Graph theory analysis of functional brain networks and mobility disability in older adults.
BACKGROUND
The brain's structural integrity is associated with mobility function in older adults. Changes in function may be evident earlier than changes in structure and may be more directly related to mobility. Therefore, we assessed whether functional brain networks varied with mobility function in older adults.


METHODS
Short Physical Performance Battery (SPPB) and resting state functional magnetic resonance imaging were collected on 24 young (mean age = 26.4±5.1) and 48 older (mean age = 72.04±5.1) participants. Older participants were divided into three groups by SPPB score: Low SPPB (score = 7-9), Mid SPPB (score = 10), High SPPB (score = 11-12).Graph theory-based methods were used to characterize and compare brain network organization.


RESULTS
Connectivity in the somatomotor cortex distinguished between groups based on SPPB score. The community structure of the somatomotor cortex was significantly less consistent in the Low SPPB group (mean = 0.097±0.05) compared with Young (mean = 0.163±0.09, p = .03) SPPB group. Striking differences were evident in second-order connections between somatomotor cortex and superior temporal gyrus and insula that reached statistical significance. The Low SPPB group (mean = 140.87±109.30) had a significantly higher number of connections than Young (mean = 45.05±33.79, p = .0003) or High (mean = 49.61±35.31, p = .002) SPPB group.


CONCLUSIONS
Older adults with poorer mobility function exhibited reduced consistency of somatomotor community structure and a greater number of secondary connections with vestibular and multisensory regions of the brain. Further study is needed to fully interpret these effects, but analysis of functional brain networks adds new insights to the contribution of the brain to mobility.
Sticht Center on Aging and Department of Internal Medicine, Section on Gerontology and Geriatric Medicine, Wake Forest School of Medicine, Winston-Salem, North Carolina. chugensc@wakehealth.edu.
Christina E
CE
Hugenschmidt
Department of Radiology, Wake Forest School of Medicine, Winston-Salem, North Carolina.
Jonathan H
JH
Burdette
Department of Radiology, Wake Forest School of Medicine, Winston-Salem, North Carolina.
Ashley R
AR
Morgan
Sticht Center on Aging and Department of Internal Medicine, Section on Gerontology and Geriatric Medicine, Wake Forest School of Medicine, Winston-Salem, North Carolina.
Jeff D
JD
Williamson
Sticht Center on Aging and Department of Internal Medicine, Section on Gerontology and Geriatric Medicine, Wake Forest School of Medicine, Winston-Salem, North Carolina.
Stephen B
SB
Kritchevsky
Department of Radiology, Wake Forest School of Medicine, Winston-Salem, North Carolina.
Paul J
PJ
Laurienti
D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D001921:Brain / Q000503:physiopathology*; D001931:Brain Mapping; D059907:Functional Neuroimaging; D006801:Humans; D008279:Magnetic Resonance Imaging; D051346:Mobility Limitation; D008959:Models, Neurological; D009415:Nerve Net / Q000503:physiopathology; D066191:Sensorimotor Cortex / Q000503:physiopathology; D055815:Young Adult
Brain aging.; Neuroimaging; Physical function