Placebo Effect on Motor Performance: Implications for Parkinson’s Disease By Gerlyn The placebo effect is when a sham medical intervention causes real improvements in a patient’s condition, simply because they believe the intervention will work. Traditionally, the placebo effect was dismissed as a ‘product of imagination’ adapted ‘more to please than benefit’ patients. However, after Beecher published ‘The Powerful Placebo’ in 1955, the placebo effect started to become recognised as a neuropsychobiological phenomenon with measurable effects (1). Neuroimaging techniques now demonstrate how placebos may release neurochemicals in a similar pharmacological action to drugs, like dopamine (2). The present study thus examines the potential of the placebo effect at treating Parkinson’s disease (PD), a neurodegenerative condition caused by a loss of dopaminergic neurons. Alarmingly, PD cases have doubled in the past 25 years, linked to an ageing population and post-COVID-19 repercussions. However, levodopa - the main treatment for Parkinson motor symptoms - remains unaffordable for low income countries and generates toxic waste during synthesis (3). The placebo effect could thus be a more sustainable approach to treating PD.
RATIONALE & HYPOTHESES Placebos may increase brain dopamine levels in a magnitude comparable to levodopa This primary research thus investigates if placebo may similarly improve motor performance, and how changing placebo pill characteristics influence its effectiveness (number, colour & open-label conditions) As existing placebo studies have not yet done this, these hypotheses are based on placebo findings investigating other conditions (4):
1
One placebo pill will cause statistically significant motor improvement
2
Two placebo pills are more effective than one at improving motor performance
3
Pink placebo pills will cause greater motor improvement than white, due to a ‘stimulant’ effect
4
Open-label placebo pills (OLPs) will still significantly improve motor performance
METHODOLOGY 20 healthy female student volunteers aged 16-17 Randomly assigned to 4 groups of 5 participants (Fig. 1) Clicks Per Second (CPS) test assessed motor performance: 3x at all intervention levels (1,2 &3) to obtain a mean CPS score for each, with a 5 minute break in between Placebos - mints. Those not in Group 3 (open-label: where participants know it is placebo) were told the placebo was a drug proven to improve motor performance All were debriefed about the study’s true purpose after completion, to uphold ethical standards. Figure 1: Mixed study design. Within-subjects factor: 3 intervention levels within groups (1,2,3). Betweensubjects factor: different intervention types (different pink shades)
A paired t-test showed if there was a statistically significant (SS) difference between baseline and mean CPS score for each intervention (5% significance level). All data met the paired t-test assumptions of normal distribution, according to the Shapiro-Wilk test.
Effect of 1 Placebo Pill
Control Group
CONCLUSION Aligning with hypotheses:
1
1 pink placebo pill significantly improved motor performance - suggests ‘stimulant coloured’ placebo pills (pink/red) may be more effective at treating Parkinson motor symptoms 1 open-label placebo pill significantly improved motor performance - suggests deception is not required for motor placebo effect to occur. Overcomes ethical issues like patient autonomy if placebos are used in the clinic to treat Parkinson motor symptoms
2
No SS difference on CPS score between baseline and after one placebo pill for Groups 1 & 2 - no motor improvement.
2 Placebo Pills
Pink Placebo Pill
Contrary to hypotheses, 1 placebo pill did not significantly affect motor performance, whereas 2 placebo pills led to a significant decrease. This is perhaps due to distrust in participants that the placebo was actually a drug, which impedes the placebo effect (5). Repeating CPS tests may also tire fingers (only 5 minute breaks given).
No SS difference on CPS score between baseline and 2 control tests - no change in motor performance. Suggests any variation in motor performance for other groups is only from placebo effect, not other factors (effect of practice).
Effect of Open-Label Placebo Pill
LIMITATIONS & FUTURE WORK Limitations: age (participants aged 16-17, but Parkinson patients aged >50), within-subjects design per group (vulnerable to confounds of order and time) and short rest breaks (tired out fingers, potentially masking motor improvement) Nonetheless, this study hopes to guide future research on the potential of the placebo effect in treating Parkinson motor symptoms by:
SS decrease in CPS score from baseline after taking two placebo pills - signfies declined motor performance.
SS increase in CPS score from the baseline after taking a pink placebo pill signifies motor improvement
SS increase in CPS score from the baseline for both open label-placebo pill tests - signifies motor improvement
References: (1) Finniss, D.G. (2018) ‘Placebo Effects: Historical and Modern Evaluation’, International Review of Neurobiology. 139, pp. 1–27. Available at: https://doi.org/10.1016/bs.irn.2018.07.010. (2) Wager, T.D. and Atlas, L.Y. (2015) ‘The Neuroscience of Placebo Effects: Connecting context, Learning and Health’, Nature Reviews Neuroscience, 16(7), pp. 403–418. Available at: https://pubmed.ncbi.nlm.nih.gov/26087681/. (3) World Health Organization (2023) Parkinson Disease. Available at: https://www.who.int/news-room/fact-sheets/detail/parkinson-disease (last accessed 02/01/2026) (4) Meissner, K. and Linde, K. (2018) ‘Are Blue Pills Better Than Green? How Treatment Features Modulate Placebo Effects’, International Review of Neurobiology. 139, pp. 357-378. Available at: https://doi.org/10.1016/bs.irn.2018.07.014 (5) Benedetti, F. (2020) ‘Placebo Effects’. 3rd edition. Oxford University Press eBooks. Available at: https://doi.org/10.1093/oso/9780198843177.001.0001 All images are copyright free, or my own images, which I give St John’s College permission to use as part of this poster.
1
Improving study designs by addressing above limitations (use older participants, counterbalancing design, longer rest breaks)
2
Encourage more research on how different placebo characteristics affects motor performance for PD. Mechanisms may be integrated into levodopa treatment, to maximise effectiveness (e.g. pink levodopa pills). Open-label placebos should be further explored (as they are more ethical for clinical use than deceptive placebos).