The insula, a grey matter of tastes: a volumetric MRI study in dementia with Lewy bodies

Abstract

Background: Despite the growing number of discoveries during the past decades about its functions, the insula remains a mysterious 'island'. In addition to its involvement in basic functions such as gustation and interoception, the insular cortex is now considered a key region for integrated functions such as emotion/motivation processing, decision-making and self-consciousness. We hypothesized that this structure, standing at the crossroads of such functions, could ground personal tastes in general, beyond food preferences and aesthetic judgements. Given that dementia with Lewy bodies is characterized by a focal atrophy within the insular cortex from the early stages, this condition provides an opportunity to test such a hypothesis.

Methods: We developed a questionnaire to assess potential changes in personal tastes, submitted it to a cohort of 23 patients with early-stage dementia with Lewy bodies and compared their questionnaire results to those of 20 age-matched healthy controls. Furthermore, we performed a global and regional neuroimaging study to test for a potential correlation between the patients' scores for changes in personal tastes and their insular cortex volumes.

Results: Our results indicate that the patients presented significant changes in personal tastes compared to the controls, in both food and non-food domains. Moreover, imaging analyses confirmed the involvement of the insular cortex atrophy in the changes in personal tastes using global analysis, and in both food and non-food domains using regional analysis.

Conclusions: These results bring new insights into the role of the insula as a 'grey matter of tastes', this structure supporting personal preferences in general, beyond the food domain. The insular cortex could be involved through its role in motivational processes by the representation of subjective awareness of bodily states during the phenomenological experience of stimulus appraisal. However, we also argue that it could support the abstract representations of personal tastes as self-concepts, acutely exemplifying embodied cognition. Finally, the questionnaire on changes in tastes could constitute an interesting tool to help early diagnosis of dementia with Lewy bodies and to assess insular dysfunction more generally.

Keywords: Dementia with Lewy bodies; Insula; Personal preferences; Personal tastes; Self.

Fig. 1

Triplanar view of the right insular cortex using the ROI analyses with Freesurfer

Fig. 2

VBM analyses for changes in tastes (total score) in the DLB group. GM volumes within bilateral insular cortices negatively correlated with the total score on the questionnaire on changes in tastes, using a threshold of P = 0.001 uncorrected, including age and TGM as nuisance covariates, k = 50

Fig. 3

VBM analyses for changes in tastes (non-food score) in the DLB group. GM volumes within the left superior frontal gyrus (a, b), anterior cingulate (c) and occipito-temporal region (d) negatively correlated with the non-food score on the questionnaire on changes in tastes, using a threshold of P = 0.001 uncorrected, including age and TGM as nuisance covariates

Fig. 4

ROI analyses for changes in tastes in the DLB group. Scatterplots showing negative correlations between scores on the questionnaire on changes in tastes and bilateral insular volumes in the DLB group with ROI analyses, using a threshold of P = 0.05, including age and TGM as nuisance covariates (panels a and b show results for the total score, panels c and d for the non-food score; panels a and c for the left insular cortex volume, panels b and d for the right insular cortex volume)