However, in the 1930s, an American by the name of David Wechsler, the designer of the most widely-used I.Q. tests, referred to the existence of “non-intellectual intelligence factors” such as motivation or the emotions. In his somatic marker theory, Antonio Damasio of the Institute for Neurological Study of Emotion and Creativity at the University of Southern California wholeheartedly agrees with this, and he demonstrates that emotional skills constitute a non-negligible element for the efficacy of reasoning processes and decision-making. In short, although executive functions are an important element for the planning of an activity, decision-making, the inhibition of non-relevant information or the definition of strategies, they are not the only processes involved.

Functioning as a network

Based on initial studies concerning patients suffering from frontal lobe lesions, it was suggested that the executive functions were situated in the frontal cortex. Later, it appeared that this approach was too restrictive. “On one hand, not all patients with frontal lobe lesions have executive function disorders. Others, however, whose cerebral lesions are located elsewhere, can show such disorders. On the other hand, the progress of cerebral imaging techniques has made it possible to explore the neuroanatomical substrates of executive functions in healthy subjects: this showed that it must be thought of in terms of a network”, explains Fabienne Collette

Indeed studies carried out in 2005 by the researcher from ULg have clearly shown that various executive tasks aimed at assessing inhibition, mental flexibility and the updating of data were statistically more significantly associated with the activation of the parietal regions involved in orientation, attention and to a lesser degree, the activation of frontal regions. Also, the substrate of executive functions is a frontoparietal network.

In addition, very recent data seems to show that the efficient transfer of information between the cerebral regions involved is the key to good executive function skills, which underlines the importance of the connections in the white matter (nerve fibers) between the parietal cortex and the frontal cortex. “During the normal ageing process, executive function skills deteriorate. Today, it appears that the phenomenon is linked not only to a loss of grey matter (neurons), notably in the frontal regions, but also to a deterioration of the white matter that ensures the transmission of information”, indicates Fabienne Collette.

As they are high-level functions, each executive process is multi-determined: it calls upon various types of data-emotional, mnemonic, (access to knowledge stored in the memory), motivational... Therefore any loss of efficiency in a sub-process (working memory, for example) or any alteration in the transmission of information between the sub-regions involved, leads to a reduction in executive performance.

Numerous arguments support the idea that the different executive functions use relatively specific regions in the frontal and parietal cortex. For example, it has been shown that inhibition, flexibility and the updating of information do not call upon the same frontal regions. Other less numerous studies have also shown that there is heterogeneity between the parietal regions activated in accordance with the executive processes implemented.