Neural substrates of anticipatory food reward in healthy young and older adults, investigated with fMRI.

This study is part of a TI Food and Nutrition project, which aims to understand
food choice in healthy younger and older adults. Perceived pleasantness while
consuming a food product must be translated into motivation in order to
influence subsequent food choice. Such motivation is also known as anticipatory
food reward. Visual features that motivate people to choose a specific food
product induce anticipatory reward, and are a strong predictor of food choice.

In recent studies, we have shown that older adults perceive sweet and salty
tastes as more pleasant while consuming these basic tastes. Other studies also
reported that older adults showed less activation in brain areas involved in
the anticipation of reward as compared to younger adults. Whereas both changes
in food choice and the neural motivation system have been observed with age,
the age-related changes in motivation towards food products has not received
much attention so far. Therefore, in the current study we aim to investigate
the neural mechanisms behind the anticipation of reward from food products in
younger and older adults.

Investigating the neural mechanisms underlying the anticipation of food reward
induced by visual cues related to different food characteristics in healthy
adults would provide 1) brain activity patterns that can be associated with the
anticipation of food reward and 2) a baseline to further investigate if and how
these brain activity patterns differ between younger and older adults. This
information, in combination with other studies within the larger project,
ultimately allows us to create tools that understand (individualized) food
choice.

This study will combine fMRI and behavioral measurements. Participants will
undergo one fMRI scanning session in which they will perform a computer-based
paradigm consisting of visual (anticipatory) food stimuli. All stimuli will
vary along two dimensions * taste (sweet or salty) and calorie (high or low).
The anticipatory reward to each visual food stimulus will be assessed by a
two-alternative forced choice methodology (i.e. an established controlled
measure of choice which is widely used to test choice behavior), designed and
executed using Matlab. In this task, the participants will be instructed to
select the food they *would most like to eat now* in a series of trials in
which a visual food stimulus from one of the four food categories will be
paired with a stimulus from either the same or another category. Each choice,
made via key-press on the keyboard, triggers the next pair of stimuli and so on
until all possible combinations (i.e. 10 combinations) are presented 16 times
in order to acquire a reliable brain response. The total amount of 160 trials
will be divided over four task blocks of 40 trials. The order of all
combinations of visual food stimuli will be randomized across all four block as
well as balanced and counter-balanced between participants.

A behavioral and neural measure of *anticipated reward* is derived in two ways.
First, the brain response derived during each choice can convey information
about the degree (on a continuous, interval unit of measurement) to which a
chosen visual food stimulus is anticipated to be rewarding relative to an
alternative. Second, the analysis of the fMRI data will take into account the
reaction times when choices are made to each food category respectively as a
covariate. This might show what brain activation can be associated to
anticipated food reward for each food category for each participant
individually.

The design of this study is single-blind; at the moment of presenting the
visual food stimulus, the participants do not know which food category they are
experiencing. However, the participants will be informed about the nature of
the stimuli, before inclusion into this study.

Functional MRI is an eminently safe technique; there are no risks that have
been associated with the acquisition of fMRI data per
se. Above certain limits, warming and/or an itching/tingling feeling
(stimulation of peripheral nerve terminations) are possible.
However, the magnetic intensities used in this research are amply below these
limits. Subjects will be exposed to a magnetic field
of 3 Tesla and rapidly alternating gradients and radio frequency fields. This
field and gradients' changes are routinely used in fMRI
and MRI research. It is worth to mention that scanners supporting a magnetic
field that is more than twice as powerful (7 Tesla) are
used in The Netherlands for research purposes. Also, no harmful side effects
have been reported there. The data collected during
the functional and anatomical MRI scans will be used for research purposes
only. However, if evident abnormalities in the brain are
noticed, then the General Practitioner, who is indicated by the subject, will
be notified. The strong magnetic fields used by fMRI can
dislocate ferromagnetic particles inside the brain and the eyes, interfere with
the functioning of electronic devices implanted inside
a person's body (pacemakers, insulin pumps, etc.), as well as induce heating in
artificially metal-rich regions (red tattoos, metallic
supports to previously fractured bones, prosthetic implants). In order to stave
off the risks involved with such possible conditions,
subjects will be required to complete a questionnaire and only if none of the
exclusion criteria is met the subject will be allowed to
participate in our experiment. The environmental conditions of being inside an
MR scanner and of being partially restrained can
induce claustrophobic feelings. Three steps will be taken to reduce this risk:
1) the subject will be explicitly asked about being
claustrophobic, 2) the subject will experience a training moment in a dummy
scanner and 3) prior to the beginning of the actual
experiment, and during pauses between scans, subject will be asked about their
well being. Additionally, they will receive an alarm
trigger that they will be able to use at any moment to interrupt the scanning.
Finally, an experimenter will be in close proximity of
the participant during the session, for the primary reason to present the
aforementioned small amounts of liquids. Such proximity
will allow a close monitoring of the subject*s well being. The subject's burden
is as follows, regarding time: a screening moment by
telephone, to ensure that all the requirements are met and to determine the
individual intensity/pleasantness curve needed for the
scanning session. Before each scanning session the subject will be required to
fill and sign a safety-specific questionnaire. The
scanning sessions will be between 16:00 and 19:00 hours; we will ask the
subjects to stop eating at least three hours before the
scan to ensure a sufficient state of hunger to induce a stronger BOLD response
to the stimuli. To undergo a fMRI scan involves:
exposure to loud noise (addressed with ear protection, by means of both ear
plugs and headphones), a moderate amount of
physical restraint (the head is inside a fMRI coil; the feeling is similar to
wearing a motorbike helmet), as well as to a strong
constant magnetic field (3Tesla), and small variable electromagnetic fields
(see question E9).