The alignment of respiration to sensory-motor events is shaped by expected effort.

Humans often align their respiration with external events, a phenomenon thought to optimize neural resources for perception and action. Indeed, in sensory-cognitive experiments participants tend to align their respiration to the upcoming expected trials and their respiratory phase relates to neurophysiological processes reflecting changes in neural excitation, attention or arousal. However, it remains unclear whether this alignment is a passive entrainment to a task's overall rhythm or an active process selectively aligning respiration based on the demands of individual events. We here tested this by recording respiration during three visual discrimination experiments that manipulated trial importance by either imposing different response deadlines or by manipulating trial value and difficulty. Our results show that participants align their respiration more consistently around stimulus onset for trials with short deadlines or trials presenting high-value and high-difficulty. These findings demonstrate that respiratory alignment is dynamically modulated on a trial-by-trial basis according to the anticipated required effort or task demands. Hence we conclude that respiration serves as an active tool to strategically allocate cognitive resources for sensory-motor challenges.