How a Strong (Pungent) Smell Can Override Amygdala Driven Emotional Arousal and Reduce Middle of the Night Insomnia

Hyperarousal is one of the most common and well‑established drivers of middle‑of‑the‑night awakenings in chronic insomnia.

During sleep, the amygdala should normally settle into a low‑reactive state, but in insomnia it remains sensitised to both internal cues, such as thoughts, bodily sensations, and emotional memories and external cues like faint sounds or odours.

Instead of returning to baseline after a brief disturbance, the amygdala continues to signal threat or emotional importance, activating connected regions such as the anterior cingulate (the brain's ‘threat/monitoring system’) and orbitofrontal cortex (the brain's ‘evaluation and decision-making system’).

This sustained limbic activation keeps the brain in a vigilant, high‑alert mode that blocks the normal transition back into sleep. As a result, even minor stimuli can trigger abrupt awakenings followed by prolonged difficulty resuming sleep, creating the characteristic pattern of nocturnal hyperarousal seen in chronic insomnia. [1-2]

Obstructive sleep apnoea

It is also important to note the effect obstructive sleep apnoea (OSA) has in hyperarousal too.

Obstructive sleep apnoea (OSA) can trigger the same amygdala‑driven hyperarousal seen in chronic insomnia, creating a powerful cycle of night‑time wakefulness. During normal sleep, the amygdala should settle into a low‑reactive, emotionally quiet state, but repeated apnoeic events act like internal alarm signals - brief drops in oxygen - surges in CO₂, and abrupt autonomic activation. Over time, these physiological shocks sensitise the amygdala to both internal cues, and external cues.

Instead of returning to baseline after each disturbance, the amygdala continues to signal threat or emotional importance, again activating the anterior cingulate and orbitofrontal cortex. This sustained limbic activation keeps the brain in a vigilant, high‑alert mode that blocks the normal transition back into sleep. As a result, even minor stimuli can trigger abrupt awakenings followed by prolonged difficulty resuming sleep, producing the same nocturnal hyperarousal pattern seen in chronic insomnia—and in many cases, OSA becomes a direct driver of it. [3]

The STOP BANG assessment can help determine if you have symptoms of OSA.

Strong Smells

A Strong smell can interrupt hyperarousal awakenings by sending a rapid, high‑intensity olfactory signal directly into the amygdala, forcing it to process a new sensory input instead of continuing the emotional‑arousal loop that keeps you awake. This ‘override’ works because smell is the only sensory pathway that reaches the amygdala without thalamic filtering, allowing odours to modulate emotional circuits almost instantaneously.

Research in the Journal of Neuroscience (Krusemark et al., 2013) shows that anxiety and heightened arousal amplify amygdala responsiveness to olfactory stimuli, while studies of sleep‑disordered breathing (Chamberlin et al., 2013) demonstrate that repeated arousals can further sensitize these limbic pathways. Together, they explain how an intense odour -pleasant or pungent - can momentarily redirect amygdala activity, interrupt the wake‑worry‑arousal cycle and help the brain reset toward sleep. [4]

Chronic Insomnia

People with chronic insomnia often begin to associate their bed with being awake, worrying, or trying hard to sleep - a form of conditioned arousal. Stimulus control, one of the cornerstone behavioural techniques in Cognitive Behavioural Therapy for Insomnia (CBT‑I, retrains the brain so that the bed once again becomes a cue for sleep rather than wakefulness.

Stimulus control is often derailed by hyperarousal, which keeps people lying awake, ruminating, and escalating into distress. A brief, intense smell can act as a fast sensory reset that interrupts the amygdala‑driven emotional surge, reduces the urge to mentally ‘do something’, and makes it easier to follow the core CBT‑I rule: ‘if you’re awake and alert, get out of bed’. By breaking the panic‑like awakening before it spirals, this simple bottom‑up intervention helps keep stimulus control intact and preserves the behavioural structure that CBT‑I depends on.

So, for stimulus control to work as intended, the behavioural rule comes first: ‘If awake and alert, get out of bed’.

The pungent‑smell ‘reset’ is most effective after getting out of bed, not while staying in it.

Used after leaving the bed, it:

• interrupts the emotional spike

• reduces the ‘do something mental’ urge

• helps the person settle enough to follow the next step (quiet activity until sleepy)

But, if used whilst still in bed, it:

• does interrupt arousal - ok

• but reinforces staying awake in bed, which is the opposite of stimulus control

CBT‑I is fundamentally about retraining conditioned associations. Every minute awake in bed strengthens the wrong association. Every minute awake out of bed strengthens the right one.

Cognitive Behaviour Therapy

Cognitive Behavioural Therapy for Insomnia (CBT-I) is widely recognised as the "gold standard" first-line treatment for chronic insomnia, as recommended by leading medical bodies such as the American College of Physicians. This structured, non-pharmacological therapy works by targeting and changing problematic behaviours and thoughts related to sleep. Notably, CBT-I has demonstrated a 70–80% success rate in improving sleep, according to clinical studies published by the American College of Physicians, which lends strong credibility to its effectiveness.

References

[1] The Journal of Neuroscience. (2013). When the Sense of Smell Meets Emotion: Anxiety-State-Dependent Olfactory Processing and Neural Circuitry Adaptation https://www.jneurosci.org/content/33/39/15324?utm_source=copilot.com

[2] National Library of Medicine. (2010). The hyperarousal model of insomnia: a review of the concept and its evidence. https://pubmed.ncbi.nlm.nih.gov/19481481/

[3] National Library of Medicine. (2014). Brain circuitry mediating arousal from obstructive sleep apnea. https://pmc.ncbi.nlm.nih.gov/articles/PMC4259289/?utm_source=copilot.com

[4]. The Journal of Neuroscience. (2013). When the Sense of Smell Meets Emotion: Anxiety-State-Dependent Olfactory Processing and Neural Circuitry Adaptation. https://www.jneurosci.org/content/33/39/15324

[5]. Science Direct. (2026). Implementation of stimulus control and sleep restriction therapy for insomnia: standard definitions and best practices. https://www.sciencedirect.com/science/article/abs/pii/S2589979125000228