Correlation Between the Wechsler Adult Intelligence Scale- 3 rd Edition Metrics and Brain Structure in Healthy Individuals: A Whole-Brain Magnetic Resonance Imaging Study

Abstract

Background: The Wechsler Adult Intelligence Scale, 3^rd edition (WAIS-III) is widely used to evaluate the intelligence quotient (IQ). We aimed to investigate the correlation between the WAIS-III metrics and whole-brain structures using magnetic resonance imaging.

Methods: The participants were 266 healthy, right-handed individuals (age: 45.6 ± 12.9 years, 98 males and 168 females). IQs were evaluated using the WAIS-III and Japanese Adult Reading Test (JART). Voxel-based morphometry and diffusion tensor imaging were performed to analyze the correlation of the WAIS-III metrics and JART score with the gray matter volume and white matter integrity, respectively.

Results: The verbal IQ significantly and positively correlated with the left gyrus rectus and anterior cingulate gyrus, left posterior insula and planum polare, and left superior and middle frontal gyri volumes (p < 0.05, corrected). The verbal comprehension group index significantly and positively correlated with the left superior and middle frontal gyri, left gyrus rectus and anterior cingulate gyrus, and left middle frontal gyrus volumes, while the processing speed group index significantly and positively correlated with the bilateral various regional white matter fractional anisotropy values (p < 0.05, corrected). In contrast, the JART score showed no correlation with any brain structure.

Conclusion: These results suggested the neurostructural bases of the WAIS-III IQs and group indices in the brain of healthy individuals.

Keywords: Japanese Adult Reading Test; Wechsler Adult Intelligence Scale; gray matter; healthy individuals; white matter; whole-brain magnetic resonance imaging.

FIGURE 1

Gray matter regions where the volume significantly correlated with the Wechsler Adult Intelligence Scale-3^rd edition verbal intelligence quotient. The upper, middle, and lower-row brain images represent the left gyrus rectus and anterior cingulate gyrus, left posterior insula and planum polare, and left superior and middle frontal gyri clusters, respectively. The color panels on the right signify the t score gradient. The coordinates are indicated in cross hair lines. a, anterior; l, left; p, posterior; r, right.

FIGURE 2

Brain regions whose volume and fractional anisotropy value significantly correlated with the Wechsler Adult Intelligence Scale-3^rd edition group indices. The upper three-row brain images represent the gray matter regions whose volume positively correlated with the verbal comprehension. The color panels on the right signify the t score gradient. The lower-row brain images represent the white matter regions whose fractional anisotropy value positively correlated with the processing speed. The coordinates are indicated in cross hair lines. a, anterior; l, left; p, posterior; r, right.