Fig. 4.

Mapping light sensitivity of pyramidal neuron. (A) Structure of a pyramidal neuron filled with Alexa 594 dye that was dialyzed from a patch pipette (to the right). Here, and in subsequent figures, the top of the image is closest to the pial surface. Circles indicate locations where photoresponses in B were evoked. (B) Changes in membrane potential evoked by light spots (488 nm; 48 mW/mm²) positioned at the sites indicated in A. Only illumination near the cell body evoked an action potential (trace 3). Bar indicates time of illumination. (C) Scanning the light spot across the specimen revealed locations where light-induced depolarizations were evoked; pseudocolor scale at right indicates the amplitude of these responses. Red reflects action potentials.