Synaptic and non-synaptic propagation of slow waves and their modulation by endogenous electric fields

The cerebral cortex is organized in complex circuits of neurons strongly interconnected in a conductive medium. During deep sleep stage, this neuronal connectivity generates recurrent synchronized synaptic activity leading to transition states where periods of activity are interspersed with periods of silence. This stereotyped pattern of alternate states is manifested as slow oscillations (SO), <1 Hz rhythm that dominates the cortical network during slow wave sleep (Steriade et al., 1993) becoming important for memory consolidation (Marshall et al., 2006), plasticity (Reig et al., 2006; Reig and Sanchez-Vives, 2007) and metabolic homeostasis (Xie et al., 2013). The spatiotemporal dynamic of the SO is more complex than the simultaneous activation of neurons in a local network. The SO travels with a pattern of propagation in the cortical network, with a preference in the anterior to posterior direction (Massimini et al., 2004; Ruiz-Mejias et al., 2011). This oscillatory rhythm generates extracellular fields that are prominent enough to be measured extracellularly on the conductive medium (local field potentials, LFP) or even from the skull surface (electroencephalograms, EEG). Many excellent studies have raised awareness of the mechanisms involved in these extracellular signals generated by neuronal populations (Kajikawa and Schroeder, 2011; Buzsáki et al., 2012; Herreras, 2016; Telen´ czuk et al., 2017). Moreover, in the last years it has been proved how the electric fields (EFs) generated by neuronal activity, in turn, induce changes in such activity of neurons (Fröhlich and McCormick, 2010; Anastassiou et al., 2011). In other words, the electric environment generated by neuronal activity has a feedback effect on the synaptic activity. In this thesis, we explore how the synaptic and non-synaptic components modulate each other during the propagation of SO. For this purpose, we describe the propagation pattern of SO across the cerebral cortex, and we investigate the endogenous EFs generated by slow waves ...