Smells, emotions, and sleep: distinctive features of the olfactory system compared to other sensory modalities

Chemosensory perception is crucial for evaluating our environment. Unlike physical sensory modalities, which deal with constant stimuli (such as light and sound), the olfactory environment is continuously changing. This dynamic nature requires the olfactory system to adapt to various situations, achieved through a vast array of olfactory receptors that facilitate combinatorial odor recognition, enabling the perception of nearly an infinite variety of odorants. Each odorant activates a specific pattern of olfactory receptors, creating a unique chord that is transmitted to the olfactory bulb. In contrast to other sensory systems, the olfactory pathway sends signals directly to the piriform cortex and amygdala, bypassing the thalamus. These regions project to the orbitofrontal cortex, interacting with the amygdala to influence emotions and play a key role in associative learning. This distinct architecture of the olfactory system contributes to its unique connections with emotions and sleep, which are discussed in this review.