Attakias T. Mertens

Cortical gradients have been shown to be an effective technique to study the functional organization of the brain by capturing patterns of functional similarities. Until now, most studies have focused on analyzing cortical gradients derived from resting‐state fMRI. With recent work highlighting the changes that functional brain networks undergo during various cognitive loads, there is a need to investigate whether cortical gradients are also sensitive to different cognitive demands, and to what degree. In this context, we collected a sample of 138 healthy individuals aged 12–25, each of whom completed a resting‐state fMRI scan as well as three task fMRI scans (social prospection, spatial working memory, and verbal working memory). All data were analyzed to examine the task dependence of cortical gradients' topological properties. By employing the measures of network gradient dispersions as well as networks centroid distances, we revealed that alterations specific to each task occurred in topological properties of gradients involving both transmodal and unimodal networks, such as the executive control network varying between each task condition and the resting‐state condition. This work highlights the promise of applying cortical gradients to task‐based fMRI data, revealing the condition‐sensitive nature of certain cortical gradients' topological properties.

Iron is essential for neurophysiological health. Prior work has shown that subcortical tissue iron levels are the highest among all brain regions but also change over the lifespan. Recent functional MRI (fMRI) studies have provided evidence that an fMRI-derived iron-sensitive signal may index relative iron concentration in subcortical regions. In this context, we aimed to characterize the lifespan trajectory of this fMRI-derived iron-sensitive signal (relative iron quantification) in 10 subcortical regions and 14 thalamic nuclei from 881 healthy participants aged 12 to 88 years, using resting-state fMRI. Regressions were run with age as a predictor, separately for males (N = 429) and females (N = 452). The main results show non-linear effects of age, with an overall increase in iron levels across most subcortical regions within each sex. Six of the 14 thalamic nuclei in male participants had similar slopes of their lifespan iron levels, showing some homogeneity. The thalamic nuclei of female participants showed less agreement in slopes. This study provides new insight into the typical trajectory of iron levels across all major subcortical regions throughout the lifespan.