FIGURE 1.

Methods (a) participant instrumentation. Participants were fitted with EEG electrodes, transcranial Doppler ultrasound, ECG, and a respiratory mask connected to a dynamic end‐tidal forcing system. (b) Schematic example of the behavioral task. During the “task” phase, participants monitored a centrally presented circular annulus that alternated between red and green. A button‐press response was made when a slightly longer duration target (10% of trials) was detected. A large checkerboard pattern was presented in the background with a contrast pattern that reversed every 8.33 Hz in order to drive a steady‐state response in the cortex. (c) Gas challenge protocol. Each gas challenge condition began with 5 min of air breathing to establish steady‐state breathing, followed by a 3‐min isocapnia‐euoxia baseline period, and then 5 min at the desired gas concentration to achieve steady‐state conditions before beginning the attention rest/task protocol. Participants then alternated between 45 s of rest (fixating on a white dot presented at the center of the screen) and 45 s of the behavioral task. After completing eight full cycles (12 min total), participants then breathed room air for 10 min (washout period)