Cortical complexity analyses and their cognitive correlate in Alzheimer’s disease and frontotemporal dementia
ABSTRACT The changes of cortical structure in Alzheimer’s disease (AD) and frontotemporal dementia (FTD) are usually described in terms of atrophy. However, neurodegenerative diseases may also affect the complexity of cortical shape, such as the fractal dimension of the brain surface. Thirty-two people with symptomatic AD-pathology (clinically probable AD, n=18, and amyloid-positive mild cognitive impairment, n=14), 24 with FTD and 28 healthy controls underwent high-resolution 3T structural brain MRI. Using surface-based morphometry, we created vertex-wise cortical thickness and fractal dimension maps for group comparisons and correlations with cognitive measures in AD and FTD. In addition to the well-established pattern of cortical thinning encompassing temporoparietal regions in AD and frontotemporal areas in FTD (FDR p< 0.05), we observed reductions of fractal dimension specifically involving precuneus and posterior cingulate for AD and orbitofrontal cortex and insula for FTD. Correlational analyses between fractal dimension and cognition showed that these regions were particularly vulnerable with regards to memory and language impairment in both AD and FTD. This study demonstrates a distinct pattern of fractal dimension impairment and correlation with cognition. Further studies are required to assess cortical complexity measures at earlier disease stages (e.g. in prodromal/ asymptomatic carriers of FTD-related gene mutations) to assess whether fractal dimension represents a sensitive imaging marker for prevention and diagnostic strategies.