ERGOGENIC WORDS: HOW PLACEBOS CHANGE OUR BRAIN

The placebo effect is an illustrative example of the mind-brain-body interaction whereby a positive physical outcome follows the administration of an inert treatment that is expected to be effective. The two main psychological determinants of the placebo effect are conscious expectations, induced through verbal suggestion, and learning, induced through classical conditioning. Accumulating behavioral data suggested that positive expectations of motor improvement result in better motor control for several motor functions in athletes, non-athletes, and patients with motor deficits. These effects have been related to changes in brain areas involved in motor planning and execution, although a deep understanding of the precise neural network underlying this complex psychobiological phenomenon is still missing.

The aim of this study was to tackle the role of frontal cortical regions after placebo manipulations using, for the first time, fNIRS (functional near infrared spectroscopy). The fNIRS is a non-invasive technique used to investigate changes in the concentration of blood oxygen levels induced by brain activity, hence, oxygenated hemoglobin (HbO) and deoxygenated hemoglobin (HbR), at the level of cortical microcirculation blood vessels. Although not having the same spatial resolution as the fMRI, fNIRS has often been compared to fMRI due to both following the same kind of signal and recording the same activity from the cortex.

For this study, 30 healthy volunteers have been recruited from the student population of the University of Turin. Participants were asked to perform a force motor task and were randomly assigned to two different groups. Participants in the Placebo Group (P group) were informed that the application of 2 electrodes (actually sham) would have improved their motor performance. Participants in the Control Group (C group) performed the motor task without positive verbal information about the effectiveness of the sham electrodes.

From a behavioral point of view, results showed that participants in the P group improved their motor performance compared with the C group (p< 0.05). Moreover, differences in HbO have been observed in the P group in different brain regions, including the left dorsolateral prefrontal cortex (DLPFC).

These findings bring new evidence on the neural underpinnings of the motor placebo effect, by showing that the left DLPFC may undermine the expectation-induced enhancement of motor performance in participants that expected a positive motor improvement.