Abstract
Nightmares are highly dysphoric dreams that are well-remembered upon awakening. Frequent nightmares have been associated with psychopathology and emotional dysregulation, yet their neural mechanisms remain largely unknown. Our neurocognitive model posits that nightmares reflect dysfunction in a limbic-prefrontal circuit comprising medial prefrontal and anterior cingulate cortices, hippocampus, and amygdala. However, there is a paucity of studies that used brain imaging to directly test the neural correlates of nightmares. One such study compared the regional homogeneity (ReHo) of resting-state functional magnetic resonance imaging blood-oxygen level-dependent signals between frequent nightmare recallers and controls. The main results were greater regional homogeneity in the left anterior cingulate cortex and right inferior parietal lobule for the nightmare recallers than for the controls. In the present study, we aimed to document the ReHo correlates of frequent nightmares using several nightmare severity measures. We acquired resting-state functional magnetic resonance imaging data from 18 frequent nightmare recallers aged 18–35 (3 males and 15 females) and 18 age- and sex-matched controls, as well as retrospective and prospective disturbed dreaming frequency estimates and scores on the Nightmare Distress Questionnaire. While there were inconsistent results for our different analyses (group comparisons, correlational analyses for frequency estimates/Nightmare Distress scores), our results suggest that nightmares are associated with altered ReHo in frontal (medial prefrontal and inferior frontal), parietal, temporal and occipital regions, as well as some subcortical regions (thalamus). We also found a positive correlation between retrospective disturbed dreaming frequency estimates and ReHo values in the hippocampus. These findings are mostly in line with a recent SPECT study from our laboratory. Our results point to the possibility that a variety of regions, including but not limited to the limbic-prefrontal circuit of our neurocognitive model, contribute to nightmare formation.
Highlights
Despite the clinical importance of diagnosing and treating nightmares (Gieselmann et al, 2019), the brain correlates of this enigmatic disorder are still largely unknown
Additional findings from this study presented in conferences are that (1) these results are independent of psychopathology (Marquis et al, 2019b) and habitual dream recall frequency (Marquis et al, 2019c) and (2) multiple regression analyses suggest a lateralization pattern by which dysphoric dream frequency correlates primarily with left-hemisphere regions, whereas nightmare distress correlates primarily with right-hemisphere regions (Marquis et al, 2019d)
Our groups did not differ on age, sex ratio, Beck Depression Inventory-II (BDI-II) and state-trait anxiety inventory (STAI) scores, and prospective dream recall frequency (p > 0.10)
Summary
Despite the clinical importance of diagnosing and treating nightmares (Gieselmann et al, 2019), the brain correlates of this enigmatic disorder are still largely unknown. Most studies of nightmare pathophysiology have focused on polysomnographically derived measures of sleep architecture (Germain and Nielsen, 2003; Nielsen et al, 2010b; Simor et al, 2012; Kis et al, 2014; Paul et al, 2015; Marquis et al, 2017; Blaskovich et al, 2019b), periodic leg movements (Germain and Nielsen, 2003), cardiac variability (Nielsen et al, 2010a; Simor et al, 2014; Perogamvros et al, 2019) or EEG metrics such as spectral power (Simor et al, 2013, 2014; Marquis et al, 2017; Blaskovich et al, 2019a), heartbeat-evoked potential (Perogamvros et al, 2019) and sleep spindle frequency and density (Nielsen et al, 2017, 2019; Picard-Deland et al, 2018a,b). Lesion studies point to alterations in temporal regions and in the basolateral amygdala as contributors to nightmares
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