Figure 3

Response of the incoherent feedforward modules. The first incoherent feedforward module (see text) is subjected to a (A) gradient signal and a (B) localized signal input. In the case illustrated here pathway X (inhibitor) is stronger than pathway Y (activator). When none of the pathways are diffusible (solid line with circles) the response is qualitatively opposite to that of the signal. When pathway X is highly diffusible (solid line), the response mirrors the signal profile. On the other hand when the activator pathway is highly diffusible (dashed line) the response is qualitatively opposite to the signal. Thus, having a diffusible element allows for the response to show greater spatial contrast. (C) The second module (eq. 3, see text) is subjected to gradient signals. In the case illustrated here pathway X (inhibitor) is stronger than pathway Y (activator). When none of the pathways are diffusible, the response of the module switches from being qualitatively similar to the signal (solid line) to being qualitatively opposite (dashed line) to that of the signal as the mean value of the signal is increased. When pathway X is highly diffusible, the response mirrors the signal profile even if the mean value of the signal is increased (solid line with circles and solid line with x markers). Thus, the presence of a diffusible element prevents the switch in spatial biasing of the response. (D) A schematic of the biphasic response is shown- here the response increases and then decreases as the value of the (temporal or homogenous) signal increases.