Laboratory mental stress tasks are commonly used in behavioral medicine to assess the physiological responses to a standardized stressor in a controlled setting (Turner 1994).
Even though originally it was thought that particularly exaggerated physiological responses to mental stress can be predictive of cardiovascular disease (Obrist 1981), there is now growing evidence that blunted physiological responses can also be associated with poor health (Carroll et al. 2009). Other evidence is available that not the responses to mental stress itself but the physiological recovery upon completion of the stress task can be related with the poor health outcomes (Larsen and Cristenfeld 2011). There is a large body of research that explores the associations between psychological traits (e.g., competitiveness and hostility) and mental disorders (e.g., depression and anxiety) with the individual differences in physiological responses to mental stress (Lovallo 1997). Participants that have been included in these stress studies comprise of young healthy participants, elderly people, and a wide variety of clinical populations. This section will describe the general setup of a laboratory stress task and the most commonly used mental stress tasks in behavioral medicine. Even though the focus will be on mental stress tasks, it is worth noting that physical tests, such as exercise, tilt test, and cold pressor, are also readily used in laboratory settings.
In order to assess the physiological responses to a mental stress task, it is important to assess the resting physiological state of the participant. To quantify the stress response, a reactivity score is calculated, which is the difference between the physiological activity during the stress task and the activity during the rest period (Turner 1994). A typical stress session starts with a resting period of 15–30 min, during which the participant is relaxed. Relaxation can be facilitated by listening to music, reading magazines, or watching a low-stimulating video. This is followed by an explanation of the stress task with, where appropriate, a brief practice session and the actual stress task. Upon completion of the stress task, a recovery period is started, during which the participant is asked again to relax, similar to the baseline rest period. The duration of the recovery period is depending on the variables that are under investigation. Whereas heart rate is known to return to baseline relatively soon after the end of the stress task, changes in other variables, in particular blood-based measures such as cytokines, will not be seen until 30 min or longer (Steptoe et al. 2007). In general, physiological data collection is conducted throughout each of these periods.
When exploring the effects of individual differences in physiological responses to mental stress, it is crucial that the testing procedures are identical between participants (Turner 1994). The conditions in the laboratory, such as temperature and number of experimenters present, but also time of day, should be kept consistent. Care should also be taken to standardize the instructions of the task, which can be done by having the instructions prerecorded. Finally, adherence of the participants to the presession instructions is important. These involve most commonly avoiding strenuous exercise, food, caffeine, and smoking, as well as instructions about the medication which could influence the physiological measurements. The presession instructions are dependent on the physiological measures that are under investigation.
Mental Stress Tasks
Public Speaking – The participant is asked to give a speech in front of an audience and/or a video camera, following a brief preparation period. The topic of speech is psychologically stressful such as “pretend that you are falsely accused of shoplifting and that you have to defend yourself to the shop owner” or “describe your personal strengths and weaknesses” or “describe a recent event that caused anger.” The participant will be told that the audience will be critically evaluating the content and delivery of the speech (Van Eck et al. 1996).
Mental Arithmetic – Different varieties are available for mental arithmetic tasks, which include serial subtraction or addition of double-digit numbers or serial addition of single-digit numbers with an element of retention. These tasks, even though not complicated in nature, have been developed to be provocative by adding components of increased time pressure, competition, harassment when a wrong answer is given, and social evaluation (Veldhuijzen van Zanten et al. 2004).
Trier Social Stress Test – This is a combination of mental arithmetic task followed by a public speech, all under conditions of social evaluation. In addition to the two varieties of mental stress, this task also has a postural component as the speech is conducted while upright (Kirschbaum and Hellhammer 1993).
Computer Games – A variety of computer games have been used to induce stress in participants, which has been mainly conducted in younger participants. These tasks often have a strong component of competition; participants are either directly competing against the experimenter (often in a modified situation to standardize the success rate between participants) or competing against the other participants in the study.
Stroop Color Word Task – The participants are presented with words which describe colors, but the color of the letters is incongruent with the color that the word is written in. For example, the word red is written with yellow ink, and the word yellow is written with red ink. The participant is asked to call out the color of the ink (Stroop 1935).
Mental stress tasks are subject to the effects task novelty and habituation (Turner 1994). For example, even though all of these tasks provoke an increase of heart rate throughout the task, typically, the peak heart rate response is seen at the start of the test. Particularly when a participant is asked to complete the task on different occasions, it is important to maintain the engagement of the participant in each session. It has been shown that the addition of stressful elements such as social evaluation and competition will help to facilitate this. To ensure that the desired levels of stress are obtained, it is common practice to add a measure of self-reported perceptions of the task to each session. These can vary from a simple Likert scale related to perceived stressfulness and difficulty or measures of state stress and anxiety levels both before and after the stress task.
The stress tasks vary in terms of generalizability to real-life settings. Interestingly, an overview of various stress task revealed that public speaking tasks were most consistently effective in inducing myocardial ischemia in patients with coronary heart disease (Strike and Steptoe 2003). It is possible that this is due to the more naturalistic nature of the task than, for example, mental arithmetic or Stroop task. However, care should be taken when interpreting the effectiveness of a certain task to induce physiological changes between studies, as it is hard to compare the stressfulness of tasks between studies. Ambulatory recording techniques are available for the assessment of physiological measurements in real-life setting. Even though these field studies cannot be standardized between participants, it is worth noting that there is evidence that the laboratory cardiovascular responses to mental stress were predictive of ambulatory physiological assessments (Strike and Steptoe 2003).
References and Further Reading
- Lovallo, W. R. (1997). Stress & health, biological and psychological interactions. Thousand Oaks: Sage.Google Scholar