FIG. 7.

Comparison of the experimental LGMD receptive field (RF) with that obtained using 3 maps of visual to dendritic space in the compartmental model. A: experimental RF obtained by local stimulation at multiple elevations and azimuths (same stimulus as in Fig. 6). The LGMD/DCMD peak spike frequency (obtained from Krapp and Gabbiani 2005) was transformed to an equivalent LGMD peak membrane potential based on the regression depicted in Fig. 6B. B: simulated RF obtained using the topographic synaptic mapping. The plot shows the peak membrane potential at the origin of dendritic field A, V̄_origin-A, elicited by a stimulus centered at a given point in visual space. The responses were simulated by activating a number of synapses equal to those covering the area of the disk at that location (see METHODS). Each synapse’s g_max was set to 47 nS so as to match maximal depolarization in the model to the experimental peak in A. C: simulated RF obtained with the uniform mapping of visual space. The plot reflects V̄_origin-A for a given stimulus center (same stimuli as in B). Each synapse’s g_max was set to 84 nS to match maximal depolarization in the model to the experimental peak in A. D: simulated RF obtained using a random, 1-to-1 mapping from optical axes in visual space to the excitatory dendritic field (g_max = 47 nS). While the wiring scheme was randomized, the local density of optical axes was respected. The plot reflects V̄_origin-A as a function of stimulus center azimuth and elevation. E: cross-sections of the experimental RF and those derived from the topographic, and uniform mappings. The left panel shows the V̄_origin-A observed with stimuli of various azimuths with elevation fixed at 0°. The black line and gray background denote the experimental data mean and 95% confidence interval across animals (t-test; n = 6), respectively. The blue and red line denote the topographic and uniform sampling RF cross-sections, respectively. The shaded regions of the colored lines denote the 95% confidence interval for simulated runs (t-test; n = 10 trials per location). Middle and right: V̄ _origin-A for various elevations with azimuth fixed at 135° (toward posterior end of animal) and 30° (toward anterior end of animal), respectively.