Abstract
Despite normal sleep timing and duration, Egr3-deficient (Egr3−/−) mice exhibit electroencephalographic (EEG) characteristics of reduced arousal, including elevated slow wave (1–4 Hz) activity during wakefulness. Here we show that these mice exhibit state-dependent instability in the EEG. Intermittent surges in EEG power were found in Egr3−/− mice during wakefulness and rapid eye movement sleep, most prominently in the beta (15–35 Hz) range compared to wild type (Egr3+/+) mice. Such surges did not coincide with sleep onset, as the surges were not associated with cessation of electromyographic tone. Cortical processing of sensory information by visual evoked responses (VEP) were found to vary as a function of vigilance state, being of higher magnitude during slow wave sleep (SWS) than wakefulness and rapid eye movement sleep. VEP responses were significantly larger during quiet wakefulness than active wakefulness, in both Egr3−/− mice and Egr3+/+ mice. EEG synchronization in the beta range, previously linked to the accumulation of sleep need over time, predicted VEP magnitude. Egr3−/− mice not only displayed elevated beta activity, but in quiet wake, this elevated beta activity coincides with an elevated evoked response similar to that of animals in SWS. These data confirm that (a) VEPs vary as a function of vigilance state, and (b) beta activity in the EEG is a predictor of state-dependent modulation of visual information processing. The phenotype of Egr3−/− mice indicates that Egr3 is a genetic regulator of these phenomena.
Highlights
Sensory evoked potentials are a rich source of information for quantifying the processing of sensory information by the central nervous system
The early growth response 3 (Egr3)−/− mice exhibited irregular surges in EEG amplitude typical for sleep onset, a surge that did not coincide with EMG quiescence, which is a behavioral marker for sleep onset (Figures 2A–C)
Genotype-dependent epoch-by-epoch EEG power fluctuations in the delta, theta and beta ranges were modulated as a function of vigilance state (Table 1); all were elevated in in Egr3−/− mice compared to Egr3+/+ mice
Summary
Sensory evoked potentials are a rich source of information for quantifying the processing of sensory information by the central nervous system. Deep SWS exhibits a further elevated magnitude of evoked potential relative to light SWS characterized by synchronized burst firing of large number of cortical cells (Nielsen-Bohlman et al, 1991) This form of modulation is specific to SWS (NielsenBohlman et al, 1991). During QW, slow oscillations in the local field potential (LFP) can be detected in individual barrels of the primary somatosensory cortex while other somatosensory barrels continue to exhibit wake-like LFPs (Rector et al, 2009) These local SWS states in the rodent barrel cortex have been important to our understanding of state-dependent modulation of somatosensory information processing. The neurobiological underpinnings of this local sleep state still remain uncertain
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