# Brain localization and morphological changes in NREM parasomnias. A systematic review study

## TL;DR

This study reviews brain activity and structure in people with NREM parasomnias, finding sleep-wake dissociation and specific brain region changes.

## Contribution

The study identifies sleep-state dissociation as a core trait in NREM parasomnias, with specific brain regions involved.

## Key findings

- Increased delta and theta EEG power precedes clinical episodes in NREM parasomnias.
- Cortico-cortical sleep-state dissociation occurs in NREM, REM sleep, and wakefulness.
- Reduced grey-matter volume in cingulate regions is linked to mixed NREM parasomnias.

## Abstract

Individuals with NREM parasomnias exhibit abnormal slow-wave activity and fragmented sleep. Sleep-state dissociation is the prevailing concept of NREM parasomnia-episodes; typically emerging from N3/N2 stages of NREM sleep’s first cycle at the turning-point of deep sleep and arousal. While these relations provide a frame to understand these conditions, their mechanism and brain-topography remain unclear.

We performed a systematic search of the literature (1/01/2015-20/06/2024) on brain-topographies and morphological changes based on neurophysiological and imaging studies in patients with NREM parasomnias.

It was shown that immediately preceding clinical episodes, the EEG spectral power of delta and theta frequency-bands increased in parallel with its reduction in the cingulate, motor, and premotor/supplementary motor cortices. Far from clinical episodes, in NREM and REM sleep as well as in wakefulness, a cortico-cortical sleep-state dissociation occurred, too. In addition, the partial arousals of episodes evolved from ‘deeper’ sleep with lower-amplitude slow waves, compared to episode-free arousals of the same people with NREM parasomnias. A single MR-morphology study revealed decreased grey-matter volume in the left dorsal posterior cingulate and mid-cingulate cortices in patients with mixed NREM parasomnias.

Based on recent research, the state-dissociation evidenced in clinical episodes might characterize each vigilance state of people with NREM parasomnias, even outside the episodes, making sleep-wake dissociation a trait-like core feature of NREM parasomnias. The anterior cingulo-frontal regions seem to have central roles.

PROSPERO registration ID: CRD42024552562.

The online version contains supplementary material available at 10.1007/s11325-025-03492-z.