In Figure 1, a brief depolarizing current pulse was injected to the soma of the 3D-reconstructed HL2/3 PCs (Their reconstructions are available in the morphs directory); the average resultant experimental voltage transients are available in the Voltage_traces folders. Detailed compartmental models for that same cells were then constructed, including dendritic spines that were globally incorporated into the model (Rapp et al. 1992). The shape, size, membrane area, and distribution of dendritic spines in the HL2/3 model were based on high-resolution 3D confocal images of several stretches of HL2/3 PCs dendrites (Benavides-Piccione et al. 2013) (see Methods). Attempts to fit the experimental transient (of one of these cells) via the model are illustrated in Figure 1a (each with its corresponding values for axial resistivity, Ra, specific membrane resistivity, Rm, and capacitance, Cm). Only when Cm was surprisingly low ~ about 0.5 uF/cm2 we found a good fit. This was also the case for the five other cells as demonstrated in Figure1cd After installing the necessary files (see install in top folder), all scripts in this folder can be run using ipython. contact: guy.eyal at mail.huji.ac.il