Original Article

Neuropsychopharmacology (2011) 36, 1557–1562; doi:10.1038/npp.2011.15; published online 13 April 2011

Inhalation of 7.5% Carbon Dioxide Increases Threat Processing in Humans

Matthew Garner1,2, Angela Attwood3, David S Baldwin1, Alexandra James3 and Marcus R Munafò3

  1. 1Clinical Neuroscience Division, School of Medicine, University of Southampton, Southampton, UK
  2. 2School of Psychology, University of Southampton, Southampton, UK
  3. 3School of Experimental Psychology, University of Bristol, Bristol, UK

Correspondence: Dr M Garner, Clinical Neuroscience Division, School of Psychology, University of Southampton, Highfield, Hampshire, Southampton SO17 1BJ, UK, Tel: +44 (0) 23 80595926, Fax: +44 (0) 23 8059 4597, E-mail: m.j.garner@soton.ac.uk

Received 9 November 2010; Revised 15 December 2010; Accepted 17 December 2010; Published online 13 April 2011.



Inhalation of 7.5% CO2 increases anxiety and autonomic arousal in humans, and elicits fear behavior in animals. However, it is not known whether CO2 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% CO2 and air. CO2 inhalation increased anxiety, autonomic arousal, and erroneous eye movements toward threat on antisaccade trials. Autonomic response to CO2 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 CO2 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.


CO2; anxiety; cognition; attention; emotion processing; antisaccade

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