Biological research on mental pain, social pain and other pains not primarily felt in the body: methodological systematic review

Abstract

Background

Researchers explore the biology of painful experiences not primarily felt in the body (‘non-physical pain’), sometimes referred to as mental, social or emotional pain. A critical challenge lies in how to operationalise this subjective experience for biological research, a crucial process for translating findings into clinical practice.

Aims

To map studies investigating biological features of non-physical pain, focusing on their conceptual features (i.e. terms and definitions of non-physical pain) and methodological characteristics (e.g. experimental paradigms and measures).

Method

This methodological systematic review searched reports of primary research on the biological features of non-physical pain across Embase, MEDLINE and Web of Science. Using a meta-research approach, we synthetised results on terms, definitions, populations, experimental paradigms, confounders, measures of non-physical pain and investigation methods (e.g. functional magnetic resonance imaging).

Results

We identified 92 human studies, involving 7778 participants. Overall, 59.1% of the studies did not report any definition of non-physical pain, and 82% of studies did not use a specific measure. Regarding the possibility of translating results to clinical settings, most of the human studies involved only healthy participants (71.7%) and the seven different experimental paradigms used to induce non-physical pain had unknown external validity. Confounders were not considered by 32.4% of the experimental studies. Animal studies were rare, with only four rodent studies.

Conclusions

Biomedical studies of non-physical pain use heterogeneous concepts with unclear overlaps and methods with unknown external validity. As has been done for physical pain, priority actions include establishing an agreed definition and measurement of non-physical pain and developing experimental paradigms with good external validity.