Learning to preserve: foreign language training as a cognitive *vaccine* to prevent old-age disorders?

As the world population is growing older, the proportion of seniors increases
and more individuals will have to face the challenges that accompany old age.
One of the most documented challenges that accompanies ageing is cognitive
decline. Although subtle losses in cognitive function are part of normal
cognitive ageing, individuals differ greatly in their susceptibility to
age-related cognitive decline. Some individuals seem able to compensate for
these changes better than others; they show cognitive reserve. It is suggested
that individuals with a higher cognitive reserve can tolerate more pathology
and can therefore shift the onset of manifestations of cognitive decline. Other
challenges that accompany ageing can cause emotional suffering, including
depression. Old age depression is associated with decreased physical, cognitive
and social functioning, which in turn contributes to a decreased quality of
life. Among the most prevalent cognitive deficits in depression are deficits in
executive functioning, especially cognitive flexibility. Deficits in cognitive
flexibility affect the disposition to adaptively regulate emotional states,
which contribute to the persistence of the depressive disorder but is also a
vulnerability factor. Therefore, increasing cognitive flexibility might trickle
down to benefit the course of depression. One experience that has repeatedly
been related to enhanced cognitive flexibility is bilingualism: lifelong
bilingualism is inherently associated with cognitive advantages and the
attenuation of cognitive decline. Bilingualism could therefore serve as a tool
to combat old-age cognitive decline and mood disorders.

The main objective of this study is to determine whether a bilingual experience
in old age affects cognitive flexibility and its neural underpinnings, which
could in turn explain health advantages. Secondarily, this study aims to
evaluate the effect of a bilingual experience on health outcomes (vulnerability
for depression, cognition and quality of life). We do so by introducing a
bilingual experience later in life, operationalized as a foreign language
course for seniors. If a bilingual experience indeed has protective effects,
foreign language learning could serve as an important tool towards healthy
ageing and, as such, have an important clinical application.

This study is an open-label randomized controlled trial with pre- and
post-intervention measurements in individuals with subjective, but not
objective, cognitive decline. Participants are pseudorandomly assigned to the
language intervention or to one of the two control groups; a music
intervention or a social (art) intervention. These control conditions are
chosen to assess the unique role of foreign language training versus other
cognitive training programs or social engagement aspects. All interventions
last three months, with the possibility to extend the training period to six
months, which allows studying *dose-response* relationships. During the study -
and following an initial screening - there are four measurements. All
participants will be measured at baseline (T0) and three months after the start
of the training (T1). For those who choose to end the training after three
months, this examination will serve as the post-intervention examination.
Participants who have chosen to extend the training period to six months will
complete the post-intervention examination (T2), at six months after the start
of the intervention. All participants have a follow-up examination (T3) six
months after the end of their intervention (either 9 or 12 months after the
start of the training, dependent on the length of the chosen intervention: 3 or
6 months, respectively). All measurements consist of questionnaires and
neuropsychological assessment and all measurements, except for the follow-up
examination (T3), include EEG/fNIRS measures to measure brain activity.
Learning progress will be measured at post-intervention (T1 and T2) and at
follow-up (T3) using IELTS. Research assistants that are blind to the training
condition will perform all clinical assessments.

All intervention methods have a duration of two times three months. The three
months option will increase a priori motivation and lower the threshold to
participate. After the first three months, participants are free to extend the
training period to six months or not.

In the language intervention group, participants will be taught a foreign
language, English. Participants will practise English at home for 45 minutes
per day, five days a week, using materials provided in an online learning
environment, provided by a certified online training institute. Besides that,
they will engage in real-life classes of 90 minutes per class every other week
in groups of approximately 15 to at most 20 participants.

Participants assigned to the music intervention will receive musical training
in which they will learn to play an instrument, learn to read music and
practise rhythm using methods provided in the same online learning environment.
Similar to the language intervention, participants are expected to practise at
home for 45 minutes per day, five days a week and to engage in real-life
classes of 90 minutes each, every other week.

In the social (art) intervention, participants will attend 90-minute social
meetings every fortnight in which they will participate in different art
workshops.

In all interventions groups, participants will be asked to log their
out-of-class exposure using a diary during the time they participate in the
intervention.

Following an initial screening, included participants are invited for the
baseline examination. All interventions, the language and both controls, start
hereafter. A post-intervention examination is planned three months after the
start of the interventions. For those who choose to continue the training for
six months, the post-intervention examination is repeated at six months after
start. Finally, participants are invited for a follow-up examination 6 months
after the end of the intervention.

The initial screening consists of an interview to assess current and past
psychopathology (30 minutes) and questionnaires (70 minutes) to assess whether
potential participants are eligible to participate. Two weeks before all
examinations, questionnaires will be sent to the home address of the
participant to reduce the burden of the examinations. Filling in these
questionnaires takes 50 to 60 minutes. The baseline and post-intervention
examinations all consist of questionnaires (approximately 25 minutes),
neuropsychological tests (40 minutes), and measures of brain activity using
simultaneous non-invasive fNIRS/EEG methods during a switching task and during
a resting state measurement (30 minutes). The baseline and post-intervention
examinations therefore take approximately 3 hours. In the follow-up examination
six months after the end of the intervention, the questionnaires and
neuropsychological testing session will be repeated in addition to a short
interview to assess psychopathology (total session duration of 2.5 hours). No
brain activity measures will be performed in this follow-up examination.

The language and music intervention have a similar intensity. In both
interventions, participants are asked to practise at home 5 days a week, 45
minutes a day. In addition, every fortnight participants will attend real-life
classes for 90 minutes each. For the social (art) intervention, participants
only attend real-life classes every other week for 90 minutes during which they
will practice several kinds of art.

Concerning the fNIRS/EEG measures, participants will be exposed to
near-infrared light, which has no known influence on health. No disadvantages
are expected with regard to any of the measures or with regard to any of the
interventions. However, participants might benefit from the interventions in
that it may increase their proficiency in English, music or art skills and it
may increase social exposure.