More importantly, pyramidal neurons in Selleckchem HDAC inhibitor the intact brain are constantly bombarded by synaptic input, so much so that they are chronically depolarized and shunted ( Bernander et al., 1991; Destexhe and Paré, 1999; for review see Destexhe et al., 2003). Moreover, sensory input causes concomitant (albeit momentarily unbalanced) increases in both excitatory

and inhibitory drive ( Borg-Graham et al., 1998; Haider et al., 2013; Pouille et al., 2009; for review see Isaacson and Scanziani, 2011), which implies further increases in total conductance. The reduction in input resistance (R = 1/g) decreases neuronal sensitivity to constant and slowly fluctuating (low-frequency) inputs, but the concomitant reduction in the membrane time constant (τ = RC) makes neurons relatively more sensitive to rapidly fluctuating (high-frequency) inputs. In addition, large membrane potential fluctuations driven by synaptic bombardment increase sensitivity to coincident inputs ( Rossant et al., 2011). This tendency is enhanced by a nonlinear increase in adaptation that can further reduce sensitivity to slow input and thus enhance selectivity for fast input ( Hong et al., 2012; Prescott

et al., 2006, 2008b). The cumulative effect is that pyramidal neurons receiving realistic conductance-based background and stimulus-evoked inputs in vivo, BVD-523 research buy and which therefore exist in a high-conductance state, behave more like coincidence detectors than is suggested by in vitro testing with artificial current-based stimuli (see also Azouz and Gray,

2000, 2003). To be clear, pyramidal neurons do not switch abruptly from one to the other operating mode but, instead, shift along a continuum (see Figure 2) and can exhibit reasonably strong coincidence detector traits. Requirement 2 is satisfied insofar as principal neurons do receive synchronous input. For one, the cortex receives sensory input via synchronized activation of thalamocortical neurons (Alonso et al., 1996; Bruno and Sakmann, 2006) originating from the coactivation of primary sensory neurons (see below). Pyramidal neurons recorded in vivo exhibit irregular out spiking (see above) driven by large fluctuations in membrane potential that, based on the small depolarization produced by unitary synaptic events, can only be accounted for by some degree of synchrony among presynaptic cells (Destexhe and Paré, 1999; DeWeese and Zador, 2006). Indeed, cross-cell correlations in membrane potential (Lampl et al., 1999; Poulet and Petersen, 2008; Yu and Ferster, 2010) and spiking (Cohen and Kohn, 2011; deCharms and Merzenich, 1996; Jadhav et al., 2009; Smith and Kohn, 2008) have been documented in vivo.