Dr Oliver Finlay
KEY POINTS
· Cold immersion induces "cold shock" with physiological changes like tachycardia and hypertension, with hemodynamic changes prioritising cerebral circulation, potentially improving brain oxygenation and cognitive performance.
· Repeated cold-water immersion, known as cold acclimation, improves cognitive performance and neurophysiological function, while short-term whole-body cold-water immersion positively impacts brain connectivity and emotional states. Sex differences in response to intermittent cold stress highlight individual variability.
· Partial body cryostimulation (PBC) improves cognitive inhibition in males, enhancing focused attention. PBC also increases parasympathetic cardiac control, calming the body, and associates with improved cerebral oxygenation, contributing to enhanced cognitive function.
· Extended cold exposure significantly affects cognitive performance, impacting attention, processing speed, executive function, and memory. Cold immersion can impair cognition even before hypothermia, highlighting the brain's sensitivity to cold conditions.
Introduction
Cold immersion, the practice of exposing the body to cold water or environments, has attracted scientific attention due to its potential to affect the brain and cognitive performance.
Recent scientific findings suggest that cold immersion can have both immediate and long-term effects on cognitive and physiological functions in the brain, related to the physical and physiological impacts of cold immersion on the brain.
Physiological Responses During Cold Immersion
Cold Shock and Initial Responses: When one first immerses themselves in cold water, they may experience what is known as "cold shock." This initial response can induce physiological changes such as tachycardia (rapid heart rate), hypertension (high blood pressure), and reduced end-tidal carbon dioxide fraction. These physiological responses were demonstrated by Stella and Bogerd (2014) and can be attributed to the body's fight-or-flight response to cold exposure.
Hemodynamic Changes and Brain Oxygenation: Bjertnaes et al (2021), investigated the hemodynamic changes that occur during cold-water immersion. These changes include a decreased heart rate and increased blood velocity in certain arteries, which prioritise cerebral circulation and may lead to improved brain oxygenation. This effect could be a key factor in the cognitive improvements observed in cold-exposed individuals.
Physiological Impacts of Cold Immersion
Cold Acclimation and Improved Cognitive Performance: Repeated cold-water immersion can lead to a phenomenon known as cold acclimation. This process results in improved cognitive performance and enhanced neurophysiological function. Jones et al. (2019), have shown that individuals who regularly immerse themselves in cold water develop an improved capacity for cognitive tasks, possibly due to adaptations in neurophysiological function.
Changes in Brain Connectivity and Emotional States: Short-term whole-body cold-water immersion can also impact brain connectivity. Yankouskaya et al. (2023) found that this practice can lead to elevated positive emotions and a reduction in negative emotional states. This change in brain connectivity may contribute to the emotional benefits experienced during and after cold immersion.
Sex Differences in Response to Intermittent Cold Stress: Solianik et al (2014) explored the responses to intermittent cold stress in both males and females. While both sexes experienced similar thermal stress, the study found that males exhibited a more pronounced decrease in maximal voluntary contraction and greater cognitive perturbation in attention and memory tasks.
This finding suggests that males and females respond differently to intermittent cold stress, particularly in terms of physical and cognitive effects. While the exact reasons for these differences are still under investigation, it highlights the need to consider individual variability in response to cold immersion practices.
Partial-Body Cryostimulation and Cognitive Performance
Theurot et al (2021) investigated the effects of a single session of partial body cryostimulation (PBC) on males. The researchers found that PBC enhanced cognitive inhibition performance in males when they performed a Stroop task. Cognitive inhibition refers to the ability to suppress irrelevant information, which is crucial for tasks that require focused attention and decision-making. The enhanced performance on the Stroop task suggests that cold immersion, in the form of PBC, can improve certain aspects of cognitive function in males.
In addition to improved cognitive performance, the study revealed that PBC led to an increase in parasympathetic cardiac control. The parasympathetic nervous system is responsible for the body's "rest and digest" functions, including calming the heart rate and promoting relaxation. The increase in parasympathetic cardiac control indicates that PBC may have a calming effect on the body, which can be beneficial for cognitive processes that require a calm and focused mind.
Gerhart et al (2019) also studied PBC and its impact on cognitive performance, but with a focus on selective attention. The authors used the method of cold-water hand immersion and reported improved selective attention, as measured by the Stroop Color Word Test, in both normoxia and hypoxia conditions.
Adkins et al (2023) used the same method of cold-water hand immersion to evaluate the impact of immersion on sleepiness and complex task execution, in the form of arithmetic calculations. They concluded that cold water hand immersion reduced sleepiness during sleep inertia and increased the speed of arithmetic calculations.
Furthermore, PBC was associated with enhanced cerebral oxygenation. This suggests that the brain received more oxygen during PBC, which is essential for optimal cognitive function. Improved brain oxygenation may contribute to the observed cognitive enhancements.
Sustained Exposure to Cold Immersion and Cognitive Performance
Sustained cold immersion, where the body is exposed to cold conditions for an extended period, has long been recognised as a significant test of human endurance. Beyond the physical challenges, it is also an area of scientific interest because of its potential effects on the brain and cognitive performance.
Falla et al. (2021) conducted a systematic review to investigate how cold exposure affects cognitive performance in healthy adults. Their findings reveal that cold exposure can indeed affect several aspects of cognition, raising important insights into how the brain responds to extended exposure to cold conditions.
Cognitive Domains Most Affected: One of the key findings from the study is that cold exposure primarily impacts specific cognitive domains. The cognitive areas most affected by cold exposure include:
· Attention and Processing Speed: Extended exposure to cold can lead to a decline in attention and processing speed, making it more challenging to focus and think quickly.
· Executive Function: Executive function, which includes skills like problem-solving, planning, and decision-making, is also compromised under cold exposure.
· Memory: Cold immersion can impact memory function, potentially affecting the ability to remember and recall information.
Impairment in Cognitive Performance: Another notable discovery is that cold exposure can lead to cognitive impairment even before reaching the critical condition of accidental hypothermia. This means that cognitive performance can be affected by cold immersion well before the body's core temperature drops dangerously low. It highlights the sensitivity of the brain to cold conditions, even when an individual is not at immediate risk of hypothermia.
Seo et al (2013) investigated the impact on cognitive function during and after water immersion and concluded that mild immersion hypothermia without shivering does not directly impair cognitive function, but the afterdrop and shivering elicited by mild immersion hypothermia during recovery from cold immersion can impair cognitive function.
The systematic review also revealed differences among the studies in terms of various factors, including environmental temperature, the duration of exposure, timing, and the type of cognitive tests administered. These variations highlight the complexity of studying the effects of cold exposure on cognition and the need for standardised protocols to better understand the relationship.
Conclusion
In conclusion, cold immersion has substantial physical and physiological impacts on the brain. Repeated cold-water immersion can lead to cold acclimation, enhancing cognitive performance and neurophysiological function. Short-term whole-body cold-water immersion can result in changes in brain connectivity, elevating positive emotions and reducing negative emotional states.
Additionally, initial responses during cold immersion, such as cold shock, induce physiological changes like tachycardia, hypertension, and altered end-tidal carbon dioxide fraction. Hemodynamic changes prioritise cerebral circulation, possibly improving brain oxygenation. Whilst partial body cryostimulation exposure can enhance cognitive inhibition performance, increase parasympathetic cardiac control, and impact cerebral oxygenation.
However, it's important to recognise that responses to cold stress can vary between individuals, as demonstrated in the comparison between males and females. Understanding these individual differences is vital when considering the potential benefits and challenges of cold immersion practices.
Sustained cold immersion can significantly impact the brain and cognitive performance in healthy adults, primarily affecting attention and processing speed, executive function, and memory. These cognitive impairments can manifest even before the onset of accidental hypothermia, emphasising the brain's vulnerability to cold conditions.
These findings underscore the intriguing and multifaceted relationship between cold immersion and cognitive and physiological functions in the brain, suggesting that cold exposure may have both immediate and long-term effects on our cognitive and emotional well-being.
References and Evaluation of Scientific Power
Adkins, M., Cox, R., Axelsson, J. and Wright, K., 2023. Impact of cold-water hand immersion on cognitive performance and sleepiness during sleep inertia. Sleep, 46(S1), pp. A73.
Overview: The study investigates the impact of cold-water hand immersion on cognitive performance and sleepiness during a state known as "sleep inertia." Sleep inertia refers to the groggy and sluggish feeling we experience upon waking. In this research, the authors aimed to explore whether immersing one's hands in cold water could help alleviate these morning sleepiness symptoms and improve cognitive function.
Strengths: The study design is rigorous and well-structured. It involves a controlled experiment, which helps establish causal relationships. Moreover, the use of cognitive performance tests and self-reported sleepiness measures adds credibility to the results.
Limitations: The study's findings are based on a specific sample and setting, so generalising these results to different populations or contexts may not be appropriate. The short-term nature of the experiment also raises questions about the long-term effects of cold-water hand immersion. It's uncertain whether the improvements observed during the experiment would persist with continued use. Additionally, the study's scientific power rating might be limited as the sample size and the scope of the research could have been more extensive to enhance the reliability of the findings.
Conclusion: The study sheds light on an interesting and practical aspect of our daily lives - how to combat morning sleepiness and enhance cognitive performance. The use of cold-water hand immersion appears to offer a promising solution. While the study has its strengths in its methodology and design, it is essential to remember that individual responses to such interventions may vary. Further research and larger-scale studies are necessary to validate the long-term effectiveness of this approach and to explore its applicability to a wider population.
Scientific Power Rating: MODERATE - The study design and methodology were well-executed, providing valuable insights into the topic. However, the limited sample size and the specific focus of the research suggest room for expansion and more extensive investigations to strengthen the findings and their applicability in real-life scenarios.
Bjertnaes, L.J., Hauge, A., Thoresen, M. and Walløe, L., 2021. Prioritized brain circulation during ergometer cycling with apnea and face immersion in ice-cold water: a case report. International Medical Case Reports Journal, pp. 675-681.
Overview: The study is a case report that explores how the brain prioritises blood circulation during a challenging scenario—ergometer cycling while holding one's breath and immersing their face in ice-cold water. This unique experiment seeks to understand how our bodies adapt to extreme conditions, particularly concerning blood flow to the brain.
Strengths: The study's main strength lies in its novelty and uniqueness. It addresses an extraordinary situation that is rarely studied. Investigating how the brain manages blood circulation during extreme stress and cold exposure is intriguing. The study also provides valuable information about physiological responses in real-life situations. This case report helps us understand how our bodies can prioritise vital functions like brain circulation in emergencies.
Limitations: The study is based on a single case, which means it may not represent the responses of the entire population accurately. Case reports are often exploratory and can't establish causation. In this case, the findings can provide insight but are not definitive. Additionally, the specific experimental conditions are unusual and may not have direct relevance to typical daily activities.
Conclusion: This case report offers a fascinating glimpse into the prioritisation of blood circulation during an extreme situation involving apnoea, cold water, and ergometer cycling. It provides valuable insights into how our bodies respond to extreme stressors and adapt to ensure essential functions like brain circulation are maintained.
Scientific Power Rating: LOW to MODERATE - While it is a unique and intriguing study, it has limitations due to the small sample size (a single case) and the highly specific experimental conditions. For a higher scientific power rating, a larger sample and a broader range of experiments would be needed to confirm and generalise the findings. Nonetheless, this case report contributes to our understanding of extreme physiological responses, making it an interesting addition to the field of medical case reports.
Falla, M., Micarelli, A., Hüfner, K. and Strapazzon, G., 2021. The effect of cold exposure on cognitive performance in healthy adults: a systematic review. International Journal of Environmental Research and Public Health, 18(18), 9725.
Overview: The study explores how cold exposure affects the thinking abilities of healthy adults. In simple terms, it investigates whether being in the cold can make our brains work differently. The researchers gathered and analysed information from various studies to give a clearer picture of how cold surroundings might impact our cognitive performance.
Strengths: This study's strength lies in its systematic review approach. The study also focuses on a real-world issue—how our brains function when we're cold—which adds practical value to the research.
Limitations: The main limitation is that the findings are based on different studies with varying methods. The differences in how each study was done might introduce some confusion or uncertainty. Also, the researchers noted that there were variations in factors like temperature and the types of cognitive tests used, which might affect the overall results.
Conclusion: In conclusion, the systematic review method helps make sense of a bunch of different studies.
Scientific Power Rating: MODERATE - The systematic review is strong because it collects evidence from various studies, but the differences in these studies and potential variations in results bring the rating down a bit. There's still a need for more consistency in how future studies are done to be more certain about the impact of cold on our brains.
Gerhart, H.D., Seo, Y., Kim, J.H., Followay, B., Vaughan, J., Quinn, T., Gunstad, J. and Glickman, E.L., 2019. Investigating effects of cold water hand immersion on selective attention in normobaric hypoxia. International Journal of Environmental Research and Public Health, 16(16), 2859.
Overview: The study dives into the intriguing world of how cold water hand immersion might affect the ability to pay attention when the oxygen levels are lower than usual. To simplify, the researchers wanted to see if putting your hands in cold water while dealing with lower oxygen levels could influence how well you focus on things.
Strengths: The strength of this study lies in its experimental design, with participants dipping their hands in cold water while experiencing reduced oxygen levels, which helps assess the specific impact of cold water on attention in challenging conditions. Also, the study uses selective attention as its focus, which means it looks at the ability to concentrate on specific things amidst distractions.
Limitations: The main constraint is the controlled environment. While it helps establish cause and effect, the study might not perfectly represent how we handle attention in everyday life.
Conclusion: The study investigates how cold water hand immersion influences selective attention, especially under conditions of lower oxygen. It's like uncovering a piece of the puzzle about how our bodies respond to cold and low oxygen, which is vital for various real-life situations.
Scientific Power Rating: MODERATE - The experimental design adds strength, but the controlled setting might limit how well we can apply the findings to our daily experiences. More studies in different conditions would strengthen the evidence.
Jones, D.M., Bailey, S.P., De Pauw, K., Folger, S., Roelands, B., Buono, M.J. and Meeusen, R., 2019. Evaluation of cognitive performance and neurophysiological function during repeated immersion in cold water. Brain Research, 1718, pp.1-9.
Overview: The study investigates repeated cold-water immersion to figure out how it affects thinking skills and brain function.
Strengths: The study provides a thorough examination of both cognitive performance and the inner workings of the brain (neurophysiological function). The repeated immersion approach is also a strength to gain reliable results, and the researchers did this to understand the long-term effects of cold water on our brains.
Limitations: The main limitation is that the researchers didn't use a control group.
Conclusion: The study investigates the effects of repeated cold-water immersion on both cognitive performance and brain function, which can be crucial for activities involving repeated exposure to chilly environments.
Scientific Power Rating: MODERATE to STRONG - The thorough examination of cognitive performance and neurophysiological function adds strength. However, not having a control group slightly brings down the rating. Nonetheless, this study gives us valuable insights into the effects of repeated cold-water immersion on our brains.
Seo, Y., Kim, C.H., Ryan, E.J., Gunstad, J., Glickman, E.L. and Muller, M.D., 2013. Cognitive function during lower body water immersion and post-immersion afterdrop. Aviation, Space, and Environmental Medicine, 84(9), pp. 921-926.
Overview: The study investigates how our brains work when our lower bodies are in cold water and what happens afterward. It's like investigating the mental effects of being in water up to your waist and checking if there are lingering impacts after you come out.
Strengths: The study's focus is on cognitive function during and after lower body water immersion. The researchers used a controlled setting, and looked at both immediate and lingering effects, providing a more comprehensive picture.
Limitations: The main limitation is the small sample size. A larger group could help confirm if the findings apply to more people. Additionally, the study only focused on immediate and short-term effects, and it would be interesting to know more about the long-term impacts.
Conclusion: The study investigates how thinking skills are influenced when our lower bodies are in water and whether there are any surprises when we step out.
Scientific Power Rating: MODERATE - The controlled setting and the examination of both immediate and lingering effects add strength. However, the small sample size brings down the rating because having more participants would increase our confidence in the findings. Nonetheless, this study contributes valuable insights into how water immersion affects our cognitive function.
Stella, A.B. and Bogerd, C.P., 2014. Cognitive and physiological initial responses during cool water immersion. Annales Kinesiologiae, 5(1).
Overview: The study explores the initial reactions of our brains and bodies when we take a dip in cool water.
Strengths: The study's strength lies in its exploration of both cognitive (thinking) and physiological (body) responses right when you get into cool water. Additionally, the researchers used a real-world scenario—cool water immersion, something many of us experience—which adds practical value to the findings.
Limitations: The main limitation is the small sample size. Having more participants would make the findings more reliable. Also, the study only looked at the initial responses, and it would be interesting to know if these effects change over a more extended period.
Conclusion: In conclusion, the study explores immediate reactions of our brains and bodies to cool water immersion.
Scientific Power Rating: MODERATE - The exploration of both cognitive and physiological responses adds strength. However, the small sample size brings down the rating because having more people in the study would increase our confidence in the results. Nonetheless, this study offers valuable insights into what happens to us mentally and physically when we first dip into cool water.
Solianik, R., Skurvydas, A., Mickevičienė, D. and Brazaitis, M., 2014. Intermittent whole-body cold immersion induces similar thermal stress but different motor and cognitive responses between males and females. Cryobiology, 69(2), pp. 323-332.
Overview: The study investigates the impact of intermittent whole-body cold immersion on both physiological and cognitive responses, with a specific focus on gender differences. The intermittent cold immersion mimics real-world conditions where individuals experience periods of cold exposure. The study aims to comprehensively understand how the body and mind react in these scenarios.
Strengths: The study's strength lies in its thorough examination of physiological and cognitive aspects during intermittent cold immersion. By considering both male and female participants, the research provides a more inclusive understanding of gender-specific responses. The controlled maintenance of consistent temperatures enhances the reliability of the findings, akin to maintaining standardized conditions in a scientific experiment.
Limitations: However, the study has limitations. Its exclusive focus on intermittent cold immersion restricts the generalisability of the findings to other cold exposure scenarios. The absence of a longitudinal perspective limits insights into the potential evolution of responses over time.
Conclusion: The study contributes valuable insights into the nuanced responses of the body and mind during intermittent cold immersion, particularly in the context of gender differences. The study adds granularity to our understanding of how individuals cope with variations in cold exposure.
Scientific Power Rating: MODERATE to STRONG - The comprehensive examination of physiological and cognitive responses strengthens the research. However, the limited scope and lack of a longitudinal view slightly diminish the overall scientific power. Nevertheless, the study offers valuable contributions to our knowledge of the effects of intermittent cold immersion on diverse aspects of human physiology and cognition.
Theurot, D., Dugué, B., Douzi, W., Guitet, P., Louis, J. and Dupuy, O., 2021. Impact of acute partial-body cryostimulation on cognitive performance, cerebral oxygenation, and cardiac autonomic activity. Scientific Reports, 11(1), 7793.
Overview: The study delves into the effects of acute partial-body cryostimulation on cognitive performance, cerebral oxygenation (how well the brain gets oxygen), and cardiac autonomic activity (how the heart and nervous system work together). It's like exploring how a short exposure to extreme cold, focused on specific body parts, influences both our thinking skills and the way our brain and heart collaborate.
Strengths: This study's strength lies in its comprehensive approach. The researchers used a controlled setting, and they included various measurements, providing a more complete understanding of how our bodies respond to partial-body cryostimulation.
Limitations: The main limitation is the relatively small sample size. Having more participants would increase our confidence in the findings. Also, the study focused on acute effects, so we don't know if the changes observed persist over a more extended period.
Conclusion: The study investigates how acute partial-body cryostimulation influences cognitive performance, cerebral oxygenation, and cardiac autonomic activity.
Scientific Power Rating: MODERATE to STRONG - The comprehensive examination of multiple factors adds strength. However, the small sample size and the focus on acute effects slightly lower the rating. Nonetheless, this research contributes valuable insights into the immediate impacts of partial-body cryostimulation on various aspects of our physiological and cognitive functions.
Yankouskaya, A., Williamson, R., Stacey, C., Totman, J.J. and Massey, H., 2023. Short-term head-out whole-body cold-water immersion facilitates positive affect and increases interaction between large-scale brain networks. Biology, 12(2), 211.
Overview: The study takes a closer look at the effects of short-term head-out whole-body cold-water immersion. Essentially, it investigates how dipping the whole body in cold water for a short period influences our mood and the way different parts of our brain communicate.
Strengths: The strength of this study lies in its exploration of both emotional well-being and brain communication. The researchers used a controlled setting, which adds reliability to the results. Moreover, the study focuses on a real-world scenario—head-out whole-body cold-water immersion—that many people can relate to.
Limitations: The main limitation is the small sample size. Having more participants would strengthen the findings. Additionally, the study primarily focuses on short-term effects, leaving us curious about what happens over a more extended period.
Conclusion: The study provides valuable insights into the positive effects of short-term head-out whole-body cold-water immersion on mood and brain communication.
Scientific Power Rating: MODERATE - The exploration of both emotional well-being and brain communication adds strength. However, the small sample size and the emphasis on short-term effects slightly lower the rating. Nonetheless, this research contributes valuable insights into the immediate impacts of whole-body cold-water immersion on our mood and brain networks.