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. 2014 Jan 27;8:4. doi: 10.3389/fncom.2014.00004

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Copyright © 2014 Manuel, Zytnicki and Meunier.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Model with somatic L-type current and passive dendrites. (A) F-I curves for G_{Ca − L} = 1.0 mS/cm². Triangular ramp of current injected in the soma from 0 to 100 μA/cm² and back (velocity: 10⁻⁴ μA/cm².s). Increasing values of G_AHP from top to bottom, see labels). α_N = 0.0045 mol/nA.cm as before, but α_L is set to 0. When G_AHP = 10 mS/cm² (top curve), firing starts at 54 Hz at the recruitment threshold (32 μA/cm²), and the F-I curve shows a large domain of quiescence/firing bistability, derecruitment occuring only for a negative current of −15 μA/cm² on the descending ramp. Firing bistability is observed for between 15 and 25 (middle curve, G_AHP = 20 mS/cm²). When G_AHP is increased beyond 25 mS/cm², bistability disappears and the F-I curve becomes graded (bottom curve, G_AHP = 30 mS/cm²). Note that the recruitment threshold remains unchanged. (B) Effect of α_L on firing. F-I curves for G_{Ca − L} = 1 mS/cm² and G_AHP = 20 mS/cm² and α_N = 0.0045 mol/nA.cm. Increasing values of α_L from top to bottom (see labels). The firing bistability displayed in A (top, α_L set to 0) persists when α_L is increased to 2% of α_N, but the firing frequency is strongly reduced. When α_L is doubled, to 4% of α_N, the abrupt transition to the low frequency state on the down ramp is replaced by a series of frequency plateaus reflecting mixed mode oscillations. (C) F-I curve for G_{Ca − L} = 0.5 mS/cm². α_L set to 0 and α_N = 0.0045 mol/nA.cm as in A. Increasing values of G_AHP (see labels). Quiescence/firing bistability occurs for G_AHP smaller than 10 mS/cm² (top), and the F-I curve is graded for larger G_AHP. No firing bistability takes place. (D) Membrane currents. G_{Ca − L} = 1 mS/cm² and G_AHP = 20 mS/cm² (regime of firing bistability, see A). Top: L-type current (positive); bottom: sum of the leak and AHP currents (negative); dashed line: sum of the three currents. All currents are time averaged over the interspike interval and plotted as a function of the current injected in the soma. The zero current line is displayed in gray. The ascending current ramp is indicated by rightward pointing arrows and the descending branch by leftward pointing arrows.