Are Spatial Memories Strengthened in the Human Hippocampus during Slow Wave Sleep?

Abstract

In rats, the firing sequences observed in hippocampal ensembles during spatial learning are replayed during subsequent sleep, suggesting a role for posttraining sleep periods in the offline processing of spatial memories. Here, using regional cerebral blood flow measurements, we show that, in humans, hippocampal areas that are activated during route learning in a virtual town are likewise activated during subsequent slow wave sleep. Most importantly, we found that the amount of hippocampal activity expressed during slow wave sleep positively correlates with the improvement of performance in route retrieval on the next day. These findings suggest that learning-dependent modulation in hippocampal activity during human sleep reflects the offline processing of recent episodic and spatial memory traces, which eventually leads to the plastic changes underlying the subsequent improvement in performance.

Fast track to the medial prefrontal cortex

“…This is largely consistent with the view that memory reactivation during sleep promotes the gradual reorganization of hippocampal-cortical memory networks (16). Also consistent with this view, waking patterns of brain activity associated with earlier learning are selectively replayed during subsequent sleep in humans (17) and other species, including rodents (18). This coordinated replay occurs in hippocampal as well hippocampalcortical and cortico-cortical networks and likely promotes gradual stabilization of memory traces in the cortex.…”

Targeted memory reactivation of newly learned words during sleep triggers REM-mediated integration of new memories and existing knowledge

“…This neocortical consolidation relies on neural replay of new memories during sleep (O'Neill et al, 2010). Neural populations or areas of the brain that were active during encoding become spontaneously reactivated during subsequent rest or sleep (Wilson & McNaughton, 1994;Maquet et al, 2000), and the extent of this reactivation predicts overnight improvement in performance (Peigneux et al, 2004).…”

Shifting from implicit to explicit knowledge: Different roles of early- and late-night sleep

“…This procedure of night-half comparison has been efficiently applied in several previous studies, which revealed differential effects of SWS-rich and REM sleeprich periods (e.g., Fowler et al 1973;Born 1997, 1999;Wagner et al 2001Wagner et al , 2003. These and other studies (Peigneux et al 2003(Peigneux et al , 2004Rasch et al 2007) have pointed to critical roles of SWS for explicit memories and of REM sleep for implicit memories. It was therefore expected that more subjects would generate explicit knowledge of the hidden regularity across SWS-rich early sleep than across REM sleep-rich late sleep.…”

“…SWS has been implicated in the consolidation of hippocampus-dependent explicit (or declarative) memory tasks, while REM sleep seems to be particularly pertinent to hippocampus-independent implicit (or nondeclarative) tasks Born 1997, 1999;Peigneux et al 2003Peigneux et al , 2004Wagner et al 2003Wagner et al , 2007Marshall et al 2007). However, little is known about the role of these two sleep stages in tasks like the NRT that involve both implicit and explicit aspects and, more specifically, in which explicit knowledge may emerge from previous implicit processing.…”