Insula and Olfaction: A Literature Review and Case Report

Frédérique Roy-Côté,Dang Khoa Nguyen,Olivier Boucher,Johannes Frasnelli,Rayane Zahal

doi:10.3390/brainsci11020198

Abstract

(1) Background: It is well established that the insula is involved in olfaction, though its specific role in olfactory processing remains uncertain. In this paper, we first review the current literature on the insula and olfaction. Then, we describe the case of a 56-year-old man with a left insular cavernoma that caused olfactory disturbances. (2) Results: Structural neuroimaging studies suggest that insular gray matter volume is related to olfactory function, and functional neuroimaging shows that various types of stimuli lead to either lateralized or bilateral insular activations. Studies using electro-cortical stimulation reveal a specific region of the insular cortex, around the central insular sulcus, that could be related to unpleasant odor processing. Previous cases of insular lesions leading to olfactory disturbances suggest that left-sided insular lesions may more frequently lead to olfactory changes. In our patient with a left insular cavernoma, odors that were previously perceived as pleasant started smelling unpleasant and were hard to distinguish. Despite these subjective complaints, olfactory function assessed with the Sniffin’ Sticks test was normal. (3) Conclusions: Current tests may not be sensitive to all types of olfactory impairments associated with insular damage, and further studies should be conducted to develop olfactory tests assessing the hedonic appreciation of odors.

Highlights

IntroductionAffective, and cognitive processing is well documented [1,2,3,4,5,6,7]
This paper aims to further explore the insula’s role in olfaction by (1) reviewing the existing literature on the topic; and (2) presenting a new case of olfactory disturbance associated with an insular lesion
We reviewed neuroimaging and electro-stimulation studies of the insula and olfaction, as well as previous case reports of olfactory dysfunction following insular lesions

Summary

Introduction

Affective, and cognitive processing is well documented [1,2,3,4,5,6,7]. Cumulative evidence indicates that the insula is involved in olfaction. Tracing studies in primates and tractography in humans have shown connections between the primary olfactory cortex and the insula, which is proposed to be part of the secondary olfactory cortex [8,9,10]. A meta-analysis combining all published data on functional neuroimaging of olfaction identified the insula among the neural substrates of olfactory processing [11]. It is known that olfaction is related to emotional processing, in which the insula plays an important role as well [12]

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Results

Conclusion