Fig. 7. Method used to analyze the effect of isoflurane on the inspiratory hypoglossal motoneuron discharge patterns. (  A ) Time-synchronized, cycle-triggered histograms of neuronal discharge frequency (Fⁿ) during control conditions (F^con) and during isoflurane (F^iso) were plotted against each other for the time period that the neuron was actively discharging. Regression analysis of the plot (  triangles ,  B ) revealed a linear relation with a slope of 0.34 and a y-intercept of 1 Hz. This indicates that isoflurane reduced the gain of the control discharge pattern. Such attenuation in gain is expected if the anesthetic causes an increase in tonic modulatory inhibition. LOI = line of identity; PNG = phrenic neurogram; T^I= inspiratory duration.