What Is the Neural Basis of Placebo Pain Relief?

To explore the neurologic basis of the placebo effect — the phenomenon in which the expectation for pain relief leads to reduced pain — investigators created a behavioral assay for placebo-like anticipatory pain relief in mice. They had the mice stand on a surface at a comfortable temperature, then moved the mice to a hot surface. They then made the comfortable surface hot and allowed the mice to choose a surface.

Analgesia induced by the expectation of pain relief in the animals (shown by preferring the hot surface that had previously been cool) was mediated by specific neuronal projections from the rostral anterior cingulate cortex to the pontine nucleus involving Purkinje cerebellar cells, based on in vivo calcium imaging and electrophysi…