Fig. 6.

Optical stimulation of ChR2-M1 terminals evoked suprathreshold responses in multiple types of S1 pyramidal neurons. A: paired recordings were normalized to the magnitude of M1 input to the L5A M1-projecting cell. M1 input was significantly greater to L6 M1-projecting cells (P < 0.05) and less to VPM-projecting cells (P < 0.05) compared with the L5A M1-projecting population. B: population average of EPSC amplitude evoked by M1 stimulation showed that L6 M1-projecting neurons received significantly larger M1 input than the other pyramidal neuron populations (P < 0.005). C: pyramidal neurons in each population with the largest M1-evoked EPSC often showed nonzero spike probabilities when recorded in current clamp. Note that the top left image shows both L5A M1-projecting (gray circles) and L6 M1-projecting (solid circles) neurons. D: average spike probability in L6 M1-projecting neurons was significantly greater than in L5A M1- and VPM-projecting neurons (P < 0.05) but not Sp5- and PoM-projecting neurons (P > 0.05). E: the average voltage difference from the resting membrane potential to AP threshold was significantly smaller in Sp5- and PoM-projecting neurons than other pyramidal neuron classes (P < 0.005). F: example Sp5-projecting neuron (left) that spiked on each trial (black) and a L6 M1-projecting neuron (right) that fired on some trials (black) but not others (gray). G: scatterplot of the distance between rest and AP threshold and the M1-evoked spike probability for all neurons that spiked. Symbol conventions are as follows: Sp5-projecting neurons (solid circles), PoM-projecting neurons (open triangles), L6 M1-projecting neurons (open circles), and VPM-projecting neurons (open square). The dashed line shows the linear least-squares fit.