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It has been reported that acupuncture is effective in alleviating abnormalities of muscle tone caused by abnormal motor neuron excitability such as spastic paralysis caused by cerebrovascular disorder. However, the underlying mechanism is unclear. Thus, we examined the effect of acupuncture stimulation on long-latency reflexes (LLR) to determine the site of action of acupuncture stimulation in modulating motor reflexes. The amplitude ratio of LLR/M was reduced by the acupuncture stimulation of LI4 (hand). Furthermore, we examined the effect of acupuncture stimulation on blink reflexes. The R2 component of blink reflexes was decreased by the acupuncture stimulation of LI4 (hand). LLR is the motor reflex of the central nervous system via such as cerebral cortex of supraspinal pathways. In addition, blink reflexes are the motor reflex of the central nervous system via such as brain stem. These findings suggest that acupuncture stimulation inhibits motor nerve reflexes via supraspinal modulation systems. Furthermore, we examined the effect of acupuncture stimulation on electromyogram F-wave to determine the effect of acupuncture stimulation on the excitability of spinal motor neurons. The result of this study indicated that acupuncture stimulation may have a greater effect on the excitability of spinal motor neurons.
Hokkaido College of Oriental Medicine, Hokkaido, Japan
*Address all correspondence to: nihonmatsu@shinkyu.ac.jp
1. Introduction
It has been reported that acupuncture is effective in alleviating abnormalities of muscle tone caused by abnormal motor neuron excitability such as spastic paralysis caused by cerebrovascular disorder and rigidity in Parkinson’s disease [1, 2]. These reports that acupuncture stimulation suppresses motor nerve excitability and may alleviate abnormalities in muscle tone. However, the underlying mechanism is unclear. The next section introduces our research on motor reflexes via the cerebral cortex, brainstem, and spinal cord through acupuncture stimulation.
2. Effect of acupuncture stimulation on the long-latency reflex
2.1 Background and purpose
Many reports have shown the effects of acupuncture stimulation on motor reflexes via the motor cortex using motor-evoked potentials (MEP) [3, 4, 5, 6, 7]. There are reports that acupuncture stimulation of the upper and lower limbs suppresses MEPs in the muscles of the upper limbs and reports that MEPs are stimulated, but this has not been determined [3, 4, 5, 6, 7]. In this study, we investigated the effects of acupuncture stimulation on long-latency reflexes (LLR), which are motor reflexes that pass through the cerebral cortex.
2.2 Materials and methods
2.2.1 Participants
Sixteen healthy volunteers (mean – standard deviation [SD]:28.9–6.6 years; 10 males and 6 females) with no known neurological dysfunction, and stable appearance of LLR agree to participate in this study. Written informed consent was obtained from all subjects. This study was approved by the Research Ethics Committee at Hokkaido College of Oriental Medicine.
2.2.2 Study design
This study applied the crossover protocol; therefore, each experiment was randomly needled on separate days. The experiments were performed under two conditions: (1) acupuncture stimulation of right LI4, (2) control (no acupuncture stimulation). To prevent a carryover effect, more than 1 week intervals between each acupuncture stimulation were maintained.
2.2.3 Apparatus and condition for the LLR recording
Prior to the experiment, the maximum amount of contraction due to the opposite movement of the thumb and middle finger on the measurement side was measured using a load transducer (Showa Sokki load cell), and 20% of that force was maintained. During continuous muscle contraction in that state, electrical stimulation was performed, and LLR was measured. LLR were recorded and analyzed by using a Neuropack MEB 9204 recorder (Nihon Koden, Tokyo, Japan) with a band-pass filter of 5 Hz to 2 kHz. Thirty-two LLR waves, elicited by electric stimulation of the median nerve to the wrist, were recorded from the opponens pollicis muscle on the right hand of each subject in a resting sitting position. The stimulus intensity used to elicit LLR was more than the 120% that is required to elicit an M-wave response. The electrical stimulus rate and duration were 1 Hz and 0.2 milliseconds, respectively. Electromyographic electrodes were attached firmly over the opponens pollicis muscle, With the anode positioned thumb phalanges. The ground electrode was placed between the stimulating and recording electrodes. The electrode impedance was below 5KΩ. The experiments were performed in a quiet room with a consistent temperature of 23–25°C.
2.2.4 Data analysis for the LLR
Sample images of the LLR and M-wave are shown inFigure 1. The LLR was analyzed with respect to three parameters: occurrence, the LLR/M amplitude ratio, and the latency. The sensitivity was set at 5 mV/div for the M-wave and 0.5 mV/div for the LLR. The occurrence was defined as the number of detected LLR responses to 32 electrical stimuli and expressed as percentage (%). The LLR/M amplitude ratio was defined as the peak-to-peak amplitudes of LLR and M-waves were measured, and the amplitude ratio of LLR/M was expressed as the ratio of LLR amplitude and the maximal amplitude of M-wave. LLR latency was defined as the period from the stimulus to the LLR evocation.
Figure 1.
Analysis of LLR. Median nerve stimulation resulted in well known two component reflex responses in the adductor pollicis muscle. The first component (SLR) is short latency (20–30 msec) responses. In contrast, the second component (LLR) is of longer latency (40–60 msec) responses (reprinted from [8]).
2.2.5 Acupuncture stimulation
An acupuncturist applied a needle at the right LI 4 (radial to the midpoint of the second metacarpal bone) (Figure 2). Disposable stainless steel needles (diameter, 0.18 mm; length, 40 mm; Seirin Co., Ltd. Shizuoka, Japan) were used. The depth of needle insertion was 10 mm, and the needle was at a right angle to the skin and was maintained in this position (needle retention) for 5 minutes. No manipulation was performed during needle retention.
Figure 2.
Acupuncture stimulation site (LI4). An acupuncturist applied a needle at the right LI 4 (radial to the midpoint of the second metacarpal bone). Disposable stainless steel needles (diameter, 0.18 mm; length, 40 mm; Seirin Co., ltd. Shizuoka, Japan) were used. The depth of needle insertion was 10 mm, and the needle was at a right angle to the skin and was maintained in this position (needle retention) for 5 minutes. No manipulation was performed during needle retention.
2.2.6 Experimental setting
M-wave and LLR wave were measured before and after acupuncture (5-minute needle retention). M-wave and LLR wave in the control group were measured at the same timepoints acupuncture.
2.2.7 Statistical analysis
The data are reported as means ± standard deviation (mean ± S.D.). A Wilcoxon signed-rank test was used to compare occurrence, the LLR/M amplitude ratio, and the latency results after acupuncture and before acupuncture. For other statistical analyses, P values <0.05 were considered significant. Statistical analyses were performed using a commercially available statistical package (SPSS, Ver11.0.1, SPSS, Tokyo, Japan).
2.3 Results
2.3.1 Typical electromyogram waveform under before acupuncture stimulation and during acupuncture stimulation
Figure 3 illustrates a sample recording of the LLR wave from a typical subject. LLR wave decreased after acupuncture stimulation (right side), compared with those before acupuncture stimulation. No effect of acupuncture stimulation was observed on the M-wave.
Figure 3.
Typical electromyogram waveform under resting condition (left side) and during acupuncture stimulation (right side). Typical electromyogram waveform under resting condition and during acupuncture stimulation. LLR was decreased during acupuncture stimulation (reprinted from [8]).
2.3.2 Changes in LLR induced by acupuncture stimulation
The changes in LLR are shown in Table 1. The LLR occurrence was significantly reduced by acupuncture stimulation. There was no significant change in the control group. The LLR/M amplitude ratio was significantly reduced by acupuncture stimulation. There was no significant change in the control group. The LLR latency was no significant change in either group.
Acupuncture
Control
Before
After
Before
After
LLR occurrence (%)
78.7 ± 18.9
62.2 ± 23.7**
87.8 ± 10.0
77.4 ± 11.8
LLR/M ratio (%)
1.95 ± 0.72
1.57 ± 0.72**
1.64 ± 0.32
1.70 ± 0.59
LLR latency (ms)
56.2 ± 3.4
57.6 ± 4.0
56.5 ± 2.3
59.1 ± 2.5
Table 1.
Changes in LLR induced by acupuncture stimulation.
Mean ± SD. **: P < 0.01 Wilcoxon signed-rank test vs. before acupuncture.
2.4 Discussion
Sudden mechanical stretch of the wrist flexor muscles gives rise to EMG responses, including both short-latency and long-latency components [9]. Marsden et al. measured electromyograms of the flexor pollicis longus by abruptly extending the thumb. They reported that following a monosynaptic spinal cord reflex with a latency of 25 ms, long-latency reflexes of 55 ms could be measured [10]. In addition, Previous studies have shown that LLR is absent in patients with dorsal column injury [11] and patients with lesions in the corticospinal tract (motor area, internal capsule) [12]. Therefore, LLR is considered to be expressed by a supraspinal mechanism such as the cerebrum. It has been shown that LLR is induced not only by mechanical stimulation but also by electrical stimulation. Previous studies have reported lacking LLR in hemiplegia, posterior spinal cord injury, and pontine hemorrhage [13, 14, 15]. Therefore, LLR induced by electrical stimulation is considered to be a reflex that occurs by descending the corticospinal tract via the spinal cord, sensory cortex, and motor cortex. In this study, LLR occurrence and LLR/M amplitude ratio were significantly reduced by acupuncture stimulation. In addition, we reported that acupuncture-induced changes in the LLR/M ratio were associated with changes in SEP N20 amplitude [8]. N20 of SEP is the potential induced when electrical stimulation ascends the dorsal cord of the spinal cord and excites the somatosensory area of the cerebral cortex [16, 17]. In addition, there is evidence that the afferent pathway for the LLR to the cortex is identical to that for the somatosensory evoked cortical potential (SEP) after median nerve stimulation [17]. Therefore, it is thought that changes in the excitability of the somatosensory area of the cerebral cortex are involved in the suppression of LLR occurrence and LLR/M amplitude ratio by acupuncture stimulation. In addition, reflexes via the brainstem such as spino-bulbo-spinal reflex and transcerebellar loop reflex are thought to be involved in LLR [18, 19]. It is also possible that acupuncture stimulation affected this mechanism. However, Previous studies have shown that brainstem-mediated reflexes have faster latencies than LLRs, and cerebellar-mediated reflexes have slower latencies than LLRs [18, 19]. In this study, no significant changes were observed in LLR latency. Therefore, it is thought that the decrease in LLR occurrence and LLR/M amplitude ratio due to acupuncture stimulation is due to an inhibitory mechanism via the cerebral cortex.
2.5 Conclusion
These findings suggest that acupuncture stimulation inhibits motor nerve reflexes via such cerebral cortex modulation systems.
3. Effect of acupuncture stimulation on the blink reflex
3.1 Background and purpose
The blink reflex can be quantitatively measured from the magnitude of the reaction of the muscle action potential of the orbicularis oculi muscle induced when the supraorbital nerve, which is the first branch of the trigeminal nerve, is electrically stimulated. The electromyogram associated with the blink reflex consists of two components called R1 and R2. R1 is a relatively stable early component that appears with a latency of 10 msec and appears only in stimulus measurements. R2 is a late component that appears bilaterally after R1. The R1 component is the potential where electrical stimulation to the supraorbital nerve alters neurons in the facial nucleus at the pons and leads to the orbicularis oculi muscle. Several studies have considered the R2 component of the blink reflex to be evoked through a polysynaptic pathway in the pons and the lateral part of the medulla [20, 21]. In fact, impulses of the R2 component travel along a longer pathway through the medulla up to the thalamus or cerebral cortex [20, 21]. Peripheral facial nerve palsy causes R1 and R2 component suppression, and hemifacial spasm causes an increase in the R2 component [20, 21]. Furthermore, it has been reported that the R2 component reflects the disappearance of Myerson’s sign upon administration of L-dopa in patients with Parkinson’s disease [22, 23]. Therefore, it is thought that not only the brainstem but also a wide range of central nervous systems, including are involved in the expression of the R2 component of the blink reflex. In this study, we investigated the effects of acupuncture stimulation on BR, which are motor reflexes that pass through the supraspinal modulation systems.
3.2 Materials and methods
3.2.1 Participants
Fifteen healthy volunteers (mean – standard deviation [SD]:30.3–6.2 years; 15 males and 1 female) with no known neurological dysfunction and stable appearance of BR agree to participate in this study. Written informed consent was obtained from all subjects. This study was approved by the Research Ethics Committee at Hokkaido College of Oriental Medicine.
3.2.2 Study design
This study applied the crossover protocol; therefore, each experiment was randomly needled on separate days. The experiments were performed under two conditions: (1) acupuncture stimulation of right LI4 and (2) control (no acupuncture stimulation). To prevent a carryover effect, intervals of more than 1 week between each acupuncture stimulation were maintained.
3.2.3 Experimental setting
BR was measured before and after acupuncture (5-minute needle retention). BR in the control group was measured at the same timepoints acupuncture.
3.2.4 Measurement of BR
BR was recorded and analyzed by using a Neuropack MEB 9204 recorder (Nihon Koden, Tokyo, Japan) with a band-pass filter of 5 Hz to 2 kHz. Five BR waves, elicited by electric stimulation of the supraorbital nerve, were recorded from the orbicularis oculi muscle of each subject. The stimulus intensity was twice the intensity the R2 component responded to. The electrical stimulus rate and duration were 0.1 Hz and 0.2 milliseconds, respectively. Electromyographic electrodes were attached firmly over the orbicularis oculi muscle, With the anode positioned lateral canthus. The ground electrode was placed forehead. The electrode impedance was below 10KΩ. The experiments were performed in a quiet room with a consistent temperature of 23–25°C.
3.2.5 Data analysis for the BR
Analysis was performed on waveforms in which the blink reflex appeared stable (Figure 4). The obtained waveforms were analyzed with R1 as the waveform rising at the latency of 10 msec and R2 as the waveform rising at the latency of 30 msec.
Figure 4.
Analysis of BR. Analysis was performed on waveforms in which the appearance of the blink reflex was stable. The obtained waveforms were analyzed with R1 as the waveform rising at the latency of 10 msec and R2 as the waveform rising at the latency of 30 msec. Lat: Latency, amp: Amuplitude, dur: Duration.
3.2.5.1 R1 component
The R1 component was analyzed with respect to two parameters: the R1 latency and R1 amplitude. The R1 latency was defined as the time from the electrical stimulation to the rise of the waveform that appeared around 10 msec was measured. The R1 amplitude ratio was defined as the peak-to-peak amplitudes of R1, An average of waveforms of 60 μV or more was obtained.
3.2.5.2 R2 component
The R1 component was analyzed with respect to three parameters: the R2 latency, R2 amplitude, and R2 duration. The R2 latency was defined as the time from the electrical stimulation to the rise of the waveform that appeared around 30 msec was measured. The average of 5 waveforms was obtained. The R2 amplitude ratio was defined as the peak-to-peak amplitudes of R2. The time from the first negative peak of the R2 waveform to the last negative peak of the waveform was measured.
3.2.5.3 Measurement of electrical stimulation pain assessment
The subjective magnitude of electrical stimulation pain was rated by visual analog scale (VAS). It was recorded as no pain at the left end (0 mm) and the maximum pain the participant experienced in the past at the right end (100 mm) on a linear scale of 100 mm.
3.2.6 Acupuncture stimulation
An acupuncturist applied a needle at the right LI 4 (radial to the midpoint of the second metacarpal bone) (Figure 2). Disposable stainless steel needles (diameter, 0.18 mm; length, 40 mm; Seirin Co., Ltd. Shizuoka, Japan) were used. The depth of needle insertion was 10 mm, and the needle was at a right angle to the skin and was maintained in this position (needle retention) for 5 minutes. No manipulation was performed during needle retention.
3.2.7 Statistical analysis
The data are reported as means ± standard deviation (mean ± S.D.). A Wilcoxon signed-rank test was used to compare BR results after acupuncture and before acupuncture. For other statistical analyses, P values <0.05 were considered significant. Statistical analyses were performed using a commercially available statistical package (SPSS, Ver11.0.1, SPSS, Tokyo, Japan).
3.3 Results
3.3.1 Typical electromyogram waveform under before acupuncture stimulation and during acupuncture stimulation
Figure 5 illustrates a sample recording of the BR from a typical subject. R2 decreased after acupuncture stimulation (right side). There was no change in the R1 component.
Figure 5.
Typical electromyogram waveform under resting condition (left side) and during acupuncture stimulation (right side). R2 component decreased after acupuncture stimulation. There was no change in the R1 component.
3.3.2 Changes in R1 component induced by acupuncture stimulation
The changes in the R1 component are shown in Table 2. The R1 latency and amplitude showed no significant change in both groups.
Acupuncture
Control
Before
After
Before
After
Right R1 latency (ms)
10.3 ± 2.0
10.4 ± 1.7
10.3 ± 2.0
10.3 ± 2.0
Right R1 amplitude (%)
281.5 ± 124.2
269.3 ± 106.5
259.5 ± 117.2
254.7 ± 106.5
Right R2 latency (ms)
34.8 ± 3.6
36.0 ± 2.8**
35.4 ± 7.2
36.9 ± 5.1
Right R2 amplitude (%)
287.9 ± 198.5
225.9 ± 154.9**
312.4 ± 281.3
290.4 ± 242.1
Right R2 duration (ms)
28.2 ± 15.9
21.2 ± 10.5**
24.3 ± 9.3
22.3 ± 9.8
Left R2 latency (ms)
37.5 ± 6.7
39.0 ± 6.3**
35.7 ± 11.2
38.5 ± 8.5
Left R2 amplitude (%)
183.8 ± 120.5
152.1 ± 102.5**
219.9 ± 148.7
203.2 ± 136.8
Left R2 duration (ms)
25.9 ± 14.0
20.6 ± 6.9**
27.2 ± 7.9
26.0 ± 11.0
Table 2.
Changes in BR induced by acupuncture stimulation.
Mean ± SD. **: P < 0.01 Wilcoxon signed-rank test vs. before acupuncture.
3.3.3 Changes in R2 component induced by acupuncture stimulation
The changes in the R2 component are shown in Table 2. Acupuncture stimulation depressed the latency, amplitude, and duration of the R2 component on both sides. There was no change in the control group.
3.3.4 Changes in electrical stimulation pain induced by acupuncture stimulation
The changes in electrical stimulation pain are shown in Table 3. The electrical stimulation pain was no significant change in either group.
Acupuncture
Control
VAS (mm)
29.14 ± 26.33
26.71 ± 23.19
Table 3.
Changes in electrical stimulation pain induced by acupuncture stimulation.
3.4 Discussion
The blink reflex can be quantitatively measured from the magnitude of the reaction of the muscle action potential of the orbicularis oculi muscle induced when the supraorbital nerve, which is the first branch of the trigeminal nerve, is electrically stimulated. The electromyogram associated with the blink reflex consists of two components called R1 and R2. R1 is a relatively stable early component that appears with a latency of 10 msec and appears only in stimulus measurements. The R1 component is the potential where electrical stimulation to the supraorbital nerve alters neurons in the facial nucleus at the pons and leads to the orbicularis oculi muscle. Several studies have considered the R2 component of the blink reflex to be evoked through a polysynaptic pathway in the pons and the lateral part of the medulla [20, 21]. Peripheral facial nerve palsy causes R1 and R2 component suppression; hemifacial spasm causes an increase in the R2 component [20, 21]. Thalamic hemorrhage and lesions in the sensory cortex have also been reported to cause R2 abnormalities [21]. Furthermore, it has been reported that the R2 component reflects the disappearance of Myerson’s sign upon administration of L-dopa in patients with Parkinson’s disease [22, 23]. Therefore, it is thought that not only the brainstem but also a wide range of central nervous systems including are involved in the expression of the R2 component of the blink reflex. No significant changes were observed in the latency and amplitude of the R1 component in both control group and acupuncture group. Thus, our results show that the R1 component of the blink reflex was not changed by acupuncture stimulation, suggesting that acupuncture stimulation has no effect on the monosynaptic reflex of the brain stem. Acupuncture stimulation depressed the latency, amplitude, and duration of the R2 component on both sides. It is well known that acupuncture activates various groups of afferent fibers. Kagitani et al. demonstrated that manual acupuncture needle stimulation to the hind limbs activated the single-unit afferents belonging to the group I, II, III, and IV fibers in the spinal dorsal roots [24]. Acupuncture signals are conveyed by afferent fibers to the dorsal horn of the spinal cord. Then, they project to the thalamus via spinothalamic tract (STT) and spinoreticulothalamic tract (SRT). It has been shown to project to various regions such as the lateral reticular formation, central midbrain gray matter, basal ganglia, and sensory cortex [25, 26]. Willer JC et al. reported that electroacupuncture stimulation depresses the R2 component. In addition, they assumed the involvement of endogenous morphine-like systems since the depression of R2 components by electroacupuncture was antagonized by naloxone administration [27]. This study found no effect of acupuncture on electrical pain. Therefore, we suggest that the depression of R2 components by acupuncture is not due to the suppression of pain caused by evoked electrical stimulation. Furthermore, it has been suggested that there is a longer pathway involving the cerebral cortex for the inhibition of R2 components by acupuncture stimulation.
3.5 Conclusion
Acupuncture stimulation may inhibit R2 components via longer pathways involving the cerebral cortex.
4. Effect of acupuncture stimulation on excitability of spinal motor neurons
4.1 Background and purpose
F-waves are muscle action potentials recorded from muscle fibers of motor units activated by antidromic action potentials ascending in motor axons to the anterior horn cell [28, 29, 30]. F-waves are late motor responses observed following supramaximal electrical stimulation of a peripheral nerve causing an antidromic activation of motor neurons [28, 29, 30]. Zhao et al. found that the F/M ratio decreased following acupuncture treatment in patients with spastic hypertonia from stroke; this result indicated that the acupuncture treatment could inhibit neuron excitability in patients with spastic hypertonia from stroke [1]. Futhermore, Matsumoto et al. reported that the F/M ratio decreased following acupuncture treatment in patients with Chronic Disorder of Consciousness Following Traumatic Brain Injury [31]. As described above, the effect of acupuncture stimulation on the induced F-wave has been mainly applied to the effect of patients with motor symptoms such as spastic paralysis. In this study, we examined the effects of acupuncture stimulation on the spinal motor neuron in healthy adults, using the electromyographic F-waves of the first dorsal interosseous muscle immediately below the acupuncture stimulation site.
4.2 Materials and methods
4.2.1 Participants
Ten healthy volunteers (mean–standard deviation [SD]:30.3–6.2 years; 15 males and 1 female) with no known neurological dysfunction agree to participate in this study. Written informed consent was obtained from all subjects. This study was approved by the Research Ethics Committee at Hokkaido College of Oriental Medicine.
4.2.2 Study design
This study applied the crossover protocol; therefore, each experiment was randomly needled on separate days. The experiments were performed under two conditions: (1) acupuncture stimulation of right LI4 and (2) control (no acupuncture stimulation). To prevent a carryover effect, more than 1 week intervals between each acupuncture stimulation were maintained.
4.2.3 Experimental setting
M-wave and F-wave were measured before and after acupuncture (5-minute needle retention). M-wave and F-wave in the control group were measured at the same timepoints acupuncture.
4.2.4 Measurement of F-wave
F-waves were recorded and analyzed by using a Neuropack MEB 9204 recorder (Nihon Koden, Tokyo, Japan) with a band-pass filter of 5 Hz to 2 kHz. Thirty-two F-waves, elicited by electric stimulation of the ulnar nerve to the wrist, were recorded from the first dorsal interosseous muscle on the right side of each subject in a resting sitting position. The stimulus intensity used to elicit F-wave was more than the 120% that is required to elicit a maximal M-wave response. The electrical stimulus rate and duration were 1 Hz and 0.2 milliseconds, respectively. Electromyographic electrodes were attached firmly over the first dorsal interosseous muscle, With the anode positioned second phalanges. The ground electrode was placed between the stimulating and recording electrodes. The electrode impedance was below 5KΩ. The experiments were performed in a quiet room with a consistent temperature of 23–25°C.
4.2.5 Data analysis for the F-wave
Sample images of the F-wave and M-wave are shown in Figure 6. The F-wave was analyzed with respect to three parameters: occurrence, the F/M amplitude ratio, and the latency. The sensitivity was set at 5 mV/div for the M-wave and 0.5 mV/div for the F-wave. The occurrence was defined as the number of detected F-wave responses to 32 electrical stimuli and expressed as percentage. The F/M amplitude ratio was defined as the peak-to-peak amplitudes of F- and M-waves were measured, and the amplitude ratio of F/M was expressed as the ratio of F amplitude and the maximal amplitude of M-wave. F-wave latency was defined as the period from the stimulus to the F-wave evocation.
Figure 6.
Analysis of F wave. The F wave was analyzed with respect to three parameters: Occurrence and the F/M amplitude ratio and the latency. The sensitivity was set at 5 mV/div for the M-wave and 0.5 mV/div for the F wave. Occurrence was defined as the number of detected F wave responses to 32 electrical stimuli and expressed as percentage. The F/M amplitude ratio was defined as the peak-to-peak amplitudes of F and M-waves were measured and the amplitude ratio of F/M was expressed as the ratio of F amplitude and the maximal amplitude of M-wave. F-wave latency was defined as the period from the stimulus to the F-wave evocation.
4.2.6 Acupuncture stimulation
An acupuncturist applied a needle at the right LI 4 (radial to the midpoint of the second metacarpal bone) (Figure 2). Disposable stainless steel needles (diameter, 0.18 mm; length, 40 mm; Seirin Co., Ltd. Shizuoka, Japan) were used. The depth of needle insertion was 10 mm, and the needle was at a right angle to the skin and was maintained in this position (needle retention) for 5 minutes. No manipulation was performed during needle retention.
4.2.7 Statistical analysis
The data are reported as means ± standard deviation (mean ± S.D.). A Wilcoxon signed-rank test was used to compare occurrence and the F/M amplitude ratio and the latency results after acupuncture and before acupuncture. For other statistical analyses, P values <0.05 were considered significant. Statistical analyses were performed using a commercially available statistical package (SPSS, Ver11.0.1, SPSS, Tokyo, Japan).
4.3 Results
4.3.1 Typical electromyogram waveform under before acupuncture stimulation and during acupuncture stimulation
Figure 7 illustrates sample recording of the F-wave from a typical subject. F-wave increased after acupuncture stimulation (right side). No effect of acupuncture stimulation was observed on the M-wave.
Figure 7.
Typical electromyogram waveform under resting condition (left side) and after acupuncture stimulation (right side). Typical electromyogram waveform under resting condition and during acupuncture stimulation. F wave increased after acupuncture stimulation (right side). No effect of acupuncture stimulation was observed on M wave.
4.3.2 Changes in F-wave induced by acupuncture stimulation
The changes in the F-wave are shown in Table 4. The F-wave occurrence was significantly increased by acupuncture stimulation. There was no significant change in the control group. The F/M amplitude ratio was significantly increased by acupuncture stimulation. There was no significant change in the control group. The F-wave latency was no significant change in either group.
Acupuncture
Control
Before
After
Before
After
F-wave occurrence (%)
40.8 ± 17.2
48.1 ± 19.0**
36.2 ± 25.6
34.3 ± 25.1
F/M ratio (%)
1.73 ± 0.98
2.39 ± 1.56**
1.65 ± 0.63
1.71 ± 0.80
F-wave latency (ms)
29.8 ± 2.6
29.5 ± 2.6
29.5 ± 2.3
29.6 ± 2.3
Table 4.
Changes in F-wave induced by acupuncture stimulation.
Mean ± SD. **: P < 0.01 Wilcoxon signed-rank test vs. before acupuncture.
4.4 Discussion
LI4 is located in the area covered by the superficial branch of the radial nerve, and the muscle innervation of the first dorsal interosseus muscle underlying the same skin is supplied by the ulnar nerve. In addition, there are motor points of the first dorsal interosseous muscle around LI4, which may be excited by acupuncture stimulation [32], which may be excited by acupuncture stimulation. Thus, It is thought that acupuncture stimulation of LI4 excites various sensory receptors in the skin and muscles, spinal motor neuron are thought to undergo various regulations. In this study, F-wave persistence and amplitude F/M ratio increased after acupuncture stimulation. Persistence reflects the number of backfiring spinal anterior horn cells, and the F/M amplitude ratio reflects the synchronization of backfiring spinal anterior horn cells [28, 29, 30]. Thus, acupuncture increases the excitability of spinal motor neurons that innervate the muscles immediately below the stimulation site. Previous studies have shown that electrical stimulation of the index finger increases MEP in the first dorsal interosseous muscle [33]. In addition, Previous studies have shown that electrical stimulation of the index finger increases motor unit in the first dorsal interosseous muscle [34]. This suggests that stimulation of the skin may induce facilitation of the spinal motor neuron. Furthermore, It has been reported that pain stimulation to the thumb increases the MEP of the thenar muscle [35]. In addition, groups III and IV muscle afferents facilitated motoneurons and inhibited the motor cortex [36]. This suggests that painful stimuli to the skin and muscles may induce facilitation of the spinal motor neuron. Furthermore, there are motor points of the first dorsal interosseous muscle around LI4, which may be excited by acupuncture stimulation [32]. In addition, it has been reported that the number of Golgi tendon organs in the intrinsic muscle of the hand is maredly small [37]. Koiwa et al. demonstrated that inserted a needle electrode into the muscle motor point of the first dorsal interosseous muscle and measuring the action potential of the ulnar nerve of the elbow, the possibility of activated muscle sensory nerves such as group Ia afferent nerves [38]. Furthermore, we reported that the amplitude F/M ratio increased by acupuncture stimulation was suppressed by vibration stimulation. It is thought that the increase in reflex excitability of spinal motor neurons caused by group Ia afferent nerves excited by acupuncture stimulation is suppressed by presynaptic inhibition caused by the excitation of group Ia afferent nerves by vibration stimulation [39]. Furthermore, we inserted an acupuncture needle into LI4 and applied electrical stimulation to confirm the appearance of F-waves (Figure 8). Therefore, it was thought that acupuncture stimulation directly excites the ulnar nerve that innervates the first dorsal interosseous muscle. It may excite various afferent nerves contained within the same nerve trunk. Gracies et al. reported changes in the motor units of each upper extremity muscle by electrical stimulation of the median, ulnar, and radial nerves. They reported that stimulation of homonymous nerves increased the firing of motor units. Furthermore, it is considered that spatial facilitation by skin-afferent nerves and muscle-afferent nerves is involved in this effect [40]. Furthermore, It is well known that acupuncture activates various groups of afferent fibers. Using single-unit nerve recording techniques in rats, Kagitani et al. demonstrated that manual acupuncture needle stimulation to the hind limbs activated the single-unit afferents belonging to groups I–IV fibers in the spinal dorsal roots [24]. This suggests that acupuncture stimulated sensory receptors and nerve fibers distributed in the skin and muscles, resulting in increased spinal motor neuron excitability. Furthermore, in our study, subjects cannot avoid paying attention to the acupuncture site during needle insertion. Previous studies have reported that attention causes the facilitation of MEPs [41]. Therefore, acupuncture effect was compensated by facilitation arising from the concentration to the stimulated site. In addition, the F-wave latency, which is an index showing the conduction velocity of motor nerves, was not affected by acupuncture stimulation. Therefore, it is considered that acupuncture stimulation does not affect the conduction velocity of motor nerves.
Figure 8.
Electromyograms recorded at the first dorsal interosseous muscle during stimulation of LI4 acupoint (right side) and ulnar nerve trunk (left side) in single subject.
4.5 Conclusion
The result of this study indicated that acupuncture stimulation may have a greater effect on the excitability of spinal motor neurons.
5. How to use of acupuncture treatment in neurorehabilitation
In our study, acupuncture stimulation caused suppression of LLR occurrence and amplitude LLR/M ratio. Therefore, the results of this study are considered to explain the mechanism of action of acupuncture for Parkinson’s disease and multiple sclerosis [42, 43, 44]. Therefore, the results of this study are considered to explain the mechanism of action of acupuncture for Parkinson’s disease and multiple sclerosis.
Furthermore, we also found that acupuncture stimulation reduced the amplitude, latency, and duration of the BR R2 component. The results of this study suggest that acupuncture can be used for facial spasms and paralysis [45]. Furthermore, it has been reported that the R2 component reflects the disappearance of Myerson’s sign upon administration of L-dopa in patients with Parkinson’s disease [22, 23]. The results of this study suggest that acupuncture can be used for Parkinson’s disease. Furthermore, it has been reported that acupuncture reduces the amplitude ratio in patients with spastic paralysis due to cerebrovascular disease [1]. In addition, acupuncture has been reported to depress the increase in F-wave frequency and amplitude ratio in patients with chronic consciousness disturbance after traumatic brain injury [31]. In addition, there is also a report that acupuncture reduces the incidence of Parkinson’s disease [2]. In our study, the F-wave persistence and amplitude F/M ratio before acupuncture stimulation were not high. Therefore, it is possible that changes in spinal motor neurons by acupuncture may have different effects depending on the state before stimulation.
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Written By
Akira Nihonmatsu
Submitted: 12 July 2023Reviewed: 12 July 2023Published: 30 August 2023
Open access peer-reviewed chapter
