Distinct aging effects for two types of inhibition in older adults: a near-infrared spectroscopy study on the Simon task and the flanker task.

The present study examined age-related changes in inhibitory processes among older and younger adults in the flanker and Simon tasks in terms of behavioral performance and prefrontal brain activity by functional near-infrared spectroscopy. The flanker task requires a quick identification of a central target in the presence of surrounding distracters, whereas the Simon task requires an individual to respond with left and right key presses to nonspatial features of the stimulus presented in the left and right locations. The reaction times of two age groups were longer under incongruent conditions than under congruent conditions in both tasks, indicating that the flanker effect (interference suppression) and the Simon effect (response suppression) were evident. In agreement with previous studies, the magnitude of the effect for the Simon task was greater for the older adults than for the younger adults, whereas the two groups showed equivalent flanker effects. The results suggest that older adults have difficulties in response inhibition, but not in stimulus interference suppression. Enhanced activity was found in different brain regions across the two tasks among the older adults. The older adults showed more activity in the superior and middle frontal gyri of the left hemisphere than younger adults in the flanker task; they showed more activity in the bilateral superior frontal gyri in the Simon task. These results suggest that the underlying mechanisms of the inhibition processes for the two tasks are distinct: they rely on different brain regions and have differential vulnerabilities to aging.