Friday Weird Science: Stimulating the Brain...and the Rectum

Dec 10 2010 Published by under Uncategorized

I think @vaughanbell described it best with this Tweet:

@scicurious @edyong209 One of the few studies where you don't want to hear the words "We've made a breakthrough"

And with that...I HAD to blog it. Garvin et al. "Cortical and spinal evoked potential response to electrical stimulation in human rectum." World Journal of Gastroenterology, 2010.

Actually, the purpose of the paper is highly important. The methods though...the methods...


"Rectal stimulation", you say. Sounds all fun and games, but actually this study is an important one. It's looking at potentials traveling up from the rectum to the brain, and trying to detect them in both the spinal cord and the cortex. Finding a good, reliable technique to look at this kind of signaling is very important for finding treatments for diseases like Irritable Bowel Syndrome and certain types of chronic pain.

But that doesn't make the technique any less painful.

The idea was to find a technique that could record evoked potentials in the spinal cord and the brain, in response to rectal stimulation. They managed to get 17 volunteers for this. I can only imagine the recruiting flyer:

Do YOU like having enemas? Enjoy electrical stimulation to the rectum? Do you like having potentials recorded from your spine and brain? If the answer to all these things is "yes", then this study is for you!

If the answer to these is not yes, well, we're offering a lot of money...

So yes. 17 participants. An overnight fast before hand (just to make you look forward to it that much more). When the patients arrived, they were given an enema (if you don't know what that's water or saline, used to flush out the colon. I think you can guess how they might do that). Following the enema, they an electrode up the rectum.


I first thought (when I was looking at the thumbnail) that the electrode was being compared in size to a silver dollar, and I was a bit concerned. But that's actually a dime. That electrode is really pretty tiny! Note that one end of it is unfortunately pointy, though.

They went to insert it about 8-16 cm about the "dentate line", which is located here:


So small electrode, but it's pretty well up in there. It also gets "attached" to your rectal mucosa. They said the procedure was usually done in 2-3 minutes with "minimal discomfort". No lubricant, you don't it interfering with the signals.

Also. There are two of them, about 3 cm apart.

Thankfully, the spine and brain only requires skin electrodes, I can only imagine how hard it would be to get volunteers for a spinal tap.

Now, what they were after here was a reliable technique for detecting evoked potentials coming up from the rectum. You'd think that detecting them in the brain would be the hardest part (it being the furthest away), but NO, the SPINE is the hardest part. In previous studies, they'd only managed to get spinal signals in 40% of the patients. With this new electrode, they were hoping for higher. And they got it! They got a nice 90% signal rate at the brain, and 80% at the spine, which is a pretty nice improvement.

It did require a bit of stimulation. Apparently the 28mA pulse was felt as a "pulse deep within the pelvis". Patients described it at someone tapping or poking your insides. Felt like they had Lemmiwinks in there.


On the left you can see the threshold potential, and the right panel is a stimulation that's 2x stronger. Both of them can be recorded on going ALL THE WAY up the spine, and then nice and strong in the cortex. Those little new electrodes works.

They even had 6 of the participants come back again (!!) and got the same thing, and it was obviously a sensory potential, as when they applied lidocaine jelly to the area, the signals disappeared.

The only problem they had was in 3 of their participants, they could not get a spinal signal. Apparently this only works if your BMI is <25. This is probably due to the fact that the electrodes for the spine are attached externally and probably couldn't sense the spine (they got cortex recordings just fine).

Now...what's the point of all this? The point was to develop technologies to detect rectal stimulation specifically in the spine and cortex. This will allow them to detect potential increases or decreases in potentials in patients with chronic pain or rectal problems for diagnosis of conditions and potential treatment. So it's a good advance in the field. But I'm not sure how much that makes up to the study participants for the electrode up your butt.

Garvin B, Lovely L, Tsodikov A, Minecan D, Hong S, & Wiley JW (2010). Cortical and spinal evoked potential response to electrical stimulation in human rectum. World journal of gastroenterology : WJG, 16 (43), 5440-6 PMID: 21086561

5 responses so far

  • JJ says:

    that's the kind of study for which you don't ask your colleagues to participate 🙂

  • Thrutch Grenadine says:

    JJ, depends on the orientation, so to speak, of the colleagues. I am sure a few people of both sexes would find it - entertaining

  • Bill says:

    As someone who has experience with a rectal ultrasound I wish to assure other readers that a couple of electrodes of the size shown would be an absolute piece of cake. Imagine that the instrument going in was larger than the dime, went further and, once it was in, was shoved around so as to 'improve the picture'.

    If anyone offers you money for accepting those just take it.

    Also - What was being done to that baby.

  • Jan says:

    The baby does look concerned..

  • "Enjoy electrical stimulation to the rectum?"

    LOL, I know I do.

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