“Non-Western Magic in the European Brain” – Return of Voodoo fMRI?

By Neuroskeptic | August 26, 2018 7:34 am

A preprint recently posted on bioRxiv has garnered a lot of attention – mainly because of its title. The article, from Jan Willem Koten Jr et al., is called Occurrence of non-western magic in the European brain, an intriguing although not very informative title for a scientific paper.

The intrigue deepens once we read the paper and find references to the famous ‘voodoo correlations’ and also a new species of neuro-monster: ‘zombie oscillations’, which the authors claim to have discovered and which, they say, may “reflect brain activity that is not under the voluntary control of the individual.”

But spooky terminology aside, what’s really going on?

As far as I can see, this preprint is not about magic or even voodoo correlations. Rather, it is about a signal processing technique called Savitzky Golay (SG) filter, widely used in chemistry and elsewhere. The authors propose that using SG filters instead of conventional filters could help improve fMRI data processing. To this end, they coded a MATLAB toolbox for SG-izing fMRI data and used it on data from a simple working memory fMRI experiment.

The trick, however, is that an SG filter is defined by two parameters: window length and polynomial order. Koten et al. didn’t know the optimal parameters so they tried, well, almost all of them – which is a lot:

For the detrending [high-pass filtering] optimization procedure, the whole window space from 3 to 487 TR’s was investigated in steps of 2. For each window size, the whole polynomial order space from one to window size -1 was investigated.

By their own description, this was a “brute force” approach to statistics. They did the whole thing again to find the optimal SG filter for low-pass filtering. This must have taken a while to run.

Having found the optimal filters, Koten et al. go on to show that they are more effective than existing approaches (unfiltered data or classical SPM filters) with a dizzying set of comparisons:

The bottom line is that the SG filters performed better, in terms of increasing the test-restest reliability of the task-related signal (there were two fMRI sessions, on the same day). SG filters also produced higher connectivity between brain regions compared to SPM (slightly):

A true connectivity of r = 0.22 was detected in raw and denoised timecourses… application of the HRF and Gaussian filters as available in the SPM packages leads to true average connectivities of r = 0.37 and r = 0.34. While application of quasi-optimal and optimal SG filters lead to true average connectivities of r = 0.37 and r = 0.43.

I’m not sure if we can really describe these as ‘true’ connectivities because we don’t know the ground truth (as the authors acknowledge), though.

So what about those ‘zombie oscillations’? These do seem to be a mystery. Koten et al. say that only SG filters, but not SPM, removes these oscillations:

Our analyses suggest that SG filters detect oscillations not related to task, which are substantially faster than oscillations removed through classic SPM high pass filters. We can exclude the possibility that zombies are related to scanner drift, physiological noise as captured by our regressors or head motions…

We can only speculate about the biological meaning of zombie oscillations. Zombie oscillations may contain physiological noise that was not removed by the standard denoising method. Furthermore, Figure S5 shows that SG filters suppress oscillations that originate from the “resting state frequency band”. Hence, one might speculate that resting state signals contaminate working state signals… zombie oscillations may reflect brain activity that is not under the voluntary control of the individual.

Here is, as far as I can tell, the only known picture of a zombie oscillation in the wild (from Fig 10) – the zombies are in red and pink:


I’m not sure what to make of this: these seem to be oscillations slightly faster than the ones picked up by the SPM detrend, but I’m sure SPM would pick them up if the parameters were changed. Whether they have any zombie-like properties remains to be seen.

Overall, this preprint has a brilliant title while the topic described is highly technical and quite preliminary. Savitzky Golay filters may be useful for fMRI, but the specific optimal filters identified by Koten et al. are unlikely to be optimal under other conditions. As they put it, “We are left with the platitude that one study is no study… It is very unlikely that our pipeline generalizes to other fMRI experiments.”

CATEGORIZED UNDER: fMRI, methods, papers, select, Top Posts, voodoo

Science’s Bullying Problem

By Neuroskeptic | August 19, 2018 10:45 am

Over the past few weeks, the stories of three high-profile scientists accused of bullying have emerged: geneticist Nazneen Rahman, psychologist Tania Singer and astrophysicist Guinevere Kauffmann.


Read More

CATEGORIZED UNDER: ethics, science, select, Top Posts

Independence: A New Performance Indicator for Researchers?

By Neuroskeptic | August 18, 2018 2:50 pm

A scientist’s achievements are often measured in terms of the number of papers they publish (productivity) and how many citations those papers get (impact). These ‘bibliometric indicators’ are widely derided but they have proven remarkably stubborn.h-index-joke

Read More

CATEGORIZED UNDER: papers, science, select, Top Posts

A Brief Guide to Neuro-Products

By Neuroskeptic | August 13, 2018 4:41 pm

On this blog I usually focus on academic, scientific neuroscience. However, there is a big world outside the laboratory and, in the real world, the concepts of neuroscience are being used (and abused) in ways that would make any honest neuroscientist blush.

Read More

CATEGORIZED UNDER: funny, media, neurofetish, select, Top Posts

How Accessible is Psychology Data?

By Neuroskeptic | August 6, 2018 5:02 pm

In a slightly depressing new paper, two researchers describe how they tried to get access to the data behind 111 of the most cited psychology and psychiatry papers published in the past decade. The researchers, Tom E. Hardwicke and John P. A. Ioannidis of Stanford, wanted to place the data into a ‘Data Ark‘ to ensure its continued preservation for science. Unfortunately, in most cases, the data was not made available.

Read More

The Kinkiest Scientific Study Ever? Neuro-BDSM

By Neuroskeptic | July 25, 2018 2:38 pm

In an eyebrow-raising new paper, neuroscientists report that they had participants wear a ball gag while watching images of people in pain. The lucky participants in this neuro-bondage were all female BDSM submissives, and their brain activity in response to the painful pictures was recorded with EEG.

Read More

CATEGORIZED UNDER: EEG, papers, select, Top Posts

“Cluster Failure”: fMRI False Positives Revisited

By Neuroskeptic | July 22, 2018 9:31 am

Two years ago, a paper by Swedish neuroscientist Anders Eklund and colleagues caused a media storm. The paper, Cluster Failure, reported that the most widely used methods for the analysis of fMRI data are flawed and produce a high rate of false positives.

Read More

CATEGORIZED UNDER: fMRI, methods, papers, select, statistics, Top Posts

The Ethics of Research on Leaked Data: Ashley Madison

By Neuroskeptic | July 14, 2018 9:07 am

A paper just published reports that Republicans are more likely to have used the adultery website Ashley Madison than Democrats, while Libertarians were even more likely to do so.

Read More

CATEGORIZED UNDER: ethics, papers, science, select, Top Posts

Scientific Self-Correction on Small Talk and Happiness

By Neuroskeptic | July 8, 2018 12:11 pm

Does idle chat and unhappiness go together? Eight years ago, a study was published (Mehl et al. 2010) suggesting that they do. The authors reported that “Well-Being Is Related to Having Less Small Talk and More Substantive Conversations”, triggering many alarming headlines.


Now, however, the same researchers have carried out a much larger study and have failed to confirm the chat-unhappiness association. The new paper is published in Psychological Science, the same journal where the original appeared. What I like about this new article is that it’s a good example of researchers revisiting their own work and openly changing their minds.

Read More

CATEGORIZED UNDER: FixingScience, papers, select, Top Posts

What Is Preregistration For?

By Neuroskeptic | July 3, 2018 4:12 pm


A paper in Psychological Science was taking a beating on Twitter last month.

Read More



No brain. No gain.

See More

@Neuro_Skeptic on Twitter


Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!

Collapse bottom bar