Fig. 2. The electropharyngeogram (EPG) reflects current movement across the pharyngeal muscle membrane. In the EPG, the large positive transient (E, blue) corresponds to depolarization of the pharyngeal muscle and onset of contraction. The large negative transient (R, green) corresponds to repolarization of the pharyngeal muscle and the end of the action potential. We defined action potential duration as the time difference between the peaks of the E and R spikes. The interval between the E and R spikes represents the plateau phase of the action potential (red portion of the trace). The negative transients during the plateau phase are pharyngeal muscle inhibitory postsynaptic potentials (IPSPs) caused by firing of the M3 motor neurons. We calculated the activity of the M3 motor neurons as the mean-square deviation about the baseline during the portion of the action potential affected only by M3-induced currents (pink box). Regions of the EPG trace not affected by pharyngeal currents (regions outside the gray and pink boxes) were used to determine the portion of baseline deviation due to random noise. This value is subtracted from the preliminary measurement of M3 activity to determine a noise-corrected value, which we report as M3 activity.