intention with Reflex Supression

[SynapticSelf]

When you reach out to grab something that is hot, or you receive an unexpected electrical shock, the normal human reaction to withdrawal the limb is reflexive, or so I understand. As such, no signal reaches the brain before the reflex begins - if this is incorrect, let me know. However, given warning that the object will be hot (but endurable), or that a mild shock will be administered, we can willfully repress the reaction.

1) How is this accomplished, exactly. No need to dumb it down - I'm trying to learn.

2) Wouldn't this provide a simple way to study "intention"? Couldn't we implement studies in which a control group is ignorant of the heat/shock, while another is completely "in the know", and then monitor brain activity to pinpoint the location of the "intention" to supress the reflex? Or has (as is most likely) this already been done? What has been concluded and where can I find papers on the subject?

 

[honestrosewater]

However, given warning that the object will be hot (but endurable), or that a mild shock will be administered, we can willfully repress the reaction.

I don't know the answers to your questions (though I have read that some reflex arcs do only travel to and from the spinal cord). But are you saying, or assuming, that the reflex is entirely repressed, i.e., it doesn't occur or the signal is interrupted somehow? It seems to me that it could simply be overpowered, i.e., you contract opposing muscles, so the reflexive contraction is partially or wholly counteracted and doesn't move the limb (or whatever) as much.

 

[Cincinnatus]

The mechanisms involved in reflex suppression vary across different reflexes. Moreover, it's not totally clear what we want to count as a reflex and what we don't.

Many circuits involved in motor control are thought to be "central pattern generators" that is, they output some kind of rhythmic activity that can then be used in further computations ultimately leading to movement. There is a lot of research into neuromodulation of these central pattern generators. The thought is that the same circuit can produce several different rhythms (e.g. walking versus running) if the dynamic properties of the circuit can be somehow affected by something called a neuromodulator.

So it might be that during voluntary movement some kind of neuromodulation is occurring which changes the state of the circuits involved in producing the reflexive behavior. There seems to be some evidence for such hypotheses, at least for the vestibular-ocular reflex...

As for your second question about studying intention; I don't know if anyone has tried that, but it sounds like an interesting experiment to me!

 

[SynapticSelf]

But are you saying, or assuming, that the reflex is entirely repressed, i.e., it doesn't occur or the signal is interrupted somehow?

You caught me - I'm assuming. I used to be a cook, though, and in this specific instance I felt my assumption was justified. But then again, we're pretty blind to the inner workings of our minds, so maybe my brain's pulling a fast one on me! I wish I could study this stuff on my own using trial and error style experiments - but alas, brain imaging is not yet condusive to the "stay at home, self taught" demographic...

 

[SynapticSelf]

The mechanisms involved in reflex suppression vary across different reflexes. Moreover, it's not totally clear what we want to count as a reflex and what we don't.

Many circuits involved in motor control are thought to be "central pattern generators" that is, they output some kind of rhythmic activity that can then be used in further computations ultimately leading to movement. There is a lot of research into neuromodulation of these central pattern generators. The thought is that the same circuit can produce several different rhythms (e.g. walking versus running) if the dynamic properties of the circuit can be somehow affected by something called a neuromodulator.

So it might be that during voluntary movement some kind of neuromodulation is occurring which changes the state of the circuits involved in producing the reflexive behavior. There seems to be some evidence for such hypotheses, at least for the vestibular-ocular reflex...

As for your second question about studying intention; I don't know if anyone has tried that, but it sounds like an interesting experiment to me!

Ahh - I recall something similar to this from a while back - patterns in the olfactory bulb. I hadn't been able to come up with a suitable absraction for an efferent pattern. I must admit it's a hell of a lot more attractive than a some unbelievably complicated schematic of individual circuits, as it implies much less genetic hard-coding.

In the case of some emergent subcortical pattern, would the modulators work on the these neurons specifically in order to increase the frequency of the pattern and thus overcome the threshold of the "outputs" of this area, or would the modulators work on the outputs themselves in order to lower the threshold for activation. Or some combination of both, perhaps - one set of modulators to change the freq of the pattern (the "command type") and another set to allow the pattern to produce an effect? (like a binary state "permission")

I realize this is horribly simplified - I find that my idea of the brain is rendered more and more inadequate by the day. I will continue reading...where might one of these general patterns be contained? (Sub-cortical leaves a lot of options!)

 

[honestrosewater]

I used to be a cook, though, and in this specific instance I felt my assumption was justified.

Oh, I was as much asking just to clarify the question for myself. But from a quick look at Wikipedia's http://en.wikipedia.org/wiki/Reflex_arc" article, it seems my idea has already been partially addressed:

[Concluding an example of the patellar reflex] The sensory input from the quadriceps also activates local interneurons that release the inhibitory neurotransmitter glycine onto motor neurons, blocking the innervation of the antagonistic (hamstring) muscle. The relaxation of the opposing muscle facilitates extension of the lower leg.

Haha. Our nervous systems are so clever.

 

[Cincinnatus]

In the case of some emergent subcortical pattern, would the modulators work on the these neurons specifically in order to increase the frequency of the pattern and thus overcome the threshold of the "outputs" of this area, or would the modulators work on the outputs themselves in order to lower the threshold for activation. Or some combination of both, perhaps - one set of modulators to change the freq of the pattern (the "command type") and another set to allow the pattern to produce an effect? (like a binary state "permission")

I realize this is horribly simplified - I find that my idea of the brain is rendered more and more inadequate by the day. I will continue reading...where might one of these general patterns be contained? (Sub-cortical leaves a lot of options!)

Neuromodulators have been observed to work through all sorts of different mechanisms so any of these possibilities you mention could be plausible.

There are several central pattern generators that have been heavily studied, one is the arthropod stomatogastric ganglion (STG) which controls some kind of rhythmic behavior involved in digestion. This is also a system in which neuromodulation has been studied a lot. If you're interested, look up papers by Eve Marder's lab on this topic.