Figure 2.

Effect of Cutoff Frequency of the Noise-Reduction Filter on SNR

(A) A representative optical regular firing trace (containing 14 fAPs; Raw, not filtered, gray trace) was filtered with Butterworth low-pass filters cutting off at 6–400 Hz (green traces). This record is a part of the dashed box in Figure 4C, and the image of recorded neuron is shown in Figure 4A (green box).

(B) The signal level was linearly correlated with the logarithm of filter frequency (log₁₀($v$)).

(C) The noise level was correlated with log₁₀($v$) by a power law. In (B) and (C), the black lines, symbols, and error bars indicate regressed curve, mean, and SD, respectively.

(D) Relationship between SNR and cutoff frequency. The signal (B) was divided with the noise (C). The black line was calculated by dividing the regression lines in (B) by that in (C). The symbols and error bars indicate mean and SD, respectively.

(E) The 14 fAPs were overlapped, showing uniform kinetics with overshoot and afterhyperpolarization. Gray traces indicate individual fAPs (filtered with a 50-Hz Butterworth low-pass filter), and green plot indicates average of the fAPs.

See also Figures S2–S5.