Shunting inhibition, a conductance increase with a reversal potential close to the resting potential of the cell, has been shown to have a divisive effect on subthreshold excitatory postsynaptic potential amplitudes. It has therefore been assumed to have the same divisive effect on firing rates. We show that shunting inhibition actually has a subtractive effect on the firing rate in most circumstances. Averaged over several interspike intervals, the spiking mechanism effectively clamps the somatic membrane potential to a value significantly above the resting potential, so that the current through the shunting conductance is approximately independent of the firing rate. This leads to a subtractive rather than a divisive effect. In addition, at distal synapses, shunting inhibition will also have an approximately subtractive effect if the excitatory conductance is not small compared to the inhibitory conductance. Therefore regulating a cell's passive membrane conductance-for instance, via massive feedback-is not an adequate mechanism for normalizing or scaling its output.

译文

分流抑制,电导增加,逆转电位接近细胞的静息电位,已显示对亚阈值兴奋性突触后电位振幅具有分裂作用。因此,人们认为它对发射速率具有相同的分裂作用。我们证明,在大多数情况下,分流抑制实际上对发射速率具有减法作用。在几个尖峰间隔内平均,尖峰机制有效地将体细胞膜电位固定到明显高于静息电位的值,因此通过分流电导的电流大致与发射速率无关。这导致减法而不是分裂效应。此外,在远端突触处,如果兴奋性电导与抑制性电导相比不小,则分流抑制也将具有近似消减作用。因此,调节细胞的被动膜电导 (例如,通过大量反馈) 并不是使其输出标准化或缩放的适当机制。

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