Daily behavior requires taking into account some information and actions planning which may seem trivial for us. However, it is the fruit of a complex and sophisticated processing from the brain. The cerebral processes underlie cognitive and motor functions in humans. In order to record in situ the temporal evolution of cerebral signals reflecting our behavior during cognitive and/or sensorimotor tasks, different non-invasive methods from Neuroergonomics could be used. Among the available functional neuroimaging methods, the near infrared spectroscopy (NIRS) allowing indirectly to measure cortical activity (ie, changes in hemodynamic response) appears relevant to appreciate continuously cortical activity. In this thesis, using NIRS, we were interested in highlighting the correlates between cortical activity (frontal lobe) and the level of stimulation induced by workload during cognitive and/or motor tasks at sub-maximal efforts and variable difficulties. Three studies were conducted. The results indicate that the hemodynamic activity changes by NIRS depend on the workload. The cortical activity is measurable at a sub-maximal intensity for cognitive and/or motor tasks, as long as the signal analysis can discriminate low to moderate loads. This work has revealed the sensitivity and usefulness of NIRS in workload application.
