Impact of inspiratory threshold loading on brain activity and cognitive performances in healthy humans.

In healthy humans, inspiratory threshold loading deteriorates cognitive performances. This can result from motor-cognitive interference (activation of motor respiratory-related cortical networks vs. executive resources allocation), sensory-cognitive interference (dyspnea vs. shift in attentional focus), or both. We hypothesized that inspiratory loading would concomitantly induce dyspnea, activate motor respiratory-related cortical networks, and deteriorate cognitive performance. We reasoned that a concomitant activation of cortical networks and cognitive deterioration would be compatible with motor-cognitive interference, particularly in case of a predominant alteration of executive cognitive performances. Symmetrically, we reasoned that a predominant alteration of attention-depending performances would suggest sensory-cognitive interference. Twenty-five volunteers (12 men; 19.5-51.5 yr) performed the Paced Auditory Serial Addition Test (PASAT-A and B; calculation capacity, working memory, attention), the Trail Making Test (TMT-A, visuospatial exploration capacity; TMT-B, visuospatial exploration capacity, and attention), and the Corsi block-tapping test (visuospatial memory, short-term, and working memory) during unloaded breathing and inspiratory threshold loading in random order. Loading consistently induced dyspnea and respiratory-related brain activation. It was associated with deteriorations in PASAT-A [52 [45.5;55.5]; (median [interquartile range]) to 48 [41;54.5], = 0.01], PASAT-B (55 [47.5;58] to 51 [44.5;57.5], = 0.01), and TMT-B (44 s [36;54.5] to 53 s [42;64], = 0.01), but did not affect TMT-A and Corsi. The concomitance of cortical activation and cognitive performance deterioration is compatible with competition for cortical resources (motor-cognitive interference), whereas the profile of cognitive impairment (PASAT and TMT-B but not TMT-A and Corsi) is compatible with a contribution of attentional distraction (sensory-cognitive interference). Both mechanisms are therefore likely at play. To our knowledge, this is the first study exploring the interferences between inspiratory loading and cognition in healthy subjects with the concomitant use of neuropsychological tests and electroencephalographic recordings. Inspiratory loading was associated with dyspnea, respiratory-related changes in brain activation, and a pattern of deterioration of neuropsychological tests suggestive of attentional disruption. Inspiratory loading is therefore likely to impact cognitive performances through both motor-cognitive interference (engagement of cortical networks) and sensory-cognitive interference (dyspnea-related shift in attentional focus).