Sickness behaviour – useful concept or psycho-humbug?

Sickness behaviour is a concept that's often referred to in relation to MECFS. I want to see what people think of it. Whether there's something in it, or whether its just a tool used by the mind-over-body crowd.

Here's a rough intro to the concept:

Sickness behaviour refers to the behavioural changes that occur when someone is ill with an infection. Strictly speaking, the term describes behaviours - like excessive sleeping, inactivity, not eating - but nowadays its usually understood to include the psychological states presumed to underlie those behaviours (e.g., depression, fatigue, pain, loss of appetite).

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At the core of sickness behaviour is the idea that these behaviours are adaptive. The inactivity serves to conserve the person’s energy resources for fighting infection, and the hypersomnia and anorexia might serve a similar purpose. Recently, it has also been suggested that these behaviours might serve a social purpose: to prevent others in the social group from getting infected.

Some researchers have argued that, if the behaviours are adaptive, then they are likely to be centrally coordinated- for example, via a mechanism within the central nervous system.

Sickness behaviour occurs following the release of pro-inflammatory cytokines. But the cytokines aren’t seen as directly causing the sickness behaviour. The idea is that the brain plays a crucial mediating role. The cytokines influence brain function, and it is the brain that regulates behaviour. So this is fundamentally different from say, being unable to move or eat because of organ failure or systemic illness (e.g. severe blood loss). In those examples, the limit is imposed by those other bodily systems, not by the brain. In the case of ‘sickness behaviour’ the idea is that there is no physical limitation of this kind – the organism makes a "decision" to invoke these behaviours when appropriate, and the brain is crucially involved in this decision.

I'll come back later and try to explain some of the findings that have been used to support the sickness behaviour concept. But feel free to pitch in if you have any thoughts.

 

For me sickness behaviour in animals is a sighn they are ill. How else could I have seen something is wrong?

 

"Behaviour" seems to be a very malleable word. Sometimes it seems to be used where others might use "symptom", but it seems to imply the possibility that the behaviour is possibly voluntary and could be altered by an act of will.

 

The symptoms attributed to major depression map fairly well to sickness behaviour. One way to interpret this is that the the mind has a powerful effect on the body. Another way to interpret this is that there is a problem with the diagnostic criteria of MD (too broad and unspecific) or with the conceptualization of MD as having a psychological etiology.

The thought that makes most sense to me at the moment is sickness behaviour is probably a survival strategy adopted in response to a variety of threats, and to treat the patient effectively it would be important to find out what the problem in each individual case is.

 

I'm not in a position to speculate about the mechanisms but here's my own personal experience for what it's worth.

I do identify with a state of permanent sickness behaviour. It characterised a period in my early 20s when I had the flu that never ends. I felt rotten all the time and although I was able to override the desire to rest if I needed to, there definitely seemed to be a process going on that was controlling my behaviour. If there wasn't, I think that I would have been constantly booming and busting, with the emphasis more on busting. So, yes, it seems adaptive to me.

My current experience some 25 years later is different. For the most part, I rest as much as I am able to and do things at my own pace. I am taking mostly conscious and deliberate decisions about that. But if I judge things incorrectly (or just don't have a choice in the matter) and I end up overexerting, the there's definitely an element of sickness behaviour in a crash. I am fully aware that if I retreat to bed, I'll recover more quickly but at the same time there's still that innate quality about it that compels. Maybe I have 'learned' the appearance of sickness behaviour so that I don't have to feel it.

What would the mind-over-body crowd make of that?

 

I think sickness behaviour is nature's way to provide the best condition to recover.

 

I did too. With a small independent bussines I could not afford to rest enough.

 

I think that I was saved from this fate because I'd been labelled with a psychosomatic illness at 15. In retrospect, I believe it was the early stages of ME.

At the time, it didn't bother me to have 'psychosomatic' symptoms - I didn't reject the psychological implications - but over the next few years my limitations started to frustrate me and at 20 I adopted a policy of denial. That was when I did my 'pushing through'.

When this culminated in a chest infection and dramatic worsening, I'd figured out that the doctors didn't have a clue. So at a crucial time in my illness, that knowledge game me the security to ignore them.

 

Animals do not speak human language so you must have something else to decide on.

 

Yes, that's it. The term carries with it the implication that you can intervene to change the behaviour without changing the bodily state that gave rise to it. (it may not be "voluntary" in the normal sense of the word though).

Yes, or that these two things only look alike because our descriptions of them are so lame.

Yea, they could operate to help the person fight the illness. But this might be by happy accident, not by design. The "sick feeling" you get with an infection is also your body doing useful stuff on a micro level - like producing interferon, raising your temperature, etc. The fact it makes you feel shitty could be purely accidental. Is it too early to suspect a (bodily) conspiracy, when a simpler account might explain all the facts?

Yes. Then taken up by animal researchers. Hence the emphasis on observable behaviours.

 

It's one step further removed from the patient. As such, it is potentially dangerous, especially in today's insurance climate.

 

The mechanism at play is the issue. One is for interpretation; one is for more than that.

 

Yes, the set of behaviours are not at issue. The idea at issue is whether these behaviours are powerfully mediated by the brain, in a way other types of illness-related behaviours are not (e.g., tiredness from anemia).

The idea is generally that emotion and the misinterpretation of bodily signals may play a role in "inappropriate" sickness behaviour (where there is no evidence of acute infection). Higher cognitive functions aren't usually given a central role.

 

I’ve always thought “sickness behavior” is an involuntary survival behavior, but it’s that damn word behavior that causes confusion. If it were voluntary, that would be more like an act of will. But maybe there’s a small part of AOW.

Quite an interesting topic.

@Jonathan Edwards what say ye?

 

I think casting my mind back a long way, behavior in animals clearly shows that these behaviours do exist in other mammals (cats, dogs, apes etc). Be interesting to see how this translates in some of the more smooth brained animals (geese?). A lot of these studies come from observations and interpretations of individuals rather than anything too scientific, so probably worth taking with a pinch of salt.

My gut says that energy conservation explains a lot. It would be interesting to see whether there are also energy hungry biological systems that are also shut down temporarily while humans are sick.

 

I think you were right the first time. The idea isn't that the behaviours are under "voluntary control" in the same way, as say, deciding whether to eat that cookie. But the implication is that the behaviour is mediated by mechanisms in the brain and CNS. Otherwise, why have a word for it at all? Obviously, if you don't have legs you can't walk, that's not sickness behaviour. That's just the limits that the body imposes on you activity. The implication is that there's something more going on in sickness behaviour.

Yes, its an important question, because the concept is at the centre of a lot of brain-based models of CFS and also of other illnesses such as depression. We need to be able to pull it apart and see what's really being claimed. Cos its a hell of a lot more than what meets the eye.