Poorer physical function is associated with elevated spatial entropy in the aging brain network landscape.

Life is a constant struggle against disorder. As we age, our ability to maintain internal order declines. In the healthy human brain, order is observable in the form of functionally segregated brain network communities that exhibit spatial consistency. These communities associate with distinct cognitive and physical functions. When mapped into the brain, they form a functional "landscape". We assessed the spatial disorder of these landscapes in older adults with a wide range of mobility using a modified version of Shannon entropy. We found that compared to younger adults, older adults had significantly higher entropy in the sensorimotor cortex, basal ganglia, hippocampus, thalamus, and occipital lobe. Higher entropy in many of these regions was associated with worse physical function and higher body mass index in older adults. Findings suggest that spatial entropy in brain network landscapes may be a marker of declining physical function. Modifiable factors, such as losing excess weight, may help to ameliorate aging-related brain entropy increases in regions such as the sensorimotor cortex, which may in turn help to preserve physical function in older adults.