Abstract
Different from the most popular thinking, the placebo effect is not a purely psychological phenomenon. A body of knowledge from multidisciplinary fields has shown that the expectation of a potential benefit when receiving a treatment induces a cascade of neurochemical-electrophysiological alterations in brain reward areas, including motor-related ones. Alterations in the dopamine, opioid, and glutamate metabolism are the neural representation converting reward-derived declarative forms into an attractive and wanted behavior, thereby changing the activation in reward subcortical and cortical structures involved in motor planning, motor execution, and emotional-cognitive attributes of decision-making. We propose that the expectation of receiving a treatment that is beneficial to motor performance triggers a cascade of activations in brain reward areas that travels from motor planning and motor command areas, passing through corticospinal pathways until driving the skeletal muscles, therefore facilitating the motor performance. Although alternative explanations cannot be totally ruled out, this mechanistic route is robust in explaining the results of placebo-induced effects on motor performance and could lead to novel insights and applications in the exercise sciences. Factors such as sex differences in reward-related mechanisms and aversion-induced nocebo effects should also be addressed.
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Abbreviations
- ACC:
-
Anterior cingulate cortex
- GABA:
-
Gamma-aminobutyric acid
- NAcc:
-
Nucleus accumbens
- NMDA:
-
N-methyl-D-aspartate
- OFC:
-
Orbitofrontal cortex
- PCC:
-
Posterior cingulate cortex
- PFC:
-
Prefrontal cortex
- PMC:
-
Primary motor cortex
- VTA:
-
Ventral tegmental area
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Acknowledgements
FOP is grateful to The São Paulo Research Foundation (FAPESP/Brazil # 2020/14730-4) and The National Council for Scientific and Technological Development (CNPq/Brazil #4 07307/2021-4) for funding projects that fall into the field of placebo studies. FOP is grateful for his research scholarship (CNPq/Brazil # 310355/2019-2), CB is grateful for his Ph.D. scholarship (FAPESP/Brazil # 2020/04827-0) and JCSC is grateful for his M.Sc. scholarship (The Coordination of Improvement of Higher Education Personnel—CAPES/Brazil # 001).
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FOP and CB conceived and designed the review. FOP, CB, and JCSC reviewed the literature and FOP, CB, and FJH wrote the manuscript. CB and JCSC diagramed the illustration. FOP, CB, JCSC, and FJH reviewed and approved the final version of the manuscript.
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Brietzke, C., Cesario, J.C.S., Hettinga, F.J. et al. The reward for placebos: mechanisms underpinning placebo-induced effects on motor performance. Eur J Appl Physiol 122, 2321–2329 (2022). https://doi.org/10.1007/s00421-022-05029-8
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DOI: https://doi.org/10.1007/s00421-022-05029-8