Sleep deprivation and dendritic architecture: a systematic review and meta-analysis.

Sleep is a well-conserved behavior, yet the functions of sleep remain uncertain and controversial. The synaptic homeostasis hypothesis proposes a central role for sleep, predicting that global synaptic strength increases after sleep deprivation (SD). Many studies have found changes in neuronal architecture following SD, but findings vary widely. This study provides the first systematic review of the effects of SD on dendritic architecture. We searched MEDLINE and Web of Science for rodent studies which reported dendritic spine density and/or dendritic length after SD compared to control. A total of 5090 records were screened, yielding 30 full texts for this meta-analysis. Studies were individually small and suffered from poor reporting regarding handling of data. Variability in structural measures was high between studies, indicating substantial methodological differences. We therefore developed a protocol for quality assessment of SD and spine/dendrite analysis, which can serve as framework for future studies. We also simulated experiments based on the included studies and showed that small sample sizes result in an overestimation of effect sizes. We conclude that current evidence does not support an effect from 24 hours or less of SD on dendritic structure. Chronic SD protocols of 72 hours or longer causes a decrease in Cornu Ammonis 1 (CA1), both in spine density and dendritic length, but it remains unclear whether this is a result of sleep loss or protocol-induced stress. This study provides a valuable overview of a field marked by conflicting findings, and clarifies which issues prevent robust conclusions from being drawn. Further progress in this field requires more robust handling of multi-level data, clearer guidelines on dendritic structure measurements and substantially higher-powered studies.