An Alternative to the Traditional Cold Pressor Test: The Cold Pressor Arm Wrap

Stress exposure is associated with activation of two stress-responsive biological systems: the hypothalamic-pituitary-adrenal (HPA) and sympatho-adrenomedullary (SAM) axes⁵. When stress is of sufficient intensity to disrupt an organism's homeostatic balance, SAM quickly triggers increased activity in the sympathetic branch of the autonomic nervous system (ANS). This is associated with release of catecholamines (e.g. adrenaline and noradrenaline; CA) from the adrenal medulla and sympathetic nerve terminals. Increased levels of these excitatory chemicals are associated with elevations in heart rate and blood pressure that characterize the classic "fight-or-flight" response⁶. Although subsequent activation of the parasympathetic ANS will eventually inhibit this excitation, ascending CA neurons interfacing with brainstem structures contribute to slower HPA activation via the hypothalamus and eventual glucocorticoid (i.e. cortisol in humans) release from the adrenal cortex⁷. Understanding the relationship between stress modality and the specific dynamics of the stress response itself will be critical as research on the relationship between stress and the neural correlates of various psychological processes (e.g. memory, learning, and decision-making) advances.

Multiple stress induction tasks have been developed for use in laboratory research. Generally, these can be classified as systemic (i.e. representing a reflexive response to a direct threat to homeostatic balance) or processive/psychogenic (i.e. requiring forebrain processing and appraisal prior to engagement of the stress response)⁸. Notably, these two distinct stress modalities Fare associated with differential patterns of SAM and HPA activation. The cold pressor test (CPT) is a common and well-validated means of inducing systemic stress involving immersion of an individual's dominant hand in ice water (typically between 0-5 °C) for a period of time^4,9,10. CPT has been used in a wide range of research examining the influence of stress on memory^11-13, learning¹⁴, and decision-making^15-17. Studies using CPT as a means of stress induction have, however, yielded mixed results in terms of cortisol reactivity. Overall mild-to-moderate cortisol increases have been observed post-CPT^13,18,19, though SAM activation is robust and reliable^4,20. In contrast, processive laboratory stressors such as the Trier Social Stress Task (TSST)^21,22, during which participants give a 5 min speech followed by 5 min of mental arithmetic while being watched and/or videotaped, have been associated with two- to three-fold increases in cortisol²³.

To maximize both SAM and HPA activation, some researchers have taken the approach of combining CPT with social evaluative components similar to those present in the TSST. For example, in the socially evaluated cold pressor test (SECPT) participants are asked to perform a traditional CPT while being video-taped and watched by an experimenter²⁴. Similarly, the Maastricht Acute Stress Test integrates SECPT with public speaking and mental arithmetic components of the TSST²⁵. While these approaches represent a significant step forward in stress research it remains important to examine the specific, and potentially dissociable, influence of SAM and HPA activation on the neural correlates of behavior, cognition, and emotion. Unfortunately CPT, involving water, is often impractical to perform in studies involving magnetic resonance imaging (MRI) unless completed prior to entry into the MRI itself. For example, spilled water can be a threat to sensitive and expensive MRI equipment (e.g. the head coil) and can interfere with MRI signal due to its high proton density²⁶. Thus, as research involving CPT expands towards use in neuroimaging contexts modifications to the traditional CPT procedure are necessary. To that end, an alternative is proposed – the cold pressor arm wrap (CPAW).

Rather than hand immersion in ice-cold water, the CPAW involves an arm wrap composed of MRI-safe gelpacs cooled to a temperature similar to the traditional CPT. It can be attached to the forearm and hand of a participant, and is easily removed at their request. Further, CPAW is versatile in its composition from a simple collection of common components. It is important to note that additional safety concerns exist in CPAW use, as it can potentially be cooled to a temperature much lower than liquid water. That said, these can be accounted for with minimal effort on the part of the researcher. Proper storage and use of the CPAW will be demonstrated with special attention paid to safety protocols.