PennNeuroKnow

When stress takes the plunge: The brain’s drive response

October 6th, 2026

Written by Stephanie Uroda

How many times have you seen a character in your favorite show or movie splash water on their face to snap themselves out of a state of panic or shock? It turns out this common cinematic cliché is not simply an overused director’s choice. It actually taps into a fascinating survival response hardwired into the brain. But before we dive into what happens when cold water hits your face, let’s take a moment to understand what happens inside your body when you experience stress.

How does our nervous system control our stress response?

The autonomic nervous system (ANS) is the part of the nervous system responsible for controlling many of the body’s automatic functions, including heart rate, digestion, breathing, body temperature, and production of body fluids like tears and sweat. The ANS helps our bodies maintain balance and respond to changes in our environment. For example, sweating when we are too hot and shivering when we are too cold are both coordinated by the ANS to help maintain a stable internal body temperature.

The ANS can be further divided into two branches: the sympathetic and parasympathetic nervous systems.

The sympathetic nervous system prepares the body to respond to a threat. It dilates the pupils, inhibits saliva production, increases heart rate, slows digestion, and redirects blood flow toward the muscles. If these changes sound familiar, that’s because they are the hallmarks of the body’s classic “fight-or-flight” response. Together, they prepare your body for rapid, strenuous activity.1

The parasympathetic nervous system, on the other hand, generally promotes functions associated with rest and recovery. It slows heart rate, stimulates digestion, and helps return the body to a calmer state via its connection to your organs through the vagus nerve.1

When your brain senses a stressor in your environment, it activates the hypothalamus, which is a region of the brain that helps coordinate the body’s response to stress. The hypothalamus communicates with the ANS through the spinal cord and brainstem, triggering sympathetic activity. Within seconds, your heart begins pounding, your breathing becomes faster, and your palms become sweaty. This response is useful when you need to respond quickly to danger. When the perceived threat has passed, parasympathetic activity helps bring the body back toward its resting state by slowing the heart and promoting digestion.2

Because the sympathetic and parasympathetic nervous systems have opposing effects, they are sometimes described as an accelerator and a brake. But this analogy is misleading because both branches can be active at the same time, and in some situations, they work together to produce a coordinated physiological response. One striking example is the mammalian diving response.

What is the mammalian diving response?

The mammalian diving response is a set of automatic physiological changes that occur when a mammal’s face is submerged in water. The response has three major components: 1) voluntary or involuntary breath holding, 2) slowing of the heart rate, and 3) constriction of blood vessels in the limbs and other peripheral tissues.3–5

Connection to Evolution

The mammalian diving response was first formally studied in the 1930s by Laurence Irving and P.F. Scholander.6 They noted evidence of the diving response across mammalian species, including humans, although it is much more pronounced in natural divers like seals.7–10

Their work has since been expanded upon by scientists theorizing the mammalian diving response has developed as a way to conserve oxygen during submersion. This theory is supported by evidence that the diving response is not triggered when other parts of the body unrelated to breathing are submerged underwater.11 When a mammal’s face is underwater, it cannot obtain oxygen through breathing, so conserving the oxygen already stored in the blood becomes critical. Slowing the heart reduces the body’s oxygen demands, while constricting blood vessels in the limbs redirects blood toward organs that are especially sensitive to oxygen deprivation, particularly the brain and heart.3,4

Interestingly, the response is particularly strong when the face is exposed to cold water compared to warmer water.11,12 This sensitivity to cold may have been particularly useful for mammals that regularly entered cold aquatic environments, although the evolutionary reason for the temperature dependence is not fully understood.

Neuroscience Explanation

The exact communication pathway between the body and the brain that is responsible for the mammalian diving response is being investigated.3,11 However, researchers generally agree that sensory information from the face carried by the trigeminal nerve, one of the major nerves of the head, plays a central role. The trigeminal nerve contains sensory receptors that detect changes in temperature and touch. When cold water contacts the face, these receptors send signals through the trigeminal nerve to the ANS in the brainstem. This is where the diving response becomes particularly interesting. Rather than simply activating one branch of the autonomic nervous system and suppressing the other, the response coordinates both.

Parasympathetic activity increases through the vagus nerve, slowing the heart. At the same time, sympathetic activity causes blood vessels in the limbs to constrict, reducing blood flow to the periphery and helping preserve blood for the heart and brain.3

Repurposing an evolutionary survival response to reduce stress

So, what does any of this have to do with stress and anxiety? When we are highly stressed or panicked, sympathetic activity can become elevated, producing many of the uncomfortable physical sensations associated with anxiety: a racing heart, rapid breathing, sweating, and a feeling that something is wrong. In these moments, simply telling ourselves that we are safe may not be enough to immediately stop the body’s physiological response. This has led researchers to ask whether we can harness the diving response to help shift the body toward a calmer physiological state.

One way to do this is through the Cold Face Test, in which cold water or another cold stimulus is applied to the face. In recent studies, researchers have found that cold facial stimulation can activate components of the diving response and produce measurable decreases in heart rate and cortisol levels.13–15 These studies also reported short-term reductions in self-reported and psychologically assessed anxiety and panic symptoms.13–15

Why might this happen? One possibility is the activation of the parasympathetic nervous system, particularly through the vagus nerve. Increased vagal activity slows the heart and is associated with the body’s recovery from acute stress. Research in animals has also found that stimulating the vagus nerve can reduce anxiety-related behaviors.16–18 Scientists therefore hypothesize that activating the diving response through cold facial stimulation may indirectly engage some of the same parasympathetic pathways involved in calming the body’s response to stress. However, there is a lot more research that needs to be done in order to link the physiological changes induced by the diving response with psychological changes associated with stress reduction.

To bring it all back to your favorite movie or TV show, that splash of cold water we so often see on screen may not simply be a dramatic Hollywood cliché. It may tap into an ancient physiological response that evolved to help mammals survive underwater and that our bodies still carry with us today.

References

  1. McCorry LK. Physiology of the Autonomic Nervous System. Am J Pharm Educ. 2007;71(4):78. doi:10.5688/aj710478
  2. Understanding the stress response. Harvard Health. June 15, 2011. Accessed September 28, 2026. https://www.health.harvard.edu/healthy-aging-and-longevity/understanding-the-stress-response
  3. Panneton WM, Gan Q. The Mammalian Diving Response: Inroads to Its Neural Control. Front Neurosci. 2020;14:524. doi:10.3389/fnins.2020.00524
  4. Michael Panneton W. The Mammalian Diving Response: An Enigmatic Reflex to Preserve Life? Physiology. 2013;28(5):284-297. doi:10.1152/physiol.00020.2013
  5. Scholander PF. The Master Switch of Life. Sci Am. 1963;209(6):92-107.
  6. Irving L. Respiration in diving mammals. Physiol Rev. 1939;19(1):112-134. doi:10.1152/physrev.1939.19.1.112
  7. Irving L, Scholander PF, Grinnell SW. The regulation of arterial blood pressure in the seal during diving. Am J Physiol-Leg Content. 1942;135(3):557-566. doi:10.1152/ajplegacy.1942.135.3.557
  8. Irving L, Scholander PF, Grinnell SW. Significance of the heart rate to the diving ability of seals. J Cell Comp Physiol. 1941;18(3):283-297. doi:10.1002/jcp.1030180302
  9. The human diving response, its function, and its control – Foster – 2005 – Scandinavian Journal of Medicine & Science in Sports – Wiley Online Library. Accessed September 28, 2026. https://onlinelibrary.wiley.com/doi/10.1111/j.1600-0838.2005.00440.x
  10. Panneton WM, Gan Q, Juric R. The rat: a laboratory model for studies of the diving response. J Appl Physiol. 2010;108(4):811-820. doi:10.1152/japplphysiol.00600.2009
  11. Gooden BA. Mechanism of the human diving response. Integr Physiol Behav Sci. 1994;29(1):6-16. doi:10.1007/BF02691277
  12. Bhaskar KV, Manohar PM, Sindhura L. Autonomic Effects of Facial Immersion at Varying Water Temperatures: A Comparative Study Across Two Age Groups. Eur J Cardiovasc Med. 2025;15:582-586. doi:10.61336/ejcm/25-04-87
  13. Kyriakoulis P, Caballero CL. The implications of the diving response in altering carbon dioxide sensitivity as measured by changes in heart rate, respiration rate and psychological measures in panic disorder patients. Front Psychiatry. 2025;16:1533019. doi:10.3389/fpsyt.2025.1533019
  14. Kyriakoulis P, Kyrios M, Nardi AE, Freire RC, Schier M. The Implications of the Diving Response in Reducing Panic Symptoms. Front Psychiatry. 2021;12:784884. doi:10.3389/fpsyt.2021.784884
  15. Richer R, Zenkner J, Küderle A, Rohleder N, Eskofier BM. Vagus activation by Cold Face Test reduces acute psychosocial stress responses. Sci Rep. 2022;12:19270. doi:10.1038/s41598-022-23222-9
  16. Souza RR, Powers MB, Rennaker RL, McIntyre CK, Hays SA, Kilgard MP. Timing of vagus nerve stimulation during fear extinction determines efficacy in a rat model of PTSD. Sci Rep. 2022;12(1):16526. doi:10.1038/s41598-022-20301-9
  17. Butler AG, Bassi JK, Connelly AA, Melo MR, Allen AM, McDougall SJ. Vagal nerve stimulation dynamically alters anxiety-like behavior in rats. Brain Stimulat. 2025;18(2):158-170. doi:10.1016/j.brs.2025.01.018
  18. Noble LJ, Gonzalez IJ, Meruva VB, et al. Effects of vagus nerve stimulation on extinction of conditioned fear and post-traumatic stress disorder symptoms in rats. Transl Psychiatry. 2017;7(8):e1217. doi:10.1038/tp.2017.191

ChatGPT version 5.6 was used to help with rewording some sentences and to come up with the title.

Cover photo by Karla Hernandez from unsplash.com.