COSYNE

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As recently shown, prefrontal pyramidal neurons remain sensitive to noisy input fluctuations even at high input currents when the firing rate otherwise saturates (Arsiero et al., 2007). This noise sensitivity contrasts the known response properties of pyramidal neurons in the somatosensory cortex, but also deviates from the properties of the classical integrate-and-fire neuron model: the stronger the input current, the less is the firing rate affected by additional fast input fluctuations in these latter cases. The noise-induced firing rate increase of prefrontal pyramidal neurons at high inputs seems to be particularly prominent in the presence of dopamine. We review the different nonlinear response properties of cortical pyramidal neurons and show that they can be captured by modifying the spike triggering mechanism of the classical integrate-and-fire neuron model towards a Hodgkin-Huxley type mechanism. In complexity the suggested model is in between the subthreshold oscillatory models and the integrate-and-fire models and can be roughly characterized as a 1.5-dimensional Hodgkin-Huxley reduction. A possible computational implication of the enhanced fluctuation sensitivity of prefrontal pyramidal neurons are discussed.