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I'm looking for a word that refers, in biology, to a negative feedback loop similar to automatic gain control.

Equilibrium is the state reached when competing forces balance out to a steady state.

Homeostasis is what biological systems do to maintain a target state.

What is the English word that means what electrical engineers call "automatic gain control" (AGC)?

For example, one theory of the allergy epidemic has it that our immune system is tuned to protect us from pathogens, but we moderns live in "clean" environments without many pathogens, so the immune system starts reacting to harmless things instead (allergies).

The word would be used like this:

"One hypothesis explaining the allergy epidemic is that it is the result of [word]."

What is this called in biology?

An AGC circuit for example, raises the gain (for example of a microphone) until some level of signal appears.

I hope this question is clear.

[Edit: Googling, I see that some people use the term "risk homeostasis" (https://en.wikipedia.org/wiki/Risk_compensation#Risk_homeostasis) or "perverse homeostasis".

These are close, but "risk homeostasis" is specific to risk.

"Perverse homeostasis" is closer to what I'm looking for, but doesn't make clear what is perverse about it or that the mechanism involves seeking a level of reaction to a (perhaps non-existent) phenomenon.]

[Edit #2: Another phrase I see used is "closed-loop mechanism to generate a fixed response level". That's exactly right, but a terrible mouthful.

Do I need to coin a new word here? What should it be?]

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    Self-adjustment? Self-regulation? Conservation of energy?
    – Ricky
    Nov 20, 2015 at 16:10
  • @Ricky That's going in the right direction, but doesn't describe the target of the adjustment/regulation. Nov 20, 2015 at 16:32
  • Are you looking for hygiene hypothesis? And it might be related to adaptive immune system.
    – ermanen
    Nov 20, 2015 at 17:14
  • @ermanen I'm not looking for something specific to allergies (that was just an example), but to biology in general - a word that means "closed-loop mechanism to generate a fixed response level". Nov 20, 2015 at 17:34
  • Isn't it the feedback mechanism then?
    – ermanen
    Nov 20, 2015 at 18:27

5 Answers 5

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Consider "positive feedback".

"Positive feedback" is a process that occurs in a feedback loop in which the effects of a small disturbance on a system include an increase in the magnitude of the perturbation. That is, A produces more of B which in turn produces more of A. In contrast, a system in which the results of a change act to reduce or counteract it has negative feedback.

  • An example is the process of blood clotting. The loop is initiated when injured tissue releases signal chemicals that activate platelets in the blood. An activated platelet releases chemicals to activate more platelets, causing a rapid cascade and the formation of a blood clot.
  • Lactation also involves positive feedback in that as the baby suckles on the nipple there is a nerve response into the spinal cord and up into the hypothalamus of the brain, which then stimulates the pituitary gland to produce more prolactin to produce more milk.

Source: wikipedia

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I think you're on the right track. Perhaps you could use risk-response overshoot or risk-response overcompensation, in the case of allergies.

You may be talking about negative feedback when you're talking about shut-off at a particular level, but maybe not. It could be positive feedback until maximum response production is reached (so no real shut-off or attenuation, per se).

You may be talking about positive feedback up until a particular level is reached, but maybe not. Depending on the system controls, it could just be production by default until a sufficient amount of negative feedback occurs.

And there could be a mix of the two at play, like in the genetic control of the digestion of certain sugars (lactose etc.).

Overall, a response to a stimulus, including an allergen, is part of the body's bid for homeostasis, certainly, but given that in the case of allergies the response is out of whack, you could use misregulated homeostasis or misregulated positive/negative feedback.

I don't know that you'd really need any additional descriptor to specify the notion of "level", because response level adjustment or maintenance is implied in homeostasis and feedback, but response-level misregulation or misregulated response-level homeostasis are also possibilities, I suppose.

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Thinking about this some more, maybe what I'm looking for is [response-level] homeostasis.

I mean a prefix noun that describes what it is that's being kept static.

For example:

signal level homeostasis - describes microphone AGC

immune response homeostasis - describes the supposed allergic mechanism

risk homeostasis - describes https://en.wikipedia.org/wiki/Risk_compensation#Risk_homeostasis

complaint level homeostasis - what happens when people get used to being pampered or lucky - after a while they complain about tiny things (that they would never have noticed if they had real problems)

Am I on the right track here?

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Try response balancing, or response stabilization.

"One hypothesis explaining the allergy epidemic is that it is the result of response balancing."

"One hypothesis explaining the allergy epidemic is that it is the result of response stabilization."

to balance: verb keep or put (something) in a steady position so that it does not fall. "a mug that she balanced on her knee" synonyms: steady, stabilize, poise, level "she balanced the book on her head"

to stabilize: verb make or become unlikely to give way or overturn. "the craft was stabilized by throwing out the remaining ballast" make or become unlikely to change, fail, or decline. "an emergency program designed to stabilize the economy"

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Damping

Damping is an influence within or upon an oscillatory system that has the effect of reducing, restricting or preventing its oscillations. https://en.wikipedia.org/wiki/Damping

I don't know if this is used to describe biological systems though.

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  • Sorry, that doesn't capture it at all. The problem I'm trying to describe isn't oscillation, it's overreaction. Nov 20, 2015 at 21:35

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