Positron emission tomography (PET) studies revealed a general decrease in regional cerebral blood flow during deep NREM sleep compared to wakefulness. Conversely, at the cortical level, a significant sleep-induced modulation of signal properties such as latency and amplitude of the ERP signal, or firing rates of single neurons has been documented in some studies, while a recent animal study has found preserved auditory response in primary auditory cortex. Both animal electrophysiology research and human event-related potential (ERP) studies have found little change in prethalamic transmission of auditory signals. Indeed a number of studies have addressed the issue of sensory processing during sleep. Thus, comparing sensory brain responses during the awake state and sleep could point to the neuronal correlates of sensory perception and awareness in the human brain. Sleep, and specifically the slow-wave, non- rapid eye movement stage (NREM), is linked to a massive disruption in conscious awareness. To that end the phenomenon of naturally occurring sleep provides a powerful and potentially informative experimental system. However, these types of studies do not address the question of how the responses to these stimuli change as participants move from a conscious to non-conscious states. The search for neuronal correlates of sensory percepts typically examines changes in awareness to different categories of sensory stimuli (including meaningless or noisy stimuli) while subjects are awake. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Ĭompeting interests: The authors have declared that no competing interests exist. įunding: This work was funded by the EU FP7 VERE, ICORE program (ISF 51/11), the EU-Flagship, Human Brain Project grants and the Helen and Martin Kimmel award to RM. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.ĭata Availability: Data Availability: the fMRI data (maps of Figs 2 and 3), and detailed beta values for all regions of interest (Figs 4 and 5) are available via figshare. Received: FebruAccepted: Published: June 16, 2016Ĭopyright: © 2016 Wilf et al. PLoS ONE 11(6):Įditor: Vladyslav Vyazovskiy, University of Oxford, UNITED KINGDOM Our results suggest that the decreased awareness to linguistic auditory stimuli during NREM sleep is linked to diminished activity in high order processing stations.Ĭitation: Wilf M, Ramot M, Furman-Haran E, Arzi A, Levkovitz Y, Malach R (2016) Diminished Auditory Responses during NREM Sleep Correlate with the Hierarchy of Language Processing. In addition to an overall activation decrease in language processing regions in superior temporal gyrus and IFG, those areas manifested a loss of semantic selectivity during NREM sleep. Specifically, the auditory thalamus showed similar activation levels during sleep and waking states, primary auditory cortex remained activated but showed a significant reduction in auditory responses during sleep, and the high order language-related representation in inferior frontal gyrus (IFG) cortex showed a complete abolishment of responses during NREM sleep. During non-rapid eye movement (NREM) sleep, we found diminishing brain activation along the hierarchy of language processing, more pronounced in higher processing regions. Participants were exposed to three types of auditory stimuli: scrambled sounds, meaningless word sentences and comprehensible sentences. Sleep staging was based on heart rate measures validated independently on 20 participants using concurrent EEG and heart rate measurements and the results were confirmed using permutation analysis. Ten participants were scanned using functional magnetic resonance imaging (fMRI) during the waking state and after falling asleep. To quantitatively map the nature of sleep-induced modulations in sensory responses we presented participants with auditory stimuli possessing different levels of linguistic complexity. Natural sleep provides a powerful model system for studying the neuronal correlates of awareness and state changes in the human brain.
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