Whether you perceive the glass as half-full or half-empty could impact the way you react to pain and other medical treatments, according to a new study into the effects of negative thinking.

In the most sophisticated study on the subject to date, British and German researchers from Oxford University and University Medical Center in Hamburg subjected 22 healthy volunteers to heat pain, and then treated that pain with a fast-metabolizing, morphine-based painkiller, all the while scanning the volunteers’ brains as they described their levels of pain.

The researchers discovered that by lying to the volunteers—for example, telling them that the painkiller was about to wear off and that they should expect pain to increase, even though the painkiller never actually stopped working—they could affect their perceived level of pain, according to the Associated Press. The brain scans confirmed increased activity in certain pain- and stress-related areas of the brain during these lies, suggesting that a patient’s outlook has actual therapy-negating effects.

Although this is a small study, researchers suspect the findings could hold true in a broad range of areas, particularly the treatment of chronic illnesses. Chronic disease patients, the vast majority of whom are elderly, are generally conditioned to expect their treatments to fail, according to the AP. By studying the effects of negative thinking on therapy, researchers could find ways to overcome pessimistic patient views to enhance medical therapies, experts believe.