Fatigue and sleep disturbance following traumatic brain injury: A role for light therapy?

Fatigue and sleep disturbances are common and disabling symptoms following traumatic brain injury (TBI). They occur chronically, and impact significantly on the ability of individuals with these injuries to return to pre-injury function, as well as overall quality of life. The aetiology of these symptoms appears to be complex and most likely multifactorial in nature, involving the primary effects of mechanical neuronal injury, but also secondary factors such as depression, anxiety, and cognitive disturbance (particularly in the domain of attention). In the context of unclear aetiology, current understandings of fatigue and sleep disturbances have primarily relied on patient self-report, particularly for fatigue which is inherently a subjective complaint, but also for sleep disturbances. Identification of suitable objective measures for fatigue and sleep or their associated symptoms may assist in further understanding these complaints. Related to the limited understanding of these complaints following TBI, is the lack of well established treatment regimens. In theory, an optimal treatment of fatigue and sleep disturbance following TBI would involve focus on the symptoms themselves as well as their associated factors, such as depression and impaired attention. Recent research in the field of sleep and chronobiology, particularly research investigating the therapeutic applications of light exposure, suggests that light therapy may offer an efficacious modality for treatment of fatigue, sleep disturbance and associated symptoms in the TBI population. The aims of the current thesis were to: (1) assess the utility of objective assessment tools in order to aid further understanding of disturbances to sleep-wakefulness and sustained attention (i.e. psychomotor vigilance) performances following TBI; and (2) investigate in a randomised controlled trial, the efficacy of blue light therapy, in the treatment of fatigue and its related symptoms in patients with TBI. This was achieved across three separate studies. Specifically, study one investigated the utility of actigraphy as an objective measure of sleep following TBI. The findings of the study revealed significant associations between actigraphic and self-reported (diary) estimates of nocturnal total sleep time (TST) and daily TST in patients with TBI and healthy age- and gender- matched controls. While stronger associations between diary and actigraphy were observed in the control group, the magnitude of these associations did not differ significantly between groups. The study thus provided preliminary support for use of actigraphy as an objective assessment of sleep duration in the TBI population. In light of previous research that has demonstrated associations between vigilance/sustained attention and both fatigue and sleep disturbances in patients with TBI, study two compared psychomotor vigilance performance in patients with TBI and healthy age- and gender- matched controls using the Psychomotor Vigilance Task (PVT). The PVT was selected as a potentially useful objective measure in patients with TBI as it has been commonly used within the sleep science field and is well accepted for its sensitivity to sleep loss, circadian timing, and countermeasures for sleepiness. Consistent with past research, study two demonstrated that patients with TBI showed slower performances and increased attentional lapses relative to healthy controls. Distribution analyses additionally revealed that patients with TBI performed more slowly across the entire performance distribution, consistent with a generalised cognitive slowing. Depression, fatigue and daytime sleepiness were found to have varying impacts on aspects of psychomotor vigilance performance. Previous use of the PVT in TBI groups has been limited and the study highlighted the sensitivity of the PVT to sustained attention deficits in patients with TBI. Taken together, the findings of study one and two have implications for the ongoing assessment of sleep and performance deficits in patients with TBI, and have potential to provide greater understanding of fatigue and sleep complaints in this population. Finally, given the lack of efficacious treatments for fatigue and sleep disturbances following TBI, study three examined the efficacy of blue light therapy as a potential treatment of fatigue and its associated symptoms in patients with TBI. Blue light therapy was selected for use given prior research findings which have demonstrated its alerting, circadian phase shifting, and mood enhancing properties. In a sample of patients with TBI who had self-reported fatigue and sleep complaints, study three demonstrated the efficacy of daily, morning exposure (45 minutes) to blue light over a 4 week treatment period in alleviation of self-reported fatigue and daytime sleepiness. This is the first demonstration of efficacy for a non-pharmacological treatment of fatigue and daytime sleepiness in patients with TBI. These findings establish the basis for large-scale randomised controlled trials of light therapy for fatigue in TBI, and have important implications for enhancing rehabilitation participation and long-term quality of life following TBI.