Figure 3:

Multiplicative control of visual signaling mediated by acetylcholine concentration. (A) Acetylcholine may act by means of a binary gate during sleep-wake cycle where visual input gets either multiplied by 0 (gate closed) or by 1 (gate open). (B) Acetylcholine may act on gain control during waking in a way that visual input gets multiplied by a value of 0 to × resulting in gradual increases of visual signaling. (C) Gain need not increase with concentration; in fact non-monotonic gain control such as the inverted U-shaped gain function has been observed for other neuromodulatory systems.