<i>I</i>_<i>h</i> activation may increase or decrease the threshold for L5PC action potential firing by a strong apical dendritic input, depending on the location of the input.

A: Somatic membrane potential time courses according to the Almog model in response to 2-ms square-pulse current with an amplitude of 100 (top), 30 (middle) or 10 nA (bottom), injected at the apical dendrite 500 μm from the soma. For control neuron (black), both 30 and 100 nA stimuli induced a spike, while for Ih-blocked neuron (blue), 100 nA stimulus induced a spike while 30 nA stimulus did not. Scale bars 5 ms and 50 mV. B: Threshold current amplitudes for 2-ms square-pulse inputs at the apical dendrite at different distances from the soma. Black: Almog-model control neuron, blue: Almog-model neuron with Ih blockage. C: Peak membrane potential at the site of current injections, given the threshold-current of (B). D: Threshold conductances for an alpha-shaped glutamatergic input with time constant 3 ms. Black: Almog-model control neuron, blue: Almog-model neuron with Ih blockage. E–F: Somatic membrane potential time courses according to the Hay model in response to 2-ms square-pulse current with an amplitude of 100 (top), 30 (middle) or 10 nA (bottom), injected at the apical dendrite 500 (E) or 800 (F) μm from the soma. For a stimulus 500 μm from the soma (E), 10.0 nA stimulus induced a spike in the control neuron (black) but not in the Ih-blocked neuron (blue), while at 800 μm this was reversed. Scale bars 5 ms and 50 mV. G–I: The experiments of (B–D) repeated for Hay model.