EPSP time-course analysis of L3 model neuron suggests that “modulatory” long-distance horizontal connections terminate proximally and vertical L4 “driver” inputs terminate distally.
A, L3 model morphology [89, see Materials and Methods for details] with colored markers indicating one set of the locations of the 4 synapses evoking the responses shown in (B). B, Four synaptic inputs were placed on 100 sets of 4 randomly selected dendrites 50, 150, and 250 µm from the soma, evoking 4.6, 3.6, and 2.9 mV EPSPs on average. EPSP half width and risetime grew with distance from the soma. Error bars indicate s.d. of the mean across random dendritic sets. Compare to Table 1 from Yoshimura et al.  showing that EPSP half widths between modulatory� long-distance horizontal and vertical L4 “driver” inputs increased (34.5±19.9 vs. 53.0±28.1ms, p<0.05, t-test) as did EPSP rise times (3.9±2.5ms vs. 5±2.5ms, p<0.04, Wilcoxon rank-sum test, Figure 2B rise time data from Yoshimura et al.  was digitized with Engauge Digitizer for statistical analysis in Matlab).