Scientists have found that people who trained their brain to have positive thoughts right after a jab produced more protective antibodies in their blood in response to vaccination.
Previous animal studies have shown that the brain’s reward system, which controls motivation and expectation, can affect immunity. However, whether such a brain-immunity link is also present in humans has remained unclear.
Researchers have theorised that such a brain network could also be behind the placebo effect – when a fake treatment leads to an actual improvement in a patient’s condition – and a better understanding of this biological process is likely to lead to new ways to make vaccines more effective.
In the new study, researchers trained 85 healthy participants to intentionally increase the activity of their brain’s reward network – known as the ventral tegmental area (VTA) – and monitored them using an advanced brain imaging technique.
Participants were trained to use mental strategies like recalling a previous trip, while activity in the VTA was simultaneously imaged by functional MRI scans.
Researchers also gave the participants real-time feedback on the effectiveness of their mental strategy, allowing them to change thoughts and adapt for increased VTA activity.
The participants were then given a vaccine against hepatitis, and their blood was obtained before, and for up to four weeks after, injection.
People who learned to maintain higher VTA activity were found to have a larger increase in levels of protective antibodies in the blood to the vaccine.
To maintain high VTA activity, people used mental strategies involving positive expectations, the study noted, hinting that the findings were likely a sign of the placebo effect.
“Sustained VTA upregulation was further linked to mental strategies involving positive expectations,” scientists wrote.
The research points to a potential link between the activity of specific brain pathways related to motivation and expectation, and the immune system.
“It remains unknown whether a similar brain-immune link exists in humans and whether it involves conscious positive expectations,” scientists wrote in the study published in the journal Nature Medicine.
It could be useful for identifying targets associated with the placebo effect in humans and future treatments.
“These findings suggest that consciously generated positive expectations can engage reward circuitry to influence immune function,” scientists wrote.
However, scientists seek to conduct further studies with more participants, as in the latest one, they only measured antibody levels, and not the clinical efficacy of the vaccine.