Order-Evoked Memories
Odor-evoked memories are notable for their emotional intensity and ability to vividly recall past experiences, more so than memories triggered by other cues. Research consistently demonstrates that autobiographical memories evoked by odors are deeply emotional, activate brain regions involved in emotional processing, and strongly transport individuals back to the original context compared to memories recalled through other senses. [1]
In the Beginning There Was the Scent
Our olfactory system is specialized in “chemosensation”: it detects volatile, airborne molecules, and is often described as our most "primitive" sensory system because of its early phylogenetic development and its connections to older regions of the brain involved in unconscious perception. Olfaction is considered one of the most crucial senses in many mammalian species because it delivers vital information about potential mates, predators, and food, which are all essential for survival and reproductive success [2].
The Nose Knows
Odor molecules enter the nose and bind to specific odor receptors, which then transmit signals to the olfactory bulb. The olfactory bulb is closely connected to the brain’s limbic system, a region that plays a key role in controlling memory, emotions, and behavior. This system is also linked to the pituitary gland and hypothalamus, areas that regulate the release of hormones influencing appetite, the nervous system, body temperature, stress levels, and concentration. Due to the close anatomical ties between the olfactory system and the limbic system, the sense of smell can powerfully affect our memory, mood, stress, and concentration, often without our conscious awareness. [3]
Privileged Access
Unique among the senses, the smell receptor cells are themselves neurons, meaning that these cells have one end in direct contact with the external world and the other in direct contact with the brain [4]. Moreover, the neuroanatomy of olfaction has a privileged connection to areas of the brain responsible for emotion and memory. Unlike other sensory systems, olfaction bypasses the thalamus which acts as a relay station, filtering and directing sensory information to appropriate areas of the cortex [5]. This creates a direct pathway for the smells to reach and influence the limbic system and the hippocampus, areas of the brain that are known to be involved in emotion and memory, respectively. This unique routing explains the olfactory system's distinct and powerful role in our sensory experience, and the ability of odorants to bring back highly specific memories [1].
Constant Renewal
Our sense of smell is exceptionally dynamic and resilient compared to other sensory systems. In most parts of the brain, neurons form early in development and remain relatively static. The olfactory system, in contrast, contains stem cells that can produce new neurons, even in adults.
Ongoing neurogenesis allows this system to continuously update and refine its capabilities in detecting a vast array of smells. Interestingly, this feature is also found in the dentate gyrus of the hippocampus, part of the brain involved in encoding memories [6].
References
[1] Herz RS. The Role of Odor-Evoked Memory in Psychological and Physiological Health. Brain Sci. 2016 Jul 19;6(3):22.
[2] Baum, M., & Cherry, J. (2009). Sexual Differentiation of Mammalian Olfactory Communication. In Elsevier eBooks (pp. 1817–1843).
[3] Sullivan, R. M., Wilson, D. A., Ravel, N., & Mouly, A. M. (2015). Olfactory memory networks: from emotional learning to social behaviors.Frontiers in Behavioral Neuroscience,9.
[4] Young, J. M., & Trask, B. J. (2002). The sense of smell: genomics of vertebrate odorant receptors. Human Molecular Genetics, 11(10), 1153–1160.
[5] Han SA, Kim JK, Cho DY, Patel ZM, Rhee CS. The Olfactory System: Basic Anatomy and Physiology for General Otorhinolaryngologists. Clin Exp Otorhinolaryngol. 2023 Nov;16(4):308-316.
[6] Ming GL, Song H. Adult neurogenesis in the mammalian brain: significant answers and significant questions. Neuron. 2011 May 26;70(4):687-702.
