Psychomotor speed and functional brain MRI 2 years after completing a physical activity treatment

Abstract

Background: Short-term adherence to physical activity (PA) in older adults improves psychomotor processing abilities and is associated with greater brain activation. It is not known whether these associations are also significant for longer-term adherence to moderate-intensity activities.

Methods: We measured the cross-sectional association of regular walking with brain activation while performing the digit symbol substitution test (DSST). Participants of the lifestyle interventions and independence for elders-pilot study were examined 2 years after completing a 1-year treatment, consisting of either PA or education in successful aging (SA). Data were obtained from 20 PA participants who reported having remained active for 2 years after the end of the treatment and from 10 SA participants who reported having remained sedentary during the same period (mean age: 81.5 and 80.8 years). Complete brain activation and behavioral data were available for 17 PA and 10 SA participants.

Results: Two years after the formal intervention had ended, the PA group engaged in more minutes of moderate activity and had significantly greater DSST score and higher brain activation within regions important for processing speed (left dorsolateral prefrontal, posterior parietal, and anterior cingulate cortices). Associations were independent of self-reported health, blood pressure, cognition, medication records, gray matter atrophy, and white matter hyperintensities.

Conclusions: Persistent engagement in PA may have beneficial effects on psychomotor processing speed and brain activation, even for moderate levels and even when started late in life. Future studies are warranted to assess whether these beneficial effects are explained by delayed neuronal degeneration and/or new neurogenesis.

Figure 1.

Digit symbol substitution test (DSST) and control condition tasks. Schematic representation of the DSST and control conditions tasks administered during the brain functional magnetic resonance imaging (fMRI) scanning session. fDSST = DSST modified for the fMRI protocol. Two examples are shown for the fDSST (matching: push right button; not matching : push left button) and for the control condition ( ‘R’: push right button; ‘L’: push left button). The participant sees on a computer screen one number–symbol matching pair (cue). After the cue disappears, an answer key (probe) appears containing a grid of four number–symbol matching pairs. The participant is instructed to push the right index finger button if the probe contains one number–symbol that matches the cue and to push the left index finger button if the probe does not contain any number–symbol that matches the cue. Instructions are to respond “as fast as you possibly can.” In the control condition, the probe is a grid of four “R-symbol” pairs or “L-symbol” pairs to which the participant is instructed to respond by pushing the right or the left button, respectively, using the index finger. Eye movements to visually scan the screen in the control condition and in the fDSST condition are estimated to account for non–task-specific brain activation (frontal eye field and visual cortex for eye movements and motor cortex for the index finger movements). In all trials, cues and a probe flashed on a black screen that had a 0.1-cm bright white fixation cross at the center, according to specific timing (cue: 1.0 seconds; pause: 0.2 seconds; probe: 3.6 seconds; pause: 1.2 seconds). The fDSST was presented using the block design, in which one block (eight trials per block) alternated with one block (eight trials per block) of a control condition. Each block lasted for 48 seconds, and the participants were reminded the instruction for 8 seconds at the start of each block. There were five fDSST blocks alternated with five control blocks for a total of 9 minutes and 20 seconds. No cue was repeated within the same block. The two task conditions (matching vs nonmatching) were randomized 1:1 across participants and block.

Figure 2.

Kilocalories expenditures were computed using the Community Healthy Activities Model Program for Seniors for participants who were in the physical activity (PA) arm and in the successful aging (SA) group. Mean kilocalories expenditures per week were measured at study entry, at closeout, and at the follow-up clinic exam at the time of the functional magnetic resonance imaging (fMRI) for the SA (dashed line, filled circles) and for the PA (solid line, triangles). Kilocalories expenditures were computed to perform the following activities: walk leisurely, walk for errands, ride a bicycle, use aerobic machines, do water exercise, stretching, heavy strength exercise, light strength exercise, and general conditioning. See Supplementary Figure 2 for percentage distribution.

Figure 3.

Functional brain magnetic resonance imaging (MRI) activation in relationship with physical activity. Highlighted regions indicate regions with functional MRI signal positively correlated with physical activity (kilocalories). t maps of analysis of brain MRI activation in relationship with physical activity (kilocalories). See text for spatial coordinates of the regions. R = right, L = left.

Figure 4.

Functional brain magnetic resonance imaging activation during fDSST performance. t maps of analysis of task-related activity from (a) the successful aging (SA) group and (b) the physical activity (PA) group and (c) between comparisons of PA > SA. Results for SA group > PA group were nonsignificant. R = right; L = Left. See Table 2 for spatial coordinates of the corresponding regions.