Cerebral dominance, sleep and dream phenomena

EEG correlates of emotions in dream narratives from typical young adults and individuals with autistic spectrum disorders

The relationship between emotional dream content and Alpha and Beta REM sleep EEG activity was investigated in typical individuals and in Autistic Spectrum Disorders (ASD). Dream narratives of persons with ASD contained fewer emotional elements. In both groups, emotions correlated positively with slow Alpha (8.0-10.0 Hz) spectral power over parieto-occipital and left central regions, as well as with a right occipital EEG asymmetry. Slow Alpha activity in ASD individuals was lower over midline and parasagittal areas and higher over lateral areas compared to controls. Both groups displayed a right-biased slow Alpha activity for midparietal and occipital (significantly higher in control) sites. Results indicate that Alpha EEG activity may represent a neurophysiological substrate associated with emotional dream content. Distinctive Alpha EEG patterns and asymmetries suggest that dream generation implies different brain connectivity in ASD.

Hemispheric lateralization of the EEG during wakefulness and REM sleep in young healthy adults

EEG recordings confirm hemispheric lateralization of brain activity during cognitive tasks. The aim of the present study was to investigate spontaneous EEG lateralization under two conditions, waking and REM sleep. Bilateral monopolar EEG was recorded in eight participants using a 12-electrode montage, before the night (5 min eyes closed) and during REM sleep. Spectral analysis (0.75-19.75 Hz) revealed left prefrontal lateralization on total spectrum amplitude power and right occipital lateralization in Delta activity during waking. In contrast, during REM sleep, right frontal lateralization in Theta and Beta activities and right lateralization in occipital Delta activity was observed. These results suggest that spontaneous EEG activities generated during waking and REM sleep are supported in part by a common thalamo-cortical neural network (right occipital Delta dominance) while additional, possibly neuro-cognitive factors modulate waking left prefrontal dominance and REM sleep right frontal dominance.

Visual dream content, graphical representation and EEG alpha activity in congenitally blind subjects

It is currently claimed that congenitally blind do not have visual imagery and are therefore unable to present visual contents in their dreams. The aim of our study was to quantitatively evaluate the existence of visual imagery in born-blind dreams and to correlate it with objective measures, such as sleep EEG frequency components, namely with alpha attenuation (regarded as an indicator of visual activity), and graphical analysis of dream pictorial representations. The investigation was carried out via simultaneous recordings of dream reports and polysomnography, during nocturnal sleep at volunteers' homes; scheduled regular awakenings during the night provided the data for dream and EEG analysis. In the morning, subjects were asked to make a drawing of their dream images. Congenitally blind (n=10) were comparable to normal sighted subjects (n=9): the two groups presented equivalent visual activity indices, and no differences in the analysis of graphical representation of dreaming imagery. However, blind subjects presented a lower rate of dream recall than sighted (27% versus 42%). Both groups had significant negative correlation between Visual Activity Index (VAI) and alpha power in the central and occipital O2 derivations (blind: C4: r=-0.615, P<0.005; O2: r=-0.608, P<0.006; sighted: C4: r=-0.633, P<0.01; O2: r=-0.506, P<0.05). This correlation was weaker for the blind in O1 (r=-0.573, P<0.05) and non-existent for the sighted. Blind individuals have significantly lower alpha activity in the central derivation. In conclusion, the congenitally blind have visual content in their dreams and are able to draw it and, as expected, their VAI is negatively correlated with EEG alpha power.

REM sleep dream mentation in right hemispherectomized patients

Investigations of dream mentation in brain damaged patients have shed some light on the controversial issue of cerebral lateralization of dreaming. To examine further the relationships between brain function and dreaming, we studied REM sleep dream recall and content in four patients having undergone right functional or anatomical hemispherectomy and eight matched control subjects. Patients were found to have the capacity to report dreams to much the same extent as control subjects. Further, the patients' dream content was overall similar to that of the control subjects. The results provide strong evidence that dreaming is not a right-hemisphere function, and that the left hemisphere may be more critical for the generation of dreams. In addition, some characteristics of hemispherectomized patients' dream content (characters, smells) are consistent with the possibility that a history of epilepsy may influence REM sleep imagery over the long term.