Fig. 10. Threshold nonlinearities in cb1 cells during light decrements.

a Responses of simultaneously recorded cb1b and cb2 cells during a long step of OD 1.0 light that was interrupted by a series of decrements (average of 3 traces; stimulus sequence in blue). Lower inset. Magnified view of the light responses during the first and second decrements. Right inset. Responses at light-off shown on the same time scale but with a compressed current axis. b Above. The normalized change in membrane current was plotted against the light intensity during the decrement (i.e., the ‘step-to’ light intensity with the result that larger decrements are plotted toward the left). Current was normalized by setting the average immediately before a decrement equal to 0 relative to the resting current, 1, in the dark. Normalized steady cb1b and cb2 responses were significantly different during all decrements (mean ± S.E.). Upper middle. Change in response variance, before versus during a decrement, is plotted against ‘step-to’ light intensity. Hash marks denote either negative change or no change (Levene’s Mean Statistic). Lower middle. Effective unit amplitude was calculated by separately analyzing each of the 3 trials and plotted against light ‘step-to’ intensity (open circles are mean ± S.E. while closed circles show individual data points). Hash marks denote n.s. difference from 0 (two-tailed one sample t test). Below. Aggregate unitary responses for 11 cb2 and 4 cb1a/b BCs independently recorded. Asterisks indicate that the values of the cb1 cell unit were significantly reduced during decrements 1–3 relative to decrement 5. See Statistics and Reproducibility for additional p values and criteria. c Decrement responses from a different cb1b and cb2 cell pair during a long OD 0.0 background step (average of 2; repetitions were limited by photopigment bleaching). The cb2 cell response displayed prominent epscs in the absence of events in the cb1b cell (decrements 3, and lower inset decrements 4 and 5). Magenta bars indicate the before and during regions used to measure the activity change in the cb1b cell in response to decrement 4 (200 ms intervals; p = 0.1930; not significantly different, two-tailed unpaired t test). BC silhouettes republished from Light, A. C. et al. Organizational motifs for ground squirrel cone bipolar cells. J Comp Neurol 520, 2864-2887 (2012).