Sarah François

The neural bases of proactive and reactive control processes in normal aging

HighlightsWe administered the Stroop test to young and older subjects during fMRI acquisitions.We examined BOLD signal changes linked to reactive and proactive cognitive control.Aging differentially affects neural networks associated with both kind of control.Very similar changes to those observed in young people with low brain dopamine level.Prefrontal dopamine availability may be a brain modulator of cognitive control. Introduction: Research on cognitive control suggests an age‐related decline in proactive control abilities (anticipatory control), whereas reactive control (following conflict detection) seems to remain intact. As proactive and reactive control abilities are associated with specific brain networks, this study investigated age‐related effects on the neural substrates associated with each kind of control. Methods: In an event‐related fMRI study, a modified version of the Stroop task was administered to groups of 20 young and 20 older healthy adults. Based on the theory of dual mechanisms of control, the Stroop task has been built to induce proactive or reactive control depending on task context. Results: Behavioral results (p < 0.05) indicated faster processing of interfering items in the mostly incongruent (MI) than the mostly congruent (MC) context in both young and older participants. fMRI results showed that reactive control is associated with increased activity in left frontal areas for older participants. For proactive control, decreased activity in the bilateral anterior cingulate cortex was associated with more activity in the right middle frontal gyrus in the older than the younger group. Conclusion: These observations support the hypothesis that aging affects the neural networks associated with reactive and proactive cognitive control differentially. These age‐related changes are very similar to those observed in young adults with low dopamine availability, suggesting that a general mechanism (prefrontal dopamine availability) may modulate brain networks associated with various kinds of cognitive control.

The effect of ageing on the neural substrates of incidental encoding leading to recollection or familiarity

&NA; It is well‐known that the ageing process disrupts episodic memory. The aim of this study was to use an fMRI visual recognition task to characterize age‐related changes in cerebral regions activated, during encoding, for images that would subsequently lead to a recollection‐based or to a familiarity‐based recognition. Results show that, for subsequent recollection, young adults activated regions related to semantic processing more extensively than older ones. On the other hand, despite putatively producing less semantic elaboration, older adults activated contralateral regions supplementary to those found in young adults (which might represent attempted compensation), as well as regions of the default‐mode network. These results suggest older adults could achieve subsequent recollection through different processes, for instance an appraisal of the self‐relevance of the stimuli. For subsequent familiarity, the comparisons only revealed greater activations in young adults, in the dorsal frontoparietal attention system as well as in the hippocampus, again suggesting that, even if older adults are able to produce recollection‐ and familiarity‐based recognition, the semantic processing might still be weaker in old adults, who might nonetheless use qualitatively different strategies in order to produce such responses. Further studies are necessary in order to characterize those strategies. HighlightsThe neural correlates of subsequent recollection and familiarity were investigated.For recollection, young adults predominantly activated semantic regions.For recollection, older adults activated regions of the default‐mode network.Familiarity was associated with decreased semantic‐related activity in older adults.Aging might lead to different strategies to achieve recollection and familiarity.