Study of Sleep Patterns Might Advance Our Knowledge on Alertness in Traumatic Brain Injury

Abstract

Traumatic brain injury (TBI) is defined as "an alteration in brain function, or other evidence of brain pathology, caused by an external force" [1]. Although the precise incidence and prevalence of TBI is not known due to the lack of consistent epidemiological data [2], between 3.6 and 5.3 million individuals in the United Statesare living with TBIrelated consequences [3]; sleep-wake neurobehavioral impairments (i.e., diminished alertness and inability to sustain attention) are among the most commonly reported [4,5]. Thus far, significant advances in sleep and TBI researchhas uncovered an association between brain injury and the delineation of the arousal system, with a raised interest in the past few years to the pattern of sleep-wake organization.Loss of consciousness (LOC) in TBI occurs due to electrophysiological disruption of the ascending reticular activating system, a fundamental structure that maintains tonic arousals as a prelude to alertness [6]. Urakami simultaneously used electroencephalography (EEG) and magnetoencephalography in patients with chronic diffuse axonal injury (i.e. a pattern of brain damage characterized by lesion in the corpus callosum and dorsolateral brain stem accompanied by widespread damage in the white matter in patients with LOC) [7] and found that, in the acute stage post injury, both the frequency of fast spindles and cortical activation source strength were significantly lower in patients with TBI than in healthy controls; the alpha activity reflected the severity of disturbed consciousness [8]. In that study, the presence of sleep spindles was found to serve as an indicator of recovery in the chronic phase after injury [8]. Similarly, Cologan and colleagues proposed that the presence of EEG patterns resembling normal human sleep [9] (i.e. well-structured patterns of non rapid eye movement and/or rapid eye movement (REM) sleep)can be markers of a favorable outcome after brain injury [10]. Moreover, the quality and quantity of spindles can provide a new index of the severity of thalamocortical injury, in accordance with brain imaging studies showing the correlation between the extent of thalamus damage and behavioral disability and outcome in disorders of consciousness [10][11][12][13].Gosselin and colleagues observed increased delta and decreased alpha activity during wakefulness in patients with mild TBI and proposed sleep intrusions in the waking state might indicate continuous sleep inertia, manifesting as fatigue and impaired functioning [14]. The clinical significance of the utility of EEG in TBI is reflected in a recent study by Teel et al. [15].While concussed participants passed all clinical concussion testing tools, they showed path physiological dysfunction with evaluation of EEG variables,supporting the hypothesis of diminishedbrain resources to compensate appropriately during activity [15].The results of the study areparticularly relevant to clinicians who make return-toplay or return-to-work decisions (i.e. in sport, first respondents, and other occupations requi...