Age-related forgetting in locomotor adaptation

Abstract

The healthy aging process affects the ability to learn and remember new facts and tasks. Prior work has shown that motor learning can be adversely affected by non-motor deficits, such as time. Here we investigated how age, and a dual task influence the learning and forgetting of a new walking pattern. We studied healthy younger (<30 yo) and older adults (>50 yo) as they alternated between 5-min bouts of split-belt treadmill walking and resting. Older subjects learned a new walking pattern at the same rate as younger subjects, but forgot some of the new pattern during the rest breaks. We tested if forgetting was due to reliance on a cognitive strategy that was not fully engaged after rest breaks. When older subjects performed a dual cognitive task to reduce strategic control of split-belt walking, their adaptation rate slowed, but they still forgot much of the new pattern during the rest breaks. Our results demonstrate that the healthy aging process is one component that weakens motor memories during rest breaks and that this phenomenon cannot be explained solely by reliance on a conscious strategy in older adults.

Keywords: Forgetting; Gait kinematics; Healthy aging; Locomotor adaptation; Motor learning.

Conflict of interest statement

Conflict of Interest: None

Copyright © 2016. Published by Elsevier Inc.

Figures

Figure 1

A. Diagram of marker location and limb angle convention. B. Experimental paradigm showing the periods of split-belt waking in gray lines and tied walking in black. All subjects sat or stood for five minutes between adaptation blocks.

Figure 2

Comparison of step symmetry adaptation across groups. Group adaptation curves (smoothed by 5 strides) and shaded standard error regions are shown. Plateau values for each exposure are plotted. Inset shows the correlation between forgetting during break 1 and 2 for each group. A. ‘Younger’ subjects showed no forgetting during ‘rest’ breaks. Notice that the first point of the subsequent exposure is not different from the plateau preceding it. B. ‘Older’ subjects demonstrated time-related forgetting. Upon re-exposure to the split-belts, the ‘Older’ group showed fast re-adaptation transients. There is a significant positive correlation between the forgetting during break 1 and 2 for ‘Older’ subjects. C. The ‘Older Distraction’ group shows a slower adaptation rate in exposure 1, but forgetting still occurred during the ‘rest’ breaks. They also never achieve complete symmetry during adaptation.

Figure 3

Adaptation and de-adaptation rates are shown. Epochs of five strides are shown for the first 50 strides in adaptation and de-adaptation. No age-related differences were found for the rate of adaptation (A) or de-adaptation (B). There was significant slowing in the adaptation rate for the ‘Older Distraction’ group compared to the ‘Older’ group (A), but not in the de-adaptation rate (B).

Figure 4

Forgetting values. The ‘Older’ healthy subjects had significantly more forgetting during break 1 than the ‘Younger’ subjects. Distraction did not significantly reduce the amount of forgetting found in the healthy older adults. * p