Figure 2.

Model of the neurophonic based on symmetry and synchrony assumptions. A, Small population of MSO neurons after injection of a retrograde tracer (BDA) in the inferior colliculus (gerbil, courtesy of Dr. T. Franken). The section is coronal: lateral is to the left, medial to the right, dorsal is up, ventral is down. The bipolar morphology, with dendrites extending medially and laterally, and the stacking of cell bodies along a dorsoventral axis, are clearly visible. B, An idealized subpopulation of MSO neurons with identical bipolar dendrites and symmetric spatial arrangement. We assume synaptic inputs to all cells are identical, so it suffices to compute V_m in one representative neuron and the V_e field in a surrounding “virtual cylinder” of extracellular space. C, V_m of representative neuron and V_e in the virtual cylinder are computed using the compartmental method. In each Δx segment, the intracellular and extracellular voltages, V_i and V_e, are dynamically coupled via transmembrane currents (green arrow), which themselves are functions of the membrane potential (V_m = V_i − V_e). Blue and red arrows indicate extracellular and intracellular currents, respectively.