Breathing-driven modulation of reticulospinal tract activity

Breathing rhythms influence brain activity, but whether they modulate the excitability of the reticulospinal tract (RST; a key pathway for motor control and recovery after stroke) remains unknown. In this study, we used the StartReact paradigm to examine how respiratory rhythms modulate RST excitability during motor tasks, measuring reaction times across visual, visual-auditory and visual-auditory startling conditions in three arm muscles (first dorsal interosseous, flexor digitorum superficialis and biceps) of healthy adults (n = 13). Reaction times decreased significantly from visual to visual-auditory to visual-auditory startling conditions. Crucially, respiratory-phase transitions, particularly from inspiration to expiration, significantly enhanced RST excitability specifically during startle-evoked responses, with StartReact effects being significantly stronger during respiratory transitions compared with mid-phases (P ≤ 0.011). These findings suggest that respiratory rhythms modulate RST excitability dynamically in a phase- and condition-specific manner. The identification of respiratory transition phases as optimal periods for RST activation could inform new neurorehabilitation strategies, such as respiratory-phase-aligned stimulation, to enhance motor recovery following corticospinal lesions.