Orchestration of “ presto ” and “ largo ” synchrony in up-down activity of cortical networks

whereas the LFPs are assessed in the low-frequency range (e.g. 1–250 Hz) (see Menendez de la Prida et al., 2006, as an example of such a type of simultaneous recording in vitro). A large number of experiments have suggested that single-unit spikes are primarily attributable to spiking activity of pyramidal or inhibitory neurons, and thus measure the cortical output. On the other hand, LFPs refl ect population synaptic potentials (Belitski et al., 2008; Rasch et al., 2008), and other types of slow activity unrelated to synaptic events, putatively including slow voltage-dependent membrane oscillations. Recordings from MEA dishes are governed by sets of excitatory and inhibitory synaptic transmission systems that have been described as consisting of indistinguishable cells capable of generating either spikes during synchronous bursting in cortical cultures in vitro (Keefer et al., 2001; Giugliano et al., 2004; Gramowski et al., 2004; Selinger et al., 2004; Van Pelt et al., 2004; Martinoia et al., 2005; Tateno et al., 2005; Eytan and Marom, 2006; Wagenaar et al., 2006), or LFPs in organotypic cultures and slices (Beggs and Plenz, 2003, 2004; Sun and Luhmann, 2007). On the contrary, applying robust sorting procedures commonly used during in vivo extracellular unit recordings (Barthò et al., 2004; Buzsàki, 2004), we provided evidence in long-term MEA networks that the autocorrelation function (AC) (and other statistical features) of each identifi ed neuron represents a very good model to fi nd appropriate clusters of cells characterized by similar activity (Gullo INTRODUCTION Action potential (AP) propagation and synaptic transmission are shared by both peripheral and central nervous systems to sustain fast responding excitability. Nevertheless, both systems are constitutively acted upon by several fundamental but confl icting properties such as serial or parallel activity, rate or temporal spike coding, independent or synchronous operation, reliable or unreliable synaptic transmission, respectively (Otmakhov et al., 1993; Lisman, 1997). Spontaneous synchronous activity, an emerging property of many central networks, is due to the interactions of many relatively simple elements such as chemical and electrical synapses, ion channels and transporters (O’Learly et al., 1994; Catalano and Shatz, 1998; Garaschuk et al., 1998; Komuro and Rakic, 1998; Corlew et al., 2004; Fellin et al., 2004; Dupont et al., 2006). It is believed that neuronal network assembly bursting is physiologically important to ensure the reliability of synaptic transmission, plasticity and information processing (Lisman, 1997; Harris, 2005). Extracellularly recorded neural signals such as those recorded from multi-electrode arrays (MEAs) consist of time-varying spatial distributions of APs (“spikes”, 1 ms) superimposed on relatively slow local fi eld potentials (LFP, 1–2 s). Usually, the former type of activity, known as multiple-unit activity (MUA), can be spatially separated if the recording electrodes are suffi ciently small and estimated in the high-frequency range (typically 250–5000 Hz), Orchestration of “presto” and “largo” synchrony in up-down activity of cortical networks