Proactive or reactive ?

One of the recent theories relative to executive functions is that of the dual mechanisms of cognitive control (DMC), developed in 2007 by Todd Braver, of the department of psychology of the University of Washington. It postulates that executive functioning is not “fixed” but, on the contrary, can adopt a proactive mode or a reactive mode according to the exact characteristics of the task to be carried out and depending on the situation.

In an article published in July 2012 in PLoS One (1), Fabienne Collette’s group wanted to verify the DMC prediction. At the heart of the experiment was Stroop’s test, which measures the ability of an individual to resist interference and therefore to inhibit non-relevant information. In its typical version, the subject has to name the colors within which there are words that themselves describe a color. While it is easy to name the color green when the word written is “green”, the operation becomes more difficult when the word “red” is written in green, for example.

When Stroop’s test with many interferent items (the word “yellow” written in blue, the word “red” written in black, etc.)was given to volunteers , it was observed that the participants placed themselves continuously in executive mode in order to exercise proactive control. In a certain way they were saying to themselves: “I’ll treat each piece of information as if it is conflictual”. On the other hand, while the test included very few interferent items, the participants reacted on a case by case basis (reactive mode), judging that it was not useful to devote important attentional resources to remaining permanently in executive mode (proactive).

What did the researchers notice with regard to the rapidity and accuracy of the answers given? In contrast to the reactive mode, the proactive mode is not characterized by a slowing down of the processing of the easier items, but rather by more efficient processing of interferent items. In reactive mode, on the other hand, while the easy items were very easily processed, the interferent items required more time than in the proactive mode and were subject to more errors. “Another fact resulting from Functional Magnetic Resonance Imaging (FMRI): the cerebral regions activated were slightly different according to the mode used”, explains Fabienne Collette.

A compensation effort

The main target of the work of the neuropsychologist from ULg is the relationship between executive functioning and normal or pathological ageing (Alzheimer’s). During laboratory tasks, we observed that executive functioning in individuals (aged between 60-65 years and older) without a pathological condition is not as good as that in younger subjects. As Fabienne Collette points out, everything seems to indicate that a more subtle deterioration has already been at work from an earlier time. Inhibition, when it does not come from quasi automatic processes, is one of the executive functions most commonly changed with increasing age. Therefore, in the individuals concerned, Stroop’s test reveals a slowing down of the processing of information and an increase in the number of errors. Equally, overall flexibility, by allowing us to move from one task to another, and which requires the maintenance in working memory of mental plans designed for the completion of each of the two tasks, weakens with age. On the other hand, specific flexibility, where the passage from task A to task B does not require a subject to retain the working plan of the initial task, seems to be better preserved. Divided attention, (carrying out two tasks simultaneously) also deteriorates with advancing age, but not systematically. Other executive functions, less studied in the laboratory, probably follow the same downward curve (decline) with regard to performance.

What is the meaning of this deterioration in neurophysiological terms? “It appears that in the executive tasks, elderly people use their brain differently than the younger subjects, as though they were trying to compensate for their difficulties. Concretely, functional cerebral imaging shows that they ‘overactivate’ some areas of the brain compared with young individuals, or that by activating these regions, they are using more contralateral areas”, explains Fabienne Collette

(1) Grandjean J., D'Ostilio K., Phillips C., Balteau E., Degueldre C., Luxen A., Maquet P., Salmon E., Collette F. (2012). Modulation of Brain Activity during a Stroop Inhibitory Task by the Kind of Cognitive Control Required, Plos One 7(7), e41513.