... Differences in the size and number of branches in the dendritic arbors of cortical pyramidal neurons affect the total number of spines contained within, reflecting putative differences in the number of excitatory inputs received by individual cells Rosa, 1997, 1998;Elston et al., 1999a,b;Elston, 2000). Varying spine densities reported on the basal dendrites may also affect electrical and biochemical compartmentalization, cooperativity between inputs, and shunting inhibition (Koch et al., 1982;Shepherd et al., 1985;Rall and Segev, 1987;Shepherd and Brayton, 1987;Koch and Zador, 1993;Mainen, 1999). In addition, differences in the total length of, number of branches in, and diameters of the dendrites determine the cable properties (Rall, 1959), the degree of nonlinear compartmentalization (Rall, 1964;Koch et al., 1982), and the propagation of potentials (Stuart and Häusser, 1994;Spruston et al., 1995;Markram et al., 1997;Vetter et al., 2001) within the arbor (for review, see Rall et al., 1992;Stuart et al., 1997;Koch, 1999;Mel, 1999;Spruston et al., 1999;Häusser et al., 2000). ...