Recalling and Forgetting Dreams: Theta and Alpha

Oscillations during Sleep Predict Subsequent Dream Recall

BY: Cristina Marzano, Michele Ferrara, Federica Mauro, Fabio Moroni, Maurizio Gorgoni, Daniela Tempesta,

Carlo Cipolli, and Luigi De Gennaro

PowerPoint By: Nirav Patel

BACKGROUND

• Journal of Neuroscience • May 4, 2011

BACKGROUND

BACKGROUND

• Beta: 15-30 Hz

• Alpha: 9-14 Hz

• Theta: 4-8 Hz

• Delta: 1-3 Hz

BACKGROUND

• Electroencephalography (EEG): Records electrical activity on the scalp

• Polysomnography (PSG): records eye movements and other bodily functions during sleep

• brain mechanisms underlying dreaming unknown• how dreams are encoded is unknown– Dreams not directly accessible

• Rely on spontaneous or provoked awakenings

BACKGROUND

• Speculate episodic memory (memory for episodes in life)– Encoded in declarative memory (memories that

can be consciously recalled) during sleep

BACKGROUND• In learning task, successful memory formation

= spike in theta wave (4-8 Hz) oscillation • Frontal theta oscillations during encoding

predict recall• Theta waves mediate interactions between

prefrontal cortex and medial temporal lobe in memory encoding

HYPOTHESIS

• 1) A higher frontal theta activity should be associated with the awakening from REM sleep followed by successful dream recall compared to those with recall failure

• 2) A successful recall after awakening from NREM stage 2 should be associated with a lower alpha power compared with awakening with no dream recall

METHODS

• 65 university students (35 males, 30 females)• Criteria– no other sleep, medical, or psychiatric disorder

(as assessed by a 1 week sleep log and a clinical interview)

– a habitual sleep time between 12:00 A.M. and 8:00 A.M.

– normal sleep duration and schedule• 7.5 hours of sleep every night

PROCEDURE

• Spend 2 nights in sleep lab– 1st night is used for adaptation– 2nd night actual recording of data

• PSG indicates what stage of sleep they’re in– start sleeping at 12:00AM and are awakened 7.5

hours later• awakened from NREM stage 2 sleep (n=35)• awakened from REM sleep (n= 30)

– After 5 minutes without stage shift

PROCEDURE

• 20/35 awoken from NREM stage 2 recalled dreams

• 20/30 awoken from REM sleep recalled dreams– NREC = non recallers– REC = recallers

PROCEDURE

• One way ANOVAs on REC and NREC groups for PSG variables after awoken from REM and stage 2 sleep– TST: total sleep time– WASO: Wakefulness after sleep onset– SEI: Sleep efficiency index

RESULTS

• No significant difference in PSG measures of sleep stage at awakening (REM/stage 2) and dream recall (success/failure).– stage of awakening did not affect success or

failure of dream recall

RESULTS

• Last 5 minutes of sleep before awakening from REM sleep is dominated by theta wave (4-8 Hz) oscillations

RESULTS

• EEG power values for REC and NREC, through the course of REM sleep, are similar except in the range of theta waves (4-8 Hz)

RESULTS

• Topographic distribution of EEG power shows a significant difference only for the theta power: REC showed higher power values than NREC subjects

RESULTS

RESULTS

• EEG power values for REC and NREC, through the course of NREM stage 2 sleep, are similar except in the range of alpha waves (9-14 Hz)

RESULTS

• Looking across all electrodes number of dreams recalled after morning awakening was associated positively with the amount of theta activity in REM sleep (top) and negatively with alpha activity in stage 2 (bottom) – Rho Values: correlation values btw/ # of dreams

recalled and, theta activity (top), and alpha activity on bottom• positive rho values indicate the presence of a positive

correlation, and vise versa

RESULTS

Discussion

• Results provide clear EEG evidence that stage-specific cortical brain oscillations in the 5 min of sleep before morning awakening are predictive of a successful dream recall.

• A higher frontal theta activity, after awakening from REM sleep, as well as a lower alpha activity of the right temporal area after awakening from stage 2 NREM sleep predicts successful dream recall

THE END