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Working memory is a cognitive system that allows us to temporary store, process, link and manipulate memory content. It is essential for complex cognitive abilities. Pathologic influences, for instance brain lesions or various diseases, lead to a decline in working memory capacity. However, it is possible to detect large differences in working memory capacity even within a healthy sample.
The present study investigated whether structural differences in healthy subjects brains can explain interindividual differences in visual working memory capacity. 681 healthy subjects were included in the study. Each subject received an neuropsychological assessment of their visual working memory capacity and a MRI scan of their brain. GMV, cortical thickness, gyrification and FA were analysed using MR-morphometry. Visual working memory capacity was assessed using a well-established block-tapping test. In order to interpret the findings, a working memory model had to be defined. Therefore, the multicomponent model of working memory by Alan Baddeley was combined with modern neuroscientific findings. Explorative analysis revealed a positive correlation of GMV and gyrification with visual working memory capacity. The localisation of the effects seem plausible. However, after correction for multiple comparison those effects were non-significant and considered not relevant due to the small effect size.
A significant relationship between thinner cortex and higher visual working memory capacity was found in frontal, parietal and occipital brain areas of both hemispheres. Taking into account the age-dependent dynamic changing of the cortical structure, those findings can be explained in a reasonable way. The effects are consistent with findings of previous studies and fit in well with the underlying working memory model. FA was found to be positively correlated with visual working memory capacity in three different white matter areas. The underlying white matter tracts interconnect important components of the working memory model. The results suggest that white matter microstructure contributes significantly to visual working memory capacity. Since FA reflects microstructural organisation in an indirect way, future studies should apply modern diffusion parameters to directly investigate microstructural differences and back up the results.
In the present study a significant relationship between brain structure (cortical thickness and FA) and visual working memory capacity was found in multiple regions. Further studies are required to analyse whether these results can be generalized and applied to other cognitive systems. Neural plasticity shapes the human cortex and white matter throughout our lives. The underlying cellular and molecular mechanisms and most of the influencing factors are largely unknown. Once we decode those mechanisms, we could explore ways to manipulate neural plasticity in a positive way. This could lead to the development of optimized learning and training strategies or new rehabilitation concepts for patients with brain injuries.