Synaptic conductances and the generation of regular 
and irregular firing patterns in cortical neurons

Investigating how cortical neurons integrate their electrical inputs has 
commonly involved injecting fixed patterns of current and observing the resulting 
membrane potential and spike responses. However, we now have accurate biophysical 
models of the ionic conductances at the postsynaptic sites of cortical synapses 
and of the conductances, which generate action potentials. Using conductance 
injection or dynamic clamp it is possible to inject point conductances which 
imitate the electrical properties of synaptic inputs, including the shunting, 
reversible nature of inhibitory GABAA receptor input, the saturating or “choking” 
behavior of AMPA receptor input; and the voltage-dependent block of NMDA receptor 
input. Complex conductance signals, which reproduce the effects of stochastic and 
oscillatory network firing can be applied repeatedly and with high precision. 
In this talk, I review our work using this approach, addressing the nature of 
the threshold and of reliability of spike generation in cortical neurons, how 
synaptic conductance input patterns are encoded into variations in action potential 
shape, and how neurons integrate network burst and gamma oscillatory activity, 
and the generation of irregular activity in the cortical network.