Recalling and Forgetting Dreams: Theta and Alpha Oscillations during Sleep Predict Subsequent Dream Recall

Stage 2 sleep. A, One 20 s segment of the PSG recording of stage 2 sleep preceding morning awakening. B, The detection of oscillations in the segment of stage 2 sleep by the BOSC method, as in Figure 1.

EEG power spectra (mean over all 19 scalp locations, obtained by collapsing EEG power across all the derivations) of EEG activity during REM sleep in the REC (black line) and NREC (gray line) groups. Mean absolute values (expressed in logarithmic scale) are plotted in the frequency range from 0.50 to 24.75 Hz for 0.25 Hz bins. SEs refer to interlocation variability.

From the left, the first two columns show the topographic distribution of absolute EEG power during REM sleep in the REC group and in the NREC group. The maps were scaled between minimal (min) and maximal (max) power values in the REC and NREC groups. The first column on the right shows topographic statistical EEG power differences (assessed by unpaired t tests) between the REC and NREC groups. Values are expressed in terms of t values: positive t values indicate a prevalence of the REC over the NREC group, and vice versa. The two-tailed level of significance (p ≤ 0.00738) corresponds to t ≥ 2.60. Average values are normalized by total power, color coded, plotted at the corresponding position on the planar projection of the scalp surface, and interpolated (biharmonic spline) between electrodes. The maps are based on the 19 unipolar EEG derivations of the international 10–20 system with averaged mastoid reference. Maps are plotted for the following EEG bands: delta (0.50–4.75 Hz), theta (5.00–7.75 Hz), alpha (8.00–11.75 Hz), sigma (12.00–15.75 Hz), and beta (16.00–24.75 Hz).

EEG power spectra (mean over all 19 scalp locations, obtained by collapsing EEG power across all the derivations) of EEG activity during stage 2 NREM sleep in the REC (black line) and NREC (gray line) groups. Mean absolute values (expressed in logarithmic scale) are plotted in the frequency range from 0.50 to 24.75 Hz for 0.25 Hz bins. SEs refer to interlocation variability.

From the left, the first two columns show the topographic distribution of absolute EEG power during stage 2 NREM sleep in the REC and NREC groups. The maps were scaled between minimal (min) and maximal (max) power values in the REC and NREC groups. The first column on the right shows topographic statistical EEG power differences (assessed by unpaired t tests) between the REC and NREC groups. Values are expressed in terms of t values: positive t values indicate a prevalence of the REC over the NREC group, and vice versa. The two-tailed level of significance (p ≤ 0.00447) corresponds to a t ≥ 2.78. Average values are normalized by total power, color coded, plotted at the corresponding position on the planar projection of the scalp surface, and interpolated (biharmonic spline) between electrodes. The maps are based on the 19 unipolar EEG derivations of the international 10–20 system with averaged mastoid reference. Maps are plotted for the following EEG bands: delta (0.50–4.75 Hz), theta (5.00–7.75 Hz), alpha (8.00–11.75 Hz), sigma (12.00–15.75 Hz), and beta (16.00–24.75 Hz).

The topographic distribution of correlation values (rho values) between the actual number of dreams recalled after morning awakenings with the amount of theta activity in REM sleep (top map) and with alpha activity in stage 2 (bottom map). Values are expressed in terms of rho values: positive rho values indicate the presence of a positive correlation, and vice versa. The alpha level for REM and NREM sleep was, respectively, adjusted to 0.007 (ρ ≥ 0.47) and to 0.004 (ρ ≥ 0.46). Average values were normalized by total power, color coded, plotted at the corresponding position on the planar projection of the scalp surface, and interpolated (biharmonic spline) between electrodes. The maps are based on the 19 unipolar EEG derivations of the international 10–20 system with averaged mastoid reference.

Mean proportion of time [P_episode (f)] of EEG activity during REM sleep during which oscillations were detected at each frequency in the 0.50–25.00 Hz frequency range. Individual oscillations detected across all frequencies by the BOSC method have been averaged across all subjects, and error bars denote SEM P_episodes (f). Units of frequency are in hertz and are plotted in five logarithmically spaced frequency values. See Materials and Methods for more details on the BOSC method.

Mean proportion of time [P_episode (f)] of EEG activity during stage 2 sleep during which oscillations were detected by the BOSC method at each frequency in the 0.25–25.00 Hz frequency range, as in Figure 8.