Consolidation of strictly episodic memories mainly requires rapid eye movement sleep.
OBJECTIVE
The aim of this study is to examine the effects of sleep deprivation during the first or second half of the night on episodic memory consolidation. Episodic memory is defined as memory for events located in time and space. It is also characterized by autonoetic consciousness, which gives a subject the conscious sensation of traveling back in time to relive the original event and forward into the future.


METHODS
Consolidation of episodic information was tested after 4-hour retention intervals, which followed learning and occurred during either the early or late half night, respectively dominated by slow wave sleep (SWS) or rapid eye movement (REM) sleep, or corresponding periods of wakefulness.


METHODS
Data collection occurred in the sleep laboratory.


METHODS
Forty-three young healthy subjects: 9 men and 34 women, age ranging from 18 to 26 years (mean 20.18 +/- 1.94 years) were included in this study.


METHODS
Waking after a 4-hour retention interval filled with early or late sleep, or 4-hour sleep deprivation, during early or late period of night.


RESULTS
The cognitive task, named the What-Where-When test, was specially designed to assess factual, spatial, and temporal components of episodic memory. This task was associated with the Remember/Know paradigm to assess autonoetic consciousness. We measured performance on immediate free recall, delayed free recall (after a 4-hour interval of wakefulness or sleep), and delayed recognition. We also calculated a forgetting rate for each feature (factual, spatial, and temporal) and, for the recognition task, scores of autonoetic consciousness (R responses). REM-sleep deprivation was associated with significantly lower recall of spatial information compared to SWS deprivation (P < .01) or late sleep (P < .05) conditions. REM-sleep deprivation was also associated with a higher forgetting rate of temporal information as compared to the early sleep condition (P< .01). Finally, REM-sleep deprivation led subjects to give significantly fewer R responses, indicative of true memories, as compared to SWS deprivation (P < .05).


CONCLUSIONS
These results suggest that consolidation of truly episodic memories mainly involves REM sleep.
Rauchs
Géraldine
G
Inserm E0218, Université de Caen, France.
Bertran
Françoise
F
Guillery-Girard
Bérengère
B
Desgranges
Béatrice
B
Kerrouche
Nacer
N
Denise
Pierre
P
Foret
Jean
J
Eustache
Francis
F
D000293:Adolescent; D000328:Adult; D003071:Cognition / Q000502:physiology; D003243:Consciousness / Q000502:physiology; D005260:Female; D006801:Humans; D007858:Learning / Q000502:physiology; D008297:Male; D008568:Memory / Q000502:physiology*; D009483:Neuropsychological Tests; D017286:Polysomnography; D012153:Retention, Psychology / Q000502:physiology; D012890:Sleep / Q000502:physiology; D012892:Sleep Deprivation / Q000175:diagnosis / Q000503:physiopathology; D012895:Sleep, REM / Q000502:physiology*; D013997:Time Factors; D014851:Wakefulness / Q000502:physiology