Placebo effect has subliminal triggers, new study shows

Subconscious cues in the environment can make patients heal faster, a study shows

PUBLISHED : Sunday, 16 September, 2012, 12:00am
UPDATED : Sunday, 16 September, 2012, 1:35am

Subliminal information can trigger the placebo effect and its opposite, the nocebo effect, researchers say.

The finding suggests that patients with certain ailments may feel better or worse depending on subtle cues their brains pick up from the environment, but which they are not consciously aware of.

Dr Karin Jensen, who led the study at Massachusetts General Hospital and Harvard Medical School, said the work had implications for how health care was delivered.

The placebo effect is the curious biological mechanism whereby patients' symptoms improve when they take fake medicines with no active ingredient, such as sugar pills or saline injections. It also boosts the effectiveness of genuine medicines.

Though placebo is the better known effect, there is an opposite reaction, called the nocebo response, where people can feel worse after an intervention that should have no ill effects.

While both are usually linked to a tangible intervention the patient is aware of, Jensen's team wondered whether subconscious cues might be enough to trigger the same effects.

"People weren't opposing the idea of unconscious processing, it just hadn't been investigated properly," she said.

In a study, scientists discovered that volunteers experienced less pain from a heating element when they saw a face they had learned to associate with relief flashed on a screen. The opposite effect occurred with a face they associated with discomfort.

But researchers also found that the faces had the same effect when the test subjects saw them for only 12 milliseconds - too short a time for the brain to consciously process the information.

"The work shows that processes like placebo and nocebo happen without us being aware of the cues that trigger them," Jensen said.

"We get these responses due to associative learning. We don't need somebody standing there saying: 'OK, now you will feel less pain.' It's being elicited naturally, and without us being aware, all the time."