Effects of bright light exposure on human fear conditioning, extinction, and associated prefrontal activation

• Published in: Physiology & behavior Vol. 194; pp. 268 - 276
• Main Authors: Yoshiike, Takuya, Honma, Motoyasu, Yamada, Naoto, Kim, Yoshiharu, Kuriyama, Kenichi
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.10.2018
• Subjects: Bright light exposure; Cerebrovascular Circulation - physiology; Conditioning (Psychology) - physiology; Cued fear conditioning; Extinction, Psychological - physiology; Fear - physiology; Fear extinction learning; Fear-circuitry disorders; fearfulness; Female; Galvanic Skin Response - physiology; hemodynamics; Humans; Male; memory; Mental Recall - physiology; Near-infrared spectroscopy; Photic Stimulation; Phototherapy - methods; Prefrontal cortex; Prefrontal Cortex - diagnostic imaging; Prefrontal Cortex - physiology; Single-Blind Method; Spectroscopy, Near-Infrared; therapeutics; Time Factors; Visual Perception - physiology; Young Adult; Cued fear conditioning; Bright light exposure; Fear extinction learning; Fear-circuitry disorders; Prefrontal cortex; Near-infrared spectroscopy
• ISSN: 0031-9384; 1873-507X; 1873-507X
• DOI: 10.1016/j.physbeh.2018.06.015

Bright light (BL) not only regulates human emotion and circadian physiology but can also directly modulate emotional memories. Impaired fear extinction and enhanced fear acquisition and consolidation are hallmarks of fear-circuitry disorders; thus, we tested whether BL facilitates fear extinction and inhibits fear acquisition. We randomly exposed 29 healthy humans to high- (9000 lx) or low-intensity light (<500 lx) for 15 min, near the nadir of the phase response to light, in a single-blind manner. Simultaneously with the light exposure, subjects performed fear extinction training and second fear acquisition, where a visual conditioned stimulus (CS), previously paired with an electric shock unconditioned stimulus (US), was presented without the US, while another CS was newly paired with the US. Conditioned responses (CRs) and changes in prefrontal cortex (PFC) activity were determined during encoding and delayed recall sessions. BL-exposed subjects exhibited lower extinction-related PFC activity and marginally higher acquisition-related PFC activity during light exposure than subjects exposed to control light. Twenty-four hours later, BL reduced CRs to both the extinguished and non-extinguished CSs with marginally lower extinction-related PFC activation, suggesting that BL enhanced fear extinction, while suppressing fear acquisition. Further, BL sustained tolerance to fear re-conditioning. Our results demonstrate that a single and brief BL exposure, synchronized with fear extinction and acquisition, instantaneously influences prefrontal hemodynamic responses and alleviates fear expression after 24 h. Although the specificity of BL effects deems further investigation, our findings indicate the clinical relevance of adjunctive BL intervention in exposure-based cognitive-behavioral therapy for fear-circuitry disorders. •The effects of bright light (BL) on fear extinction and conditioning were not known.•Brief BL exposure acutely influences prefrontal hemodynamic responses at encoding.•BL reduces conditioned responses more than control light at 24-h fear recall.•BL augmentation is clinically relevant for response prevention.