Neurological and Neuropsychiatric Disorders in Relation to Olfactory Dysfunction

Abstract

Olfaction is an underestimated sensory modality in terms of its predictive value as an indicator of disorders. It is a well-known phenomenon that a significant percentage of people afflicted with certain prevalent disorders causing degenerative neuropathology, progressive loss of memory and communication function, normal age-based decline of physiological functions, intellectual challenges, depressive and anxiety disorders as well as post-traumatic stress disorders, present with a range of olfactory deficits. Here, we review our understanding of these deficits and their relation to various clinical manifestations such as neurological and neuropsychiatric diseases and disorders. At the outset, we will briefly describe the olfactory pathway from olfactory sensory neurons in the nasal epithelium to the olfactory bulb and on to olfactory cortical and subcortical structures involved in olfaction such as the amygdala.

The Olfactory System as Marker of Neurodegeneration in Aging, Neurological and Neuropsychiatric Disorders

“…Declining olfactory acuity and olfactory dysfunction ranging from subtle to severe have now become a well-established feature of the normal aging process [ 28 , 29 , 30 , 31 , 32 ]. These are detectable in an age-dependent manner: in 50% of tested subjects ranging from 65 to 80 years in age, while increasing to 75% of those who are above 80 years [ 8 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ]. Age-associated ossification and closure of foramina of the cribriform plate [ 34 , 36 ], as well as quantitative reduction of the olfactory epithelium and its replacement by respiratory epithelium [ 37 ], are anatomical and histological factors leading to olfactory decline and dysfunction.…”

“…Experimental evidence suggests a concomitant role of olfactory bulb neurons in the onset of decline in olfactory acuity as well as the initiation of neurodegenerative pathology [ 7 ]. Conversion of olfactory stimuli into electrical signals occurs primarily through multiple pathways of olfactory bulb cell layers prior to conveying the signal to higher-order brain structures for further processing [ 8 ]. Olfactory receptor neurons (ORNs) undergo specific adaptations at the anatomical, physiological and functional levels based on chronic exposure to stimuli [ 9 , 10 ].…”

Neurons, Nose, and Neurodegenerative Diseases: Olfactory Function and Cognitive Impairment

“…Experimental evidence suggests a concomitant role of olfactory bulb neurons in the onset of olfactory acuity decline and the onset of neurodegenerative pathology [3]. Olfactory stimuli are transduced through olfactory neuronal cell pathways before relaying the information to cortical brain structures for further processing [4].…”