Figure 7. Differentiating delayed onset neurons from tonic and phasic neurons.

A, sample responses showing the irregular spiking in delayed onset neurons. This irregularity in spiking pattern contrasted the pattern observed in tonic and phasic cells, where f tended to drift but did not fluctuate erratically. B, the irregularity in firing was quantified for tonic, phasic, and delayed onset neurons as the coefficient of variation (c.v.), defined as standard deviation of f/〈f〉. This was determined for each neuron as the average c.v. across the first three responses (i.e. responses to the three lowest stimulus intensities) comprising four or more spikes. One phasic and one delayed onset neuron which did not exhibit three responses with sufficient spikes were excluded from this analysis. Bars show means ± s.e.m. The ANOVA was significant (P < 0.001), with the delayed onset neurons displaying a significantly higher c.v. than tonic or phasic neurons (Tukey tests; *P < 0.001).