For thousands of years, questions about the soul, mind, and body have been discussed by philosophers, scientists, and doctors. Two major currents have emerged: the dualism, a strict separation between body and soul, developed by Plato, and the monism, considering the body as an indivisible whole, on the other hand. Today, majority of the questions about consciousness remain unanswered.

In medicine and revalidation, it is clear that the dualistic approach still prevails today. Indeed, only a few specialties are interested in the body as a whole and, a fortiori, analyze the links and relations between these two entities.

The new “transhumanist” and “posthumanist” philosophico-medical currents always pinpoint this body–mind dichotomy by considering the brain as a transmitter of commands that can be artificially recreated (neural stimulation, transcranial magnetic stimulation, etc.) and as a hard disk for memories and emotions. Researchers even focus on “mind uploading,” literally downloading the mind and knowledge to a computer. Some scientists believe that fiction will become reality around 2045 (Wiley 2014)!

Yet, as we will see, patients would benefit from a holistic approach by making the most of each entity.

A better understanding of mind–body interactions has been made possible by a better understanding of brain’s physiology and functioning. Two technologies have allowed major advances in this field, on the one hand, functional imaging of the brain and, on the other hand, brain operations performed on awake patients. The work and the discoveries made in these two fields have shown that the hypotheses of Broca developed nearly 150 years ago were not, fully, correct. According to Broca, each cognitive function is located in a specific area of the brain. A lesion located in this area will automatically cause a loss of the function of this area: the famous aphasia of Broca, for example. Research in functional imaging, nuclear magnetic resonance, magnetoencephalography, and especially brain operations in awake patients during which the neurosurgeon specifically tests various areas of the brain, ensuring him that the patient is always able to perform certain tasks (e.g., talking, playing music, performing calculation) showed that the locations described were not as precise as what was commonly described and admitted and especially that the most important element for brain function was not these areas but the connections between the different regions involved in a neural function (Duffeau 2016). In physical rehabilitation and movements training, it is thus not only important to stimulate the motor cortex but also to stimulate all the different zones involved: pre-motor cortex, motor, cerebellum, basal ganglia—and the connections between those zones but also the areas in charge of the cognitive functions. It is therefore important to maximize the different types of simulation.

The interest of the brain–body relationship is not new in medicine. The best-known example of “brain deception” is the “placebo” effect, the suggestion of the treatment leads to physiologic changes induced by the brain that thinks it has been treated (Finniss et al. 2010). This mechanism also works in the opposite direction, when the administration of a treatment without active principles triggers undesirable effects: the “nocebo” effect (Zaccara et al. 2016).

This principle of luring the brain is also found in physical revalidation in the mirror therapy. Created in 1996 and intended initially for amputees of an upper limb, this therapy aims to delude the brain by projecting an image of the limb on the amputated limb, thanks to the use of a mirror (Altschuler et al. 1999). This technique is now applied to hemiplegic patients: the image of the healthy limb is projected of the affected limb. When the patients are moving the healthy limb the brain thinks that it is the affected limb that is moving and significant improvement of the affected limb are observed.

Today, this principle of mirror revalidation is integrated into virtual revalidation solutions: augmented reality (adding visual information that overlays reality) fits perfectly to this theory and allows immersion and more complex motions than those possible with the simple mirror.

We have already seen that virtual reality and new technologies allow to (re)create environment to perform dual-task training. There are many possibilities to perform cognitive tasks coupled with motor activity or to disturb the brain (e.g., inversion of left and right movements, top and bottom) and force it to use and create other neural connection.

In addition to these techniques of virtual reality, simple cognitive exercises carried out using video games would have a favorable effect on the physical condition. We already presented this study that demonstrated the positive effect of a daily program of 12 mental training sessions with the game “How old is your brain” directly after the total hip replacement. After this program, mentally trained patients showed a better clinical outcome than those in the control group while they did not have more physical exercises than in the control group. Mental activity improves the revalidation of patients after total hip replacement (Lehrl et al. 2012). This proves the importance of neuronal plasticity and the complexity of the different neural circuits responsible for motor function.

Another study demonstrated the close interaction between brain and body. Researchers studied the correlation between the activation on the prefrontal cortex during the gait and the risk of fall. They observed that prefrontal brain activity levels while performing a cognitively demanding walking condition predicted falls in high-functioning seniors. These findings implicate neurobiological processes early in the pathogenesis of falls (Verghese et al. 2017)

We have seen that a cognitive training has a positive influence on the motor aspects, is the opposite true? Since the 1990s, the number of published studies on the link between physical activity and cognitive performance has increased exponentially. Two questions could be raised: Does physical activity have an immediate and/or long-term effect on cognitive functions?

Concerning the short-term effect, the activation of the cerebral cortex after a period of 20 min of walk compared to a group of subjects that do not move is much more important, leading de facto to an increase in cognitive abilities (Hillman et al. 2009).