NONINVASIVE BRAIN STIMULATION INCREASES THE COMPLEXITY OF RESTING-STATE BRAIN NETWORK ACTIVITY IN OLDER ADULTS

摘要

Successful completion of cognitive and motor tasks requires functional interactions between numerous brain networks over multiple temporal scales. Biological aging reduces the multi-scale “complexity” of the spontaneous fluctuations in network activity. Still, it is unknown if such “resting-state” complexity is sensitive to functional status, or modifiable via intervention. We hypothesized that resting-state complexity is lower in older adults with functional limitations, and, that it can be increased via repeated exposure to transcranial direct current stimulation (tDCS). Twelve older adults with mild-to-moderate executive dysfunction (i.e., Trail Making Test B time below the 25th percentile of age- and education-based norm) and slow gait (i.e., gait speed <1.0m/s), along with 12 age- and sex-matched controls, completed a baseline resting-state fMRI. Ten participants within the functionally-limited group then completed a 2-week, 10-session tDCS (n=6) or sham (n=4) intervention targeting the left dorsolateral prefrontal cortex (dlPFC). A follow-up fMRI was acquired 2–3 days following intervention. The complexity of seven well-established functional networks was quantified by averaging the ‘multiscale entropy’ of the blood-oxygen-level-dependent time-series across all voxels within each network. Compared to controls, older adults with functional impairments exhibited lower complexity in the motor, ventral attention, executive and limbic networks (F>4.7, p<0.04). Within this group, exposure to real tDCS, compared to sham, increased the complexity within the executive and limbic networks (F>4.9, p<0.04). These results suggest the older adults with functional limitations exhibit lower resting-state complexity, and, that repeated exposure to tDCS targeting the left dlPFC may increase such complexity within this vulnerable cohort.