Figure 5.

Extra generators may rarely arise due to intracellular interactions of coincident synaptic currents. (A) An inhibitory perisomatic (GABA_A) input (G1, red) was combined with a non-overlapping dendritic excitatory input (G2, blue), both under irregular regimes. The ICA returned three generators, two of them matching the spatial distributions of the original individual inputs. The extra generator (G3, gray) presented an intermediate spatial distribution, and its time course revealed activity when the inputs coincided. (B) A slight shift of the inhibitory input away from the excitatory one reduced the variance of the extra generator down to the 5% border of significance (see Materials and Methods). (C) A further spatial shift of the inhibitory input toward the opposite dendritic tree yielded a perfect separation of the mixed LFPs into the two generators. (D) A distal shift of the excitatory input also led to perfect separation of the contributing LFP-generators [to be compared with (A)]. (E) To assess the intracellular origin of the extra generator we applied an ICA to mixed LFPs with the same synaptic inputs but obtained by numerical addition of their respective currents (without neurons). In this case (to be compared with A), the separation of the generators was optimal. The slight deviations of neuron-mediated (black) and numerically obtained LFPs (green) quantitatively estimate the mutual interactions of synaptic currents converging on the same neuron.