Relative regional cerebral metabolic rate of glucose in rapid eye movement (REM) sleep and wakefulness was explored in combat veterans with and without PTSD, using positron emission tomography. Hypermetabolism in brain regions involved in arousal regulation, fear responses, and reward processing persist during REM sleep in combat veterans with PTSD.
"Studies have demonstrated that neural substrate (i.e., amygdala, hippocampus, medial prefrontal cortex) activity governing arousal and threat response is in fact exaggerated in anxiety disorders, such as PTSD (Rauch et al., 2003, 2000; Stein and Nesse, 2011). As such, the present findings revealing decreased rCMRglc in these structures suggest that REM sleep, as well as wakefulness, may be compromised following exposure to mTBI, independent of the effects of PTSD symptomology (Germain et al., 2013). Future research should continue to focus on the neurobiological sequelae of blast exposure, relative to other types of mTBI and after adjusting for PTSD, during wakefulness, REM sleep, and NREM sleep. "
[Show abstract][Hide abstract] ABSTRACT: Traumatic Brain Injury (TBI), a signature wound of Operations Enduring and Iraqi Freedom, can result from blunt head trauma or exposure to a blast/explosion. While TBI affects sleep, the neurobiological underpinnings between TBI and sleep are largely unknown. To examine the neurobiological underpinnings of this relationship in military veterans, [(18)F]-fluorodeoxyglucose positron emission tomography (FDG PET) was used to compare mTBI-related changes in relative cerebral metabolic rate of glucose (rCMRglc) during wakefulness, Rapid Eye Movement (REM) sleep, and non-REM (NREM) sleep, after adjusting for the effects of posttraumatic stress (PTS). Fourteen Veterans with a history of Blast Exposure and/or mTBI (B/mTBI) (age 27.5±3.9) and eleven Veterans with no history (No B/mTBI) (age 27.7±3.8) completed FDG PET studies during wakefulness, REM sleep, and NREM sleep. Whole-brain analyses were conducted using Statistical Parametric Mapping (SPM8). Between group comparisons revealed that B/mTBI was associated with significantly lower rCMRglc during wakefulness and REM sleep in the amygdala, hippocampus, parahippocampal gyrus, thalamus, insula, uncus, culmen, visual association cortices, and midline medial frontal cortices. These results suggest alterations in neurobiological networks during Wakefulness and REM sleep subsequent to B/mTBI exposure, may contribute to chronic sleep disturbances, and differ in individuals with acute symptoms.
[Show abstract][Hide abstract] ABSTRACT: Evening chronotypes exhibit increased rates of affective dyregulation and sleep disturbances (e.g., insomnia and nightmares). Such symptoms are common to military veterans with posttraumatic stress disorder (PTSD); however, the influence of chronotype on this population remains unknown. We examined behavioral, psychological, and neural correlates of chronotype in 36 combat-exposed military veterans with varying degrees of posttraumatic stress symptomatology. We employed FDG-PET to assess neural activity across wakefulness and rapid eye movement (REM) sleep. We used polysomnography and diaries to monitor sleep, and a self-report survey to measure chronotype. Eveningness was associated with greater lifetime PTSD symptoms, more disturbed sleep, and more frequent and intense nightmares. Eveningness was also associated with greater brain activity in posterior cingulate/precuneus and brainstem regions across wakefulness and REM sleep, overlapping with regions related to arousal and REM sleep generation. Chronotype may be an important correlate of neural activity in REM sleep-generating and/or arousal regulatory regions among combat-exposed veterans with PTSD symptoms. Further investigations of the role of chronotype in PTSD are warranted.
[Show abstract][Hide abstract] ABSTRACT: Isolated reports have long suggested a similarity in content and thought processes across mind wandering (MW) during waking, and dream mentation during sleep. This overlap has encouraged speculation that both "daydreaming" and dreaming may engage similar brain mechanisms. To explore this possibility, we systematically examined published first-person experiential reports of MW and dreaming and found many similarities: in both states, content is largely audiovisual and emotional, follows loose narratives tinged with fantasy, is strongly related to current concerns, draws on long-term memory, and simulates social interactions. Both states are also characterized by a relative lack of meta-awareness. To relate first-person reports to neural evidence, we compared meta-analytic data from numerous functional neuroimaging (PET, fMRI) studies of the default mode network (DMN, with high chances of MW) and rapid eye movement (REM) sleep (with high chances of dreaming). Our findings show large overlaps in activation patterns of cortical regions: similar to MW/DMN activity, dreaming and REM sleep activate regions implicated in self-referential thought and memory, including medial prefrontal cortex (PFC), medial temporal lobe structures, and posterior cingulate. Conversely, in REM sleep numerous PFC executive regions are deactivated, even beyond levels seen during waking MW. We argue that dreaming can be understood as an "intensified" version of waking MW: though the two share many similarities, dreams tend to be longer, more visual and immersive, and to more strongly recruit numerous key hubs of the DMN. Further, whereas MW recruits fewer PFC regions than goal-directed thought, dreaming appears to be characterized by an even deeper quiescence of PFC regions involved in cognitive control and metacognition, with a corresponding lack of insight and meta-awareness. We suggest, then, that dreaming amplifies the same features that distinguish MW from goal-directed waking thought.
Frontiers in Human Neuroscience 07/2013; 7:412. DOI:10.3389/fnhum.2013.00412 · 2.99 Impact Factor
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