Neural Correlates of Dreaming: An In-Depth Exploration
Dreaming remains a fascinating and complex area of study within neuroscience. Traditionally, dreaming has been linked to rapid eye-movement (REM) sleep, which is characterized by high-frequency electroencephalographic activity similar to that observed during wakefulness. However, dream experiences also occur during non-REM (NREM) sleep, which is characterized by prominent low-frequency activity. This challenges our understanding of the neural correlates of conscious experiences in sleep.
Consciousness never fades during waking. However, when awakened from sleep, we sometimes recall dreams and sometimes recall no experiences. This raises fundamental questions about the neural basis of dreaming and its relationship to consciousness.
To investigate the neural correlates of dreaming, researchers have employed high-density electroencephalography (EEG) to contrast the presence and absence of dreaming in NREM and REM sleep.
Neural Activity and Dream Experience
In both NREM and REM sleep, reports of dream experience were associated with local decreases in low-frequency activity in posterior cortical regions. Furthermore, high-frequency activity in these regions correlated with specific dream contents.
NREM Sleep:
Figure 1. Dreaming experience vs. A. Cortical distribution of t-values for the contrast between DEs and NEs at the source level for low-frequency power (1-4 Hz) in NREM sleep (20s before the awakening). p<0.05, after correction for multiple comparisons (two-tailed, paired t-tests, 32 subjects, t(31) > 2.04). B.
NREM Sleep Hypnogram.
REM Sleep:
Figure 2. Dreaming experience vs. A. Cortical distribution of t-values for the contrast between DEs and NEs at the source level for low-frequency (1-4 Hz) power in REM sleep (20s before the awakening). p<0.05 after correction for multiple comparisons (two-tailed, paired t-tests, 10 subjects, t(9)>2.26). B.
REM Sleep Hypnogram.
High-Frequency Power:
Figure 3. Dreaming experience vs. A. Cortical distribution of t-values for the contrast between DEs and NEs at the source level for high-frequency power (20-50 Hz) in NREM sleep (20s before the awakening). p<0.05 after correction for multiple comparisons (two-tailed, paired t-tests, 32 subjects, t(31) > 2.04). B. Same as A for the contrast between DE and DEWR in NREM sleep (two-tailed, paired t-tests, 20 subjects, t(19) > 2.09) C.
Specific Dream Contents:
Figure 4. A. Correlation between the thinking/perceiving score and 25-50 Hz power (last 8s, 7 subjects). Left: mean Spearman rank correlation coefficients (7 subjects). Right: significant voxels p<0.05 (one-tailed permutation test, r>0.14). Left: 25-50 Hz power differences (DE with face minus DE without face). ROI contrast R FFA p=0.023; one-tailed paired t-test (7 subjects, t(6) = 2.52). Right: fusiform face area (red). C. Upper row: 25-50 Hz average power differences between DEs with and without a spatial setting (6 subjects, t(5) > 2.57). Right: right posterior parietal cortex. Middle row: movement vs. no movement (7 subjects, t(6) > 2.45). Right: superior temporal sulcus. Bottom row: speech vs. no speech (7 subjects, t(6) > 2.45). Right: Wernicke’s area. Two-tailed paired t-tests.
Predicting Dream Experience
To further understand the relationship between neural activity and dream experience, researchers have explored the possibility of predicting whether a person is dreaming based on their brain activity patterns.
Figure 5. A. Awakenings were performed in NREM when neural activity surpassed a bispectral threshold in low- frequency (LF; 0.5-4.5 Hz) and high-frequency (HF; 18-25 Hz) power over the posterior hot zone. B. DE trials had significantly lower LF activity and significantly higher HF activity in DE compared to NE prediction trials. The bottom and top of the boxes show the 25th and 75th percentile (the lower and upper quartiles), the inner band shows the median, and the whiskers show the upper and lower quartiles +/− 1.5 * IQR (inter quartile range). Asterisks indicate significant differences (p=0.001; two-tailed t-test) between CE and NCE trials. C. Prediction accuracy for DE (55) and NE (27) trials. Asterisks indicate significant differences (p<0.001; one sample t-test two-tailed) between CE and NCE prediction accuracy and chance (50%). D. J Thorac Dis. 2017 Sep;9(9):2732-2735.
The study revealed that dream experience trials had significantly lower low-frequency (LF) activity and significantly higher high-frequency (HF) activity compared to no dream experience trials. This suggests that specific patterns of neural activity can be used to predict the presence or absence of dreaming.
Table 1: Brain Activity and Dream Experience
| Brain Activity | Dream Experience (DE) | No Dream Experience (NE) |
|---|---|---|
| Low-Frequency (LF) Activity | Lower | Higher |
| High-Frequency (HF) Activity | Higher | Lower |
These findings contribute to our understanding of the neural basis of consciousness and the complex relationship between brain activity and subjective experience during sleep.