Chapter 3 – Acupressure Causes a Physiological Change in the Brain

         Our second goal in this project was to find a physiological basis for acupressure treatment. The anatomy clearly suggested that acupressure treatment might induce a neural response.  Pomeranz et al. had previously worked on acupuncture and they found that acupuncture treatment caused the release of endorphins from the pituitary and this was one way of causing anesthesia within the pain pathway [3, 9].  Diamond [4] collected the results of electrophysiological studies and reported that the evoked potentials elicited in rabbit’s cerebral cortex by painful stimulation was reduced in amplitude by acupuncture.

The question we sought to answer was “Is there a difference in the brain’s response to tactile stimuli after acupressure treatment?”  Our approach to this question was to record somatosensory evoked potentials in barn owls.  Since the introduction of an averager by Dawson [5] to the physiological society in 1951, somatosensory evoked potential (SEP) following stimulation of peripheral nerves has become a valuable supplementary tool in diagnostic neurology.  We chose to apply SEP methodology to the nerurophysiological study of acupressure mechanism.  Somatosensory evoked potentials are waveforms of voltage vs. time that indicate the brain’s response to a given stimulus.   This technique is non-invasive and electrodes for recording the SEPs are placed on the scalp.  We used owls because they were already being used for a similar project that used recording of evoked potentials.  Owls are also vertebrates and have many analogous anatomical structures to humans such as the lumbar plexus and the corresponding sensory nerves (Figure 4).

Figure 4 - The avian lumbar plexus – The nerve locations and names are similar to nerves in humans.

Our results from this suggest that acupressure treatment has an effect on the somatosensory pathway and the brain’s response to the same stimulus varies upon giving acupressure treatment.

Methods and Results:

        Evoked potentials were used to record the brain's activity to the given stimulus.  Recordings were made by placing 3 electrodes on the scalp, just touching the skin of the animal (Figure 5).  Our stimulus generator was a metal probe that was attached to a loud speaker.  The computer controlled the movement of a loud speaker and as it moved, the probe touched a part of the animal's foot, thus creating a tactile stimulus. 

Figure 5 – Experimental Setup

We also had a position sensor near the probe and we used this unit to record the position of our stimulus so we could compare it with the actual evoked potential.   

Figure 6 – Typical Somatosensory Evoked Potential curve

            Figure 6 illustrates a typical evoked potential waveform and the corresponding stimulus that generated the SEP. 

            In order to test our setup and ensure that we had a clear SEP and that there was no noise in the system, we did a series of recordings. At times we would raise the speaker high enough such that the probe would not touch the foot.  The waveforms from such runs show almost no response, while in runs during which the probe touched the foot we could see a clear response, localized to the time when the stimulus was given (Figures 7a and 7b).

Figure 7a – Typical SEP

Figure 7b – No SEP seen when the probe is not touching the foot

While we did the above recordings, we found that the brain's response was extremely sensitive to stimulus position.  Even if the stimulus was moved 1 mm, the waveforms differed dramatically in amplitude and structure (Figures 8a and 8b). 

Figure 8a - SEP

Figure 8b – SEP to same stimulus strength, 1mm away from original stimulus position.

These runs were indicative of receptive field properties of the cells in the cortex.  It was quite amazing that even a single millimeter difference in position of the same stimulus could result in a difference in SEPs. 

            Our purpose again was to look for differences in the brain's response to tactile stimuli pre and post acupressure treatment.  Figure 9a shows a typical SEP curve. 

Figure 9a – Typical SEP before treatment

Figure 9b – SEP after treatment

Immediately after that recording, a 5-minute treatment was given to the animal.  Treatment consisted of applying light pressure to 3 acupressure points on the head, analogous to acupressure points from the human meridian anatomy map.   Upon completion of treatment, we recorded another SEP (Figure 9b).  By comparing these curves, we see a change in amplitude and form of the SEP after giving treatment, suggesting a change in the brain’s response to the same stimulus after treatment. 

            We further tested this observation for consistency.  To do so, we set up two experiments. In the first experiment, we recorded SEPs every 5 minutes for 30 minutes. No treatment was given during this period.  The SEPs were then averaged and we plotted the average SEP curve with plus and minus standard deviation (Figure 10a).  By observation of the standard deviations, we see little variation in the SEPs during this 30-minute period.  The second experiment was identical in set-up to the latter, except prior to recording the SEPs, the animal was given treatment.  The average SEP from this run was plotted with its standard deviation (Figure 10b).  In contrast to the previous experiment, we see considerably large variation in the SEPs during this 30-minute period.  If we had more time, our next step would have been to check for statistical significance in our analysis of these plots.

Figures 10a (top) and 10b. The smaller figure within these represents the stimulus.