Figure 4.

Synaptic integration experiments. (A) Layer V pyramidal cell with uncaging sites in two planes 5 μm apart (1 and 2 are in one plane, 3 and 4 in another) as viewed in the xy and yz planes. Scale bar 25 μm. (B) Individual uncaging-evoked EPSPs obtained by turning ON stimulation sites in a static hologram one at a time with the DMD. Stimulus duration (3 ms) is indicated by red bars at the start of the EPSP. (C) Summary of results for different combinations of uncaging sites. Linearity is expressed as the ratio of the peak amplitudes of the measured compound EPSP and the arithmetic sum of individual EPSPs. Dashed line denotes linear summation (100%). Blue bar corresponds to within-branch summation; red, between-branch summation. Data are shown as mean ± s.e.m. for all combinations. (D) Layer II/III pyramidal cell with five uncaging sites situated along three apical oblique branches and all in a single plane. Scale bar 25 μm. (E) Representative membrane potential time courses generated by two repeats of the same train of random stimulus for uncaging glutamate at the sites in D. In the stimulus, the spatial selections and their time intervals are both random. The resting membrane potential at the soma was set to −55 mV. Several action potentials (APs) align in time triggered by the same uncaging patterns. Laser intensity in the sample plane is indicative of the number of simultaneously active stimulus sites. (E') Magnified view showing membrane potential (black) and laser intensity (red) for a time window from 60 ms before to 20 ms after the peak of the AP. (F) Mean membrane potential and laser intensity (n = 53 APs) from 60 ms preceding peak of AP to 20 ms after. AP is driven by a significant increase in laser intensity shortly (~23 ms) before its peak.