Analysis of interspike intervals during adapted discharge to maintained stretch. a, Rapid circumferential stretch (2 mm at 5 mm/sec for 30 sec) evoked firing in two units, which adapted to a constant rate after the first 10 sec.b shows the distribution of interspike intervals in the same units from 10 to 30 sec after the onset of stretch. Note the normal distribution and relatively small variance in intervals.c, Interspike intervals during adapted discharge in a unit from another preparation, identified as having two hot spots (open bars). A simulated unit, with identical mean and variance is superimposed (thick line). The simulated interspike intervals for a unit with two independent spike-generating sites, with the same variance, is shown as small filled circles; the uniform distribution suggests that multiple hot spots are unlikely to generate action potentials independently, when the preparation is stretched. d, Simulated firing of a single unit with two independent spike-generating sites with identical means and variance, initially set 180° out of phase. Note that spikes from the two sites (visually distinguished by amplitude) rapidly go in and out of phase to generate the uniform distribution of intervals shown in c.