img: Chung et al. (2016)

ten years after the discoverers of 'theta-burst stimulation' also discovered that it doesn't work the way they discovered it, other researchers continue to discuss why it doesn't seem always to work they way other researchers say it does.  

original articles: Park, 2022 (Journal of Neurophysiology), Chung et al., 2016 (Neuroscience and Biobehavioral Reviews), image source

this story was in episode 30 #brainstim #TBS #TMS #methods #reliability

the error bar says

every few months i am given the opportunity, via the academic channels that i paddle in, to scratch a favourite itch of mine, & ask: does theta-burst magnetic brain stimulation actually work?

this story follows-on nicely from the previous one about electrical brain stimulation, but with some important differences - while electrical brain stimulation doesn't generally work, some forms of magnetic brain stimulation do actually work. & that's not just my opinion, that's science.

but there are many different types of electrical & magnetic brain stimulation. one of the magnetic kinds is called theta-burst stimulation. it's a different but related kind of 'theta' to the 'theta' frequency used in other stimulation methods, including the one we just talked about in the previous story. in the magnetic case, theta means that a short burst of three electromagnetic pulses is repeated five times per second for forty seconds. this '5 times per second' is in the so-called 'theta' range of frequencies.

in 2005, a single study reported in the journal Neuron invented & then tested three different kinds of theta-burst stimulation on nine healthy human volunteers. they tested the effects of these three stimulations on how excitable the brain was afterwards. just like Goldilocks tasting porridge in the Three Bears' cabin in the woods, one kind of stimulation decreased excitability, one didn't do much at all & one increased excitability.

seventeen years later, this is exactly the story that most researchers still tell about this paper & this method of theta-burst stimulation. so, it was of course really very lucky indeed that the very first paper on the topic got it exactly right & collected enough data - from those nine participants - to show just exactly how this method must be interpreted for ever more. so it's great that we don't have to read any of the hundred or so follow-up papers.


do you detect some cynicism, reader?

i hope so.

the original Goldilocks paper has been cited by others about 3000 times. but a second paper, published by the same group of researchers eight years later & with six times as much data, has only been cited about 700 times. that's still pretty good! but lots of researchers are still ignoring it & repeating the Goldilocks story from 2005. why?

the reason, i imagine, is that the much better, more careful later paper did not find evidence to support the Goldilocks effects at all. instead, both of the forms of theta-burst stimulation tested did nothing, on average, across their 56 volunteers. awkward.

worse still, a meta-analysis of around 80 studies published a few more years later also found that the Goldilocks effects were: a) relatively small compared to the previous studies, b) affected by strong biases for researchers only to report data that supports the Goldilocks effects & c) very small or negative in the largest, most-precise studies.

that is not good news for the Goldilocks effect.

i've never used this method of theta-burst brain stimulation. one reason is that i don't have access easily to the equipment i'd need, but another is that it is just insane - 600 pulses of electromagnetism are sent into a person's head over a period of forty seconds. for that much electro-zapping, i want to know that it might, just might, actually work.

don't get me wrong: i am not saying that it doesn't work at all, or that there aren't good papers on it. no. i'm just saying we need to change the way we talk about theta-burst stimulation. it is not 'an established effect which is known to show blah blah blah'. rather, 'the effects of theta-burst stimulation are not currently well understood.'

i am telling you all of this because i recently saw yet another paper talking about 'individual variability' in the Goldilocks effect. i am amazed to watch, seemingly in slow motion, a whole research field continue to talk about how some people show the Goldilocks effect & some don't, & how that's really very interesting indeed & we need to know more about it. this is 10 long years after the discoverers of the effect showed so beautifully how it categorically does not work the way they first said it did.

theta-burst researchers: it's time to admit you have a problem.


give it up while you can