Neuron types are highly specific for one odor receptor type. Collectively members of the same neuron type will elicit a specific scent response from the brain. The MMB/dREAM protein complex may be the major selector, at least when smelling carbon dioxide. Initially, all neurons are repressed then one neuron is de-respressed. The olfactory process is likened to a braking mechanism that is eventually released.
An individiual’s sense of smell signals the limbic system in the brain, and is thereby believed to affect emotions during dreaming. One study used the scent of roses and rotten eggs to test this hypothesis on a small group of subjects with a normal sense of smell. A pleasant versus unpleasant smell was found to affect the tone of dreams in a positive and negative manner, respectively.
Another study garnered similar conclusions when using perfume fragrance. The smell of perfume increased positive tones in dream content, and simultaneously decreased negative tones. The study also accounted for some gender differences. Men were found to respond even more positively than women to perfume scent during dream time.
A decrease in overall olfactory function is linked to sleep disorders, including those that are secondary to other diseases. The decrease in function is comparable among idiopathic REM sleep behavior disorder and Lewy body disease, including Parkinson’s disease and Lewy body dementia. Olfactory function diminishes with age and is less developed in males compared to females. Nonetheless, this highlights the importance of routine exams in diagnosing and treating patients in a timely manner.
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