Odors enhance slow-wave activity in non-rapid eye movement sleep

Abstract

Most forms of suprathreshold sensory stimulation perturb sleep. In contrast, presentation of pure olfactory or mild trigeminal odorants does not lead to behavioral or physiological arousal. In fact, some odors promote objective and subjective measures of sleep quality in humans and rodents. The brain mechanisms underlying these sleep-protective properties of olfaction remain unclear. Slow oscillations in the electroencephalogram (EEG) are a marker of deep sleep, and K complexes (KCs) are an EEG marker of cortical response to sensory interference. We therefore hypothesized that odorants presented during sleep will increase power in slow EEG oscillations. Moreover, given that odorants do not drive sleep interruption, we hypothesized that unlike other sensory stimuli odorants would not drive KCs. To test these hypotheses we used polysomnography to measure sleep in 34 healthy subjects (19 women, 15 men; mean age 26.5 ± 2.5 yr) who were repeatedly presented with odor stimuli via a computer-controlled air-dilution olfactometer over the course of a single night. Each participant was exposed to one of four odorants, lavender oil (n = 13), vetiver oil (n = 5), vanillin (n = 12), or ammonium sulfide (n = 4), for durations of 5, 10, and 20 s every 9-15 min. Consistent with our hypotheses, we found that odor presentation during sleep enhanced the power of delta (0.5-4 Hz) and slow spindle (9-12 Hz) frequencies during non-rapid eye movement sleep. The increase was proportionate to odor duration. In addition, odor presentation did not modulate the occurrence of KCs. These findings imply a sleep-promoting olfactory mechanism that may deepen sleep through driving increased slow-frequency oscillations.

Local Targeted Memory Reactivation in Human Sleep

“…The local TMR effects on cortical sleep oscillations extend previous studies showing that olfactory stimulation during sleep enhances SWA [23,44]. We found that SWA increase was lower in the cued hemisphere and negatively correlates with memory for cued items (but not for uncued items).…”

Behavioral and Neurobiological Convergence of Odor, Mood and Emotion: A Review

“…Sleep plays a critical role in emotional regulation and memory consolidation (Yoo et al, 2007;Altena et al, 2016), and sleep is often impaired in normal and pathological ageing (Mander et al, 2017). Although odor detection is greatly reduced during NREM sleep in humans (Carskadon and Herz, 2004) and animal models (Barnes et al, 2011), odors presented during NREM sleep in humans modulate respiration (Arzi et al, 2010) and enhance NREM delta power (Perl et al, 2016), which could enhance sleep quality. Finally, sensory stimulation, including odor training, can improve sensory function in the elderly, which in turn can enhance cognitive functioning (Birte-Antina et al, 2018;Leon and Woo, 2018).…”

Targeting Arousal and Sleep through Noninvasive Brain Stimulation to Improve Mental Health

“…Auditory stimulation uses tones to modify cortical activity. In principle, all senses, including vision, hearing, scent [26], and touch, can be used for sensory stimulation [6], yet in humans auditory stimulation appears to be particularly well suited to modulate sleep. More specifically, auditory stimulation is the most reliable way to induce single slow oscillations (K-complexes) in humans [27][28][29].…”