FIGURE 10.

Passive and active currents cancel when many synaptic inputs are distributed over the dendrites. (A) When a single conductance is placed on different somato-dendritic compartments, the strong active current is surrounded by weaker passive currents spread out according to the orientation of dendrites. In each block the left graph shows currents recorded by a simulated electrode array from different layers, while the right (mostly green) panel shows the CSD in 2D (along the X- and Y-axes). In the first block a 2D projection of the modeled PC is shown in gray. (B,C) When synaptic inputs are scattered according to anatomical rules over the dendrites, the active currents of one input are canceled by the passive currents of the other inputs. In the case of 50 inputs (C) the cancelation is stronger than for five inputs (B). For the centrally located, dense perisomatic inputs active and passive currents are consistently located within the same region and thus sum, resulting in a substantially stronger LFP signal than for the dendritic inputs. The scales are the same for all panels in a single row, and are changed in proportion to the number of inputs across rows. Numbers indicating color scales are in pA. (D) These panels compare the CSD depth profiles (shown individually in panels A–C) for different numbers of synaptic input (1, 5, or 50) to specific parts of the cell. Note the strongest summation for the perisomatic inhibition and canceling interactions for dendritic locations.