Memory-guided force control in healthy younger and older adults

Abstract

Successful performance of a memory-guided motor task requires participants to store and then recall an accurate representation of the motor goal. Further, participants must monitor motor output to make adjustments in the absence of visual feedback. The goal of this study was to examine memory-guided grip force in healthy younger and older adults and compare it to performance on behavioral tasks of working memory. Previous work demonstrates that healthy adults decrease force output as a function of time when visual feedback is not available. We hypothesized that older adults would decrease force output at a faster rate than younger adults, due to age-related deficits in working memory. Two groups of participants, younger adults (YA: N = 32, mean age 21.5 years) and older adults (OA: N = 33, mean age 69.3 years), completed four 20-s trials of isometric force with their index finger and thumb, equal to 25% of their maximum voluntary contraction. In the full-vision condition, visual feedback was available for the duration of the trial. In the no vision condition, visual feedback was removed for the last 12 s of each trial. Participants were asked to maintain constant force output in the absence of visual feedback. Participants also completed tasks of word recall and recognition and visuospatial working memory. Counter to our predictions, when visual feedback was removed, younger adults decreased force at a faster rate compared to older adults and the rate of decay was not associated with behavioral performance on tests of working memory.

Keywords: Grip force; Healthy aging; Motor control; Visuomotor memory; Working memory.

Figure 1

Healthy young (N = 33) and older (N = 33) adults completed 20-second trials of isometric force with their index finger and thumb to produce 25% of their maximum voluntary contraction. (A) The precision grip apparatus. (B) The experimental timeline for the full-vision (FV) and no-vision (NV) conditions. (C) The visual display for the FV and NV conditions. (D) Raw force output from one trial for an exemplar healthy older adult participant during the FV and NV conditions. Hatched blue line represents when visual feedback was removed.

Figure 2

Mean force, in percent MVC, as a function of visual condition, group, and time. Data represent the last 12 s of trials in the full-vision (FV) and no-vision (NV) conditions. Error bars represent standard error of the mean.