The way in which a neuron transduces the population activity of its synaptic inputs into action potentials is a fundamental step in understanding information processing in the brain. Through the use of computer simulated synaptic inputs and in vitro slice electrophysiology we will examine three important factors that can affect the transformation of inputs to output. The first is the rate of dendriticconductances: is the cell's firing rate the same whether the inputs are injected in the dendrite or the soma? Will dendritic conductances that have been shown to boost individual, subthreshold, synaptic potentials also boost suprathreshold trains of synaptic inputs? A second influential factor is the location of the inputs relative to each other on the dendritic tree, which may determine how the inputs are combined. Passive cable theory predicts sublinear summation if the inputs occur on the same dendritic branch due to mutual shunt, and linear summation if they occur on different branches, but will active dendritic conductances counter sublinear summation? The third factor we will examine is the interaction between excitatory and inhibitory synaptic inputs on the dendritic tree. We will mainly focus on how the effects of inhibition on firing depend on where the inhibitory inputs are located relative to the excitatory. In all three cases we will use channel blockers to identifythe dendritic conductances responsible for the nonlinear effects we may see in the transduction from input to output.
