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.

Using functional magnetic resonance imaging, we found that when bilinguals named pictures or read words aloud, in their native or nonnative language, activation was higher relative to monolinguals in 5 left hemisphere regions: dorsal precentral gyrus, pars triangularis, pars opercularis, superior temporal gyrus, and planum temporale. We further demonstrate that these areas are sensitive to increasing demands on speech production in monolinguals. This suggests that the advantage of being bilingual comes at the expense of increased work in brain areas that support monolingual word processing. By comparing the effect of bilingualism across a range of tasks, we argue that activation is higher in bilinguals compared with monolinguals because word retrieval is more demanding; articulation of each word is less rehearsed; and speech output needs careful monitoring to avoid errors when competition for word selection occurs between, as well as within, language.

Language difficulties after stroke are commonly thought to stabilise within a year. Hope et al. report surprising evidence to the contrary, showing that the language skills of patients with post-stroke aphasia continue to change even years after stroke. The changes are associated with structural adaptation in the intact right hemisphere.