For example, an important prediction of the HR-EMD model is that the time constant of the delay line shapes the temporal tuning of fly motion detection and thus the shape of the optomotor response curve (Figures 1B and 3C; Reichardt, 1961). However, we found that silencing some lamina neurons (L1, L2, and L4) specifically decreased the tendency of flies to follow very fast motion stimuli, while silencing L3 had the opposite effect,

increasing fly responses to fast motion stimuli (Figure 7C). Consistent with our behavioral and simulation results, L3 neurons in larger flies have a higher input resistance than L1 or L2 (Hardie and Weckström, 1990), which could result in attenuation of high-frequency signals in L3 (although this attenuation PS-341 clinical trial may also occur in neurons downstream of L3). The simulation results of Figures 7F and 7G strongly suggest that processing by individual cell types (and subsequent downstream pathways) contribute to the aggregate tuning of motion vision. Specifically, the temporal frequency optimum of the elaborated HR-EMD (Figure 7F) is no longer determined strictly by the time constant of the delay line but is affected by the time constants of the input pathways as well (and would be further influenced by the dynamics of feedback pathways if included in the model). This

simulation illustrates one example of a potentially general principal of the fly lamina: anatomically related www.selleckchem.com/products/torin-1.html cell types carry out similar functions but with distinct temporal properties. The two classes of reverse-optomotor phenotypes (Figure 6) suggest that L2 those and L4, C2 and C3, and Lawf1 and Lawf2 may in each case represent two “arms” of a balanced network. The duplication of function with temporal specializations that we propose need not be independent (as in our model of Figure 7F) from the recently described bifurcation into pathways specialized for the detection of luminance increments and decrements (Joesch et al., 2013). Overall the diverse range of phenotypes related to motion responses at different speeds (Figures 6 and 7) suggests that

many lamina cell types contribute to shaping the temporal tuning of early visual processing. By structuring the inputs to downstream motion circuits, lamina neurons appear to play an important role in shaping the tuning of visual behaviors, such as the optomotor response, that have previously been compactly described by the HR-EMD model. These observations provide one possible explanation for the apparent mismatch between the minimal complexity of motion detection models and the elaborate diversity of lamina and medulla neuron classes. Our data also do not support the hypothesis that specific lamina neurons serve as dedicated pathways for encoding global stimulus features, such as patterns of optic flow.