Growing intelligence in growing brains?

Ed Carr, University of Cambridge School of Clinical Medicine, Addenbrooke's Hospital, Hills Road, Cambridge, CB2 0SP

In Nature this week, Ramsden et al. show – for the first time – that changes brain structure are linked to changes in IQ (1).

Ramsden and colleagues, working in London, noted that whilst an individual’s IQ scores correlate well over time, there is some variation.  They speculated that this variation could be explained by (or at least correlated with) changes in brain structure.  Ramsden et al. performed IQ testing on 33 healthy, neurologically normal adolescents at 2 time points.  At the earlier time point (in 2004), the mean age was 14.1 years and 17.7 years at the second time point (2007/8).  On both occasions a brain MRI was also performed.  Importantly, Ramsden et al. did not inform the volunteers or their families that they would be invited for re-testing at the first appointment.

IQ measurements at the two time points showed a positive correlation.  There were however volunteers for whom a large change had occurred: overall IQ changes of -18 and +21 were found, alongside changes in the parts of the IQ test concerned with verbal (-20 to +23) and performance skills (-18 to +17).  Ramsden et al. correlated these changes with changes in brain structure, as measured by MRI.  As Ramsden et al. had paired samples (from recalling the same 33 volunteers), their experimental design controlled for variations in brain structure due to age, gender, size or handedness.

Increased verbal IQ was correlated with an increased density and size of a speech centre in the left motor cortex.  Changes in performance IQ were correlated with changes in the region of the anterior cerebellum involved in hand movements.  No other changes in brain structure were related to IQ changes, after statistical testing.  Given the functions of these regions, it is plausible that changes in their size could directly cause the observed changes in IQ.  Whether these changes in brain structure can occur at all ages is unknown.

This study suggests that deciding your own strengths and weaknesses (at least in terms of IQ) is best left till adulthood.

References: 

1. Ramsden S, Richardson FM, Josse G, Thomas MSC, Ellis C, Shakeshaft C, Seghier ML, Price CJ. Verbal and non-verbal intelligence changes in the teenage brain. Nature 2011 Nov;479(7371):113-116.
doi: 10.1038/nature10514

Story image from Wikimedia Commons.