Thalamic influence on slow wave slope renormalization during sleep

OBJECTIVE Slow waves are thought to mediate an overall reduction in synaptic strength during sleep. The specific contribution of the thalamus to this so-called synaptic renormalization is unknown. Thalamic stroke is associated with daytime sleepiness, along with changes to sleep electroencephalography and cognition making it a unique "experiment of nature" to assess the relationship between sleep rhythms, synaptic renormalization, and daytime functions. METHODS Sleep was studied by polysomnography and high-density electroencephalography over 17 nights in patients with thalamic (n = 12) and 15 nights in patients with extra-thalamic (n = 11) stroke. Sleep electroencephalography overnight slow wave slope changes, and their relationship with subjective daytime sleepiness, cognition, and other functional tests were assessed. RESULTS Thalamic and extra-thalamic patients did not differ in terms of age, sleep duration or apnea-hypopnea index. Conversely, overnight slope changes were reduced in a large cluster of electrodes in thalamic compared to extra-thalamic stroke patients. This reduction was related to increased daytime sleepiness. No significant differences were found in other functional tests between the two groups. INTERPRETATION In patients with thalamic stroke a reduction in overnight slow wave slope change and increased daytime sleepiness was found. Sleep- and wake-centered mechanisms for this relationship are discussed. Overall, this study suggests a central role of the thalamus in synaptic renormalization. This article is protected by copyright. All rights reserved.