Defensive eye-blink startle responses in a human experimental model of anxiety

Abstract

Inhalation of low concentrations of carbon dioxide (CO₂) triggers anxious behaviours in rodents via chemosensors in the amygdala, and increases anxiety, autonomic arousal and hypervigilance in healthy humans. However it is not known whether CO₂ inhalation modulates defensive behaviours coordinated by this network in humans. We examined the effect of 7.5% CO₂ challenge on the defensive eye-blink startle response. 27 healthy volunteers completed an affective startle task during inhalation of 7.5% CO₂ and air. Magnitude and latency of startle eye-blinks were.recorded whilst participants viewed aversive and neutral pictures. 7.5% CO₂ increased state anxiety and raised concurrent measures of skin conductance and heart rate. CO₂ challenge did not increase startle magnitude but slowed the onset of startle eye-blinks. The effect of CO₂ challenge on heart rate covaried with its effects on both subjective anxiety and startle latency. Findings are discussed with reference to startle profiles during conditions of interoceptive threat, increased cognitive load and in
populations characterised by anxiety, compared with acute fear and panic.

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ORCID for D.S. Baldwin: orcid.org/0000-0003-3343-0907

ORCID for M. Garner: orcid.org/0000-0001-9481-2226

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