Arousal Thresholds: Exploring the Sensitivity to Being Awakened During Different Stages

Whether or not you’re a heavy or light sleeper may be related to your arousal threshold. Explore what can influence how easily you wake during the night.

WEB-1057 – Arousal Thresholds Exploring the Sensitivity to Being Awakened During Different Stages

Some people can wake up at the drop of a hat, while others can sleep through five alarms. Our sensitivity to being awoken is tied to our arousal threshold, or what is needed in order to wake up. Even more, arousal thresholds vary not only by person but also by the stage of sleep you’re in.  

What is the Arousal Threshold? 

The arousal threshold refers to the amount of respiratory effort needed to trigger an arousal from sleep—the lower the threshold, the less respiratory work that is required in order to wake up. In some cases, an arousal threshold is used to refer to how strong a stimulus must be to wake someone up; a high arousal threshold means it takes a strong stimulus to be awoken and a lot of respiratory effort to transition out of sleep.  
 
Essentially, those with a low arousal threshold are more likely to be awoken during the night and are often referred to as light sleepers. Conversely, those with a high arousal threshold are also known as heavy sleepers because it takes a lot to wake them up.  
 
Many things can affect your arousal threshold, including: 

  • How long you were awake. The longer you have been awake, the more deeply you may sleep when you finally get a chance to rest. 

  • Your sleep stage. Different stages of sleep have different arousal thresholds, with light sleep (the first few sleep stages) having a lower threshold than deep sleep and REM sleep.  

  • Stress levels. Those who are stressed tend to have more disturbed sleep, and this may be because they have a lower arousal threshold. 

  • Age. As you age, it’s common to become a light sleeper and wake up more often during the night.  
     

How Arousal Thresholds Vary Throughout Sleep Stages

Throughout the night, you cycle through four different stages of sleep: N1, N2, N3, and REM sleep. The first three are part of non-rapid eye movement (NREM) sleep, while the last is rapid eye movement (REM) sleep. Each stage displays differences in muscle movement and brain activity, including differences in arousal threshold.  
 
One researcher found that the arousal threshold was highest during the N3 stage of sleep, which is also known as deep sleep. This finding makes sense since the name itself characterizes how, during this stage of sleep, you sleep more deeply and are harder to rouse. That’s not to say it’s impossible to be awoken during deep sleep, but those who wake during deep sleep may be more likely to experience sleep inertia because of the body’s desire to return to sleep.  
 
While N3 sleep has the highest threshold, stages N1 and N2 have the lowest, which are lighter stages that occur just as you’re drifting off to sleep. The arousal threshold of REM sleep falls between N3 and N1/N2.  

The Role of Sleep Spindles 

Sleep spindles are spontaneous rhythms in the brain, and researchers have found that the more sleep spindles someone generates, the less likely they are to wake up when loud noises and other nighttime distractions occur. In this way, sleep spindles and arousal thresholds may correlate—the more sleep spindles you have, the higher your arousal threshold.  
 
However, while the amount of sleep spindles can vary by person, for each person it’s stable. This means that the amount of sleep spindles you produce may be a factor of genetics that cannot be changed; if you’re a light sleeper, you may always be destined to be a light sleeper.  
 
There is one exception: sleep spindle activity may change as you get older. Specifically, research shows that sleep spindles in older adults occur less often, are smaller, and last for less time. This finding may explain why those who are older wake up more often during the night.  

Arousal Threshold and Sleep Apnea 

One area that is seeing increasing study is the connection between arousal thresholds and those with obstructive sleep apnea. This sleep disorder is characterized by episodes of stopping breathing during the night due to airway blockages that result in frequent arousals.  
 
One concern is that a low arousal threshold may prevent those with obstructive sleep apnea from achieving stable breathing. This is because increased ventilatory drive can activate muscles in the throat and keep the airways open—premature termination of sleep would prevent this muscle activation, creating unstable breathing. In this way, a low arousal threshold may contribute to sleep apnea. 
 
Research has found that those with sleep apnea and a low arousal threshold are less obese, more likely to be female, older, and more likely to have REM sleep-predominant sleep apnea. Additionally, a low arousal threshold is associated with poor PAP therapy compliance, which may be because those who wake up easily during the night take off their PAP mask so that they can go back to sleep. 
 
Based on these findings, not only may a low arousal threshold contribute to sleep apnea, but it may make someone’s treatment less successful.  

Tips for Sleeping More Soundly 

If you have a low arousal threshold, you may find yourself more easily woken up during the night. Many factors can play into how easily you wake up, including the number of sleep spindles you have, your health status, and your age. However, you do not have to resign yourself to a night of interrupted sleep. 
 
The key to a sounder night of sleep is keeping yourself in a state where distractions do not interfere—you may be unable to change your arousal threshold, but you can change how many distractions get through. 
 
Consider trying out these tips if you find yourself waking up frequently during the night.  

  • Block the lights. Light can be a significant disruptor of sleep simply because the brain interprets light as a sign of the day—if it senses light, it thinks that it’s time to wake up. Knowing this, do what you can to keep your bedroom dark throughout the night, such as using blackout curtains to block out the early morning sun or late-night headlights from traffic. You can also try using an eye mask to block out light from your bedroom or the hallway.  

  • Tone down the sounds. Sound is another key sleep disruptor, and if you don’t have the sleep spindles needed to block its impact, you need to take alternative precautions. Consider using earplugs to block out noise that you cannot control or use a sound machine to help mask any sudden sounds. 
     
  • Destress. Stress is associated with nighttime arousals, so do what you can during the day to lower your stress levels and potentially sleep better during the night. You can also try to incorporate certain relaxation techniques into your nighttime routine, such as aromatherapy or deep breathing exercises.  

Sleeping soundly through the night is an important goal for those looking to improve their sleep quality, and understanding arousal thresholds can help explain why you may be more likely to wake during the night and during which sleep stages. By doing what you can to limit distractions, you can keep yourself from surpassing the arousal threshold and waking up.  

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Written by

Jessica G

Medical writer freelancer who has written hundreds of articles on varying topics. Masters of Engineering degree in Biomedical Engineering.

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