Do the neural correlates of acupuncture and placebo effects differ?

Abstract

The neurophysiological basis of therapeutic acupuncture is not well understood but is likely to consist of both specific and non-specific (e.g. placebo) effects. Data from animal studies suggest that endogenous anti-nociceptive networks may play a large role in therapeutic acupuncture. These networks have also been demonstrated to support placebo analgesia making differentiation between acupuncture specific and non-specific networks challenging. However, modern neuroimaging techniques such as functional magnetic resonance imaging (fMRI), positron emission tomography (PET), electroencephalography (EEG) and magnetoencephalography (MEG) provide a means to safely monitor brain activity in humans and may be used to help map the neural correlates of acupuncture. Recent neuroimaging studies have explored brain activity during acupuncture stimulation and/or the analgesic effects of acupuncture on pain stimulus processing. Although controversy regarding appropriate control methodology (e.g. sham acupuncture) continues, data suggest that modulation of certain limbic brain networks may differentiate between specific and placebo components of acupuncture.

Figure 1. fMRI Evaluation of Acupuncture Stimulation and its Effects on Somatosensory processing: A) Acupuncture induced fMRI signal decreases in the amygdala within healthy adults

Both manual (MA) and electro-acupuncture (EA) but not tactile control stimulation at ST-36 induces fMRI signal decrease in the amygdala. (adapted from Napadow et al. 2005). B) fMRI of somatosensory processing in Carpal Tunnel Syndrome (CTS) patients before and after therapeutic acupuncture: In CTS, the brain demonstrates sensorimotor hyperactivation to innocuous stimulation of the 3^rd finger (median nerve innervated) of the affected hand.. After a 5-week course of acupuncture treatment, CTS patients demonstrated less hyperactivation, and more focused SI finger representation (adapted from Napadow et al. 2006b). C) Effects of acupuncture treatment on somatotopy in CTS patients: Compared to healthy controls (HC), CTS patients demonstrated less separation of somatotopic representations for the 2^nd and 3^rd fingers (both median nerve innervated). After acupuncture treatment, the 2^nd and 3^rd finger representations were more separated, approximating normal somatotopy in HC (adapted from Napadow et al. 2006b).