Olfaction as the link between flavor preference formation and retrieval during food consumption

Project Information

OLFLINK

Grant agreement ID: 947886

DOI

10.3030/947886

EC signature date 22 October 2020

Start date 1 May 2021

End date 31 December 2026

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 499 600,00

EU contribution

€ 1 499 600,00

Coordinated by

KAROLINSKA INSTITUTET
Sweden

Periodic Reporting for period 3 - OLFLINK (Olfaction as the link between flavor preference formation and retrieval during food consumption)

Reporting period: 2024-05-01 to 2025-10-31

Summary of the context and overall objectives of the project

Human food consumption habits pose a significant threat to public health and ecological sustainability, yet changing one’s habitual consumption patterns remains challenging for many. To date, few strategies exist that can facilitate dietary change. There is still a fundamental lack of knowledge about the perceptual and emotional mechanisms that link reward experiences during food consumption, to food evaluation before consumption, which ultimately drives dietary decisions. The aim of OLFLINK is to integrate insights from metabolic, consummatory and appetitive processing into a common theoretical framework of anticipatory food reward processing in the brain.
A first series of experiments determines the distributed CODE by which odors acquire and evoke taste associations (WP1). Using brain imaging data, we are identifying the coding principles which allow odors to be linked to “sweet” or “salty” sensations during food consumption, and test the hypothesis that the ability of environmental odors to evoke these taste responses when sniffed is directly linked to their ability to elicit appetite more effectively than pictures of food.
Another series delineates the cortical CONTROL mechanisms that facilitate retrieval of taste associations from odors(WP2). Attention, past knowledge about the hedonic properties of the stimulus, and motivational states of the observer will be considered as potentially relevant influencing factors. We will then delineate changes in cortical connectivity structure that drive these changes.
Finally, we investigate interactions of perceptual-cognitive food processing with the digestive feedback that REGULATEs this circuitry (WP3). Building on the results from WP2, participants will be familiarized with new odor-taste combinations that share odor and taste properties, but vary in their caloric value. Contextual influences of metabolic state on the acquisition of a new preference will be defined, and we will describe the role of specific metabolic markers on preference acquisition.
Integration of these three nested layers of investigation will yield a unique research program that promises impactful insights into the human capacity to change our food choices.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Work is progressing on all three research lines of the grant.
WP1(CODE):
For WP1.1 we have developed a odor battery of odors that systematically varies motivation for consumption, but not perceived pleasantness. We established an odor battery, defined a set of content-matched pictures, and presented all stimuli in a single experiment to demonstrate continued separability by stimulus category. With this battery experimentally separates liking and wanting, two concepts often unclear to participants. We are planning to use the stimulus battery in future studies to separate the cognitive processing differences attributable to liking and wanting.
WP1.2 aims to demonstrate that food odors that carry a specific taste association evoke taste-like activity in the mid-insular cortex. We opted a multi-session experiment acquiring a larger amount of data from half the number of participants, and currently finishing data acquisition. Preliminary data analyses show successful cross-decoding of smell and taste signals mid-insular cortex. Data analysis of the final sample is planned for Q1/2024, with a manuscript being prepared by Q3/2024.
Data collection for WP1.3 is planned for Q2/2024. This project will determine whether similar pattern similarity as in WP1.2 can be observed for odors perceived by sniffing, and to what extent the evoked patterns in insular cortex differ from those evoked by food images.

WP2 (CONTROL) aims to understand cortical control of perceptual deviation and learning.
WP2.1 addresses the impact of cognition on odor familiarity perception. We extended the conceptual framework to incorporate a hunger modulation, which required a two-session design. Participants’ ability to pick up deviations in odors are modelled depending on their attentional focus, the behavioral relevance of the content (food vs non-food) and the metabolic need at the time of testing (hungry versus sated). Data collection is almost concluded, with data analysis scheduled for Q1/2024 and preparation of a manuscript for Q3/2024. Preliminary analyses indicate increased sensitivity for nonfood contaminants in food odors, which is robust to attentional manipulation, but enhanced by hunger.
WP2.2 addresses changes in cortical connectivity which facilitate the increased deviation sensitivity for food odors. This study is currently in planning, with piloting expected to start Q2 and data collection in Q3/2024.
WP 2.3 is planned to commence in 2025.

WP3 (REGULATE) studies metabolic regulation of cortical food processing.

Pilot work for WP3 has been completed, which sought to determine effects of hunger on hedonic assessments of odors in participants who completed the task in a sated or hungry state. This study learning effects by mere exposure which partially superseded observed effects of hunger and will now be controlled for in all remaining studies. A manuscript is published as preprint and currently under review. Staff recruitment problems have delayed work on this package, but are now resolved to increase work on the package from spring 2024 onwards.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Main achievements to date include
- a reproducible and reliable protocol for combined odor/taste stimulation in the MRI scanner
- innovative experimental paradigms and answer formats to study sensitivity to contamination of familiar food odors
- a reproducible stimulus battery to behaviorally dissociate hedonic valence from incentive to eat in odors and pictures
- reproducible ad libitum food consumption paradigm that allows for systematic investigation of influences of metabolic state on food odor perception
- definition of important pitfalls and confounding factors in olfactory food research: first, documenting the need to account for differences in odor and picture valence judgments, and second, by demonstrating session-to-session learning effects by mere exposure, which increase hedonic value of the stimulus material and compete with other contextual factors such as hunger manipulations

Making use of these achievements, we are expecting to be able to demonstrate by the end of the project that
- Food odors elicit appetite by evoking taste-like activation patterns in mid-insular cortex
- That contextual factors such as prior knowledge, attention, and metabolic state can exert top-down control on connectivity between olfactory and taste cortices, and between taste cortices and reward areas, regulating the ability to retrieve odor-taste associations and assigning value to them.

Due to logistical problems in the startup phase and the need for careful piloting of our experimental paradigms, significant progress is expected for the next year of the grant as two large data acquisitions are currently being concluded.

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