Activity in the primary somatosensory cortex induced by reflexological stimulation is unaffected by pseudo-information: a functional magnetic resonance imaging study

Miura et al. BMC Complementary and Alternative Medicine 2013, 13:114 http://www.biomedcentral.com/1472-6882/13/114 RESEARCH ARTICLE Open Access Activity in the primary somatosensory cortex induced by reflexological stimulation is unaffected by pseudo-information: a functional magnetic resonance imaging study Naoki Miura1,2*, Yuko Akitsuki2,3†, Atsushi Sekiguchi2,4† and Ryuta Kawashima2,3,5† Abstract Background: Reflexology is an alternative medical practice that produces beneficial effects by applying pressure to specific reflex areas. Our previous study suggested that reflexological stimulation induced cortical activation in somatosensory cortex corresponding to the stimulated reflex area; however, we could not rule out the possibility of a placebo effect resulting from instructions given during the experimental task. We used functional magnetic resonance imaging (fMRI) to investigate how reflexological stimulation of the reflex area is processed in the primary somatosensory cortex when correct and pseudo-information about the reflex area is provided. Furthermore, the laterality of activation to the reflexological stimulation was investigated. Methods: Thirty-two healthy Japanese volunteers participated. The experiment followed a double-blind design. Half of the subjects received correct information, that the base of the second toe was the eye reflex area, and pseudoinformation, that the base of the third toe was the shoulder reflex area. The other half of the subjects received the opposite information. fMRI time series data were acquired during reflexological stimulation to both feet. The experimenter stimulated each reflex area in accordance with an auditory cue. The fMRI data were analyzed using a conventional two-stage approach. The hemodynamic responses produced by the stimulation of each reflex area were assessed using a general linear model on an intra-subject basis, and a two-way repeated-measures analysis of variance was performed on an intersubject basis to determine the effect of reflex area laterality and information accuracy. Results: Our results indicated that stimulation of the eye reflex area in either foot induced activity in the left middle postcentral gyrus, the area to which tactile sensation to the face projects, as well as in the postcentral gyrus contralateral foot representation area. This activity was not affected by pseudo information. The results also indicate that the relationship between the reflex area and the projection to the primary somatosensory cortex has a lateral pattern that differs from that of the actual somatotopical representation of the body. (Continued on next page) * Correspondence: † Equal contributors 1 Department of Information and Communication Engineering, Faculty of Engineering, Tohoku Institute of Technology, Yagiyama kasumicho 35-1 Taihaku-ku, Sendai 982-8577, Japan 2 Department of Functional Brain Imaging, Institute of Development, Aging and Cancer (IDAC), Tohoku University, Seiryo-machi 4-1, Aoba-ku, Sendai 980-8575, Japan Full list of author information is available at the end of the article © 2013 Miura et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Miura et al. BMC Complementary and Alternative Medicine 2013, 13:114 http://www.biomedcentral.com/1472-6882/13/114 Page 2 of 11 (Continued from previous page) Conclusion: These findings suggest that a robust relationship exists between neural processing of somatosensory percepts for reflexological stimulation and the tactile sensation of a specific reflex area. Keywords: Reflexology, Neuroimaging, Functional magnetic resonance imaging, Primary somatosensory cortex, Placebo effect Background Reflexology is an alternative medical practice that produces beneficial effects on the human body by applying pressure to specific points or areas on the feet, hands, and ears called “reflex areas.” It is a kind of massage therapy that is performed without using any special instruments (i.e., uses hands only). The modern concept of reflexology was introduced in both the U.S. and Europe in the early 20th century [1], and it is believed to help eliminate stress, improve blood circulation, and restore the psychological balance of the body [2]. Although it is practiced throughout the world and several clinical studies have shown positive effects of this practice, the precise mechanisms underpinning its clinical effectiveness have not been elucidated [3-5]. Furthermore, the physiological basis of reflexology is not fully understood. Each reflex area is believed to correspond to an organ or part of the human body; however, this correspondence had not been sufficiently investigated. Recently, neuroscientific research has examined the scientific underpinnings of complementary and alternative medicine such as acupuncture. Goldmann et al. [6] found that adenosine metabolism may influence the local antinociceptive effect of acupuncture, and Imai et al. [7] reported with acupuncture an improvement in autonomic function imbalance in rats under restraint stress. Previous neuroimaging studies using acupuncture have reported that acupoints related to different functions activate different areas of the primary somatosensory cortex (SI) [8] or different patterns of neural activity in the frontal–limbic–striatal regions [9]. Yoo et al. reported a difference in neural activity between real and sham acupunctural stimulation in the primary and secondary somatosensory cortex [10]. As for touch massage, including reflexology, a relaxing effect of reflexology was observed using electroencephalography (EEG) [11], pleasant touch massage induced activation of the pregenual anterior cingulate cortex [12], and reflexological treatments affected resting-state neural activity in the retrosplenial/posterior cingulated cortex [13]. In our previous study, we sought to provide experimental evidence of a somatotopical relationship between cortical activity in SI and sensory stimulation of reflex areas on the foot using functional magnetic resonance imaging (fMRI) [14]. We found that the area activated by stimulation of the reflex area was consistent with the somatotopic representation of the corresponding or a neighboring body part in SI. We interpreted these results as evidence of a physiological relationship between the reflex area and a body part or organ. However, an alternative interpretation is that the findings were the result of the placebo effect; it is possible that a sensory expectation resulting from a priori knowledge of the reflex area influenced the cognitive processing of the perceived reflexological stimulation. Blankenburg [15] reported that a somatosensory illusion called the “cutaneous rabbit” [16] evoked cortical activity in (...truncated)