Neural correlates of intelligence and general knowledge obtained by magnetic resonance imaging

Für die vorliegende Dissertation wurde mittels Magnetresonanztomographie untersucht, inwiefern interindividuelle Unterschiede bei Intelligenz und Allgemeinwissen auf Unterschiede in den strukturellen und funktionellen Eigenschaften des Gehirns zurückgeführt werden können. Im Rahmen der ersten Studie konnte gezeigt werden, dass das Allgemeinwissen eines Individuums mit einem graphentheoretischen Maß der strukturellen Hirnkonnektivität assoziiert ist. In der zweiten Studie konnte mittels "Neurite Orientation Dispersion and Density Imaging" nachgewiesen werden, dass die fluide Intelligenz eines Individuums negativ mit der Dendritendichte und -verästelung im Kortex korreliert ist. Für die dritte Studie wurde die Assoziation zwischen fluider Intelligenz und funktioneller Hirnkonnektivität im Ruhezustand untersucht. Hierbei zeigte sich, dass relevante funktionelle Verbindungen in erster Linie durch Hirnregionen konstituiert werden, die Teil der "Parieto-Frontal Integration Theory" sind

Neurite density imaging in amygdala nuclei reveals interindividual differences in neuroticism

Neuroticism is known to have significant health implications. While previous research revealed that interindividual differences in the amygdala function are associated with interindividual differences in neuroticism, the impact of the amygdala's structure and especially microstructure on variations in neuroticism remains unclear. Here, we present the first study using NODDI to examine the association between the in vivo microstructural architecture of the amygdala and neuroticism at the level of neurites. We, therefore, acquired brain images from 221 healthy participants using advanced multi-shell diffusion-weighted imaging. Because the amygdala comprises several nuclei, we, moreover, used a high-resolution T1 image to automatically segment the amygdala into eight different nuclei. Neuroticism and its facets have been assessed using the NEO-PI-R. Finally, we associated neuroticism and its facets with the volume and microstructure of the amygdala nuclei. Statistical analysis revealed that lower neurite density in the lateral amygdala nucleus (La) was significantly associated with higher scores in depression, one of the six neuroticism facets. The La is the sensory relay of the amygdala, filtering incoming information based on previous experiences. Reduced neurite density and related changes in the dendritic structure of the La could impair its filtering function. This again might cause harmless sensory information to be misevaluated as threatening and lead to the altered amygdala responsivity as reported in previous studies investigating the functional correlates of neuroticism and neuroticism-related disorders like depression

Interindividual differences in matrix reasoning are linked to functional connectivity between brain regions nominated by Parieto-Frontal Integration Theory

The Parieto-Frontal Integration Theory (P-FIT) predicts that human intelligence is closely linked to structural and functional properties of several brain regions mainly located in the parietal and frontal cortices. It also proposes that solving abstract reasoning tasks involves multiple processing stages and thus requires the harmonic interplay of these brain regions. However, empirical studies directly investigating the relationship between intellectual performance and the strength of individual functional connections related to the P-FIT network are scarce. Here we demonstrate, in two independent samples comprising a total of 1489 healthy individuals, that fMRI resting- state connectivity, especially between P-FIT regions, is associated with interindividual differences in matrix reasoning performance. Interestingly, respective associations were only present in the overall samples and the female subsamples but not in the male subsamples, indicating a sex-specific effect. We found five statistically significant connections which replicated across both samples. These were constituted by BAs 8, 10, 22, 39, 46, and 47 in the left as well as BAs 44 and 45 in the right hemisphere. Given that many of these brain regions are predominantly involved in language processing, we hypothesized that our results reflect the importance of inner speech for solving matrix reasoning tasks. Complementary to previous research investigating the association between intelligence and functional brain connectivity by means of comprehensive network metrics, our study is the first to identify specific connections from the P-FIT network whose functional connectivity strength at rest can be considered an indicator of intellectual capability

<i>MORC1 </i>methylation and BDI are associated with microstructural features of the hippocampus and medial prefrontal cortex

BACKGROUND: Alterations in the hippocampus and prefrontal cortex (PFC) have frequently been reported in depressed patients. These parameters might prove to be a consistent finding in depression. In addition, peripheral DNA methylation of the MORC1 gene promoter showed stable associations with depression across independent samples. However, the question arises whether MORC1, supposedly acting as transcription factor, might also be involved in neurobiological alterations accompanying depression. This study further analyses the role of MORC1 in depression by investigating a potential correlation between peripheral MORC1 DNA methylation and neuronal structural properties previously associated with depression in humans.METHODS: Beck Depression Inventory (BDI) was assessed in 52 healthy participants. DNA was extracted from buccal cells and MORC1 methylation correlated with micro- and macrostructural properties derived from magnetic resonance imaging (MRI) and neurite orientation dispersion and density imaging (NODDI) in the hippocampus and medial prefrontal cortex (mPFC).RESULTS: MORC1 methylation was associated with volume reduction and neurite orientation dispersion and density markers in the hippocampus and mPFC. BDI was positively associated with neurite orientation dispersion and density markers in the hippocampus.LIMITATIONS: The study was conducted in a small sample of healthy participants with subclinical depressive symptoms. Peripheral tissue was analyzed.CONCLUSION: We found significant negative associations between peripheral MORC1 methylation and macro- and microstructural markers in the hippocampus and mPFC. Thus, MORC1 might be involved in neurobiological properties. Studies investigating neuronal methylation patterns of MORC1 are needed to support this hypothesis.</p

The Neural Architecture of General Knowledge

Cognitive performance varies widely between individuals and is highly influenced by structural and functional properties of the brain. In the past, neuroscientific research was principally concerned with fluid intelligence, while neglecting its equally important counterpart crystallized intelligence. Crystallized intelligence is defined as the depth and breadth of knowledge and skills that are valued by one's culture. The accumulation of crystallized intelligence is guided by information storage capacities and is likely to be reflected in an individual's level of general knowledge. In spite of the significant role general knowledge plays for everyday life, its neural foundation largely remains unknown. In a large sample of 324 healthy individuals, we used standard magnetic resonance imaging along with functional magnetic resonance imaging and diffusion tensor imaging to examine different estimates of brain volume and brain network connectivity and assessed their predictive power with regard to both general knowledge and fluid intelligence. Our results demonstrate that an individual's level of general knowledge is associated with structural brain network connectivity beyond any confounding effects exerted by age or sex. Moreover, we found fluid intelligence to be best predicted by cortex volume in male subjects and functional network connectivity in female subjects. Combined, these findings potentially indicate different neural architectures for information storage and information processing.Peer Reviewe

Polygenic scores for handedness and their association with asymmetries in brain structure

Handedness is the most widely investigated motor preference in humans. The genetics of handedness and especially the link between genetic variation, brain structure, and right-left preference have not been investigated in detail. Recently, several well-powered genome-wide association studies (GWAS) on handedness have been published, significantly advancing the understanding of the genetic determinants of left and right-handedness. In the present study, we estimated polygenic scores (PGS) of handedness-based on the GWAS by de Kovel and Francks (Sci Rep 9: 5986, 2019) in an independent validation cohort (n = 296). PGS reflect the sum effect of trait-associated alleles across many genetic loci. For the first time, we could show that these GWAS-based PGS are significantly associated with individual handedness lateralization quotients in an independent validation cohort. Additionally, we investigated whether handedness-derived polygenic scores are associated with asymmetries in gray matter macrostructure across the whole brain determined using magnetic resonance imaging. None of these associations reached significance after correction for multiple comparisons. Our results implicate that PGS obtained from large-scale handedness GWAS are significantly associated with individual handedness in smaller validation samples with more detailed phenotypic assessment. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00429-021-02335-3

Diffusion markers of dendritic density and arborization in gray matter predict differences in intelligence

Previous studies suggest that individual differences in intelligence correlate with circuit complexity and dendritic arborization in the brain. Here the authors use NODDI, a diffusion MRI technique, to confirm that neurite density and arborization are inversely related to measures of intelligence