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Inhibition and the Mind

7 Post author: Annoyance 21 May 2009 05:34PM

Babies have a curious set of reflexes: lightly brush their palms, or the soles of their feet, and they will immediately grasp whatever caused the contact. In the case of feet, it’s more of an attempt than a successful grasping; human feet, while far more flexible and manipulative than most creatures’, are no longer the virtual hands possessed by our tree-dwelling ancestors and relatives.

These and a few other basic responses are commonly called the “primitive, or infantile, reflexes“, and are unusual for a variety of reasons. For one thing, they’re not permanent. As babies age, the reflexes disappear.

But they’re not gone. Unlike many other reflexes, they don’t originate in the peripheral nerves, but the central nervous system. The reflex patterns don’t cease to exist, and they don’t cease to act. They’re eventually inhibited by more sophisticated parts of the brain associated with the frontal cortex. We know that the reflexes don’t cease to exist because there are conditions that cause them to reappear in adults; most of them involve major brain damage, particularly to the frontal areas, and are used to diagnose the severity of injury in cases of head trauma.. People with cerebral palsy frequently possess the responses as well, although they can often learn to control and prevent the reflexes consciously.

These points illustrate a very important basic principle: the mind is made out of ‘layers’ of modules and functions, starting with the most rudimentary, basic, and primitive, and moving to the most complex and subtle. At no point do the lower levels cease to exist or to produce output; we can act in complex ways only because the more basic reactions are held back and prevented from exerting control.

As various factors reduce the efficiency and health of our nervous system, it’s the most complex subsystems that fail first. The more basic, the more hardwired, and the less emulated the system, the less vulnerable it is to widespread damage or malfunctioning.  This has long been observed with intoxicants and conditions that impair central nervous system functioning, and is one of the ways neuroscientists understand how the brain creates such complex behaviors as a sense of humor.  (Curiously, that's not an aspect of the more modern and recent neurological modules, but is associated with very primitive responses.  That may be discussed later.)

But all inhibition can fail. The more powerful the activity of the lower processes, the less likely it will be that the frontal lobes will be able to control them. Faced with more than it can handle, the 'angel brain' can be overwhelmed, letting the more basic modules to influence behavior and thinking.

This is the primary reason why IQ isn’t adequate to access someone’s intellectual capacity, a topic I will address further in another post.

 

Comments (29)

Comment author: thomblake 21 May 2009 06:15:25PM 7 points [-]

This article seems to be missing either a thesis or a takeaway.

Comment author: Annoyance 22 May 2009 03:01:18AM 0 points [-]

I must disagree with you on both points. The introduction to the piece takes up most of it, I acknowledge, and this is intended as an introduction to a later piece.

People complained that previous posts were too long, so I thought I'd try to keep this short and incremental.

Comment author: CannibalSmith 22 May 2009 10:26:25AM 3 points [-]

In my humble opinion, splitting long articles up is cheating. You should actually make them more concise.

Comment author: JGWeissman 22 May 2009 03:30:34AM 6 points [-]

It boggles my mind that you, in disagreeing with the assertion that your article lacks a thesis or takeaway, do not explicitly state what you claim to be the thesis and takeaway.

Comment author: Annoyance 22 May 2009 06:39:09PM 0 points [-]

I have one person telling me to be terse and succinct, and another insisting that I should repeat myself.

I can't do both.

Comment author: thomblake 22 May 2009 07:03:38PM 1 point [-]

I don't think anyone was telling you to repeat yourself. JGWeissman seems to ask you to make your thesis and/or takeaway explicit. For example, "My thesis is X" or "I argue that X" or "To sum up, X" or "therefore, X".

Comment author: Annoyance 22 May 2009 07:23:55PM 4 points [-]

Thesis: the mind is made out of ‘layers’ of modules and functions, starting with the most rudimentary, basic, and primitive, and moving to the most complex and subtle.

Takeaway: all inhibition can fail. The more powerful the activity of the lower processes, the less likely it will be that the frontal lobes will be able to control them. Faced with more than it can handle, the 'angel brain' can be overwhelmed, letting the more basic modules to influence behavior and thinking.

Comment author: SoullessAutomaton 22 May 2009 10:01:00AM 1 point [-]

People complained that previous posts were too long, so I thought I'd try to keep this short and incremental.

I believe the relevant aphorism here is "make it as short as possible, but no shorter". People complaining about length is preferable to incomplete thoughts.

Comment author: MrShaggy 22 May 2009 05:19:48AM 0 points [-]

Sure, but this is basically only worthwhile to us as an introduction...meaning you just gave us an introduction, the point of which is for something more substantial to come after it. Neat example yes, but still wordy for that neat example. This could've been two paragraphs.

Comment author: PhilGoetz 22 May 2009 06:13:41PM *  0 points [-]

I agree; I have the impression that the takeaway is going to be that "IQ isn’t adequate to access someone’s intellectual capacity", which will be explained in another post. Bit of a tease. :)

Comment author: SoullessAutomaton 22 May 2009 01:03:12AM 1 point [-]

the mind is made out of ‘layers’ of modules and functions,

I'm inherently skeptical of these kinds of computer-influenced metaphors of the mind. In programming terms, evolution is not known for producing well-factored designs with clean interfaces, as the phrasing here would imply.

It seems to me much more likely that the mind is a made out of piles of spaghetti code, with millions of global variables, random important-sounding lines commented out for no obvious reason, and probably numerous security flaws and concurrency-related bugs.

This doesn't necessarily undermine your point, but be careful not to be led astray by the metaphor.

Comment author: Annoyance 22 May 2009 02:57:45AM 1 point [-]

In programming terms, evolution is not known for producing well-factored designs with clean interfaces, as the phrasing here would imply.

True enough, but there are still roughly definable regions and roughly definable functions. The degree to which this is clearly reflected in the underlying neurology is unknown.

We need to distinguish between computers, and the electronic devices that have become popular. The brain is clearly the first, and clearly not the second.

Comment author: kpreid 22 May 2009 01:17:01AM *  0 points [-]

What evidence I know of indicates that brains do have functions somewhat distributed among physical parts -- a fixed set of parallelly-operating modules. Now, this doesn't mean that the modules will be neatly divided with well-defined interfaces like we would consider good practice, but this structure means that the way it operates is more like concurrent/distributed object-oriented programming than like function calls and large imperative procedures. So while I would reject "functions", "layers of modules" is probably more useful than "spaghetti code" for thinking about the overall behavior of our evolved minds.

(Evolution has produced more obvious modules, too; we call them organs. I also suspect that in general "modularity" is very useful for evolvability: if you have modules then it's more likely that a random change (which affects some modules but not the whole organism) won't produce something completely broken.)

(Disclaimer: I am not a biologist, and I am a programmer working with distributed object-oriented systems, so I may be just doing that thing of applying the metaphors I particularly think in.)

Comment author: SoullessAutomaton 22 May 2009 03:01:31AM 1 point [-]

There is certainly localization of functionality, but crazy interdependencies are common at almost all levels. Somewhat less so in many organs, but look instead at the genetic code--discrete units with particular function, but lots of unpredictable interactions and side-effects.

Also note that once you get away from straightforward organs like the heart or lungs, things get a little less clear. Consider the humble liver; it synthesizes certain proteins, produces bile, and breaks down toxins, among other assorted tasks. Why does it do all those things? Why not! Probably each was an easy hack to put into the existing organ.

I'm not saying there's no coherent organizational structure, as that's parently false. However, I think we should be cautious about applying metaphors that prime us to think in terms of human designs when what we're trying to make sense of is the handiwork of Azathoth.

Comment author: pwno 22 May 2009 11:01:01PM 1 point [-]

Was IQ ever an adequate measure of intellectual capacity? IQ has some predictive power, but as a society, we often overestimate that power.

Comment author: MrShaggy 22 May 2009 05:24:22AM 1 point [-]

"These points illustrate a very important basic principle: the mind is made out of ‘layers’ of modules and functions, starting with the most rudimentary, basic, and primitive, and moving to the most complex and subtle."

The evidence you gave doesn't point to this conclusion. Modules and functions are the dominate way of thinking about how the brain works currently, but what you've shown is only that the brain isn't a single process free of contradiction. More importantly, even in the view of modules and functions, the rudimentary/basic/primitive ladder to complex/subtle doesn't follow. Sure the front cortext is more recently evolved, but according to what measure is it more complex than another part of the brain? I could be wrong, but I think you're sort of anthropomorphizing parts of the brain (the reptilian part is primitive, the 'human' part is complex).

Comment author: Annoyance 22 May 2009 06:42:30PM 1 point [-]

but according to what measure is it more complex than another part of the brain?

It directs, integrates, and regulates many of the other parts of the brain, and causes them to work together in particular ways or suppresses their output.

It is responsible for the complexity of what we regard as human behavior. The losses when this part of the brain is damaged are horrifying. Sufficient damage, and it is questionable whether the resulting creature can be considered 'human' in any meaningful abstract sense. (The biological sense is met, of course. But concepts like 'personhood' no longer seem to apply.)

Comment author: MrShaggy 23 May 2009 04:17:09AM 0 points [-]

Right, it's responsible for the complexity of what we regard as human behavior, but that doesn't meant that part of the brain is more complex than other parts. Also, I doubt but do not know that it's the only part that regulates or suppresses other parts.

Comment author: RichardKennaway 21 May 2009 06:33:39PM 1 point [-]

we can act in complex ways only because the more basic reactions are held back and prevented from exerting control.

I don't believe this is the case. The higher levels operate by means of the lower, not instead of them. The lower processes show through on their own not when they are especially powerful, but when the higher processes are conflicted or absent.

Comment author: Annoyance 22 May 2009 02:59:35AM 2 points [-]

The higher levels operate by means of the lower, not instead of them.

In the case of the cortex vs. the limbic system, that is clearly not the case. The two inhibit each other - when one becomes active, the other's activity is reduced.

The layers are even approximately reflected in the brain's gross structure - the newer layers are usually stretched above and across the more primitive ones. This is especially clear when brains from different animals are compared.

Comment author: PhilGoetz 22 May 2009 06:12:02PM 0 points [-]

The models of brain behavior taken from AI architectures - which is going in the wrong direction, but that's what some people do - would say that there is an ordered hierarchy of behaviors. That is, if behavior A sometimes inhibits behavior B, then behavior B never inhibits behavior A.

I think that's wrong for the brain in general. But I don't know if older layers can inhibit newer layers. Can they?

Comment author: Annoyance 22 May 2009 06:45:21PM 3 points [-]

But I don't know if older layers can inhibit newer layers. Can they?

The answer is a resounding 'yes', at least in the sense that sufficient activation of the older parts retards the functioning of the newer.

People with sufficient limbic system activation (rage, disgust, sexual arousal, etc.) literally cannot think in a rational or sophisticated manner. Their ability to control and direct their behavior becomes impaired, and they tend to act impulsively.

Comment author: thomblake 21 May 2009 06:38:00PM 0 points [-]

The higher levels operate by means of the lower, not instead of them.

Probably both. Adults don't normally show the grasping reflex at all. But certainly some actions are built from others.

Comment author: RichardKennaway 21 May 2009 07:02:06PM 0 points [-]

Adults don't normally show the grasping reflex at all.

It needn't look like the grasping reflex when in use by another system. I'm not familiar with the neurology, but if the grasping reflex that can appear in case of trauma is produced by the same system as in the baby (rather than being a chance similarity), then I'd bet money that that system is a functional component of the healthy adult, not a piece of scrap that is being suppressed.

Does anyone want to put up £100 against my £100? I've just googled it, and although I've seen the suppression hypothesis asserted in several places, I haven't found any investigation of the matter.

Comment author: Annoyance 22 May 2009 06:50:37PM 1 point [-]

I think there's some confusion here about what I mean. I will attempt to clarify.

The grasping reflex only occurs when something foreign touches a baby's hand or foot, not when the baby touches itself. It requires the processing resources of the brain to distinguish between the two, which is why this reflex is not mediated by the peripheral nervous system.

As the baby ages, the reflex - by which I mean the action of grasping - dwindles and ceases. It no longer occurs.

The parts of the brain responsible for triggering the action still exist and are known to continue to function. However, their final result no longer occurs.

When sufficient frontal lobe damage takes place, the reflex appears again, which suggests that they either counter the signal from the reflex center or override it.

Comment author: thomblake 21 May 2009 07:05:40PM 0 points [-]

Seems like it would be hard to test. You looking for a long-term bet?

Bald assertion here

Comment author: RichardKennaway 21 May 2009 07:18:04PM 0 points [-]

I think it will have to be long-term. I'll even make a more general hypothesis that this applies to all infant reflexes of all species: for any reflex that can reappear in the adult under abnormal circumstances, the system producing it is a functioning part of the healthy adult.

Comment author: Cyan 21 May 2009 07:23:20PM 1 point [-]

What are some examples of observations or conclusions that would lead to you winning this bet? Likewise losing.

Comment author: RichardKennaway 21 May 2009 07:46:31PM 0 points [-]

What are some examples of observations or conclusions that would lead to you winning this bet? Likewise losing.

Good question. A candidate for deciding the bet would arise if:

Someone investigates some infant reflex in some species, that reappears in the adult under reproducible abnormal circumstances.

They physically locate the mechanism producing it in both cases and demonstrate it to be the mechanism, and the same mechanism in each case, not just a chance mimicry.

They examine that mechanism in the healthy adult.

Then I lose if it is present but having no effect, which might be demonstrated by excising it.

I win if it is found to be a functional part of the nervous system with an identifiable function.

Bet to be decided by the first such candidate that comes to the betters' attention.