the study was approved by the joint ethics committee of the institute of neurology and the national hospital for neurology and neurosurgery , london , uk .
all structural and functional scans at time 1 and time 2 were acquired from the same siemens 1.5 t sonata mri scanner ( siemens medical systems , erlangen , germany ) .
the structural images were acquired using a t1-weighted modified driven equilibrium fourier transform sequence with 176 sagittal partitions and an image matrix of 256  224 , yielding a final resolution of 1 mm [ repetition time / echo time / inversion time = 12.24 ms / 3.56 ms / 530 ms ] .
pre - processing of 66 structural images ( 33 participants  2 time points ) used spm8 ( http://www.fil.ion.ucl.ac.uk/spm ) with the dartel toolbox to segment and spatially normalize the brains into the same template ; with and without modulation .
modulated images incorporate a measure of local brain volume while unmodulated images , used with proportional scaling to correct for global grey matter , provide a measure of regional grey matter density .
previous studies have shown the correlations between brain structure and cognitive ability are better detected by grey matter density .
images were smoothed using an 8 mm isotropic gaussian kernel at full width half maximum ( fwhm ) . the relationship between change in iq and change in brain structure
was investigated by entering the appropriate pre - processed images ( modulated or unmodulated grey or white matter ) into within subjects paired t - tests , with change in iq ( viq , piq or fsiq ) and year of scan as covariates . the degree to which time 2 iq was predicted by changes in brain structure
was investigated in a hierarchical regression analysis with time 1 iq entered before change in brain structure .
details of the functional imaging paradigm have been reported elsewhere and are summarised in supplementary information ) .
 intelligence quotient ( iq ) is a standardized measure of intellectual ability that taps a wide range of cognitive skills1 . across life span 
 , iq is generally considered to be stable with scores at one time point used to predict educational achievement and employment prospects in later years1 . 
 neuro - imaging allows us to test whether unexpected longitudinal fluctuations in measured iq are related to brain development . 
 here we show that verbal and nonverbal iq can rise or fall in the teenage years , with these changes in performance validated by their close correlation with changes in local brain structure . 
 a combination of structural and functional imaging showed that verbal iq changed with grey matter in an area that was activated by speech , while nonverbal iq changed with grey matter in an area that was activated by finger movements . by using longitudinal assessments of the same individuals 
 , we eschewed the many sources of variation in brain structure that confound cross sectional studies . 
 this allowed us to dissociate neural markers for verbal and nonverbal iq and to show that these general abilities are closely linked to the sensorimotor skills involved in learning . 
 more generally , our results emphasize the possibility that an individual s intellectual capacity relative to their peers can weaken or strengthen in the teenage years . 
 this would be encouraging to those whose intellectual potential may improve ; and a warning that early achievers may not maintain their potential . 