The effect of aging on the inhibitory function in middle-aged subjects: a functional MRI study coupled with a color-matched Stroop task.

Objective: The effects of aging on the inhibitory function are largely described in the neuroimaging literature but little data is available on the beginning of this age-related impairment.

Methods: In this study, we described the cortical activation of middle-aged (mean age +/- standard error to the mean, 51.7 +/- 3.1) subjects compared to young (26.8 +/- 3.4) and elderly subjects (62.8 +/- 3) while they performed a color-matched Stroop task during functional magnetic resonance imaging. The task consisted in identifying the printing color of a word regardless of its meaning. Three conditions were defined depending on the meaning of this word; neutral (no meaning), congruent (color name matching the printing color), incongruent (color name mismatching the printing color), with interference effect in the latter.

Results: Middle-aged subjects were as slow as elderly compared to young for all conditions and both were less accurate than young subjects during interference condition. Elderly showed an activity more bilateral and greater in the parietal lobule, the dorsolateral and ventrolateral prefrontal cortex (DLPFC, VLPFC) during both congruent and incongruent conditions compared to young. Middle-aged showed an intermediary level of activity between those of elderly and young subjects in the left DLPFC, VLPFC and parietal lobule only during incongruent condition.

Conclusion: These results suggested that the age-related impairment of the inhibitory process could already occur around the age of 50 years and consist in an increase of the activity in the left prefrontal and parietal cortex before increasing more and becoming bilateral around the age of 60 years.