Fig. 2. (A) Coefficient of variation plotted against spontaneous spike rates of DON (open circles) and tectum (filled diamonds) units. Units in both areas can be clearly separated by these two parameters. (B,C) Fourier transformations of ongoing spike trains in primary afferent fibers (B) and DON (C). In addition to the large peak caused by the spike generator, primary afferents show another smaller peak at 25 Hz (arrow), which is absent in DON units (C).