How Endogenous Opioids Tune Responses To Other People’s Pain

The way in which the human brain’s opioid system modulates responses to other people’s pain has been elucidated by a recent study from researchers at Turku PET Centre and Aalto University.

Seeing others experiencing pain activated brain circuits that are known to support actual first-hand experience of pain. The fewer opioid receptors in the participants’ brains, the stronger were their emotion and pain circuits’ response to seeing others in distress.

Similar association was not found for the dopamine system despite its known importance in pain management.

“Capacity for vicarious experiences is a fundamental aspect of human social behaviour. Our results demonstrate the importance of the endogenous opioid system in helping us to relate with others’ feelings. Interindividual differences in the opioid system could explain why some individuals react more strongly than others to someone else’s distress,”

says Researcher Tomi Karjalainen from Turku PET Centre.

Opioids And Dopamine

The study was conducted by using positron emission tomography (PET) and functional magnetic resonance imaging (fMRI). The participants were injected with radioactive compounds that bind to their brain’s opioid and dopamine receptors.

Radioactivity in the brain was measured twice with the PET camera to map the distribution of opioid and dopamine receptors. Subsequently, the participants’ brain activity was measured with fMRI while they viewed videos depicting humans in various painful and painless situations.

“The results show that first-hand and vicarious pain experiences are supported by the same neurotransmitter system. This finding could explain why seeing others in pain often feels unpleasant. High opioid-receptor availability may, however, protect against excessive distress resulting from negative social signals, such as other people’s distress. Our findings thus suggest that the brain’s opioid system could constitute an important social resiliency factor,”

says Professor Lauri Nummenmaa from Turku PET Centre and Department of Psychology at the University of Turku.

Funding for the work came from the Jalmari and Rauha Ahokas Foundation, the Päivikki and Sakari Sohlberg Foundation, the Finnish Cultural Foundation, the Academy of Finland and The Finnish Cultural Foundation.

Tomi Karjalainen et al.
Dissociable Roles of Cerebral μ-Opioid and Type 2 Dopamine Receptors in Vicarious Pain: A Combined PET–fMRI Study
Cerebral Cortex (2017). DOI: 10.1093/cercor/bhx129

Image: VinceHuang CC-BY

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