Reactivating memories during sleep by odors: odor specificity and associated changes in sleep oscillations

J Cogn Neurosci. 2014 Aug;26(8):1806-18. doi: 10.1162/jocn_a_00579. Epub 2014 Jan 23.

Abstract

Memories are reactivated during sleep. Re-exposure to olfactory cues during sleep triggers this reactivation and improves later recall performance. Here, we tested if the effects of odor-induced memory reactivations are odor-specific, that is, requiring the same odor during learning and subsequent sleep. We also tested whether odor-induced memory reactivation affects oscillatory EEG activity during sleep, as a putative mechanism underlying memory processing during sleep. Participants learned a visuospatial memory task under the presence of an odor. During subsequent SWS, the same odor, a different odor, or an odorless vehicle was presented. We found that odor re-exposure during sleep significantly improves memory only when the same odor was presented again, whereas exposure to a new odor or the odorless vehicle had no effect. The memory-enhancing effect of the congruent odor was accompanied by significant increases in frontal delta (1.5-4.5 Hz) and parietal fast spindle (13.0-15.0 Hz) power as well as by an increased negative-to-positive slope of the frontal slow oscillation. Our results indicate that odor-induced memory reactivations are odor specific and trigger changes in slow-wave and spindle power possibly reflecting a bottom-up influence of hippocampal memory replay on cortical slow oscillations as well as thalamo-cortical sleep spindles.

MeSH terms

  • Adult
  • Brain Waves / physiology*
  • Cerebrum / physiology*
  • Delta Rhythm / physiology
  • Electromyography
  • Female
  • Humans
  • Learning / physiology*
  • Male
  • Mental Recall / physiology*
  • Odorants
  • Sleep / physiology*
  • Smell / physiology*
  • Young Adult