Olfaction and Executive Cognitive Performance: A Systematic Review

Abstract

Objective tests of olfaction are widely available to aid in the assessment of olfaction. Their clearest role is in the characterization of olfactory changes, either reported by or suspected in a patient. There is a rapidly growing literature concerned with the association of olfactory changes with certain neuropsychiatric conditions and the use of olfactory testing to supplement conventional assessments in clinical and research practice is evolving. Neural pathways important for olfactory processing overlap extensively with pathways important for cognitive functioning, and especially those important for executive functioning, many of which are concentrated in the frontal lobes. Previous work has identified associations between performance on certain olfactory tests (most frequently olfactory identification) and executive functioning and behavioral measures (e.g. of impulsivity). More recently, similar associations have also been identified in non-clinical samples, raising new questions as to the utility of olfactory test scores as proxy measures for non-olfactory phenomena. In this systemic review, we sought to identify studies, both clinical and non-clinical, that investigated the associations of olfaction with performance on tasks sensitive to frontal lobe functioning. Our search criteria led to the identification of 70 studies published in English. We examined in detail and tabulated the data from these studies, highlighted each study's key findings, and critically evaluated these studies. We use the results of this review to reflect on some of the current and future challenges concerning the use of olfactory testing in clinical neuropsychiatric practice and research and speculate on the potential benefits of administering phonemic fluency in combination with olfactory testing to enhance its predictive value.

Post-COVID-19 physical and cognitive impairments and associations with quality of life: a cross-sectional study

“…However, some studies have shown that SARS-CoV-2 can damage the CNS in different ways including direct infection, viruses entering through blood circulation and neuronal pathways, hypoxic and immune injury, and also binding to the angiotensin-converting enzyme 2 (ACE2) receptor, ultimately producing acute and long-term neurological effects ( 37 ). Furthermore, as the olfaction and cognitive functions share common neurocircuitry in the frontal lobe, the high incidence of anosmia following COVID-19 infection, which is also one of the most common persistent symptoms in post-COVID-19 cases, draws attention to the role of olfactory neuroinflammation in cognitive changes, especially executive function ( 35 , 38 ).…”

Olfaction and neurocognition after COVID-19: a scoping review

“…There are many studies which have examined the general relationship between olfaction and cognition with the majority showing that olfactory performance tends to have significant associations with measurements of frontal lobe executive function ( Westervelt et al, 2005 ; Challakere Ramaswamy and Schofield, 2022 ; Mattos et al, 2022 ). There are a variety of medical conditions in which there is evidence for a positive association between olfactory performance and cognitive functioning.…”

Neuropsychiatric correlates of olfactory identification and traumatic brain injury in a sample of impulsive violent offenders

“…In terms of practical applications, as we have discussed elsewhere, moving from the findings from group studies of olfaction and its correlates to considering the potential benefits of OI testing of individuals raises many questions and challenges (Ramaswamy and Schofield, 2022). The clearest benefit of OI is to detect olfactory impairments that would confer risk from failure to detect hazards such as smoke or spoiled food.…”

“…Olfactory dysfunction (OD) is commonly observed in certain neurodegenerative diseases and may occur in the context of neuropsychiatric disorders such as schizophrenia, depression and panic disorder (Ryo et al, 2017;Fóz et al, 2022). Neural pathways for olfactory processing overlap with those important for aspects of executive functioning concentrated in the frontal lobe, and tests of executive function and olfaction have been shown to positively correlate across a broad array of measures, as recently reviewed (Ramaswamy and Schofield, 2022). Indeed, some investigators have suggested that olfactory tests could serve as a rapid screen for cognitive impairment (Jung et al, 2019;Vance et al, 2023).…”