In response, a parent of two girls with autism tweeted "gutted to read this. B's statement has been final for 1 yr but no therapy has been done. we're still waiting."
I was really angry. A parent who is waiting for therapy for a child has many reasons to be upset. But the study described on the BBC Website did NOT identify a 'critical window'. It was not about autism and not about intervention.
I was aware of the study because I'd been asked by the Science Media Centre to comment on an embargoed version a couple of days ago.
These requests for commentary on embargoed papers always occur very late in the day, which makes it difficult to give a thorough appraisal. But I felt I'd got the gist: the researchers had recruited 108 children aged between 1 and 6 years and done scans to look at the development of white matter in the brain. They also gave children a well-known test of cognitive development, the Mullen scales, which assesses language, visual and fine motor skills.
It's not clear where the children came from, but their scores on the Mullen scales were pretty average, and as far as I can tell, none of them had any developmental disorders.
The researchers were particularly interested in lateralisation: the tendency to have more white matter on one side of the brain than the other. Left-sided lateralisation of white matter in some brain regions is well-established in adults but there's been debate as to whether this is something that develops early in life, or whether it is present from birth. In the introduction, the authors state that this lateralisation is strongly heritable, but although that's often claimed, the evidence doesn't support it (Bishop, 2013). A preponderance of white matter in the left hemisphere is of interest because in most people, the left side of the brain is strongly involved in language processing.
The authors estimated lateralisation in numerous regions of the left and right brain using a measure termed the myelin water fraction. Myelin is a fatty sheath that develops around the axons of cells in the brain, leading to improved efficiency of neural transmission. Myelination is a well-established phenomenon in brain development.
The main findings I took away from the paper were (a) myelin is asymmetrically distributed in the brains of young children, with many regions showing greater myelin density in the left than the right; (b) although the amount of myelin increases with age, the extent of lateralisation is stable from 1 to 6 years. This is an important finding.
The authors, however, put most focus on another aspect of the study: the relationship between myelin lateralisation and language level. Overall, there was no relationship with asymmetry of a temporal-occipital region that overlapped with the arcuate fasciculus, a fibre tract important for language that previously had given rather inconsistent results (see Bishop, 2013). However, looking at a total of eight brain regions and four cognitive measures, they found two regions where leftward asymmetry was related to language or visual measures, and one where rightward asymmetry was related to expressive and receptive language.
Their primary emphasis, however, was on another finding, that there were interactions between age and lateralisation, so that, for instance, left-sided lateralisation of myelin in a region encompassing caudate/thalamus and frontal cortex only became correlated with language level in older children. I found it hard to know how much confidence to place in this result: the authors stated that they corrected for multiple comparisons using false discovery rate, but if, as seems the case, they looked at both main effects and interaction terms in 32 statistical analyses, then some of these findings could be chance.
Be that as it may, it is an odd result. Remember that this was a cross-sectional study and that on no index was there an age effect on lateralisation. So it does not show that changes in language ability - which are substantial over this age range - are driven by changes in lateralisation of myelin. So what do the authors say? Well, in the paper, they conclude "The data presented here are cross sectional, longitudinal analysis will allow us to confirm these findings; however, the changing interaction between ability and myelin may be mediated by progressive functional specialization in these connected cortical regions, which itself is partly mediated by environmental influences" (p. 16175). But this is pure speculation: they have not measured functional specialisation, and, as they appear to recognise, without longitudinal data, it is premature to interpret their results as indicating change with age.
If you've followed me so far, you may be wondering when I'm going to get on to the bit about intervention for autism and critical periods. Well, there's no data in this paper on that topic. So why did the BBC publish an account of the paper likely to cause dismay and alarm in parents of children with language and communication problems? The answer is because King's College London put out a press release about this study that contained at least as much speculation as fact. We are told that the study "reveals a particular window, from 2 years to the age of 4, during which environmental influence on language development may be greatest." It doesn't do anything of the kind. They say: "the findings help explain why, in a bilingual environment, very young typically developing children are better capable of becoming fluent in both languages; and why interventions for neurodevelopmental disorders where language is impaired, such as autism, may be much more successful if implemented at a very young age. " Poppycock.
A few months ago the same press office put out a similarly misleading press release about another study, quoting the principal researcher as stating: “Now we understand that this is how we learn new words, our concern is that children will have less vocabulary as much of their interaction is via screen, text and email rather than using their external prosthetic memory. This research reinforces the need for us to maintain the oral tradition of talking to our children.” As I noted elsewhere, the study was not about children, computers or word learning.
I can see that there is a problem for researchers doing studies of structural brain development. It can be hard to excite the general public about the results unless you talk about potential implications. It is frankly irresponsible, though, to go so far beyond your data that the headline is based on the speculation rather than the findings.
I am tired of researchers trying to make their studies relevant by dragging in potential applications to autism, schizophrenia, or dyslexia, when they haven't done any research on clinical groups. They need to remember that there are real people out there whose everyday life is affected by these conditions, and that neither they nor the media can easily discriminate what a study actually found from speculations about its implications. It is the duty of researchers and press officers to be crystal clear about that distinction to avoid causing confusion and distress.
POSTSCRIPT
11/10/13: Dr O'Muircheartaigh has commented below to absolve the KCL Press Office of any responsibility for the content of their press release. I apologise for assuming that they were involved in decisions about how to publicise this research and have reworded parts of this blogpost to remove that implication.
References
Bishop, D. V. M. (2013). Cerebral asymmetry and language development: Cause, correlate, or consequence? Science, 340 (6138) DOI: 10.1126/science.1230531
O'Muircheartaigh, J., Dean, D. C., Dirks, H., Waskiewicz, N., Lehman, K., Jerskey, B. A., & Deoni, S. C. L. (2013). Interactions between white matter asymmetry and language during neurodevelopment. Journal of Neuroscience, 33(41), 16170-16177. doi: 10.1523/jneurosci.1463-13.2013
