Olfaction is more essential than sight and hearing: what makes it unique?

A study conducted in the United States examined how individuals assess their sense of smell in comparison to other senses and personal belongings. The results revealed that the sense of smell ranks significantly lower than sight and hearing, and is considered less valuable than items such as hair or even a mobile phone. Notably, half of the surveyed women stated they would prefer to keep their hair rather than their sense of smell. Despite this ranking, the sense of smell plays a crucial role in various aspects of human life, including memory, emotions, and mental health, as reported by The Conversation.

The existing connection between smell and memory is well-documented, first established by psychologist Donald Hebb in 1935. Odors are perceived through the olfactory bulb, which is directly linked to the limbic system of the brain, responsible for emotions and memory. This direct pathway explains why certain smells can evoke vivid memories and strong emotional responses, explains Lynn Nazareth, a researcher in the olfactory biology department at CSIRO.

Unlike sight and hearing, which do not have a direct connection to the limbic system, smell can elicit much stronger emotional reactions, as confirmed by researchers in a 2004 study published in the journal Neuropshycologia using functional magnetic resonance imaging (fMRI).

Another distinguishing feature of the olfactory system is its regenerative ability. Unlike most parts of the nervous system that cannot recover after damage, olfactory nerve cells regenerate every few months. This regeneration helps counteract damage caused by environmental toxins, infections, and injuries, Nazareth explains.

However, in some cases, particularly after COVID-19 infection, the regeneration process can be disrupted, leading to prolonged or even irreversible loss of smell. Research indicates that this occurs due to lasting damage inflicted by the immune system on the supporting cells responsible for regenerating olfactory neurons.

The loss of smell has significant implications for our mental health, presenting a serious complication, as scientists estimate that 5% of the global population suffers from complete anosmia (total loss of smell) and 15-20% from hyposmia (partial loss), figures that have likely increased since the onset of COVID-19. The inability to perceive odors can affect personal and social relationships, as it diminishes overall sensory experiences, such as eating and intimacy.

Studies also indicate a link between decreased olfactory function and depression, particularly in older adults, as well as an increased risk of mortality, although the reasons for this correlation remain unclear to science. Olfactory dysfunction is also an early sign of neurodegenerative diseases, including Alzheimer's and Parkinson's. Many patients report losing their sense of smell years before noticeable symptoms appear.

Despite this, the decline in smell often goes unnoticed, and many individuals may not realize they are experiencing it, states Nazareth. Various smell tests, both medical and home-based, can help assess olfactory function. Using common items such as coffee or soap, an individual can easily determine whether their sense of smell is intact.

There is also a concept known as smell training, a form of olfactory rehabilitation that has emerged as a potential treatment method for those experiencing smell loss, especially following COVID-19 illness. This process was first introduced in a German study published in 2009 in the journal Laryngoscope and involves sniffing strong scents, such as citrus or floral aromas, twice a day while concentrating on the memories and characteristics of the scent. Research shows that this practice helps reorganize neural connections, gradually improving olfactory functions over time.

Olfactory training has also been linked by researchers to a reduction in depressive symptoms and an improvement in cognitive abilities among older adults and patients with dementia. Similar to physical therapy for injuries, this method serves as a structured way to retrain the brain's ability to detect and interpret smells.

This material is for informational purposes only and does not contain advice that may affect your health. If you are experiencing issues, please consult a specialist.