A brain scan pattern tracked how strongly Parkinson's patients responded to placebo, across three separate trials

A preprint reports that a specific pattern of brain network activity, measured before treatment began, predicted the size of each patient's placebo response in a Parkinson's gene therapy trial, and held up in two further drug trials tested by mouth and by injection under the skin.

A pattern of brain network activity measured on PET scans before treatment began predicted how strongly individual Parkinson's disease patients would respond to placebo, and the pattern held across three separate, independent randomized trials, according to a preprint posted to Research Square on June 24, 2026, and mirrored on PubMed Central. The pattern, called the sham surgery related pattern, or SSRP, was first described in 2014 by the same research group, led by David Eidelberg, after they used FDG-PET brain imaging to study patients who had been randomized to sham surgery as part of a double-blind Parkinson's gene therapy trial; patients who expressed more of the pattern before their sham operation went on to show larger motor improvements afterward, as reported in the Journal of Clinical Investigation.

The new preprint revisits that same gene therapy dataset and then tests whether baseline SSRP expression, measured before anyone was randomized, also predicts placebo response in two further, independent placebo-controlled trials of Parkinson's drugs, one given by mouth and one given by subcutaneous injection. In both validation trials, the authors report, baseline SSRP levels again correlated with the size of each patient's placebo response. Using a separate brain scan technique, diffusion tensor imaging, the team also reports that how strongly a person expressed the network tracked with the density of nerve fiber tracts connecting two of its hubs, the nucleus accumbens and the anterior cingulate cortex, regions long linked to reward and expectation.

The work is presented as a candidate biomarker for trial design: if a baseline scan can flag which patients are likely to show a large placebo response, researchers could in principle account for that statistically when judging whether a drug's effect is real. But the finding comes from a preprint that, as PubMed Central states plainly on the article page, has not yet been peer reviewed by a journal, and it was generated and validated using datasets collected by the same research group. It says nothing about who has Parkinson's disease, what causes it, or what any individual patient should do; it is a question about how to interpret clinical trial results, not a clinical test.

Whether SSRP expression proves useful outside this group's own trial archives, and whether it holds in other disorders where placebo responses complicate drug testing, is a question for peer review and independent replication, not for this preprint alone.