Acupuncture modulates the limbic system and subcortical gray structures of the human brain: evidence from fMRI studies in normal subjects

Abstract

Acupuncture, an ancient therapeutic technique, is emerging as an important modality of complementary medicine in the United States. The use and efficacy of acupuncture treatment are not yet widely accepted in Western scientific and medical communities. Demonstration of regionally specific, quantifiable acupuncture effects on relevant structures of the human brain would facilitate acceptance and integration of this therapeutic modality into the practice of modern medicine. Research with animal models of acupuncture indicates that many of the beneficial effects may be mediated at the subcortical level in the brain. We used functional magnetic resonance imaging (fMRI) to investigate the effects of acupuncture in normal subjects and to provide a foundation for future studies on mechanisms of acupuncture action in therapeutic interventions. Acupuncture needle manipulation was performed at Large Intestine 4 (LI 4, Hegu) on the hand in 13 subjects [Stux, 1997]. Needle manipulation on either hand produced prominent decreases of fMRI signals in the nucleus accumbens, amygdala, hippocampus, parahippocampus, hypothalamus, ventral tegmental area, anterior cingulate gyrus (BA 24), caudate, putamen, temporal pole, and insula in all 11 subjects who experienced acupuncture sensation. In marked contrast, signal increases were observed primarily in the somatosensory cortex. The two subjects who experienced pain instead of acupuncture sensation exhibited signal increases instead of decreases in the anterior cingulate gyrus (BA 24), caudate, putamen, anterior thalamus, and posterior insula. Superficial tactile stimulation to the same area elicited signal increases in the somatosensory cortex as expected, but no signal decreases in the deep structures. These preliminary results suggest that acupuncture needle manipulation modulates the activity of the limbic system and subcortical structures. We hypothesize that modulation of subcortical structures may be an important mechanism by which acupuncture exerts its complex multisystem effects.

Figure 1

Experimental paradigm. Acupuncture needle manipulation was performed at LI 4 (arrow pointing to red dot) in the first interosseous muscle (gray shading). Scanning began 2 min prior to needle insertion. The needle was left at rest for 2 min before manipulation. Two epochs of needle manipulation (M1, M2) each lasting 2 min, were administered separated by a rest interval of 4 min. The needle was removed 2 min after M2. Scanning was continued for an additional 2 min. For statistical analyses, the mean signal intensity of the three periods of needle at rest (R1, R2, R3) served as the baseline for changes in signal intensity during needling. For the control experiments tactile stimulation was delivered to the skin surface overlying the acupuncture point with the tip of a flexible wire during M1 and M2. Total scanning time was 16 min.

Figure 2

Bilateral fMRI signal increases in somatosensory cortices and signal decreases in deep structures: acupuncture needle manipulation of the left LI 4 versus tactile stimulation in a single subject. Pseudocolor KS statistical maps of signal increases (left column, a, b) and signal decreases (right column, c, d) overlaid on high‐resolution scans in gray scale at the indicated slice plane relative to the anterior commissure. Both tactile stimulation and acupuncture needle manipulation elicited signal increases in the primary and secondary somatosensory cortices (SI, SII), but the changes were more marked during tactile stimulation (a) than during acupuncture (b). Acupuncture needle manipulation elicited signal decreases in the parahippocampus/fusiform gyrus (PH/FusG) and insula (Ins) (d), whereas tactile stimulation did not (c). Also shown are acupuncture needle manipulation associated signal decreases in the middle temporal gyrus (TGm) and precentral gyrus (PrCG). Color bar shows significance, same color if signal increased or decreased.

Figure 3

Signal increases in SII: tactile stimulation versus acupuncture needle manipulation at left LI 4 in the same subjects (n = 3). Group averaged data is presented in pseudocolor KS‐statistical maps of signal increases overlaid on gray scale high resolution scan with the time course of normalized signal intensity from the activated voxels as indicated by the green box. Note that SII signal increases occurred during both treatments, but the regional extent of brain activation was greater and the statistical significance more robust during tactile stimulation (a) than during acupuncture (b) see Table I. The time course of signal change correlated with the experimental paradigm. The horizontal line of each epoch represents the average signal intensity of that epoch.

Figure 4

Signal decreases in deep structures during acupuncture needle manipulation: group averaged data. Left LI 4 stimulation (n = 5): putamen (a), nucleus accumbens (b). Right LI 4 stimulation (n = 7): amygdala (c), hippocampus (d). The onset and recovery of signal changes showed good temporal correlation with the experimental paradigm. There was no evidence of adaptation, but rather a suggestion of enhanced effect during M2 for the amygdala (c) and the hippocampus (d).