Postural adjustment errors reveal deficits in inhibition during lateral step

23 Postural dual task studies have demonstrated effects of various executive function 24 components on gait and postural control in older adults. The purpose of the study was 25 to explore the role of inhibition during lateral step initiation. Forty older adults 26 participated (range 70-94 y). Subjects stepped to the left or right in response to 27 congruous and incongruous visual cues that consisted of left and right arrows appearing 28 on left or right sides of a monitor. The timing of postural adjustments was identified by 29 inflection points in the vertical ground reaction forces (VGRF) measured separately 30 under each foot. Step responses could be classified into preferred and non-preferred 31 step behavior based on the number of postural adjustments that were made. Delays in 32 onset of the first postural adjustment (PA1) and liftoff (LO) of the step leg during 33 preferred steps progressively increased among the simple, choice, congruous and 34 incongruous tasks, indicating interference in processing the relevant visuo-spatial cue. 35 Incongruous cues induced subjects to make more postural adjustments than they 36 typically would (i.e. non-preferred steps), representing errors in selection of the 37 appropriate motor program. During these non-preferred steps, the onset of the PA1 38 was earlier than during the preferred steps, indicating a failure to inhibit an inappropriate 39 initial postural adjustment. The functional consequence of the additional postural 40 adjustments was a delay in the LO compared with steps in which they did not make an 41 error. These results suggest that deficits in inhibitory function may detrimentally affect 42 step decision processing, by delaying voluntary step responses. 43 44