Membrane potential responses to sine-wave modulation of light intensity express stronger attenuation of high frequencies than responses to intracellular current injection.

<p><b>A:</b> Membrane potential responses (blue traces) of a layer 2/3 pyramidal neuron expressing ChR2 to a 488 nm diode light modulated by sine-wave signals at 10, 50 and 100 Hz (light blue traces). The amplitude of the sine-wave modulation of light intensity was kept constant. <b>B:</b> Membrane potential responses (red traces) of a neuron to injection of sine-wave current at 10, 50 and 100 Hz (green traces). Two-electrode experiment. One electrode was used for current injection, and another electrode for recording of membrane potential responses. The amplitude of the sine-wave current was kept constant. <b>C:</b> Attenuation of the amplitude of membrane potential modulation in responses to sine-wave signals of different frequencies injected through the intracellular electrode or induced by photostimulation.