Figure 8.

Schematic of the potential dependence of photopreference on the activity of aminergic neurons. Depending on several factors (e.g. the status of its flight apparatus), individual flies may fall anywhere on the photopreference spectrum (greyscale): approaching light, avoiding it or behaving indifferently. Increasing neuronal activity in tdc2-GAL4 positive neurons (red) or decreasing synaptic release in th-GAL4 positive neurons (blue), each alone promoted a preference of darkness (shift to the right of the spectrum) in flies able to fly, which normally prefer brightness over darkness. In contrast, increasing neuronal activity in th-GAL4 neurons (blue) or decreasing neuronal activity in tdc2-GAL4 neurons (red), each alone promoted preference of brightness (shift to the left of the spectrum) in wing-clipped flies, which normally tend to avoid brightness. It is straightforward to hypothesize that the quantitative relationship between two opponent processes (potentially based on OA/TA and DA action) constitutes one mechanism mediating photopreference in Drosophila. In this figure, we depicted this relationship as linear for illustrative purposes only.