In agreement with recent work (Lindén et al., 2011, Pettersen et al., 2008 and Schomburg et al., buy GSK1120212 2012), we find that the LFP length scale depends on the temporal coordination of the oscillatory inputs. Importantly, spiking and spike-related currents impact the LFP not only in the higher bandwidths but also in lower ones (<50 Hz) traditionally thought to reflect purely postsynaptic activity. We found that L4 pyramids impacted the LFP and CSD within both layers, with their extracellular contribution greatly affected by the presence or absence of active membranes. Conversely, L5 pyramids with their large somata, thick apical dendrites, and strong synaptic input contribute not

only to the LFP within L5 but also to the LFP in L4, especially at the onset of coordinated synaptic input. Given their large size and powerful synaptic

input, it is conceivable that L5 pyramids could also contribute to the LFP in other layers, such as L2/3 or L6, not simulated here. Thus, whereas the LFP reflects processing of neurons whose cell bodies are situated within that layer, the extended nature of pyramidal neurons gives rise to multipoles that reach into nearby layers. Importantly, we found this to be broadly true in simulations exhibiting varying see more degrees of input correlation. In agreement with others (Pettersen et al., 2008 and Schomburg et al., 2012), we find that L4/5 basket cells with their fairly low density (compared to excitatory neurons), localized and symmetric dendritic arbor, spatially uniform synaptic Liothyronine Sodium input, the small temporal width of their somatic spikes, and lack of strong afterpotentials have only a small impact on the LFP and CSD, even though their spike frequency is substantially higher than that of their excitatory neighbors (Figure 3C). Of course, this does not suggest that extracellular action potentials from individual basket cells are small. When considering LFP characteristics, such as amplitude and spatiotemporal width, we observed that these are markedly shaped by the impinging

pattern of postsynaptic currents and membrane characteristics. Increasing model complexity from only postsynaptic to using fully reconstructed active neurons attenuates the LFP amplitude, alters its spatiotemporal width and changes the sink-source location. Additionally, our findings regarding the LFP length scale (depending on input correlation, approximately 200–600 μm along the cortical depth and 100–300 μm tangentially) points to the necessity of large-scale models to study the origin and functionality of the LFP. How do these observations compare with LFPs recorded during whisker stimulation (Riera et al., 2012)? Such stimulation triggers prominent thalamocortical input into L4 in somatosensory cortex (Brecht and Sakmann, 2002).