Figure 1.

Assessing the Frequency Tuning of Signals Transmitted to the Inner Retina

(A) Examples of SyGCaMP2 responses in three individual bipolar cell terminals. The stimulus (lower trace) consisted of a light step followed by modulation at different frequencies between 0.2 and 25 Hz (90% contrast, square wave, mean intensity 55 nW/mm²). An ON terminal activated by contrast is shown in green and an OFF terminal in red. An example of an ON terminal inhibited by contrast is shown in black (contrast-suppressed response). The polarity of the terminal was determined in response to an initial step of light shown in the boxed area.

(B) Transfer functions of the individual terminals shown in (A). The response at each frequency was calculated as the average value of change in fluorescence (ΔF/F) during the stimulus. Dotted lines represent cutoff frequencies (fc) at −3 dB of the maximum response for the ON (green) and OFF (red) terminals with values of ∼4 Hz and ∼5.3 Hz, respectively. Note the band-pass characteristic with attenuation of the response at both low and high frequency in both ON and OFF response. The black trace is the transfer function of the contrast-suppressed terminal shown in (A).

(C) Histogram of the cutoff frequency (fc) of 264 activated-by-contrast ON bipolar terminals (green) and 263 activated-by-contrast OFF bipolar terminals (red) from 7 fish. The function fitted to the distribution of fc in ON terminals is a Gaussian with m = 6.4 Hz and width = 2.7 Hz. The function fitted to the distribution of fc in OFF terminals is the sum of three Gaussians with (m = 1.1 Hz and width = 1 Hz for peak 1), (m = 4.9 Hz and width = 1.7 Hz for peak 2), and (m = 9 Hz and width = 2.2 Hz for peak 3).