Lex (KC) are the electroencephalographic 1516647 (EEG) hallmarks of the second stage of human non-rapid eye movement (NREM) sleep. Defined as a high-voltage biphasic slow wave with a negative phase that may be followed by a positive phase, the KC is one of the most distinguished graphoelements of the EEG [1,2]. The sleep spindle, an oscillatory rhythm (11?5 Hz) of a waxing and waning shape, lasting 0.5? s is also a clearly distinguishable EEG event unique to sleep [3]. Fast (,13?5 Hz) and slow (,11?2 Hz) spindles are readily distinguishable with maximal power in centro-parietal and centrofrontal regions respectively [4?]. A JSI-124 site notable observation since the first description of the KC [7] is that it may appear either spontaneously or after a sensory stimulus, in which case it is named ‘evoked’. This fact has led to a series of experiments over the decades on a search of its functional significance, with many researchers correlating the appearance of a KC with autonomic alterations and forthcoming arousals [8?12], thus assuming it is an arousing reaction. On the other hand, some suggest that the KC represents a sleep-protecting mechanism averting arousals [2]. Finally, a combined view of KC being a sleep promoting reaction to arousing stimuli seems to gain acceptance [13]. The role of the sleep spindle is also a subject of research since its first description [14] with data supporting its sleep preservation role as an arousal inhibitor [15]. The importance of understanding the mechanisms underlying KCs, spindles and their possible interaction extends also beyond their role in sleep maintenance, Gracillin asthey have been proposed to be implicated in memory consolidation [16], stroke and spindle-coma [17], schizophrenia [18] and epilepsy [1,2,19,20]. The relationship between KCs and spindles has been described as antagonistic. Administration of benzodiazepines increases spindle appearance and decreases KCs [21?3]. In a period of 10 s before transient arousals, the incidence of spontaneous KCs increases while there is a decrease of both isolated sleep spindles and of spindles associated with KCs [24,25]. Halasz [13] reported a suppression of spindles power for 5?5 s following evoked KCs that were part of a microarousal, thus proposing that these states allow a window of improved sensory inflow at the thalamocortical (TC) circuits while preserving sleep continuity. KC is also seen as the forerunner of delta waves of slow-wave sleep (SWS) and this scheme resembles the reciprocal relationship of sleep spindles and delta waves [3,26]. Curcio et al [27] showed an increase of sleep spindles throughout the night while the occurrence of spontaneous KC decreased. Other studies support independent roles for spindles and KCs. Following stroke spindles disappear while KCs remain [28]. Church et al [29] found that there is 
no suppression of evoked KC by spindles, a result confirmed by Crowley et al [30]. In the underlying network level, sleep spindles are paced by TC networks whereas KCs by intracortical networks [31], independently from the thalamus [32] (but see Crunelli et al [33] and Bonjean et al [34]). Kokkinos and Kostopoulos [35] using time-frequency analysis (TFA) showed that fast spindles which happen to coincide with spontaneous KCs are interrupted, during that interruption a slowerSpindle Power Is Not Affected after Spontaneous KCoscillation most often appears over the negative peak of the KC and spindles following KCs always had a higher spectral frequency than.Lex (KC) are the electroencephalographic 1516647 (EEG) hallmarks of the second stage of human non-rapid eye movement (NREM) sleep. Defined as a high-voltage biphasic slow wave with a negative phase that may be followed by a positive phase, the KC is one of the most distinguished graphoelements of the EEG [1,2]. The sleep spindle, an oscillatory rhythm (11?5 Hz) of a waxing and waning shape, lasting 0.5? s is also a clearly distinguishable EEG event unique to sleep [3]. Fast (,13?5 Hz) and slow (,11?2 Hz) spindles are readily distinguishable with maximal power in centro-parietal and centrofrontal regions respectively [4?]. A notable observation since the first description of the KC [7] is that it may appear either spontaneously or after a sensory stimulus, in which case it is named ‘evoked’. This fact has led to a series of experiments over the decades on a search of its functional significance, with many researchers correlating the appearance of a KC with autonomic alterations and forthcoming arousals [8?12], thus assuming it is an arousing reaction. On the other hand, some suggest that the KC represents a sleep-protecting mechanism averting arousals [2]. Finally, a combined view of KC being a sleep promoting reaction to arousing stimuli seems to gain acceptance [13]. The role of the sleep spindle is also a subject of research since its first description [14] with data supporting its sleep preservation role as an arousal inhibitor [15]. The importance of understanding the mechanisms underlying KCs, spindles and their possible interaction extends also beyond their role in sleep maintenance, asthey have been proposed to be implicated in memory consolidation [16], stroke and spindle-coma [17], schizophrenia [18] and epilepsy [1,2,19,20]. The relationship between KCs and spindles has been described as antagonistic. Administration of benzodiazepines increases spindle appearance and decreases KCs [21?3]. In a period of 10 s before transient arousals, the incidence of spontaneous KCs increases while there is a decrease of both isolated sleep spindles and of spindles associated with KCs [24,25]. Halasz [13] reported a suppression of spindles power for 5?5 s following evoked KCs that were part of a microarousal, thus proposing that these states allow a window of improved sensory inflow at the thalamocortical (TC) circuits while preserving sleep continuity. KC is also seen as the forerunner of delta waves of slow-wave sleep (SWS) and this scheme resembles the reciprocal relationship of sleep spindles and delta waves [3,26]. Curcio et al [27] showed an increase of sleep spindles throughout the night while the occurrence of spontaneous KC decreased. Other studies support independent roles for spindles and KCs. Following stroke spindles disappear while KCs remain [28]. Church et al [29] found that there is no suppression of evoked KC by spindles, a result confirmed by Crowley et al [30]. In the underlying network level, sleep spindles are paced by TC networks whereas KCs by intracortical networks [31], independently from the thalamus [32] (but see Crunelli et al 
[33] and Bonjean et al [34]). Kokkinos and Kostopoulos [35] using time-frequency analysis (TFA) showed that fast spindles which happen to coincide with spontaneous KCs are interrupted, during that interruption a slowerSpindle Power Is Not Affected after Spontaneous KCoscillation most often appears over the negative peak of the KC and spindles following KCs always had a higher spectral frequency than.
