Neurophysiological Outcomes of Human Touch and Related Clinical Assessments: A Scoping Review.

Objectives: The purpose of this study was to summarize literature exploring pain modulation pathways in healthy humans undergoing human-hand touch via professional care without specific intervention as comparator. A secondary aim was to describe the clinical outcomes considered in the literature reporting neurophysiological outcomes.

Methods: A scoping review was performed on PubMed, Scopus, and Web of Science up to 10 September 2022. Included studies had to be primary and describe a human-hand touch intervention performed by professionals on healthy humans. Studies that described only patient-reported outcome measures or drug administration to subjects during touch stimulation were excluded. The study design, Country, setting, type of sample and number of subjects, age, number of females, intervention, type of professionals involved, assessed outcomes, and results were extracted.

Results: We included 1 observational study, 4clinical trials, and 5 randomized studies involving 323 subjects, conducted in clinical (n = 3) or academic (n = 7) settings. The summary of the findings suggest that human touch may induce activation and functional neurophysiological change in "pain matrix" through a convergence of the exteroceptive and interoceptive sensations which comes from lamina I to insula cortex and thalamus. This brain activation may be correlated with clinical improvements, especially in weight gain for preterm/neonates, and in pain modulation for adults. Dynamic human touch may be more pleasant and useful in pain relief than static touch and non-human touch. Finally, the cognitive status of operators may play a role in brain change of touched subjects.

Conclusions: This scoping review identified literature that suggests human touch may be associated with a central convergence and elaboration of sensory information from external and internal milieu, but also with a bi-directional cognitive modulation between operator and touched subject.