Figure 4.

Input–ouput properties in YFP-16 and GIN neurons. Shown are examples of responses to depolarizing current steps in a YFP-16 neuron (A) and a GIN neuron (B). Steps of increasing amplitude were given until the neuron could no longer fire action potentials throughout the whole step. Bottom panels, Mean firing rate evoked during depolarization is plotted versus the amplitude of the current step for each neuron shown above. The break in line fit indicates the measurement of gain below and above 80 Hz for each neuron. C, Scatterplot of maximum firing rate (average over whole step) versus input resistance measured below spike threshold. Each point represents one neuron (YFP-16, n = 40; GIN, n = 43; unidentified neurons, n = 61). D, Maximum input current for which a neuron could sustain action potentials during 1 s of depolarization. YFP-16 neurons can respond to approximately threefold more current than GIN neurons (p < 0.0001) (Table 2). Bars indicate means. Three YFP-16 neurons whose maximum input current exceeded 4 nA are not shown here for graphical clarity. E, Histogram of adaptation ratio, defined as the firing rate at the end of the 1 s depolarization divided by firing rate at the beginning. YFP-16 neurons adapted significantly more than GIN neurons (p < 0.0001) (Table 2). F, Ratio of cellular gain in high range (>80 spikes per second) to gain in low range (<80 spikes per second). GIN neurons were significantly more linear than YFP-16 neurons (p < 0.0001) (Table 2).