Hirnmorphologische Assoziationen in Abhängigkeit der Leistung im Trail Making Test bei gesunden Probanden

When completing any cognitive task in everyday life, the executive functions are existential to that. In terms of anatomic location of this cognitive ability along with the processing speed, many studies have shown the frontal lobe as the only brain location associated. But within time there were other studies opposing this theory and showing other brain areas that are accountable for cognitive function. In this study the Trail Making Test is used to depict the processing speed with part A and the executive functions with part B. Previously, there was a common association of the Trail Making Test with the frontal lobe function. But using various brain morphometric methods we want to investigate whether there are additional brain areas responsible for the executive functions and if we can describe some form of cortical network as a foundation of executive function. Our study population contained 681 healthy subjects from 18 to 65 years of age who got MRI brain scans and a neuropsychological testing using the Trail Making Test. There were T1-images collected to perform voxel- and surface-based analysis of the cortex such as DTI-images to examine the white brain structure. Using SPM and the CAT12-toolbox, we examined the gray matter brain structures regarding the volume, cortical thickness and gyrification. Additionally, the FA-scores were computed so the neural pathways and the alignment of the fibers could be displayed. The results were analyzed within a statistical model where we used a multiple regression and compared the processing time of the Trail Making Test with the brain structure and corrected with FDR- and FWE- corrections, respectively. In the first place the results showed an increased processing time of the Trail Making Test with increasing age. The performance on the Trail Making Test did not show any associations with the volume or the gyrification of the gray matter. The scoring time of part B of the Trail Making Test showed a positive correlation with the cortical thickness in temporal, parietal and frontal brain areas, which implicates a thinner cortex as suitable for better cognitive function. The analysis of the white matter structure using DTI-images showed various negative correlations regarding the scoring time of Trail Making Test part A with the fractional anisotropy in distributed brain tracts on both hemispheres. This displays an increased integrity of the fibers when completing the Trail Making Test more efficient. Further on we could demonstrate that the Trail Making Test part B is connected to the anterior thalamic radiation and the fasciculus longitudinalis superior in the right hemisphere by showing a negative correlation. In addition further negative correlations of the TMT-difference with the forceps major and minor as interhemispheric connections could be depicted. Our findings refute the image of the Trail Making Test as an indicator of the frontal lobe function only. We could display various modifications in the white matter structure connected to better processing speed using part A of the Trail Making Test. This can be compared to a network-model of processing speed using different cortical areas to operate. Regarding the executive functions, which were represented by part B of the Trail Making Test and the TMT-difference, an association between a better performance and a thinner cortex could be shown. These results projected on the right hemisphere including frontal, temporal and parietal areas as well as on interhemispheric connections, and thereby displayed a network combining known frontoparietal and -striatal networks. This contradicts the concept of associating the executive functions solely with the frontal lobe. We suggest further investigation especially concerning the parietal lobe and possible impact by lateralization.