The aim of the present study is thus to provide a detailed and systematic analysis of human sleep directly recorded from the hippocampus and the neocortex in a group of epileptic patients undergoing presurgical examinations. Moreover, some of these studies did not record sleep directly from deep structures, but used electrocorticography with subdural electrodes, or with foramen ovale electrodes –.

Although there have been previous reports on human sleep recorded from subcortical regions, they were mainly focused on the analysis of single EEG bands during specific sleep stages –. These recordings can provide unique insights into brain functions, including sleep. Clinical approaches, however, sometimes allow invasive recordings to be taken from the human brain, mainly in epileptic patients. Indubitably, the EEG spatial resolution is insufficient to show physiological processes in deep brain structures. Do this characteristic and basic feature of human scalp-recorded sleep EEG also apply to sleep recorded from deep brain structures, such as the hippocampus? the EEG power in the 0.75–4.5 Hz range quantified by spectral analysis, is considered a marker of NREM sleep intensity and the electrophysiological correlate of a sleep-wake dependent process (Process S) underlying sleep homeostasis. Slow-wave activity (SWA) in non-REM (NREM) sleep, i.e. Based on these data, the two-process model of sleep regulation posits that sleep propensity exponentially rises during waking and declines during sleep. Non-invasive methods such as the electroencephalogram (EEG) still provide most of the current data about the human sleep. However, despite the surge of interest in the coordinated hippocampal-cortical activity during sleep, not much is known about the exact features of the human sleep recorded from the hippocampus. Hippocampal reactivations during SWS, correlated with an improvement in spatial memory performance, have been reported also in humans. In this replay, a temporally sequential firing order across multiple cells is recaptured during sleep, possibly reflecting the consolidation of episodic memory traces. For example, high order replay of waking activity has been observed in the hippocampus during both SWS and REM sleep –. In recent years a series of papers have provided electrophysiological evidence pointing to the involvement of the hippocampus in memory processing also during sleep. The hippocampal formation is crucial for the storage of facts, episodes and spatial informations, the so-called declarative memories.

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