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. 2014 Feb 1;86:326-34.
doi: 10.1016/j.neuroimage.2013.10.016. Epub 2013 Oct 12.

Age-related Variability in Performance of a Motor Action Selection Task Is Related to Differences in Brain Function and Structure Among Older Adults

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Free PMC article

Age-related Variability in Performance of a Motor Action Selection Task Is Related to Differences in Brain Function and Structure Among Older Adults

Jill Campbell Stewart et al. Neuroimage. .
Free PMC article

Abstract

Task performance for behaviors that engage motor cognitive processes may be particularly sensitive to age-related changes. One well-studied model of cognitive motor function involves engagement of action selection (AS) processes. In young adults, task conditions that add AS demands result in increased preparation times and greater engagement of bilateral dorsal premotor (PMd) and parietal cortices. The current study investigated the behavioral and neural response to a change in motor cognitive demands in older adults through the addition of AS to a movement task. Sixteen older adults made a joystick movement under two conditions during functional magnetic resonance imaging. In the AS condition, participants moved right or left based on an abstract rule; in the execution only (EO) condition, participants moved in the same direction on every trial. Across participants, the AS condition, as compared to the EO condition, was associated with longer reaction time and increased activation of left inferior parietal lobule. Variability in behavioral response to the AS task between participants related to differences in brain function and structure. Overall, individuals with poorer AS task performance showed greater activation in left PMd and dorsolateral prefrontal cortex and decreased structural integrity of white matter tracts that connect sensorimotor, frontal, and parietal regions-key regions for AS task performance. Additionally, two distinct patterns of functional connectivity were found. Participants with a pattern of decreased primary motor-PMd connectivity in response to the AS condition, compared to those with a pattern of increased connectivity, were older and had poorer behavioral performance. These neural changes in response to increased motor cognitive demands may be a marker for age-related changes in the motor system and have an impact on the learning of novel, complex motor skills in older adults.

Keywords: Action selection; Aging; Functional connectivity; Imaging; Movement.

Figures

Figure 1
Figure 1
Participants moved the joystick under two experimental conditions. During action selection, movement direction was dictated by an abstract rule (large square or small circle=move left; small square or large circle=move right). During execution only, movement direction was the same on every trial regardless of visual cue. Movement direction (right/left) for execution only was counterbalance across participants.
Figure 2
Figure 2
Behavioral performance for both experimental conditions shown for task accuracy (A), reaction time (B), and reaction time cost (C). Each data point represents the group mean with standard error bars. Practice through Block 3 was completed in the laboratory before MRI.
Figure 3
Figure 3
Results of one-sample t-test for each condition (execution only, action selection) and for paired t-test comparing action selection to execution only (AS>EO) with movement time added as a regressor of no interest. There were no regions significantly more active during execution only compared to action selection.
Figure 4
Figure 4
Results of whole brain regression analysis between reaction time (RT) cost during MRI and brain activation during the action selection condition with age and movement time included as regressors of no interest: A) left dorsal premotor cortex (PMd), and B) left dorsolateral premotor cortex (DLPFC). For scatter plots, percent signal change was extracted from the significant cluster (p<0.001 uncorrected for multiple comparisons) during action selection; each data point represents performance for a single participant.
Figure 5
Figure 5
Results of psychophysiological interaction analysis. Connectivity between left dorsal premotor (PMd) and left primary motor (M1) cortices during action selection compared to execution only increased for the participant shown in A and decreased for the participant shown in B (each data point represents activity for a single brain volume). Slope and correlation coefficient (r) were extracted for each participant and condition. Participants were split into two subgroups based on the direction of change in M1-PMd connectivity for the action selection task: Increased Connectivity (n=9) and Decreased Connectivity (n=7). The Increased Connectivity subgroup had significantly lower reaction time cost (C); trends for differences in activation between these two subgroups are presented in the bottom row.
Figure 6
Figure 6
Tract based spatial statistics (TBSS) results comparing variability in fractional anisotropy (FA) with variability in reaction time (RT) cost during the initial practice block (A), and with age (B). Mean FA skeleton (green) and TBSS results (negative correlation with FA in blue) are shown on a template brain in MNI space on axial slices.

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