“Badass”. That was the word Harvard University neuroscientist Steve Ramirez used in a Tweet to describe research published online by fellow neuroscientist Ali Güler and colleagues in the journal Nature Neuroscience last March. Güler’s group, based at the University of Virginia in the US, reported having altered the behaviour of mice and other animals by using a magnetic field to remotely activate certain neurons in their brains. For Ramirez, the research was an exciting step forward in the emerging field of “magnetogenetics”, which aims to use genetic engineering to render specific regions of the brain sensitive to magnetism – in this case by joining proteins containing iron with others that control the flow of electric current through nerve-cell membranes.

By allowing neurons deep in the brain to be switched on and off quickly and accurately as well as non-invasively, Ramirez says that magnetogenetics could potentially be a boon for our basic understanding of behaviour and might also lead to new ways of treating anxiety and other psychological disorders. Indeed, biologist Kenneth Lohmann of the University of North Carolina in the US says that if the findings of Güler and co-workers are confirmed then magnetogenetics would constitute a “revolutionary new tool in neuroscience”

The word “if” here is important. In a paper posted on the arXiv preprint server in April last year and then published in a slightly revised form in the journal eLife last August, physicist-turned-neuroscientist Markus Meister of the California Institute of Technology laid out a series of what he describes as “back-of-the-envelope” calculations to check the physical basis for the claims made in the research. He did likewise for an earlier magnetogenetics paper published by another group in the US as well as for research by a group of scientists in China positing a solution to the decades-old problem of how animals use the Earth’s magnetic field to navigate – papers that were also published in Nature journals.