Delays in auditory-cued step initiation are related to increased volume of white matter hyperintensities in older adults.

An increased volume of white matter hyperintensities (WMH) on MRI has been associated with mobility impairments in older adults. The objective of this preliminary study was to investigate the relationship between the volume of WMH and the delays in auditory-cued step initiation. Eight subjects aged 75-83 years participated. The WMH volume in the corticospinal tracts and anterior thalamic radiations were summed. Subjects performed an auditory-cued stepping task that included two simple reaction time (SRT) trials and three choice reaction time (CRT) trials. SRT trials required subjects to step as quickly as possible with the right foot from a symmetric standing position to a single target position in response to an auditory stimulus. For the CRT trials, subjects stepped as quickly as possible to one of two possible locations, depending on the auditory stimulus. The time from the stimulus onset to the reaction time of the anticipatory postural adjustment (APA(RT)) and liftoff (LO) of the right foot was computed for each stimulus. The mean APA(RT) and LO were greater for the CRT steps compared with the SRT steps to the same location. Increases in WMH were significantly associated with larger APA(RT) and LO during both SRT and CRT for both target locations. These data suggest that increased volume of WMH is associated with greater central processing time during voluntary step initiation, and highlight a possible mechanism that can help to explain how damage to white matter tracts affects mobility in older adults.