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The placebo effect increases strength and improves movement

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A study published in Scientific Reports showed that placebo treatments also affect movement. After sham electrical stimulation of the arm, participants performed “goal-directed” movements faster – a finding that could help develop rehabilitation strategies for people with movement disabilities.

 

There has been evidence in the past that placebos can increase athletic performance and improve motor function in diseases such as Parkinson’s. One theory is that, after knowing that a drug or supplement will improve their motor skills, people have positive expectations about their performance, and these expectations lead to better “top-down” control of movements, such as improving how they plan and predict the outcome of actions.

In the new study, Mirta Fiorio and colleagues at the University of Verona examined whether a placebo actually affected movement. The team recruited 24 participants, who were told the study was designed to test whether electrical stimulation delivered by a TENS machine improved motor performance. Participants learned that in two separate sessions they would receive different stimulation frequencies and complete a movement task.

The study in practice

To establish the participants’ baseline performance level, they performed the task without any electrical stimulation at the beginning of both sessions. Next, they sat in front of a touch screen and held a pen with their right hand so that they touched a small square on the left of the screen. Then, one to two seconds later, a beep sounded and a rectangle appeared on the right of the screen; participants had to move their arm and hand as fast as possible to tap the pen on this new rectangle. Participants completed a series of trials in which the size of the target rectangle and its distance from the starting point varied to adjust the difficulty of the task.

 

The team then introduced electrical stimulation, which was applied to his right arm. In both sessions, the TENS machine was set to a limp mode , so as not to affect the motor skills of the participants. However, participants were only told this in one of the sessions.

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The other session was designed to elicit a placebo effect : participants were told that the machine was set to an active mode and would stimulate their arm at a frequency known to be effective in improving speed and accuracy of movement . After receiving the stimulation, the participants completed another set of trials. Then they completed another stimulation period and a third block of trials.

The team found that participants were quicker to move the pen from the starting square to the target rectangle in the placebo condition compared to the control condition. This was true regardless of the difficulty of the test, based on the distance to be covered and the size of the target. Furthermore, in the placebo condition people ran even faster after the second period of electrical stimulation than the first, suggesting that a larger “dose” of placebo produced even stronger results.

 

The researchers hypothesize that the positive expectations of people in the placebo condition (those who thought they were being helped by the electrical stimulus) led them to rely more on their own internal predictions about how and where to move. Alternatively, the positive expectations may have led them to pay more attention to their body and movement, making them perform better.

The findings could have implications for rehabilitation after limb injury or stroke. According to the team, encouraging patients to have more positive expectations about their motor skills could have tangible effects on their recovery, especially if they already suffer from low motivation. “We believe that exploiting the placebo effect could inspire future long-term rehabilitation strategies,” the researchers conclude.

  • The placebo effect in the motor domain is differently modulated by the external and internal focus of attention. (nature.com)
 

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