Inhalation of 7.5% carbon dioxide increases threat processing in humans

Inhalation of 7.5% CO ₂ increases anxiety and autonomic arousal in humans, and elicits fear behavior in animals. However, it is not known whether CO ₂ challenge in humans induces dysfunction in neurocognitive processes that characterize generalized anxiety, notably selective attention to environmental threat. Healthy volunteers completed an emotional antisaccade task in which they looked toward or away from (inhibited) negative and neutral stimuli during inhalation of 7.5% CO ₂ and air. CO ₂ inhalation increased anxiety, autonomic arousal, and erroneous eye movements toward threat on antisaccade trials. Autonomic response to CO ₂ correlated with hypervigilance to threat (speed to initiate prosaccades) and reduced threat inhibition (increased orienting toward and slower orienting away from threat on antisaccade trials) independent of change in mood. Findings extend evidence that CO ₂ triggers fear behavior in animals via direct innervation of a distributed fear network that mobilizes the detection of and allocation of processing resources toward environmental threat in humans.