In prospective work we intend to further investigate Fluorouracil in vivo the theta rhythm as a functional correlate of the process of creating such cell assemblies through Hebbian learning. This computational study has been, to the best of our knowledge, the first attempt to explore the rich oscillatory dynamics with spatial aspects of coherence and synchronization patterns, and cross-frequency effects emerging in a functional

biophysically detailed model. We adapted a biophysically detailed network model of cortical layer 2/3 developed earlier (Lundqvist et al., 2006, Lundqvist et al., 2010 and Djurfeldt et al., 2008) and used it for two distinct memory simulation paradigms. The only conceptual difference in the model configuration between the two paradigms was the addition of augmentation (please see Section 2.4 for details) in the network simulating periodic memory replay. In addition, some connectivity strengths and the background noise excitation were different for the two networks (Table 1), otherwise they were identical. They both had a hypercolumnar and minicolumnar organization (Fig. 1). Neurons within a hypercolumn were organized in 49 non-overlapping subpopulations (minicolumns) and the network was composed of 9 such hypercolumns. The minicolumns were spread out on a two-dimensional square grid with 1.5 mm side and each minicolumn had a diameter of 30 µm. All pyramidal cells in a minicolumn shared the same

x and y coordinates but were spread out on the z-axis along 500 µm. Interneurons were placed near the center of each minicolumn with respect to the z-axis. All conduction delays were calculated assuming a conduction CP-868596 in vivo speed of 0.5 m/s. The cells included were layer 2/3 pyramidal cells and soma targeting basket cells assumed to correspond to fast spiking

cells. Each layer 2/3 portion of a minicolumn contained 30 pyramidal cells (Peters and Yilmaz, 1993) and one basket cell. The layer 2/3 cells within each minicolumn were recurrently connected and shared layer 4 inputs (Yoshimura et al., 2005). Synaptic weights and connectivity were motivated by biological data (Thomson et al., 2002, Lundqvist et al., 2006 and Lundqvist et al., 2010). Neuron models were multi-compartmental and conductance-based following the Hodgkin–Huxley and Rall formalisms. Similar to previous studies (Lundqvist et al., Thiamet G 2006 and Lundqvist et al., 2010), the connectivity was set up to store non-overlapping memory patterns. In this work 49 such cell assemblies comprising 9 equally selective minicolumns from different hypercolumns were set up by hand before the onset of the simulations and were assumed to have been formed during learning. The patterns were stored by the long-range connectivity between pyramidal cells belonging to the minicolumns constituting the pattern (Fig. 1). Locally, the pyramidal cells in a minicolumn were connected to 25% of the other pyramidal cells in their own minicolumn (Thomson et al.