Method

Study Design

The study is divided into two consecutive laboratory sessions. In the first session, we will administer the cognitive tasks and a series of computer-based questionnaires. During the second session, participants will complete the MAST (Smeets et al., 2012). The study has received ethical approval from the UCLouvain-St Luc Biomedical Committee.

Participants

Participants will be recruited through social media (e.g., UCLouvain student groups on Facebook), posters placed around Louvain-La-Neuve and Brussels (Belgium), as well as emails sent out to the UCLouvain pool of participants and students at the Faculty of Psychology and Educational Sciences. The target sample size will be 85 in the MAST stressor induction group. This was estimated using G*Power 3.1.9.7 for a regression model with an estimated effect size of 0.15, an alpha of 0.05, power of 0.80, four predictors (each cognitive task) and four covariates (age, gender, chronic stress, and baseline or reactivity stress to calculate change indices). A further 43 individuals will be recruited for the control group (placebo-MAST), and 22 more across both groups for estimated participant dropout and equipment malfunction. We will stop recruitment once we have reached 150 participants for the current study.
Inclusion criteria will include being over 18 years of age, having French as one’s mother tongue language (or having acquired it before age 10), and presenting a Body Mass Index between 18 and 30 (Shapiro et al., 1996). Participants will be excluded if they smoke, consume more than 25 units of alcohol per week, have a habit of using soft or hard drugs, or present a current diagnosis or treatment for specific physical disorders (i.e., cardiovascular, endocrine, diabetes; Jennings et al., 1981; Narvaez Linares et al., 2020; Quintana et al., 2016; Shapiro et al., 1996; Shilton et al., 2017). They will also be free of current psychiatric diagnosis or treatment (e.g., for depression, anxiety; Quintana et al., 2016; Stone et al., 2021; Vila et al., 2019) and will be systematically excluded if they were diagnosed with stress- or anxiety-related disorders (e.g., post-traumatic stress disorder, general anxiety disorder) in their lifetime, if they are undergoing an unusually stressful period (e.g., separation, divorce, examination, current events), or if they have been previously exposed to the MAST (e.g., Gianferante et al., 2014; Stone et al., 2021).

Measures

Online Questionnaires

Sociodemographic and Physical Information . We will include items relating to one’s age, gender, education, weight and height to calculate body mass index, and handedness.
Chronic Stress. The Perceived Stress Scale (Bellinghausen et al., 2009; Cohen et al., 1994) will evaluate perceived stress over the last month. The scale is composed of 10 items, four of which require reversing. All items are assessed on a Likert scale ranging from 0 (never) to 4 (very often). The total sum score represents an index of chronic stress. The scale has shown good consistency in previous studies (e.g., Cohen et al., 1994, Grimm & Agrigoroaei, in prep. ).

Executive Functioning

All cognitive tasks were originally programmed by Millisecond Software and will run on Inquisit 6 (2021). The order of task presentation will be counterbalanced across participants.
Inhibition. The Stop Signal Task script was modified to meet recent recommendations (Verbruggen et al., 2019). On each trial, a fixation circle will appear at the center of the computer screen, following which an arrow pointing left or right will appear within a circle. Participants will indicate the arrow direction (left or right) using the “D” and “K” keys, respectively. Participants must respond as quickly as possible without waiting for the stop signal to occur, as that would otherwise delay stimuli presentation. On specific trials, participants will hear a beep through the headphones, indicating that they must omit from responding. The ratio for signal to no-signal trials will be 1:3 and the target response inhibition probability fixed at 0.5.
The task is divided into four blocks of 64 trials, with arrows pointing to the left and right half of the time. The arrow direction will be randomized for each trial. The initial Stop Signal Delay will be set at 250ms and adjusted up or down by increments of 50s depending upon successful (i.e., increases) or unsuccessful (i.e., decreases) performance. The minimum and maximum delays will be 50ms and 1150ms, respectively. Each trial (signal or no-signal) will last 2000ms, preceded by a pre-trial 500ms pause. A 15-second pause between each block will provide participants with prior block results and instruction reminders. The test will be preceded by a 32-trial practice block, with 25% signal trials (i.e., 8 signals).
Following previous recommendations (Verbruggen et al., 2008), the first trial in each test block will not be analyzed. Inquisit 6 (2021) will automatically calculate the Stop-Signal Reaction Time using the integration model, as well as the response time for go responses on unsuccessful stop signals. We will verify whether the race model is violated (i.e., where the reaction time on Stop Signal trials is numerically longer than reaction times on Go trials that are successfully inhibited) and will ensure that all p(respond|signal) are above 0.25 and below 0.75, as recommended (Congdon et al., 2012; Verbruggen et al., 2019). Participants will be omitted from further analysis if this is not the case.
Flexibility . Cognitive flexibility will be operationalized using the Letter-Number Task (Miyake et al., 2000). Letter-number pairs (e.g., “7G”), moving in clockwise fashion to the next box on each new trial, will appear within a 2x2 quadrant. Participants will respond to one of two categorization tasks depending on the position of the pair onscreen. If it appears in the top two squares, participants will indicate whether the letter is a consonant (“E” key) or a vowel (“I” key) (i.e., Letter Task). If the pair appears on the two lower quadrants, participants will indicate whether the number is even (“E”) or odd (“I”) (i.e., Number Task). The task will begin with two practice blocks, during which the participants will complete 32 trials of both tasks, separately. The order for task presentation (i.e., Letter followed Number, or vice versa) is randomized across participants. Participants will complete a combined practice block of 16 trials (i.e., the two tasks simultaneously). The test consists of 128 trials (64 switch trials, 64 non-switch trials). The stimuli will disappear 150ms after the response if correct and after 1500ms if not. The outcome for this task will be the latency shift cost, calculated as the difference between average correct response times on switch trials and non-switch trials in the combined test block. A positive value will designate longer time to switch between the two tasks and, therefore, poorer flexibility. We will compare accuracy and latency across switch and non-switch trials to confirm task validity.
Working Memory. The Automated version of the Operation Span Task will be administered (Conway et al., 2005), which alternates between two tasks: a letter memory test and a mathematical problem. Three- to seven spans of individual letters will be presented onscreen. Participants will need to recall as many as possible in the correct order using a letter matrix. Between letter trials, simple addition, subtraction, multiplication, or division problems, as well as a possible solution, will be presented. Participants will choose whether the proposed solution is correct. The practice block comprises (a) four trials of recalling letter spans (with set sizes of two to three in ascending order), (b) 15 trials of the mathematical task, and (c) three trials of the combined tasks (letter set size of two and one math problem). The test block comprises 15 trials, in which five set sizes will be repeated three times each. The presentation order of the set sizes will be randomized. A math problem will precede each letter. The traditional Ospan score – the sum of all perfectly recalled sets – will be used as a proxy for working memory. Following previous recommendations (Unsworth et al., 2005), we will remove participants with accuracy scores of less than 85% on the mathematical problems.
Working Memory Updating. In the Letter Memory Task (Friedman et al., 2008), participants will see a fixation cross for 1000ms, followed by individual letters. For each new letter, they will name the last three letters they have seen, which they will select on a letter matrix. Each letter will appear for 2500ms, and each letter set will contain five, seven, or nine letters. Three trials (one for each set size) will be presented in random order during the practice block. The test block will consist of 12 trials (four per set size), with the order randomized but constrained so that each set size appears once every three trials. The proportion of letters correctly recalled across all test trials will be the dependent variable.

Measures throughout the MAST