A brain network called the default mode network (DMN), previously studied mainly in humans and primates, also exists in rats. The DMN in rats is broadly similar to that in nonhuman primates and humans, suggesting it is a fundamental feature of mammalian brains. The network appears to integrate sensory and emotional information to guide behavior in anticipation of changing environmental conditions, despite the distinct evolutionary paths of rodents and primates. The findings help clarify the DMN's core functions, which remain poorly understood in humans.
The default mode network (DMN), a set of brain regions active at rest, shows higher functional connectivity and stronger low-frequency fluctuations when people keep their eyes open (with or without a fixation point) than when they keep them closed. Although the overall connectivity patterns look similar across conditions, statistical comparisons reveal these differences. An order effect also appears: two eyes-closed sessions differ from each other. These findings suggest that having eyes open during rest may involve more non-specific visual gathering, evaluation, and mind wandering, and that researchers should carefully choose and order resting-state conditions in experimental designs.
People who more frequently recall their dreams have less cortical volume in the medial portion of the right fusiform gyrus and parahippocampal gyrus, as well as lower fractional anisotropy in the white matter fibers connected to those regions. These relationships were not affected by regular sleep. The findings provide direct evidence that brain structure is linked to individual differences in dream recall frequency.
Dream recall frequency and REM sleep percentage are linked to different brain functional networks. In 43 healthy adults, resting-state fMRI and polysomnography showed that both measures negatively correlated with multiple networks. Dream recall frequency was mainly associated with connectivity in the lateral visual network and thalamus, while REM sleep percentage was mainly associated with connectivity in frontoparietal networks and cerebellum. A time-of-day effect emerged: dream recall frequency had stronger coupling with the lateral visual network at night, and REM sleep percentage had stronger coupling with the cerebellum in the morning. The findings indicate that the neural substrates for dream recall and REM sleep are distinct.