Differential brain effects of laser and needle acupuncture at LR8 using functional MRI
Im Quah-Smith,1 Mark A Williams,2 Thomas Lundeberg,3 Chao Suo,1 and Perminder Sachdev1
1School of Psychiatry, University of New South Wales and Neuropsychiatric Institute (NPI), Prince of Wales Hospital, Sydney, New South Wales, Australia
Acupuncture is a popular form of complementary medical intervention used to treat a number of disorders including neuropsychiatric illnesses.1–8 The traditional modality of acupuncture has been with needles applied manually. A number of investigators have examined the possible mechanisms by which needle acupuncture (NA) may produce physiological effects, with many neural structures being implicated including peripheral nerves, neurovascular bundles, mechanoreceptors, nerve endings and neuromuscular attachments.9–18
In the 1970s, with the advent of laser technology, low intensity laser acupuncture (LA) emerged as a new modality of acupuncture and increased in popularity. The main advantages of LA were that it was painless and infection-free because there was no needle puncture. It was also easy to deliver, making it time-efficient and cost-effective. Because of the lack of any skin sensation, low intensity laser was also easy to blind in any experimental design, making it an ideal research tool. In spite of these qualities and its increasing clinical importance, there is a dearth of investigations into its neurophysiological effects and clinical efficacy.19–21 Little is known about the peripheral pathways and spinal and central mechanisms involved in LA.
The application of functional MRI (fMRI) to acupuncture research has opened up an avenue to investigate the CNS effects of the various modalities of acupuncture.22–34 In our previous studies, fMRI was used to examine the brain response to LA on four acupuncture points (LR8, LR14, CV14 and HT7) in both healthy participants and those with depression.35 36 The choice of acupuncture points in the fMRI studies was based on a pilot clinical study to demonstrate the effectiveness of a suite of acupuncture points in the treatment of mild to moderate depression in primary care,8 with LR8 stimulation having produced the most salient effect. These studies showed that the brain activation patterns in depression during LA were different from those in healthy participants, with a significant shift from the frontolimbic cortices to the parieto-temporal-cerebellar regions in those with depression. Another network of interest found with the brain effects of acupuncture is the default mode network (DMN),37 38also known as the resting state network. The DMN is active when the brain is not involved in any specific task. When the DMN is active, self- referential activity occurs in the resting brain as part of its preparation before the next task.37 38 This self-referential activity is associated with the ‘sense of self’ important in the well-being of the individual.
In this study we chose LR8 (which produced the most salient antidepressant effect in our previous work) to compare the brain effects of the two modalities (LA vs NA) in healthy individuals. We also wanted to record their impact on the DMN.
Sixteen healthy individuals (eight women and eight men) aged 18–60?years (mean 48.2?years) were recruited by advertisement through the University of New South Wales, Black Dog Institute and a private medical acupuncture clinic in Sydney.
Each participant received LA on the medial knee acupuncture point LR8 (at the junction of the semitendinosus and semimembranosus tendon insertion site above the knee) and NA at LR8 on the other leg, with the side of stimulation being counterbalanced across the group; in other words, for the whole sample there was equivalent left- and right-sided stimulation with NA and LA.
During the fMRI scan, two runs were used for either LA or NA condition in randomised order. Each run had alternating rest/active phases, beginning with a rest phase, and consisted of 17 blocks with eight active phases (block) alternating with nine rest phases (block). The duration of each active block was 20 s, including 2 s preparation time, 16s of continuous acupuncture stimulation and 2 s of repetition time (TR) at the end for the scanner to pick up the BOLD signal. The rest block was set at 20 s to match the active block. Both laser stimulation and needle stimulation were time-locked to signalling.
Participants were right-handed, had no history of significant medical or psychiatric disorder, were not currently on any medication other than vitamin supplements, had no contraindications to an MRI scan and provided written informed consent.
Exclusion criteria included ongoing uncontrolled systemic illness, acute illness, brain injury, past surgery involving the lower limbs and any contraindications to MRI (pacemaker, ferromagnetic implants or foreign body, claustrophobia).
Subjects were withdrawn if any of the abovementioned exclusion criteria occurred in the interim before the procedure or if the subject became agitated or anxious during the procedure.
Randomisation and blinding
Randomisation has been described above in the study design. There was no blinding of either the participant or the acupuncturist. The block (rest/active) design accommodated for the placebo response to both needle and laser stimulation.
LA and NA were conducted by IQ-S and TL. IQ-S is a Fellow of the Australian Medical Acupuncture College (AMAC) and has been a clinical acupuncturist for 20 years. TL has expertise in integrative neurophysiology and is a rehabilitation medicine specialist
Single usage Helio-sourced non-ferrous silver needles with dimensions 0.22 mm×25mm, which are compatible with the magnet, were used. The location of LR8 was confirmed by anatomical landmarks and needle puncture was followed by rotation in 1 Hz cycles in a 45 degrees clockwise direction to produce the de qi sensation typical of manual acupuncture while undergoing MRI acquisition. The needling blocks were achieved with time-lock to signalling for MRI acquisition.
A Moxla prototype fibreoptic infrared light laser (Euryphaessa AB, Stockholm, Sweden), 808 nm with 20 mW capacity and a fibreoptic arm was developed for use in the scanning room. Location was confirmed by anatomical location. A stably-held laser was applied to the skin by the acupuncturist for the duration of the laser session according to the time signal. The switching on and off was achieved with a computer signal time-locked to the MRI acquisition.
Sensory stimulation reporting
After the acupuncture intervention under fMRI acquisition the participants were each asked to assess the sensory stimulation they underwent; the sensory descriptions were light touch, pressure, fullness, heaviness, ache, soreness, numbness, tingling, warmth, pain and ‘other’
Imaging was performed on a 3T Philips Intera MRI scanner (Philips Medical Systems, Best, The Netherlands) for both T1-weighted three-dimensional (3D) structural and BOLD contrast functional MRI. The 3D structural MRI was acquired in sagittal orientation using a T1-weighted TFE sequence (TR/TE=6.39/2.9 ms; flip angle=8; matrix size=256×256; FOV=256×256 mm; slice thickness 1.0 mm), yielding sagittal slices of 1.0?mm thick and an in-plane spatial resolution of 1.0×1.0?mm, producing an isotropic voxel of 1.0×1.0×1.0?mm. A gradient echo-planar imaging (EPI) technique (TR/TE=2000/40 ms; matrix size=128×128; FOV=250×250 mm; in-plane pixel size 1.953×1.953?mm) was used to acquire T2-weighted BOLD contrast fMRI in axial orientation. The whole brain was covered using 21 slices at 5.0 mm slice thickness.
Imaging data were analysed using statistical parametric mapping (SPM2, Wellcome Department of Cognitive Neurology, London, UK) implemented in Matlab V.6 (The Mathworks). All volumes were realigned spatially to the first volume and the time series for voxels within each slice realigned temporally to acquisition of the middle slice. Resulting volumes were normalised to a standard EPI template based on the MNI. The normalised images were smoothed with an isotropic 8 mm full-width half-maximal Gaussian kernel. The time series in each voxel was highpass filtered to 1/120 Hz to remove low-frequency noise.
Statistical analysis was performed in two stages assuming a random effects design. Each stimulation site was compared with the rest condition for first-level analysis. The BOLD response to the acupuncture stimulation was modelled by a canonical haemodynamic response function (HRF).
Half the participants’ images were flipped and the group was then processed as a whole under second-level analysis (ANOVA) at the whole brain level. Each individual participant's contrast images, which were effectively the statistical parametric maps of the t-statistics for each voxel from the first-level analysis, were put into this second-level design. We used a one-sample t test to examine the activation pattern of each acupuncture group and a within-subject two-sample t test to compare the activation differences between the two types of acupuncture. To correct for multiple comparisons, areas with a p value<0.05 following cluster-level Family Wise Error (FWE) correction were considered significant, with an initial uncorrected p value threshold of <0.001 and the extent threshold to 15 contiguous voxels.
NA at LR8 showed increased activation at the right insula (pFWE=0.001) and left precentral gyrus and insula (pFWE<0.001) (figure 1, table 1). There was also deactivation at the left precuneus (pFWE=0.002). No significant results were found for LA acupuncture at LR8, indicating that there was no consistent activation or deactivation at the first level.
When the activation patterns for LA and NA were compared, NA produced greater activation in the left precentral gyrus (pFWE=0.023) and LA produced more activation in the left precuneus (pFWE=0.003) (figure 2, table 2).
Sensory stimulation: laser versus needle
All participants felt the touch of the laser probe but only a few reported any sensation produced by the laser beam itself, with three reporting a tingling sensation, one a feeling of warmth and one reporting both these sensations. Needle acupuncture with de qi produced more sensory changes, with all participants reporting pressure and tingling and three reporting pain (see online appendix, supplementary tables S1 and S2).
Adverse effects: laser and needle acupuncture, MRI experience
On a scale of 0 (none) to 6 (severe), mean scores of adverse effects with LA were: transient tiredness and dizziness (0.13), vagueness (0.125) and nausea (0.06). Adverse effects with NA were: pain (0.50) and unwell (0.13). The MRI experience caused mild discomfort (0.44) and anxiety (0.44) (see online appendix, supplementary table S3).
Functional MRI studies with NA have indicated that deactivation of the limbic-paralimbic-neocortical network and activation of the somatosensory cortex are involved during NA intervention. Deactivation of the limbic system occurs with correct de qi needling technique, whereas poor technique resulting in the pain sensation causes the opposite reaction (activation of the limbic system). Some of the limbic-paralimbic regions were identifiable as being part of the DMN.12 13 22 23 These studies have selected acupuncture points which are clinically known to be uncomfortable when de qi needling is applied (eg, LI4 and ST36). The insula is involved in NA and our first-level findings confirmed those in the literature.12 13 27–34 The limited literature on the brain effects of LA suggests limbic-paralimbic-neocortical activation but no significant activation of the somatosensory cortex.20 21 Ipsilateral brain activation was also observed. One study on healthy participants reported that this ipsilaterality was only seen with limb acupuncture points and not truncal acupuncture points.35 The ipsilaterality suggests the involvement of the autonomic nervous system in LA mechanisms of action. There was no significant activation or deactivation of the somatosensory cortex, with the low intensity laser stimulation being free of pain or ache. This may contribute to the interindividual variability in the first-level analysis with LA while first-level analysis with NA demonstrated significant activation of the insula, important in pain pathways and deactivation of the posterior DMN. Unlike previous NA studies reporting somatosensory cortical changes, the precentral gyrus linked to the primary motor cortex was activated. The above literature therefore suggests that the NA and LA acupuncture afferent pathways may be different, the former due to its somatosensory and sensorimotor input following afferent pain pathways9 10and the latter possibly more autonomically driven.19 35 36
The literature shows that both NA and LA modulate the DMN. The DMN is a composite of brain regions activated when the brain is at rest and not involved in an active task. It is therefore also referred to as the task negative brain network. During DMN time the healthy individual reflects on his or her life and his or her hopes and aspirations.39 It may be that activation of the DMN is responsible for the feeling of well-being from acupuncture intervention. Some may argue the case that the well-being is from the placebo effect. The DMN may be an integral part of every acupuncture intervention, directly contributing to the maintenance of ‘sense of self’ and well-being.3740
The posterior DMN is important in depression.40 41 LR8 is the most important acupuncture point in the LA treatment regime for depression that was tested in our previous work.35 The significant activation of the left precuneus (as part of the posterior DMN) after FWE correction when LA is applied to LR8 across the group in the second-level analysis is further confirmation of the clinical efficacy of LA in depression.8 In NA, deactivation of the left precuneus was noted at the first-level analysis, confirming the deactivation of this part of the posterior DMN. This could be part of an antidepressant effect of NA at LR8. Further needle fMRI acupuncture studies are needed to confirm the efficacy of this acupuncture point in depression.
In the first-and second-level analyses, measuring activation less than or greater than a baseline (in this case, rest) are referred to as deactivation and activation, respectively. However, in this study, for second-level analysis, deactivation is impossible to interpret as we are subtracting two tasks from each other (NA vs LA) and not comparing them with rest. We found that NA significantly stimulated the left precentral gyrus compared with LA, and the latter significantly activated the left precuneus compared with the former. It is not known why the left precentral gyrus in NA and the left precuneus in LA are stimulated for these modalities in this comparison. In the protocol it was ensured that equivalent numbers of left- and right-sided NA and LA were conducted. The left-sidedness may be limited to our sample alone. Further studies may be required to clarify the brain functions of LR8 when stimulated by different modalities of acupuncture.
Interestingly, in spite of NA at this acupuncture point using the de qi method to cause the traditional ‘achy’ sensation, there was no significant stimulation of the somatosensory cortex (represented as the post-central gyrus). Instead, NA at LR8 produced significant activation at the precentral gyrus after FWE correction. The precentral gyrus is an important region which includes the motor cortical regions42 (primary motor or somatomotor cortex and the lateral premotor cortex). Previously, sensorimotor implicated acupuncture points (GB34, GB35, GB39, ST36 on the leg and LI9, LI10, LI13, LI14 on the arm) have been shown to increase brain activation of the premotor and supplementary motor regions.43 Another study showed that NA at GB34/BL57 caused deactivation of the primary motor cortex and premotor cortex.44 The findings of NA at LR8 in this study are only preliminary fMRI evidence. More investigations are warranted to evaluate the role of NA at LR8 in the modulation of motor cortical regions and hence its likely usefulness in motor rehabilitation clinically.
Empirically, LR8 is not particularly uncomfortable or painful when needled to produce the de qi sensation, unlike widely investigated acupuncture points ST36 or LI4 which are known to be uncomfortable to similar needling. This observation suggests that maybe not all acupuncture points produce somatosensory changes when needled.12 25In the case of LR8, the outcome from this study is that NA at this acupuncture point is significantly somatomotor. In the literature, among its applications, LR8 is empirically used for muscle spasms, pareses and paretic tendencies.45 Classically, it is meant to ‘benefit the sinews’. It would be interesting to perform further work on other mid lower limb acupuncture points to test their sensorimotor implications.
The sensory signalling (if any) perceived by the participants from LA was light touch (for all participants) and tingling and/or warmth (n=2), and only one participant felt pressure. Warmth being C fibre-linked and light touch and tingling being more so, A-β linked sensations may be part of LA's afferent fibres. Evaluation of the sensory signalling with NA showed that pressure and tingling (n=10) were felt by more participants than light touch (n=6) or ache (n=5). Interestingly, with LA all of the participants felt light touch and only three participants felt anything more than light touch. This may suggest an A–β and possibly non-nociceptive C afferent involvement with LA, whereas NA probably sets up activity in A-β, A-δ and C fibres (nociceptive as well as non-nociceptive).9 46More investigations are warranted to identify definitively the afferent fibre types involved in LA.
There are limitations to these findings. They may be confined to this low intensity laser (808?nm). Although we had 16 participants, this is still a relatively small sample size. This study was conducted on healthy participants and NA or LA at LR8 may produce totally different brain patterns in participants with health problems.
NA and LA at LR8 produce different brain patterns, highlighting the differential application of these two modalities of acupuncture. These activation patterns are consistent with the suggestion that LA at LR8 may be useful in the treatment of mood disorders while NA at LR8 may be useful in the modulation of motor cortical regions and hence may have a place in motor rehabilitation. These are only preliminary findings and further investigations with larger samples are warranted.
We thank Helio Australia for supplying the MRI friendly silver needles. Thanks to all our participants for their time and contribution, to Julie-Ann Ho for their recruitment and to Kate Bromley and Beverley Stanton for their help in laser signalling.
Contributors: IQ-Sdesigned and managed the study, recruited participants, conducted the laser/needle intervention under fMRI, analysed the data and wrote the manuscript. MW helped with study design and data analysis. TL conducted the laser/needle intervention under fMRI and helped with writing the manuscript. CS analysed the data and helped with writing the manuscript. PS contributed to the study design, ethical application and writing the manuscript.
Funding: This project was funded by Thyne Reid Foundation and Louise Dobson and family. We thank them for their support.
Competing interests: None.
Ethics approval: This study was approved by the Human Research Ethics Committee, South East Health, South Eastern Illawarra Area Health Service, Sydney, Australia.
Provenance and peer review: Not commissioned; internally peer reviewed.
Data sharing statement: We are happy to discuss data sharing as approved by the senior author Professor Perminder Sachdev.
The Brain Effects of Laser Acupuncture in Healthy Individuals: An fMRI Investigation
Pedro Antonio Valdes-Sosa, Editor
Copyright Quah-Smith et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Despite the remarkable developments in Western Medicine in modern times, public interest in Traditional, Complementary and Alternative Medicine (TCAM), such as acupuncture, remains high , . This may be because TCAM is perceived as holistic and relatively free of adverse effects. However, these treatments sit uncomfortably alongside scientific medicine because of strikingly different explanatory systems and the empirical tests applied by each discipline. In order to bridge the gulf between high public acceptability and the lack of empirical evidence for many of these treatments, it is important to reconcile them with modern scientific concepts. Our focus here is on laser acupuncture, and we address the question whether laser acupuncture produces brain effects that are biologically plausible.
There have been many studies – some of which have involved functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) of the brain effects of needle acupuncture. Some neuroimaging and neuroendocrine studies have suggested that needle acupuncture affects hypothalamic as well as extrahypothalamic functions and modulates mood , –. Needling of the leg acupoint ST36 and the hand acupoint LI4 was shown to activate the hypothalamus and nucleus accumbens and deactivate the rostral anterior cingulate cortex (rACC) . Superficial needling (i.e. needling that did not produce the classical de qi sensation – tingling, numbness or other sensations that occur after an acupuncture needle has been properly placed in the body) and non-acupoints (i.e. points on the skin that do not lie on recognized meridians in Traditional Chinese Medicine [TCM]) did not activate the hypothalamus . Stimulation of the acupoint PC6, located above the wrist, recommended for a wide range of conditions from nausea to stress management, resulted in activation of the cerebellum, dorsomedial nucleus of the thalamus, anterior cingulate gyrus and left superior frontal gyrus . All of these studies have used needle acupuncture which, although more traditional, is invasive.
While laser acupuncture has become an increasingly common clinical method, particularly in primary care, its empirical basis has been less well studied to date. Whereas needle acupuncture studies have shown activation and deactivation of the somatosensory cortex , , , , –, superficial needling and laser intervention appear to stimulate cortical and subcortical structures other than the somatosensory cortex , , . This is consistent with the observation that low intensity laser stimulation does not produce a skin sensation. For example, laser acupuncture of a foot acupoint, classically used for treating visual problems, was demonstrated to cause activation of the occipital cortex .
This study has used laser delivered at low intensity as used in primary care. Other studies have reported high intensity lasers can produce de qi sensation . High intensity laser is not commonly used in primary care situations and therefore was not used in the current study. Further, as low intensity laser does not result in sensory sensation it is ideal for double blind randomized controlled studies where the subjects could not differentiate between placebo (laser off) and verum laser (laser on).
The evidence suggests that cortical activation does occur with acupuncture and this activation may be specific to certain brain regions in relation to the site and type of stimulation –. In practice, acupoint efficacy is not specific, and one acupoint can be used for several different conditions, just as one medical condition can be managed with several acupoint locations. For instance, the antidepressant effect of laser acupuncture  has been attributed to a group of acupoints – CV14, LR14, LR8 and HT7 (see fig.1 for anatomical location), however there are other acupoint combinations that are also applicable for the management of depression. The neurological effects of stimulation of these acupoints CV14, LR14, HT7 and LR8 in combination have yet to be investigated.
Materials and Methods
The study was approved by the human research ethics committee of the South Eastern Sydney & Illawarra Area Health Service and participants provided written informed consent before participation.
The participants (n=10) (7 women, 3 men) were healthy volunteers aged 18–50 years (mean age =39.8 years) who were recruited by advertisement from the staff and students of the University of New South Wales and Prince of Wales Hospital, Sydney, Australia. All participants were right-handed and had no past history of depression or other psychiatric disorder, a Beck Depression Inventory  score <10, no history of drug or alcohol abuse, no medication intake within 3 months of the study, and no neurological or systemic disorders. Eight were acupuncture naïve and two had had needle acupuncture more than 3 months previously and did not know what to expect from laser intervention. Any contra-indications to MRI (pacemaker, ferromagnetic implants or foreign body, claustrophobia) were exclusionary.
Choice of acupoints and control point
The acupoints were selected based on results from our previous study  and the TCM for mood disorders, . These acupoints lay on the classically named liver (LR), heart (HT) and conception vessel (CV) meridians. The selected points, labelled LR8, LR14, HT7 and CV14 in TCM, are shown in Figure 1. LR8 is in the medial knee region, between the insertions of the sartorius and semitendinosus muscles. LR14 is in the vicinity of the 6th intercostal space on the mid clavicular line. HT7 is at the wrist crease, in the vicinity of the radial side of the flexor carpi ulnaris. CV14 is in the anterior midline, approximately 5 cm below the xiphisternum. A control non-acupoint was selected on the abdominal surface, midway between SP15 (four cun from the umbilicus) and ST25 (two cun from the umbilicus) away from the abdominal meridians.
A block design was used, with each block of 20 seconds duration during which the subject received either laser stimulation (switched ‘on’) or placebo stimulation (switched ‘off’) at one acupoint. The infra red laser was held with light touch on the skin surface by the acupuncturist. Since the laser produces no sensation, the subject was able to be kept blind to the phase of stimulation. The on-off cycle was repeated 4 times for each acupoint (LR14, LR8, CV14, HT7), with the 4 acupoints being stimulated twice in random order. The control point near ST25 was stimulated once per subject. The block design accomodated for the placebo (laser off) condition during its rest phases. In total there were nine runs per subject. The subject was told to relax and keep his/her eyes closed during the entire time in the scanner.
A MoxlaR prototype fiberoptic infra-red light laser (808 nm) with 25 mW capacity and a fiber optic arm was developed for usage in the scanning room. The laser parameters are similar to the one used in the clinical study we have based our investigation upon . The acupoints were marked with a skin marking pencil prior to entry into the scanning room. A stably held laser was applied to the skin by the acupuncturist (IQ-S) who moved it from point to point according to the time signal. The switching on and off was achieved with a computer signal time-locked to the MRI acquisition.
Imaging was performed on a 3T Philips Intera MRI scanner (Philips Medical Systems, Best, Netherlands) for both T1-weighted 3D structural and BOLD contrast functional MRI. The 3D structural MRI was acquired in sagittal orientation using a T1-weighted TFE sequence (TR/TE =6.39/2.9 ms; flip angle =8; matrix size =256×256; FOV =256×256 mm; slice thickness 1.0 mm), yielding sagittal slices of 1.0 mm thick and an in-plane spatial resolution of 1.0×1.0 mm, producing an isotropic voxel of 1.0×1.0×1.0 mm. A gradient echo-planar imaging (EPI) technique (TR/TE=2000/40 ms; matrix size =128×128; FOV=250×250 mm; in plane pixel size 1.953×1.953 mm) was used to acquire T2-weighted BOLD contrast fMRI in axial orientation. The whole brain was covered using 21 slices at 5.0 mm slice thickness and 0.5 mm gap for each volume. Each session of 96 volumes were collected with the rate of 2s/volume.
Image preprocessing and statistical analysis
Imaging data were analyzed using statistical parametric mapping (SPM2, Wellcome Department of Cognitive Neurology, London, UK) implemented in Matlab version 6 (The Mathworks Inc., USA). All volumes were realigned spatially to the first volume and the time-series for voxels within each slice realigned temporally to acquisition of the middle slice. Resulting volumes were normalized to a standard EPI template based on the Montreal Neurological Institute (MNI). The normalized images were smoothed with an isotropic 8 mm full-width half-maximal Gaussian kernel. The time-series in each voxel were highpass-filtered to 1/120 Hz to remove low-frequency noise.
Statistical analysis was performed in two stages, assuming a random effects design. Each stimulation site was compared to the placebo (laser off) condition for first level analysis. The BOLD response to the laser acupuncture stimulation was modeled by a canonical hemodynamic response function (HRF). The second level analysis (ANOVA) used each individual subject's contrast images, which were effectively the statistical parametric maps of the t-statistics for each voxel. The data had a threshold of p <0.001 with a spatial extent of 15 contiguous voxels.
After the scanning session, subjects rated selected items on the Spielberger State Anxiety Inventory  to describe their mental state during the period of the scanning. The ratings were: 1 (not at all), 2 (somewhat), 3 (moderately so) and 4 (very much so).
At the group level, there were significant increases (activation) in BOLD levels in some brain regions for acupoints LR14, CV14, LR8 and the control point compared to all the other points (verum laser per point > all others, p<0.001; see Table 1). Further, there were significant decreases (deactivation) in BOLD levels for acupoints LR14, LR8 and the control point compared to all the other points (all others > verum laser per point, p<0.001; see Table 1) in other brain regions.
Somatosensory cortex and laterality of cerebral activation and deactivation
Our study involved randomized stimulation of the 4 acupoints and a control point. Although there was activation of contralateral postcentral gyrus (primary somatosensory cortex or SSI) with LR14 and control point, none of the other acupoints showed any activation of the somatosensory cortex. The cortical and subcortical structures activated with stimulation of the limb acupoints tended to be largely ipsilateral to the side of stimulation.
All the acupoints and control point did not have deactivation at the somatosensory cortex. However they all had contralateral deactivations with the exception of LR8 that had bilateral middle frontal gyrus deactivation.
Participants did not describe anxiety or discomfort during scanning, except for one who found the headphones uncomfortable. The mean Spielberger scale ratings were on select items were: feeling calm (3.3), secure (3.3), relaxed (3.3), nervous (1.4), jittery (1.1), worried (1.1) or overexcited and rattled (1.1).
This is the first fMRI study to examine the effects of laser stimulation of a suite of acupoints found to be efficacious in a clinical condition (depression). A salient feature of this study was that four acupoints and a control non-acupoint (sham point) were stimulated in a random design. The subjects were unaware of the relative significance of different acupoints. The use of low level laser acupuncture, which does not produce a skin sensation, permitted the blinding of subjects to verum or placebo stimulation, something difficult to achieve with needle acupuncture.
The main finding of our study was that each acupoint or control point resulted in a different pattern of brain activity when contrasted against all the other acupoints or control point. The acupoints we investigated in this study were those that have been used in our previous treatment study for depression . This finding suggests that although these acupoints are all used in the treatment of depression, the neural locus of this effect differs depending upon the site stimulated. The efficacy of these acupoints in the treatment of depression may vary greatly between patients and site stimulated, and our findings may shed some light on these effects .
The neuroanatomical basis of depression is not completely understood, however a number of studies have implicated abnormalities in certain brain regions, in particular the medial and dorsolateral prefrontal cortex, the cingulate gyrus and the so-called limbic brain regions (hippocampus, parahippocampal gyrus, amygdala, septal nuclei, insula, thalamus) and paralimbic regions (orbitofrontal cortex, anterior temporal lobe) –. There is converging evidence from drug treatment, cognitive-behavior therapy and brain stimulation techniques that antidepressant treatments work by modulating frontal-subcortical neuronal circuits. The most consistently reported finding is that antidepressant treatments lead to a normalization of activity in the dorsolateral prefrontal cortex, with additional changes in the subgenual cingulate region, the posterior cingulate, parahippocampal gyrus and insula. Whether the change in prefrontal cortex is a primary event or secondary to changes in subcortical nuclei is unclear, but the relationship of treatment response to this suggests that it is biologically plausible that laser acupuncture could be an effective antidepressant treatment through its effects on the above brain regions.
The results show this combination of acupoints activating frontal cortex, limbic cortex and subcortical caudate. The trend is for ipsilateral activation suggestive of neurological circuitry outside the dorsal spinal columns and more likely to be autonomically driven –. Most of the deactivations were contralateral. Also LR14 and control point activations included primary somatosensory cortical activations (SSI). None of the deactivations involved SSI, however they did include the regions as described earlier that could collectively be called the affective cortex (the frontal, limbic and temporal cortices as well as the subcortical caudate). This combination of ipsilateral and contralateral activations and deactivations may perhaps be representative of the combined actions of both the spinal and autonomic nervous systems during laser acupuncture.
In classical acupuncture, there are primary and secondary acupoints for the treatment of any disorder. The approach to acupoint selection can be variable, with primary acupoints being considered essential and secondary acupoints additive for some patients. In our study, we cannot predict from these results whether any acupoint should be preferred over others for clinical use, even though LR8 deactivated more brain regions (middle and superior frontal gyrus, middle temporal gyrus and the subcortical caudate) than all the other points. These are results from a sample of healthy subjects. The question of whether the results would be different in a sample of clinically depressed subjects, needs to still be answered. Further studies are required to explore the relative value of different acupoints, the final test for which naturally lies in a clinical trial. It also cannot be stated from our study whether the treatment response can be achieved with stimulation at one point alone, or if multiple points are necessary.
There is conflicting evidence regarding acupoint specificity and whether that specificity is relative rather than absolute for any particular disorder –. Furthermore, it is debatable whether the clinical effects of acupuncture are restricted to stimulation on points that lie on the classical meridians in TCM. Our finding that laser stimulation of a non-acupoint produced some brain activation suggest that there is unlikely to be a completely neutral control non-acupoint, and this should prompt a re-examination of the use of sham points (in needle acupuncture studies) as control hence minimizing the true statistical effects of any acupoint –. It is also interesting that laser acupuncture in this study appeared to preferentially activate the limbic cortex ipsilaterally and deactivate the limbic cortex contralaterally. It has been suggested that laser stimulation preferentially activates unmyelinated afferent fibers that project ipsilaterally to the insula –, which might also explain the differences from needle acupuncture.
This laser acupuncture fMRI study demonstrated the central effects of stimulation of a suite of acupoints found to be efficacious in treating depression in a primary care setting. The multiple acupoints each activated different groupings of frontal-limbic-striatal brain regions, suggesting some acupoint specificity but also a commonality in the regions affected. There was a trend for the limb acupoints to cause ipsilateral activation and contralateral de-activation. The results of the study suggest that laser acupuncture is a biologically plausible anti-depressant treatment. Its efficacy and the relative merits of the different proposed acupoints must be empirically examined.
The authors would like to thank Dr Ron Shnier (Radiologist) for his contribution and Ms Angie Russell for assistance with manuscript preparation and submission.
Competing Interests: The authors have declared that no competing interests exist.
Funding: The authors acknowledge financial support from Louise and Gary Dobson, James Fairfax and the Thyne Reid Foundation. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.