How Long Can a Brain Dead Person Live?

This blog will answer the question regarding how long can a brain dead person live for and will discuss the various research findings of the same, interesting facts about the brain, as well as answers to some frequently asked questions regarding the topic.

How Long Can a Brain Dead Person Live?

The accepted consensus amongst neuroscientists is that the brain dead person survives about six minutes after death, after which the oxygen supply to the brain is cut down, and it shuts down permanently. However, human bodies differ from each other, and so does our brain. 

This article will cover some newer findings in the field of neuroscience, as well as some cases that may be considered to be outliers from the general human experience.

When considering brain death, it is important to note that it is not the same as coma. In a coma, an individual is alive and is just unconscious. However, in brain death, the person is critically ill and kept alive on life support, but eventually dies. This can take place after a stroke. 

The heart beats are continuous and the ventilator gives oxygen to the lungs, but despite that the person is essentially dead. Since the brain is the organ which is dead, or not working, the person will not be able to breathe without ventilator support. 

Signs of Brain Death

Here are some signs that a person’s brain is dead: 

The individual’s pupils do not react to pain. The eyes fail to blink even when exposed to bright light or when the eye surface is touched. There is no movement of the eyes when the head is moved. No evidence of ant gag reflex even when the back of the throat is touched. The person cannot perform automatic breathing and the electroencephalogram test does not report any brain activity. 

We will be discussing the following points in the course of this article:

  • Near-Death Experiences
  • Research findings
  • Challenges in Understanding the Findings/Generalising Them

We know that humans and rats have similar brain structures, and hence we have studied many ‘lab rats’ to understand our brain activity. Interestingly, experiments have found that after a few seconds of death, consciousness is completely lost in rats. 

After about 40 seconds, it was noticed that almost all neural activity in the brain of rats had completely disappeared. Studies have also demonstrated that there is a three-fold release of serotonin in the brains of rats before dying, which could increase feelings of happiness, bliss, and serenity. 

But what about humans? Research has shown that humans can be resuscitated after 10 minutes of death, which essentially means that there is some level of conscious activity present immediately after death. 

Near-Death Experiences 

One way in which neuroscientists have tried understanding the activity of the brain when nearing death is by studying near-death experiences. 

Near-death experiences are characterised by a rare experience taking place where the person is on the brink of death and can be recalled by the person on recovery. It is usually an out-of-body experience and individuals report seeing a vision of a tunnel light throughout the experience. 

These events have been associated with the individual feeling profound bliss, a calling, but sometimes also immense anxiety and crippling fear. 

However, before we understand what research has to say about these experiences, it is important to understand that these studies usually only focus on the nature of near-death experiences, and do not consider the events triggering or preceding them. It has always been a question for neuroscientists to understand what happens in the brain during these experiences. 

Research Findings 

We have some answers from a study done recently. According to researchers, the brain can stay alive, active, and coordinated during as well as after the transition to death. 

Hence, this means that, even when your body has shut down or is nearing death, your brain can remain active for several minutes. This explains why people who have near-death experiences can often recall the incident in detail, and remember it well because their brain was still active during the entire episode.

The study also examined the electrical brain activity of an 87-year-old man who was suffering from a head injury as a result of falling and passing away due to a series of epileptic seizure attacks and cardiac arrest. 

The researchers discovered that brain waves such as alpha and gamma continued to change patterns even after the blood flow to the brain had stopped.

 It is understood that cross-coupling between alpha and gamma wave activity is usually involved in cognitive processes such as memory recall in individuals. 

Hence, the researchers speculate that this activity being witnessed in the 87-year old subject could indicate the last ‘recall of life’ that takes place when an individual is nearing death.

The study by Vicente and colleagues (2022) challenges our understanding of how the brain functions during the process of death as well as after it. 

Researchers claim that right before the heart stops beating, they observed changes not just in gamma waves, but also in delta, theta, and alpha waves. These findings also challenge and generate important questions about the time limit for donating organs after death.

However, we should maintain caution before generalising these results, as it is not uncommon to notice the same activity between alpha and gamma waves in healthy brains, and thus this does not mean that our lives are flashing before our eyes. 

The study also does not answer the question of how long does the neural activity last after the cessation of oxygen supply to the brain. The study only recorded the brain activity of the subject for about 15 minutes including activity nearing death as well as a few minutes after death. 

Moreover, similar gamma wave activity has been observed in rats when kept in controlled conditions. Thus, it could also mean that the human brain, when dying, organises as well as carries out biological responses which are similar across species. 

Another issue with generalising this study is that it is a single case study based on a subject who suffered from a head injury as well as severe epileptic seizures. The healthy brain cannot be compared with the subject’s brain due to these conditions that the subject was suffering from. The study has low external validity and thus limited generalisation. 

Conclusion

This blog answered the question regarding how long can a brain dead person live for and discussed the various research findings of the same, interesting facts about the brain, as well as answers to some frequently asked questions regarding the topic.

Frequently Asked Questions: How Long Does a Brain Dead Person Live?

When someone is dying, what do they see or hear?

In many cases, visual or auditory hallucinations are common in the dying experiences. Individuals tend to see family members/loved ones who have passed away before, welcoming them to the “afterlife”. They may also talk to people that others do not tend to see. These visions of loved ones passing away are considered to be normal.

How does the brain shut down before dying?

After the heart stops beating, there is a significant loss of blood flow in the brain. This is when the brain starts shutting down. Due to the lack of blood flow, there is considerable loss of oxygen in the brain which forces neural activity to slow down, and eventually stop after a few minutes. However, the entire shutting down of the brain may take several hours, and thus the person may be mildly aware of their surroundings even after death. 

Which part of the brain shuts down first? 

Neuroscientists have theorised that since the supply to the brain is pumped from underneath, the brain would shut down from the top to downwards. This means that our conscious awareness of ourselves, our sense of humour, and our ability to plan fades out first in about 10-20 seconds, and then eventually our memories, knowledge of the language, as well as hearing ability fade out later.

References

Borjigin, J., Lee, U., Liu, T., Pal, D., Huff, S., Klarr, D., … & Mashour, G. A. (2013). Surge of neurophysiological coherence and connectivity in the dying brain. Proceedings of the National Academy of Sciences, 110(35), 14432-14437.

Vicente R, Rizzuto M, Sarica C, Yamamoto K, Sadr M, Khajuria T, Fatehi M, Moien-Afshari F, Haw CS, Llinas RR, Lozano AM, Neimat JS and Zemmar A (2022) Enhanced Interplay of Neuronal Coherence and Coupling in the Dying Human Brain. Front. Aging Neurosci. 14:813531. doi: 10.3389/fnagi.2022.813531

Wutzler, A., Mavrogiorgou, P., Winter, C., & Juckel, G. (2011). Elevation of brain serotonin during dying. Neuroscience letters, 498(1), 20-21.

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