The detection of discrete spindles

and the event correlation histograms calculated across all spindle events (peaks and troughs) of all detected spindles clearly showed that those spindles detected during the stimulation were grouped by the up-phases of the oscillating stimulation signal. This observation not only corroborates the acute effectiveness of tSOS, but also strongly supports the conclusion that tSOS-induced SWA does indeed mimic physiologically normal conditions, because, also under natural conditions, endogenous slow oscillations drive spindle generation such that spindles occur preferentially during the slow oscillation up-phase (Mölle et al., 2002, 2011; Steriade, 2003; Steriade & Timofeev, 2003). On the other hand, this finding tempts us to speculate that phase-coupling of spindle activity might secondarily contribute Selleckchem GPCR Compound Library to the enhancing effects of tSOS-induced slow oscillations on encoding. However spindle activity as such is unlikely to be an effective mediator

of the enhanced encoding capabilities after tSOS, as spindle activity as such did not differ between the stimulation and sham conditions, and was also not positively correlated in any way with measures this website of encoding. The fact that induction of slow oscillations by tSOS prevents any direct measurement of endogenous slow oscillations is an obvious limitation of our approach. However, it is of importance in this context that, for tSOS, we chose the maximum current amplitude, such that it induced, in the underlying Rutecarpine neocortex, potential fields of a similar

amplitude as those naturally observed during SWA, thus closely mimicking endogenous slow oscillations (Steriade et al., 1996). Together, these observations justify the conclusion that the potential fields associated with the occurrence of slow oscillations and SWA do indeed play a causal role in the beneficial effect that these brain oscillations during sleep have on the encoding of information during succeeding wakefulness. The main finding of our study is that tSOS-induced slow oscillation activity during a nap consistently improved subsequent learning on different declarative tasks, whereas training of a procedural skill (finger sequence tapping) was completely unaffected. As training of finger sequence tapping skills is less dependent on hippocampal function than is learning of the declarative tasks, this pattern of findings suggests that SWA particularly benefits encoding in the hippocampus-dependent declarative memory system (Squire et al., 1993; Squire & Zola, 1996; Gais & Born, 2004; Debas et al., 2010). In fact, our pattern of findings is well in line with recent findings by Van Der Werf et al.