Is there a connection between familiar smells and nightmares?

Our sense of smell is perhaps the most neglected in terms of scientific scrutiny. This makes sense to a degree - we do rely more on our sense of sight, hearing and touch to navigate life. Losing your ability to smell or taste might not be as devastating as not being able to see. A small study carried out in Japan looked at how olfactory stimuli affect our dreams. But it highlights more what we don’t know rather than offering a compelling explanation of the findings. According to the study, the exposure to strong, familiar smells is more likely to trigger nightmares than the presence of unfamiliar or no smells. The findings, published in  Sleep Journal, are based on sleep studies conducted on 14 undergraduate students averaging 18 years of age.   [caption id=“attachment_2683690” align=“alignleft” width=“380”]  Representational image. Getty Images[/caption]

The ability to smell when asleep

It is still unclear how well we perceive smells when we are asleep and dreaming as the research on it remains scant. Previously, a small study looked at whether smells affected the quality of dreams. Fifteen participants were separated randomly - half of them were exposed to the smell of rotten eggs while they slept, and the other half smelled roses in their sleep. It was found that those who smelled roses experienced more pleasant dreams while others had negative dream experiences. The researchers said that this indicates that olfactory sense remains intact, to a degree, when we are asleep. This could be because the olfactory assembly is a part of the limbic system, which deals with memory and emotions. The limbic system remains active even during deep sleep.    

The brain’s default mode

The researchers from the Japanese study said that the ‘olfactory bulb’, which processes smell, can sense smell even during sleep. It transmits this information to the brain, and during REM sleep (which is the stage of sleep in which we dream), only certain parts of the brain are ‘switched on’. One of those parts is the amygdala, which plays a role in processing fear. Similarly, the hippocampus, which deals with memories, is also awake. This combination probably explains why the participants had unpleasant dreams.

Unanswered questions

The researchers emphasized that the smell must be familiar since this will make it more likely to stand out and be perceived by the brain. Again, this was an extremely small study that did not employ any methods that would prove causality. There were no imaging tests that examined which parts of the brain lit up during the process. The explanations are theoretical and can’t be taken at face value.

What we actually know about nightmares

According to the DSM (the Diagnostic and Statistical Manual of Mental Disorders), for a bad dream to be called a nightmare, the person must remember it afterwards and also must be awakened by it. In other words, if you remain asleep during a bad dream, technically it will not classify as a nightmare.

1. REM Sleep: The most vivid, remembered dreams occur just as we are slipping out of REM sleep, later on in our sleep cycle. During REM, the limbic system (which has a major role in processing fear) is still firing, but the prefrontal cortex, which is the seat of reason is muted. This could explain why dreams appear nonsensical and often frightening. Also during REM, you become temporarily paralyzed. This is why you don’t go about acting your dreams and injuring yourself and others.
2. At-risk of nightmares: Stress, and PTSD, are the most widely reported causes of nightmares. Natural disaster, traumatic events, scary movies all contribute. Those suffering from depression and related mental health disorders are more likely to have nightmares.
3. Image reversal therapy: A new type of therapy, known as Image Reversal Therapy (IRT) involves journaling about the nightmare and changing the end to a happier, more positive one. Studies have shown that confronting nightmares in such a manner, and rehearsing them during the day, lowered the frequency of nightmares in participants. Similarly, VR (virtual reality) could have some promise as the person can interact with and change the images the machine produces. The sense of agency, in theory, could work to undermine nightmares.

Read our tips on   How to fall asleep  for more information. Health articles in Firstpost are written by myUpchar.com, India’s first and biggest resource for verified medical information. At myUpchar, researchers and journalists work with doctors to bring you information on all things health.