Fig. 6.
Optical stimulation profile. A: current injection threshold at each individual model compartment required to generate an action potential in a nonilluminated neuron. 500-μm scale bar is valid for all x-axes. B–D: fiber optic is oriented perpendicular to the long axis of the neuron (1-mm fiber-optic-to-neuron distance), illuminating the neuron at 40-μm intervals along the longitudinal position of the neuron. Stimulations were performed with a 0.2-mm-diameter fiber optic, and 5-ms stimulus duration. The threshold irradiance was calculated for each longitudinal position. B: area of membrane illuminated (transmittance > 0.001). C: percentage of total ChR2 channels in the open state at the end of a threshold stimulation pulse. D: distance from the output end of the fiber optic to either the closest illuminated neuron compartment, or the average position of all illuminated compartments (transmittance > 0.001). E: threshold irradiance level (±0.1%) required to generate a propagating action potential from different fiber-optic-to-neuron distances.