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Rectal ballon inflation

In my previous neuroscience life I worked as a radioactive urine cleaner at UCLA.

The lab I worked in did some really cool research on the long-term neurological and behavioral effects of methamphetamine abuse. One of the researchers I worked with in that lab, Dr. Berman, was a great guy who had a pretty esoteric research specialty.

A few years ago he published an interesting, unique paper in The Journal of Neuroscience titled "Reduced brainstem inhibition during anticipated pelvic visceral pain correlates with enhanced brain response to the visceral stimulus in women with irritable bowel syndrome".

(CDC website woman indicating bowel discomfort)

Irritable bowel syndrome is an interesting condition which, according to wikipedia and its sources (I know... lazy me), has no clear organic cause, but definitely has a physical effect on sufferers. As Berman et al. say:

Symptom-related anxiety is a key predictor of IBS diagnostic status and mediates the relationship between psychological distress and symptom severity. Brain mechanisms underlying this relationship are unknown but may involve altered preparation for expected pain.

Their idea was simple, and the experiment--while weird--was well done and fairly straightforward. They set out with three hypotheses to test via fMRI; namely that patients with IBS would have:

(1) failure to inhibit arousal and limbic brain circuits during expectation, which would correlate with (2) affective stimulus ratings and (3) brain responses to the aversive stimulus.

What was so weird about this study was the way they induced expectation of pain:

The current study sought to characterize abnormalities in preparatory brain response before aversive pelvic visceral distention in irritable bowel syndrome (IBS) patients and their possible relationship to the consequences of distention.

(Emphasis mine.)

According to their visceral distention procedure:

Distention of the rectum was accomplished using a computer-driven pump (barostat) programmed to deliver phasic pressure steps (38 ml/s) separated by interinflation intervals at the resting pressure... All studies were performed after an 8 h fast and application of 2 Fleet enemas. Affective and perceptual responses to controlled rectal distention were assessed before the MRI protocol.

Basically they took a bunch of IBS patients and control subjects and inflated a balloon in their buttholes until it kinda hurt.

That must have been an interesting IRB meeting.

But you can't say that it's not an effective technique. How do you make people anxious about their bowels hurting? Well, you let them know you're about to make their bowels hurt by blowing up a balloon in their anus. QED.

So, what'd they find?

During anticipation of visceral pain, healthy subjects, but not IBS patients, downregulate homeostatic afferent processing network activity... Anticipatory downregulation is inhibited by negative emotions (stress, anxiety, anger), and these are higher in IBS patients.

The image above shows their major IBS patient finding.

Covariation of negative affect with anticipatory BOLD response. Higher BOLD signal during the cue period (less deactivation) was directly correlated with negative affect (p < 0.01; shown in red) in [the locus coeruleus] (location of crosshairs) and left amygdala (for anger and stress)...

There's a nice behavioral effect here, too, wherein:

Negative emotions support a competing strategy of tonic [locus coeruleus] arousal to disinhibit behavioral response, consistent with IBS patients having greater DBS and dACC activation during actual distention and false positive detection of interoceptive information (INS activity) during sham distention.

It's actually a really cool finding in a well-controlled study. It's just... kinda out there methodologically.

I'm not sure that I'd have volunteered as a control for that experiment.

Berman SM, Naliboff BD, Suyenobu B, Labus JS, Stains J, Ohning G, Kilpatrick L, Bueller JA, Ruby K, Jarcho J, & Mayer EA (2008). Reduced brainstem inhibition during anticipated pelvic visceral pain correlates with enhanced brain response to the visceral stimulus in women with irritable bowel syndrome. The Journal of neuroscience : the official journal of the Society for Neuroscience, 28 (2), 349-59 PMID: 18184777

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