Sensing the body
In attending many presentations and talks about eating disorders, one of the more fascinating topics I've heard mentioned was interoceptive awareness. Interoceptive awareness (IA), as a research article on the subject succinctly put it in the title, is "the sense of the physiological condition of the body." What this means is that when you sense things like "pain, temperature, itch, sensual touch, muscular and visceral sensations, vasomotor activity, hunger, thirst, and 'air hunger,'" you are using IA. The input is internal, unlike other senses that are more external. Visual input comes from outside your body; a sense of exhaustion is more internal. Furthermore, an ability to recognize your emotions is also considered part of IA, and all of these IA tasks occur in an area of the brain known as the insula. Wikipedia tells us that the functions of the insula "include perception, motor control, self-awareness, cognitive functioning, and interpersonal experience."
Scientists have long speculated that people with eating disorders have impaired IA. A recent research review article by Walter Kaye examines the evidence of dysfunction in both the insula and in IA as one of the drivers of ED behaviors (Kaye, Fudge, and Paulus, 2009). Research on the relationship between EDs and IA dates back to this paper from 1978 by Garfinkel et al. Impaired IA would help explain how a person with AN might be able to continue to starve themselves--their hunger cues might be impaired. Or how someone with BN might be able to continue to binge--their satiety cues might be impaired. Furthermore, people with eating disorders often struggle with identifying emotions, body size and shape, and fulfilling other biological needs (such as sleep). Poorer IA is also associated with poorer ED outcome (Lilienfeld et al, 2006). I've blogged on my own (mis)adventures with IA here.
I'm still not very talented at figuring out whether I'm hungry or full, whether I'm tired and need a nap or just need to stretch my legs. Some of the hunger/satiety issues were probably thrown off by the eating disorder, but some of it may just be the way I'm wired. I've been in the midst of several full-blown hypoglycemic episodes (feeling faint, shaking, sweating, vomiting) and thinking "How could that be? I don't feel hungry." Obviously. I wasn't trying to delude myself- I've had ED-induced hypoglycemic episodes where I knew damn well it was because I hadn't eaten and I played the green-eyed ingenue. But there were plenty of times where I delayed a meal because I didn't feel hungry and then WHAM! Which is a great example of impaired IA, if nothing else.
A new study published this week found that levels of Brain Derived Neurotropic Factor (BDNF; which encourages the growth of new neurons and helps existing ones thrive) were correlated with interoceptive awareness and maturity fears in people with anorexia and/or bulimia (Mercader et al, 2010). Specifically, the researchers found that higher levels of BDNF were correlated with lower interoceptive awareness and higher maturity fears. The authors suggest that BDNF levels may play a role in regulating ED psychopathology via impaired IA.
Previous research has explored a link between BDNF and both anorexia nervosa and bulimia nervosa.
I'm not thinking that testing BDNF levels are going to become standard of care anytime soon--BDNF is associated with impaired IA but that doesn't tell us much. Does BDNF have an affect on IA or is it just a bystander? How might BDNF affect IA? Does decreasing BDNF levels increase IA?
Like so much research, this paper raises more questions than it really answers. Still, I find it all very interesting.
Our data suggest that BDNF levels may influence the severity of the ED by modulating the associated psychopathology, in particular through the impairment of interoceptive awareness.
6 comments:
I'm half asleep (and should be fully asleep), so if this is a little disjointed, forgive me. But... one of the practitioners I work with told me about a study (that I have not researched) that used balance boards/rocker boards to help people with body dysmorphic disorder to get a better sense of physical self/self in space, and I believe it showed some improvement. She also told me about a study done back in the 80's, I think, where people with anorexia and people with no history of eating disorders were told the measurements of their arms, wrist circumference, legs, waist, etc, etc and then given string that they were supposed to cut to each of the lengths. And on average, the group with anorexia got each measurement about 1 1/2 times longer than it should have been.
Seeing as I struggle with figuring out my body in space (and I think that's partly why I fall down a lot), I find this all fascinating!
Interesting research Carrie - thanks - as ever :)
As a biomedical scientist I love this type of research. It makes much more sense to me than the socio-cultural hypotheses surrounding EDs. However, biomedical research is always accompanied by that important question of 'what to do with the data'.
My worry about this type of research is that it will be taken up by researchers attached to, or funded by pharmaceutical companies who will develop a new drug (e.g. a 'BDNF blocker') to 'treat' EDs.
For all we know, the many metabolic and neurological abnormalities observed in people with EDs may simply be adaptations to disordered eating and starvation. After all, many ED symptoms improve with adherence to an adequate diet and in anorexia nervosa, weight gain.
As you imply, Carrie, this type of research goes a lot further to explaining symptoms rather than curing them. Furthermore, it has the potential to be misused - in the production of yet another centrally-acting drug. We have more than enough 'happy pills' to treat mental illness already, many of which have potentially serious side-effects.
I have a lifelong history of under-eating, long before I ever became anorexic. Now weight restored I still find eating difficult and am inclined to under-eat unless I make an effort to adhere to a meal plan that I know balances my energy expenditure and intake and prevents weight loss. It's better and safer than a pill to improve my IA.
Thanks for posting about this. I too think this is so interesting since I have about zero interoceptive awareness at this time in my life. And I've always been bad at sensing what's going on with my body even before I developed AN. I've always had a hard time telling if I was hungry, if I was sick, and on and on. I get very caught up in research like this because it explains my experiences with AN so well and makes so much sense to me--much more so than socio-cultural explanations of eating disorders. But I think Cathy is right to point out that whereas this helps explain a lot of things, it doesn't necessarily get to what we do next. And I think there is such a danger with research of this type of jumping the gun and assuming we know much more than we do about the brain and how it works. Like you said, it's not clear how BDNF impacts IA and I think there is a tendency to oversimplify these things which is not helpful. I know for me just understanding the biological issues going on with my AN helped me because it made me aware that what I was experiencing had a biological basis and an explanation and helped me to address my behaviors and traits in that way. So maybe some of the way in which this research is helpful is just in creating understanding and awareness. Thanks for posting!
I would love to know how interoceptive awareness difficulties vary amongst people with eating disorders. I know I must have this problem because I generally have no idea when I'm hungry, thirsty or tired, but equally I am very oversensitive to things like temperature, pain (despite a history of self harm), and other uncomfortable stimuli like certain fabrics. I seem to switch between being having the volume turned off and the volume turned way up when it comes to sensation!
I giggled about one of the other authors on Kaye's article being called Fudge. I need to grow up!
Libby,
I did that estimating thing with the string, and it was pretty funny to see just how off I was.
Cathy,
I agree- I don't think BDNF "pills" are the way to go to treat EDs. It would be interesting to see what happens in the mouse model of activity-based anorexia as BDNF levels are manipulated. Because you're right- the BDNF levels could very well be a marker of malnutrition rather than ED psychopathology.
like some of the others, I thought 'huh, this applies to me totally in some ways but not at all in others'. I wasn't able to sense hunger in any way other than abstracts such as being irritable, passing out etc from very early on in my illness. but I've always been almost too aware of the other physiological changes that go along with starvation and refeeding. I was always acutely aware of how cold or hot I was, and cold was safe, warm was not. same for muscle aches, dizziness, pins & needles and so on.
I think some of the impaired hunger cues are definitely related to the physical impact of the eating disorder though. now while refeeding, I most definitely know when I'm hungry, despite eating over 10x what I was a few months ago, and I'm pretty sure I haven't been sneaking any BDNF supplements :P and I know some of this possibly applies more to purging AN than bulimia, but inability to feel satiety is almost certainly related to a) starvation/low weight and your body actually needing large amounts of food, b) eating too fast and c) altered mental state while bingeing. so not all of the hunger/fullness issues even need to be explained by an outside cause, they're part of the eating disorder itself.
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