Simultaneous estimation of global background synaptic inhibition and excitation from membrane potential fluctuations in layer III layer III neurons of the rat entorhinal cortex in vitro

It is becoming clear that the detection and integration of synaptic input and its conversion into an output signal in cortical neurones is strongly influenced by background synaptic activity or “noise”. The majority of this noise results from the spontaneous release of synaptic transmitters, interacting with ligand-gated ion channels in the postsynaptic neurone (e.g. Berretta and Jones, 1996; Jones and Woodhall, 2005; LoTurco et al., 1990; Otis et al., 1991; Ropert et al., 1991; Salin and Prince, 1996; Staley, 1999; Woodhall et al., 2005). The function of synaptic noise has been the subject of debate for some years, but there is increasing evidence that it modifies or controls neuronal excitability and, thus, the integrative properties of cortical neurones. In the present study we have investigated a novel approach (Rudolph et al., 2004) to simultaneously quantify synaptic inhibitory and excitatory synaptic noise, together with postsynaptic excitability, in rat entorhinal cortical neurons in vitro. The results suggest that this is a viable and useful approach to the study of the function of synaptic noise in cortical networks.