transcript of episode 31: THE SHAVING FOAM FIRE HOSE OF BRAIN NEWS, 10th October 2022

[🎶 INTRO: "Spring Swing" by Dee Yan-Kee 🎶]

welcome to the error bar: over-simplifying brain science since 2021

in this episode: how the mouse eye tells the mouse brain that a mouse is scratching itself, how dogs are everywhere & the two scientific cultures of simplifiers & complificators

here is the brain news on the 10th October 2022:



the New Scientist reports that the reflex pathway for contagious itching has been found, suggesting that contagious itching evolved to protect animals from threats.

you are probably already itching as i speak. i had this experience recently when i was editing a chapter in a forthcoming volume about Somatosensory Research Methods. just reading, seeing, hearing or thinking about itch can make you feel itchy & want to scratch.

this is called 'contagious itch'. it can be annoying. a series of papers report that mice show the same behaviour as humans, even when watching videos of other mice scratching.

this week a paper in the journal Cell Reports makes the case that this visually-induced itching response - in mice - depends on specific chemical signals in a specific brain pathway that takes visual signals from the eyes to the brain.


has the neural basis of contagious itch been found?


the error bar can only hope to scratch the surface of this work. it's deeply biochemical, molecular work that is way, way beyond my expertise. but it was by far the most interesting neuroscience story covered by the news in the last two weeks. so i have tried - tried - to read it.

for background, i also read a 2017 paper by the same group in Science magazine. this paper was easier to follow & contained both behavioural & biochemical tests of visually-induced itching - in mice.

the behavioural experiments were done on 7 or 8 mice in different groups. each mouse was paired-up with a demonstrator mouse in an adjacent, transparent box. the experimenters noted how long each mouse looked at the demonstrator mouse & when it scratched itself. one group of demonstrator mice had a chronic itch condition which meant they scratched themselves a lot. the question was: would the observer mice scratch themselves after viewing the demonstrator mice?

yes. a lot. over a 60-minute period, mice watching a very scratchy mouse would imitate them about 5 times each, while only one of the mice watching a non-scratchy mouse gave a single imitatory scratch. & this was not because the mice did not look, or because they didn't, in general, scratch; & it still worked via video-feed rather than in person, so to speak.

then it got complex. a chemical called c-Fos was found more often in the dissected brains of mice that had been 'perfused & processed' - a biological synonym for killed. the brain areas implicated were the suprachiasmatic nucleus, nucleus accumbens, caudate putamen & amygla - urgh - & amygdala - which are all important brain areas involved in lots and lots of things. the suprachiasmatic nucleus was then focused on - this brain area receives visual inputs directly from the eyes, so the researchers assumed that it plays an important role in contagious itch.

one comment from me: despite this paper being in the world's most prestigious, journal, Science, the statistics are incorrect here: only 3 mice were studied in each group, with each mouse contributing 10 slices of brain to the c-Fos analysis; but the statistical test did not take this nested data structure into account - we have 10 brain samples from 3 independent mice, we don't have 30 independent samples, as the test assumed.

then it got more complex. the legend to Figure 3 is 231 words long, but only 137 of those are actual words - the rest is acronyms, symbols & numbers. so i shall summarise the rest of the Science paper by saying: the authors proposed that a chemical called GRP in the SCN is responsible for contagious itch in mice & that its input comes directly from light-sensitive cells in the eye.

now back to the new article from 2022.

the new paper replicates these basic effects - mice scratch themselves more after watching another mouse scratch - & the authors then rule in & out other chemicals, visual pathways & mechanisms that might account for this behaviour. but it's done in so much jargon- & acronym-laden detail that...

...i have given up, dear listeners. perhaps this is how most science journalists feel when confronted with scientific papers so dense & so full of technical terms that they are almost impossible to read, even with a science background.

i shall say only this: if true, this would be a remarkably-specific visual pathway. the claim is that light-sensitive cells in the eye are able to extract the specific visual features of another mouse scratching itself & that this visual scratching signal is sent directly to a part of the brain that processes the information & cues the mouse to scratch itself. that would be remarkable.

but it's probably worth pointing out that a second group of researchers replicated the original 2017 study, in Science, under identical conditions & with larger numbers of mice. they concluded:

"Despite using mice of the same strain, age, sex, & supplier as [the former paper by Yu & colleauges], we found no evidence for itch contagion in mice using either their definition of imitative scratching or other, less stringent, definitions."


detailed & unreplicated


the science was by Gao et al. 2022: Cell Reports, Yu et al. 2017: Science, Liljencrantz et al. 2017: Science, & Barry et al. 2017: Science; reported in The New Scientist by @so_dendritic on 4/Oct/22



fans of the English popular music combo 'Pulp' will recognise the title of this story. in their song 'dogs are everywhere', they predicted:

"Oh, dogs are everywhere
Almost everywhere
That I go
They have too much and then
They have too much again
And then more"

these lyrics from their 1987 album 'Freaks' serve as a remarkable prediction of the state of the British tabloid newspapers' coverage of brain science news in October 2022. here are the dog-related headlines & brain science papers from the last two weeks:

1) "Why stroking dogs is GOOD for you (not that you need an excuse): Petting pooches engages the part of the brain responsible for social and emotional interactions, study finds"

2) "Effects of contact with a dog on prefrontal brain activity: A controlled trial"

3) "From smelling when we're stressed to sensing when we're lying: These are all the things dogs know about us after 30,000 years living alongside humans"

4) "Dogs can sniff out the scent of stress, new study suggests"

5) "Your dog NOSE when you're stressed: Pooches can smell changes in your breath and sweat that indicate you feel under pressure, study finds"

6) "Exploring behaviours perceived as important for human—Dog bonding and their translation to a robotic platform"

i mean six fu[BONG]ng dog stories in one episode.


are there no other studies


the science was by Riddoch et al. 2022: Public Library of Science ONE, & Marti et al. 2022: Public Library of Science ONE; reported in The Daily Mail by Fiona Jackson on 5/Oct/22, & The Daily Mail by @jwillchad on 30/Sep/22, & The Independent by @ninamasseypa on 28/Sep/22, & The Daily Mail by Fiona Jackson on 28/Sep/22



inspired partly by this week's paper on the excruciatingly-specific neural basis of contagious itch in a very particular strain of mouse; along with my own chequered history of rarely believing scientific papers on face value, especially the complicated ones, i wish to discuss Occam's razor.

William of Occam, a Catholic friar & philosopher, lived 675 years ago in the small village of Ockham in South East England. in modern times, the parish of Ockham contains a golf club, a craniosacral therapist, two paintball games parks & Junction 10 of London's popular orbital motorway & car park.

but Occam is perhaps best known for his 'Razor' - the philosophical principle that "entities should not be multiplied beyond necessity". we should always prefer the simplest explanation available.

it is with Occam's razor that i have shaved the faces of many neuroscience topics in my career, from my PhD looking at the complex concepts of the 'body schema' (what Occam might have called 'the brain') & 'peripersonal space' (which Occam found rather tricky to distinguish from the very similar & well-studied mechanisms of selective attention), to some of my postdoctoral work on the lofty 'principle of inverse effectiveness' (for which Occam used the word 'correlation').

yet William was not the only principled philosopher in 14th century Surrey. much lesser-known is Frank of Effingham, who lived just the other side of the golf club from William. Effingham believed, to Occam's great annoyance, that knowledge is disseminated most swiftly when concepts are "befuddled, confused & multiplied with little care or attention".

this principle has become known as Effingham's Shaving Foam Fire Hose.

one of Effingham's great contributions to brain science is in the application of his principle to scientific progress. Effingham realised that, just as soon as most researchers fail to replicate the key findings in a particular field or method, is exactly the time to invent a new method, only very slightly different to the old & failing one; not close enough to be united; not far enough to be unrelated.

in my own field, for example, transcranial magnetic stimulation was invented because its forerunner, transcranial electrical stimulation was too painful; transcranial direct current stimulation was invented because transcranial magnetic stimulation was too difficult; transcranial alternating current stimulation was invented because transcranial direct current stimulation didn't work; & transcranial random noise stimulation was invented because most of the other acronyms had already been used.

so on this, the 675th anniversary of William of Occam's 'Razor', i celebrate the 649th anniversary of Frank of Effingham's Shaving Foam Fire Hose: spreading scientific concepts around with little regard for parsimony or taste.

eight hundred years ago today, in 1322, Frank of Effingham founded the journal 'Current Biology'.


let us pray


[🎶 OUTRO: "Cosmopolitan - Margarita - Bellini" by Dee Yan-Kee 🎶]

it's closing time at the error bar, but do drop in next time for more brain news, fact-checking & neuro-opinions. take care.

the error bar was devised & produced by Dr Nick Holmes from the University of Nottingham. the music by Dee Yan-Kee is available from the free music archive. find us at the error bar dot com, on twitter at bar error, or email talk at the error bar dot com