Placebo Conditioning by Means of Functional Magnetic Resonance Imaging

Lui et al. (2010) showed dynamic changes in prefrontal areas during placebo conditioning by means of functional magnetic resonance imaging. Brief laser heat stimuli delivered to one foot, either right or left, were preceded by different visual cues, signaling either painful stimuli alone, or painful stimuli accompanied by a sham analgesic procedure. Cues signaling the analgesic procedure were followed by stimuli of lower intensity in the conditioning session, whereas in the test session both cues were followed by painful stimuli of the same intensity.

During the first conditioning trials, progressive signal increases over time were found during anticipation of analgesia compared to anticipation of pain, in a medial prefrontal focus and in bilateral lateral prefrontal foci. These frontal foci were adjacent to, and partially overlapped, those active during anticipation of analgesia in the test session, whose signal changes were related to the magnitude of the placebo behavioral response, and those active during placebo analgesia. This finding suggests that the neural events that lead to learned placebo analgesia are located in both medial and lateral prefrontal regions.