Extraction of the EPP Component from the Surface EMG

For an ionic synapse mechanism, the post-synaptic membrane forms the sink for the current of the depolarizing potential. A negative potential field should be produced in the external medium around the end plate, with reference to a distant point which may be detectable from the monopolar surface EMG. If the potential corresponding to the endplate potential or EPP can be detected from the skin surface, it will provide useful information for various medical fields.

Hi, I am Kuma with and Max Maxillofacial Laboratory in the Department of Oral Medicine at Mass University. Today I will show you a procedure for extracting the EPP component from the surface EMG. We use this procedure in our laboratory to study the EPP futures.

So let's get started. Begin by preparing nine electrodes. Connect them to the amplifier in their appropriate positions.

Eight of them are used for recording signals from sites over the muscle, and one is a reference electrode. After connecting the recording and reference electrodes to the amplifier, fill the discs with electric conductance paste, any type of paste will work. But a low fluid type is better.

Before attaching the electrodes to the skin, have the subject bite down firmly and determine the approximate location of the masseter muscle on the face. The superior tendon of the masseter muscle attaches to the zygomatic arch and its inferior tendon to the angle of mandible using a long piece of adhesive tape. Mark eight recording sites for the zygomatic arch and the angle of mandible.

Now place the eight recording electrodes onto the tape in equal inter electrode distance and attach the array to the skin surface. The first recording electrode is placed on the zygomatic arch and the last one on the angle of mandible. Finally, attach the reference electrode to the tip of the nose.

With the electrodes in place, ELECTROMYOGRAM or EMG recording can commence to begin recording. First set the parameters of the multichannel analog amplifier. Set the gain to X 500, the lowpass filter to 0.5 hertz and the high pass filter to 10 kilohertz.

Connect the a outputs of the analog amplifier to an analog digital converter. The digital signal is processed with LabVIEW software with a sampling rate of 20 kilohertz when everything is connected. Record EMGs during quick chewing gum clenching on the ipsilateral side.

The traces from the eight channels are presented on the lab view display immediately after the recording process has been completed. Now let's see how to extract the endplate potential component of the signal to extract the EPP component. First, remove the action potential component from the raw EMGs.

Using a high cut digital filter, begin applying the filter with a cutoff frequency of 10 hertz. A slow wave that deflects in the positive or negative direction should appear. This wave corresponds to the EPP, and the difference in polarity reflects the sync source relation of the endplate current.

When recording from the masseter muscle, the most negative deflection of the wave is expected in the trace from the most inferior recording site, and the polarity should shift around three sites away from that site. The magnitude of the EPP component can be measured as a peak point of the deflection or an area during the deflection. By plotting the EPP wave from each channel against a reference channel that showed the most negative deflection, the polarity change of the EPP component can be determined.

Now by increasing the cutoff frequency of the applied filter, the slow wave will become oscillatory. The oscillation will increase with increasing cutoff frequency and will generally become obvious at a cutoff frequency of 30 hertz. The phase of the wave will reverse across the trace in which the polarity of the 10 hertz filtered EPP wave showed a reversal.

The phase shift of the oscillation can be checked with the same graphs that were applied to the 10 hertz filtered EPP wave from the interval between neighboring positive and or negative peaks of the oscillation. We can get an approximation of the frequency of the oscillation shown here is a schematic of the eight sites along the masser muscle that were recorded from. Now we see a sample of the monopolar EMGs recorded simultaneously from the sites over the masseter muscle.

In response to quick gum clenching on the ipsilateral side, the EPP component was extracted using a high cut digital filter with a cutoff frequency of 10 hertz, which is superimposed on each raw EMG. In this trial, the most negative deflection was observed in traces minus five and minus six, and the polarity changed across trace minus three when the cutoff frequency of the high cut digital filter was set to 30 hertz. The slow wave exhibited an oscillation.

Its phase also shifted across trace three where the polarity of the 10 hertz filtered EPP wave changed. The interval between neighboring positive peaks of the oscillation was measured in this subject. The average inter peak interval was 31.7 milliseconds over 16 recordings.

We have just shown you how to extract the EPP component from the surface EMG recording. When doing this procedure, it is important to remember to set various recording parameters suitable to the EPP signal and to record EMGs in monopolar manner. So that's it.

Thanks for watching and good track with your experiments.