Sullivan, E. V., Zahr, N. M., Rohlfing, T., & Pfefferbaum, A. (2010). Fiber tracking functionally distinct components of the internal capsule. Neuropsychologia, 48(14), 4155-4163.
The internal capsule conveys information from primary and supplementary motor areas, frontopontine and thalamic peduncles to brain stem and cerebellar regions, and from thalamus to prefrontal cortex. Neurological accidents involving the internal capsule indicate differential functional correlates with its sectors. To examine the microstructural condition of this fiber system and to test functional correlates of its sectors in health and aging, 12 younger and 12 older adults were examined with diffusion tensor imaging (DTI) fiber tracking and neuropsychological tests. Greater age-related degradation was evident in the anterior than posterior limb and in the superior than inferior division of the internal capsule. The superior division age effect was especially notable in axial and radial diffusivity. Fractional anisotropy (FA) across the three (anterior, genu, posterior) fiber bundles of the inferior division accounted for 27–73% of the variance for each neuropsychological domain. Identification of a triple dissociation indicated selective correlations between anterior FA and set shifting, genu FA and motor skills, and posterior FA and fluency. Quantitative fiber tracking combined with assessment of cognitive and motor functions enabled the identification of selective brain structure–function relations in healthy adults without lesions that were previously observed only in patients with lesions of the internal capsule.
▶ The internal capsule conveys information from primary and supplementary motor areas, frontopontine and thalamic peduncles to brain stem and cerebellar regions, and from thalamus to prefrontal cortex.
▶ Diffusion tensor imaging (DTI) fiber tracking conducted in young and elderly men and women revealed two gradients of age effects: greater age-related degradation of the anterior than posterior and superior than inferior sectors of the internal capsule.
▶ Correlations between microstructural condition of the inferior sector of the internal capsule and tests of selective cognitive and motor functions identified a triple dissociation: greater anterior limb degradation related to poorer set shifting scores, genu degradation related to motor skills, and posterior degradation related to fluency.