Sex change and reverse inference
One of my favourite things to rant about to a captive audience of undergraduate students during my lectures is reverse inference, especially in the context of how the popular press covers neuroscience research. What is reverse inference, I hear you ask? It’s when results which measure changes in a physiological measure (e.g., brain structure or function) are interpreted as automatically implying a change in cognition or behaviour. This might seem a little…abstract. But some recent reporting on how testosterone (administered for sex change) alters various structural properties of the brain provides a timely demonstration of this common error.
The Daily Mail, the Telegraph, and the Independent all report on a recent scientific presentation at the European College of Neuropsychopharmacology Conference (which has, itself, been quite a font of newsworthy science in the past week, such as these press releases about hangovers and brain stimulation to treat depression). The scientific presentation appears to have described a study which examined brain changes before and after a month-long period of testosterone treatment in a group of 18 female-to-male transsexual men. As there is no formal research article to examine, it’s hard to verify the details of the study itself. However, most of the news outlets are pretty consistent with their description of the study, in addition to providing the same lengthy quotes from various scientists who were presumably involved in the research.
As mentioned above, the study itself highlighted a series of changes in the volume of certain brain regions, and the degree to which these brain regions are connected before and after testosterone treatment. These findings represent an interesting case study of plasticity – hormones such as testosterone (which is naturally occurring in both genders, although to a greater degree in men) are well known to interact with brain development (a nice undergraduate-level overview can be found here), but it’s rare to find an opportunity to able to study these effects in adults. However, quality of the research, which is difficult to assess without a publication to refer to, and the appropriately detailed descriptions of the study itself are not the main issue with the press coverage here.
The big problem is that, instead of focusing on the brain changes that occur as a result of the testosterone treatment, the news coverage spends an inordinate amount of time referring to implied cognitive changes as a result of the treatment. Remember, no cognitive tests were performed here – only brain scans. Yet, the coverage from the Independent starts off with “Women given testosterone while undergoing a sex change start to think more like men after the treatment, research suggests”. The Telegraph article starts off on a slightly more patronizing tone: “It is a commonly held belief, certainly among the fairer sex, that women are better at multitasking than men. And scientists have now discovered that women undergoing a sex change start to think more like men after treatment as their brains are rewired”. The Daily Mail takes a similar approach with it’s opening: “It is a commonly held, yet widely argued, belief that women are better at multitasking than their male peers. And the findings of a new study have added weight on the female side of the debate”. It continues with the breathtaking leap of faith: “Women are known to have better verbal and multi-tasking skills than men, while men are believed to have a superior spatial ability. And now scientists have discovered that so closely linked is gender – and the ability to take on more than one task at a time – that women undergoing a sex change start to lose the skill.” The BT news website gets a special mention for managing to outdo the Mail. Their headline that “Sex change hormone finally proves men are better at parking, but women can multi-task” is only outdone by the picture of a woman on a telephone with the caption: “Hormones make women better at effective chatting”. This sort of stuff is disappointingly close to a spoof article published in the Onion from a couple of years ago on a similar topic.
Again, just to emphasize, these individuals have not undertaken any cognitive test of their multi-tasking skill (although they certainly could have, which would make for some interesting and complementary science) – they have only had brain scans and the scientists have noted changes in regions of the brain which are associated with certain cognitive processes. This is the reverse inference. That something which has not been tested (multi-tasking skill) must have changed based on changes in something which has been measured (the volume and connectivity of certain brain areas). The article in the Telegraph is perhaps the most egregious offender, stating that “They found that qualities more traditionally attributed to women, such as verbal and multitasking skills, diminished, while others increased”.
This might not seem so unreasonable, but it’s a dangerous game to play. For one, logically-speaking, the reverse inference only holds true if brain areas only perform a certain function. They don’t. Secondly, it’s also only appropriate to make reverse inferences if a cognitive process (such as multi-tasking) relies only on a single brain region. It doesn’t. Indeed, almost all parts of our brain have been implicated in a huge range of diverse processes, and almost all cognitive processes call upon a network of ‘regions’. For those of you who want a hands-on demonstration of this, Neurosynth.org is great fun to play about with, allowing you to click on a particular part of the brain and seeing all of the (amazingly diverse) research associated with that region, or examine which brain areas are frequently associated with different cognitive skills (e.g., visuospatial ability).
As is becoming the norm, none of the articles in question link to an official press release, the researchers, or the conference website. In an amusing failure of editorial control, however, the Telegraph article includes the old trope: “But the study reinforces the idea that “men are from Mars and women from Venus“ because of the way their brains are wired”, while embedding a link to a different Telegraph article aimed at debunking the myth that male and female brains are wired differently from one another.