Verbal and non-verbal intelligence changes in the teenage brain

Abstract

Intelligence quotient (IQ) is a standardized measure of human intellectual capacity that takes into account a wide range of cognitive skills. IQ is generally considered to be stable across the lifespan, with scores at one time point used to predict educational achievement and employment prospects in later years. Neuroimaging allows us to test whether unexpected longitudinal fluctuations in measured IQ are related to brain development. Here we show that verbal and non-verbal 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 a region that was activated by speech, whereas non-verbal IQ changed with grey matter in a region that was activated by finger movements. By using longitudinal assessments of the same individuals, we obviated the many sources of variation in brain structure that confound cross-sectional studies. This allowed us to dissociate neural markers for the two types of IQ and to show that general verbal and non-verbal 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 decrease or increase in the teenage years. This would be encouraging to those whose intellectual potential may improve, and would be a warning that early achievers may not maintain their potential.

Figure 1

Location of brain areas where grey matter changed with VIQ and PIQ. Top the correlation between change in grey matter density and change in VIQ (yellow) in the left motor speech area [peak in the left precentral gyrus at x=−47, y=−9, z=+30; with Z score of 5.2 and 681 voxels at p<.001]. The corresponding effect on volume was slightly less significant (Z score =3.5; 118 voxels at p<.001). Bottom, the correlation between change in PIQ (red) and change in grey matter density in the anterior cerebellum [peak at x=+6, y=−46; z= +3; with Z score of 3.9 with 210 voxels at p<.001]. Both effects were significant at p<0.05 after FWE correction for multiple comparisons in extent based on the number of voxels in a cluster that survived p<0.001 uncorrected. In addition, the VIQ effect was significant at p<0.05 after FWE correction for multiple comparisons in height. The statistical threshold used in the Figure (p<0.001) illustrates the extent of the effects. Plots show the change in grey matter density against the change in both VIQ and PIQ at the voxel with the highest Z score in the appropriate area. Changes in the motor speech area correlated with changes in VIQ but not changes in PIQ, while changes in the anterior cerebellum correlated with changes in PIQ but not changes in VIQ (p<.001). n = 33. GMD = grey matter density.

Figure 2

Functional activations in the areas identified by the structural analysis The motor speech area was more activated by articulation tasks than by finger press tasks: [x=−48, y=−10, z=+30; t=14.7; p<0.05 FWE corrected for multiple comparisons across the whole brain], and corresponds to the area identified in the structural analysis for VIQ. These effects were consistently observed at the same coordinates for all individual subjects. In the three exemplar participants shown here (P1, P2, P3), the Z scores were 3.9, 3.5 and 3.0 respectively. The anterior cerebellum area was more activated during finger presses than articulation at both the Group level [peak at x=+6, y=-48; z= −4; Z score = 3.7; 216 voxels at p<.001 corrected for multiple comparisons in extent] and individual level [P1: x=+12, y=−48, z=+2; Z score = 3.7; P2: x=+6, y=−50, z=−6; Z score = 3.3; P3: x=+12, y=−46, z=+2; Z score = 4.9]. In all cases, the activation peaks were identified from whole brain analyses and the peak effects for the correlation with structure are illustrated with blue cross hairs in both the structural and functional results. This illustrates that the location of the structural effects is within the areas identified in the functional effects.