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Models of Neocortical Layer 5b Pyramidal Cells Capturing a Wide Range of Dendritic and Perisomatic Active Properties

Figure 1

Models constrained only by BAC firing may fail to respond properly to perisomatic step current.

A. Reconstructed morphology of an L5b neocortical pyramidal cell, age p36, used for the fitting and simulations. Recording and stimulation sites are indicated by schematic electrodes at the soma (black), proximal apical dendrite (400 µm from the soma, blue) and distal apical site (620 µm from the soma, red). (B–E). Model simulation of BAC firing (compare to [6]). B. EPSP-like current injection at the distal dendrites (Istim, red trace) with peak amplitude of 0.5 nA produced a subthreshold depolarization of 2.5 mV at the soma (Vm, black trace). C. Suprathreshold step current at the soma evoked a somatic AP that back-propagated into the dendrites. D. BAC firing. The combination of somatic and dendritic current injection (separated by an interval of 5 ms) evoked a dendritic Ca2+ spike (Vm, red trace) followed by a burst of two additional somatic APs. E. Dendritic Ca2+ spike could be evoked by an intense (2.5 nA) current injection to the distal dendrite alone, also evoking two APs at the soma. F. Top: the model's firing response to somatic step current injection did not agree with the experimentally observed response (black–model, magenta–experiment). Bottom: 300 ms of the response corresponding to the bar in the top part.

Figure 1