Are sleep complaints following mild traumatic brain injury associated with changes in the characteristics of sleep slow waves?

Abstract

Slow waves (SW) are low frequency ( < 4 Hz) and high amplitude ( > 75 μ V ) waves that occur during non-rapid eye movement (NREM) sleep, and which are known to play a crucial role in synaptic plasticity and in the restorative function of sleep. In the present study, we sought to determine if changes in SW characteristics are observed after a mild traumatic brain injury (mTBI) and whether SW characteristics are associated with sleep complaints, which are reported by approximately 30–80% of individuals with mTBI. 34 mTBI subjects (mean age 34,2 ± 11,9 yrs) and 33 controls (mean age; 31,5 ± 11,4 yrs) matched for age, sex and education were included. Subjects with mTBI were tested on average 10,5 ± 10,4 weeks after their brain injury. All subjects underwent a laboratory polysomnography and filled out the Pittsburgh Sleep Quality Inventory (PSQI) and the Beck Depression Index (BDI). Student t -tests were used to compare groups on demographic characteristics, PSQI scores, BDI scores and sleep architecture. ANOVA with one repeated measure (sleep cycles (1 to 4)) were performed on C3 lead to compare groups for the following SW characteristics: density, amplitude, frequency, negative/positive phase duration and slope. Association between SW characteristics, clinical features, PSQI scores and BDI scores were measured in the mTBI group using Pearson partial correlations with age as a covariable. We found higher BDI scores in mTBI compared to control subjects ( t (52) = 6,1; p < 0,001), reflecting more depression symptoms in the mTBI group. Subjects with mTBI also reported more sleep disturbances on the PSQI questionnaire compared to control subjects ( t (52) = 6,3; p < 0,001). However, no significant group differences were found for sleep architecture and for SW characteristics. There were no significant correlations between SW characteristics, clinical features, PSQI and BDI scores. Individuals with mTBI report depression symptoms and sleep disturbances, but these symptoms were not associated with altered sleep architecture or SW characteristics. Supported by the Canadian Institutes of Health Research and the Fonds de recherche du Québec – Santé.