NEW YORK (Reuters Health) – Nightmares occurring during non-rapid eye movement (NREM) sleep might be related to bursts of brain activity called spindles in people who are prone to the nocturnal disturbances, researchers have found.
In an article online November 3 in Sleep Medicine, Dr. Tore Nielsen and colleagues at the University of Montreal, Canada, note that sleep spindles are “linked to both pathophysiology and sleep-dependent memory consolidation, but they have not yet been evaluated in frequent nightmare recallers.”
To investigate, the team recorded and evaluated morning naps in 38 people with frequent idiopathic nightmares and 25 matched controls. A custom spindle detector assessed NREM sleep stage 2 (N2) sleep spindles on six EEG derivations.
Compared with controls, the nightmare group had a longer and a marginally greater proportion of N2 sleep. They also had a lower-than-normal density of slow (11-13 Hz) spindles in most EEG derivations, a higher density of fast (14-16 Hz) spindles in frontal derivations, and an elevated fast-spindle oscillatory frequency.
As to dream content, say the researchers, the nightmare group “showed positive correlations between slow spindle density and dreamed fear and word count – and negative correlations with dreamed positive-emotion.” Controls showed opposite trends. These dreaming attributes “may be related to spindles in a state-specific manner.”
Thus, “the fact that these spindle/dreaming relationships were either absent or opposite . . . for the control group further supports the notion that the groups differed in how spindles are implicated in state-related mechanisms,” the team writes.
One limitation of the study, they concede, is that “no actual nightmare episodes occurred during our monitored naps, which may mean that the intensity of fearful emotions and the sleep structure recorded were not entirely representative of the habitual dreams and sleep of frequent nightmare recallers.”
Moreover, in an email to Reuters Health, Dr. Nielsen cautioned that as “these findings constitute brand-new discoveries, it would be premature to draw firm conclusions. But if they are replicated independently, they would contribute to a more complete understanding of how and why some individuals become prone to nightmares.”
“Because we know that N2 sleep spindles are associated with, if not central to, memory consolidation,” he concluded, “the spindle anomalies that we documented for nightmare-prone subjects (fewer slow spindles, ‘faster’ fast spindles) might serve as biomarkers of a basic dysfunction of memory mechanisms afflicting these individuals – possibly mechanisms that process emotional memories.”
SOURCE: http://bit.ly/2mZke1E
Sleep Med 2017.
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