Brain activity in sleep compared to wakefulness: A meta-analysis

Objective: Neuroimaging studies using a variety of techniques have been conducted in sleep to explore the changes in brain activity during the different sleep stages. The current study employed a quantitative meta-analytic technique in an attempt to integrate the findings from such studies. Methods: Using an updated version of the Activation Likelihood Estimation (ALE) method, individual meta-analyses were carried out on: 1) studies contrasting REM sleep and wakefulness, and 2) studies contrasting NREM sleep and wakefulness. Results: Based on the results of the current meta-analyses, a number of cortical and subcortical brain regions appear to be involved in sleep and sleep processes, with both decreases and increases noted across NREM and REM sleep. Specifically, areas of decreased activity comprised thalamic structures (pulvinar, dorsomedial thalamus) and frontal regions (inferior, superior, and middle frontal gyrus). Furthermore, increased and decreased activity was noted in the anterior cingulate during sleep. Conclusions: Despite limited overlap across these sleep stages among regions identified, consistent decreases were revealed in NREM sleep (thalamus) and REM sleep (frontal cortex) when compared to wakefulness. Such findings suggest that these regions may ultimately play a key role in the loss of consciousness characteristic of sleep. Further research is needed to determine if and how such activity may be related to dreaming