Glutamatergic neurons are the main excitatory units in these networks, typically linked through multiple recurrent connections that are critical for computational performance (Binzegger et al., 2004 and Somogyi et al., 1998). GABAergic interneurons, on the other hand, comprise a highly heterogeneous group of neurons that maintain the stability of cortical networks through synaptic inhibition. In addition,

interneurons modulate network activity by shaping the spatiotemporal dynamics of different forms of synchronized oscillations (Klausberger and Somogyi, 2008). The organization of neuronal assemblies in the cortex seems to obey certain rules that guarantee a critical balance between VX-770 solubility dmso excitation and inhibition while maximizing their computational ability. In the cerebral cortex, for example, the ratio between excitatory and inhibitory neurons is relatively constant across Selleck CB-839 regions and species (Fishell and Rudy, 2011, Hendry et al., 1987 and Sahara et al., 2012). In the adult olfactory bulb, where interneurons are continuously added throughout life, the proportion of newborn neurons that integrates into the mature network is tightly regulated (Kohwi et al., 2007 and Winner

et al., 2002). In addition, GABAergic interneurons in the cerebral cortex and olfactory bulb come in a rich variety of classes, each having highly stereotypical laminar arrangements, unique patterns of connectivity, and functions (Fishell and Rudy, 2011, Klausberger and Somogyi, 2008 and Lledo et al., 2008). This enormous variety of interneuron classes provides cortical circuits with the required flexibility

to carry out complex computational operations during information processing. Considering until the highly stereotypical organization of cortical networks, the most striking aspect of their assembly is that their cellular ingredients are born in separate locations. While glutamatergic neurons of the olfactory bulb and the cerebral cortex are generated locally by progenitor cells in the developing pallium (Molyneaux et al., 2007 and Rakic, 2007), GABAergic interneurons populating these structures derive from the subpallium, the base of the telencephalon (Batista-Brito and Fishell, 2009, Gelman and Marín, 2010 and Wonders and Anderson, 2006). Consequently, glutamatergic neurons and GABAergic interneurons follow very different strategies to reach their final destination. Glutamatergic neurons migrate radially to form the different layers of cortical structures (Rakic, 2006). In contrast, interneurons first migrate tangentially from their birthplace to the cerebral cortex and olfactory bulb and subsequently switch their mode of migration to radial to adopt their final position in these structures (Marín and Rubenstein, 2001).