Olfactory training (OT), which involves repeated exposure to odors, is being increasingly studied as a potential method to improve both olfactory and cognitive function. Given the close neurological connection between olfaction and cognition, researchers have questioned whether OT can enhance brain function and cognitive abilities. This systematic review, conducted by Vance et al., explores whether OT leads to improved cognition and changes in brain morphology and connectivity.

The review included 18 studies from three major databases—MEDLINE, Scopus, and Embase—examining whether OT positively impacts cognition, brain structure, and functional connectivity. The analyzed studies included both individuals with olfactory loss (hyposmia and anosmia) and those with normal olfactory function (normosmia).

Findings showed that OT was consistently linked to improvements in verbal fluency, verbal learning, and memory. Neuroimaging studies demonstrated increases in the volume of olfactory-related brain structures, including the olfactory bulb and hippocampus, as well as altered functional connectivity in key brain regions. Importantly, these benefits were not restricted to individuals with olfactory impairments; even normosmic participants exhibited cognitive improvements.

Loss of smell, which can occur due to aging, infections, brain injuries, or neurodegenerative diseases like Parkinson’s and Alzheimer’s, is known to be an early predictor of cognitive decline. The review highlights that olfactory impairment is strongly correlated with future risk of dementia and increased mortality rates. Given that olfactory processing directly engages key cognitive areas, such as the orbitofrontal cortex, amygdala, and entorhinal cortex, OT could serve as an effective, non-invasive cognitive intervention.

The methodology of OT varied across studies, but most followed a standard protocol of smelling four specific odors (e.g., rose, eucalyptus, lemon, cloves) twice daily for 12 to 56 weeks. Some studies explored variations, such as rotating odorants or increasing exposure frequency. Results suggested that the most significant improvements in olfactory function and cognition occurred between weeks 13 and 18, reinforcing the need for sustained training over several months.

Neuroimaging findings revealed that OT not only improved olfactory function but also induced neuroplastic changes in the brain. Participants showed increased connectivity in brain regions associated with memory and executive function, as well as structural enhancements in the olfactory bulb, hippocampus, and frontal cortex. These findings suggest that OT has the potential to counteract age-related neural decline.

However, the review identified key limitations in current OT research. One major issue was the lack of standardized adherence measures, as most studies relied on self-reported training diaries. This made it difficult to verify compliance and assess the true impact of OT. Additionally, sample sizes were often small, and long-term follow-up data were scarce, leaving uncertainty about the durability of OT-induced improvements. Future research should focus on larger, more diverse participant pools and objective tracking of OT adherence.

Overall, the review concludes that olfactory training is a promising intervention for enhancing cognition and brain function, particularly in older adults. While further research is needed, these findings support the idea that OT could serve as a low-cost, non-invasive strategy to improve cognitive health and reduce dementia risk.