Fig. 5.

Neurons with strong PRF and FRA experience a phase-lead during sinusoidal current input.A, Comparison of a neuron with strong rebound firing (filled symbols) and one with weak rebound firing (open symbols) as they modulate their firing rate in response to sinusoidal input current at 0.125 Hz. Top trace, Input current versus time; bottom trace,firing rate versus time. The phase of the neuron with strong PRF was +16°, and the phase of the neuron with weak PRF was +4°, relative to the input sine wave. The difference between the two neurons can be clearly seen as a relative offset along the time axis. Dashed line indicates the baseline firing rate before current injection (30 spikes/sec). B, Response of the same neurons shown in A to a 0.25 Hz stimulus. Baseline firing rate of 12 spikes/sec is indicated by the dashed line. The phases were +11° and +2° for the strong and the weak PRF neuron, respectively. C, The phase of best-fitting sine waves is plotted against input frequency. Shown are averages for 12 neurons with strong PRF (>30 spikes/sec, mean 60 ± 7 spikes/sec; filled symbols), and eight neurons with weak PRF (≤10 spikes/sec, mean 5 ± 1 spikes/sec; open symbols). Data from firing rate modulation around 30 spikes/sec (as in A) were used to generate this plot. D, Summary plot of the phase of 25 neurons as a function of adaptation. Phase was measured at an input frequency of 0.25 Hz and was well correlated with FRA (dashed line;R² = 0.70).