Neuro Science    





Neuroscience of Death

When we die, what happens inside our brains? This big question has many answers, and science is helping us understand more. In this note, we look at how the brain works when life ends. In other words, this is about the last part of life and how the brain slowly stops working. Join us to learn more about this important topic in a way that's easy to understand.

What happens during the process of death ?

When we talk about the end of life, it's important to understand what happens in our brains during this final stage. This can be a complex topic, but let's break it down into simpler terms. Our brain is like the control center of our body, and when it stops working, it signals the end of life. In this note, I will go through some of the key changes that occur in the brain as life comes to an end. I'll discuss how the brain stops getting the blood and oxygen it needs, how this affects the brain's energy, and the various changes in brain cells and chemicals. I will also talk about how these changes are detected and what they mean for the overall process of death.  My goal is to provide a clear and straightforward explanation of this profound and universal aspect of human life

Followings are list of key changes happening during the final stages of our life.

  • Just Before Cessation: In the moments leading up to the cessation of blood flow, the brain may experience a decrease in oxygen and nutrient supply due to declining heart function. This can result in subtle changes in brain activity, with potential alterations in consciousness or neurological function. During this phase, the body may attempt to compensate for the reduced blood flow, but these efforts are typically insufficient to maintain normal brain function
  • Blood Flow Stops(Cessation of Blood Flow and Oxygen): The main thing that happens when life ends is that blood stops flowing to the brain. This means the brain doesn't get oxygen and other important things it needs. When this happens, brain cells start to die very quickly.
  • Loss of Energy(Energy Depletion): Brain cells need oxygen and a sugar called glucose for energy. Without blood flow, the brain runs out of energy and starts to not work properly, leading to the death of its cells.
  • Chemical Changes(Neurochemical Changes): As brain cells die, they release different chemicals. These chemicals are usually used for brain cells to talk to each other. But when they're released in this way, it can make the brain very active for a short time before it starts to slow down a lot.
  • Imbalance of Ions(Ionic Imbalance): Brain cells have a careful balance of things like sodium, potassium, and calcium. When brain cells die, this balance is upset, which causes more damage to the cells and eventually leads to their death.
  • Swelling and Inflammation(Inflammation and Swelling): When the brain dies, it can become swollen and inflamed. This swelling makes the brain's condition even worse.
  • Changes in Brain Waves(Brain Wave Changes): As life ends, the brain's wave patterns change. At first, there might be a quick burst of activity. But as the brain gets less oxygen, the faster waves that help with thinking and being awake get weaker. Slower waves take over, showing that the brain is not as active. Finally, there are no waves at all, which an EEG test can show, meaning there is no brain activity.
  • Brain Stops Working(Loss of Brain Function): As more brain cells die, the brain can't do its jobs anymore. This includes simple things like reflexes and more complex things like thinking. The brain also stops doing things that keep us alive, like breathing and keeping our heart beating.
  • No Turning Back(Irreversible Cessation): After a certain point, the damage to the brain is too much and can't be fixed. This is usually shown by an EEG test that finds no activity in the brain at all. This means that the end of life has truly come.

Timeline of the last stage

Just arranging the changes during the death along a time line, it can be aligned as follows.

Time Relative to Blood Flow Cessation

Neurological Change

Just Before Cessation

Pre-Cessation Changes (e.g., reduced blood flow, oxygen levels begin to drop)

0-4 minutes

Cessation of Blood Flow and Oxygen, Initial Neurochemical Changes

4-10 minutes

Energy Depletion, Continued Neurochemical Changes, Ionic Imbalance

10-15 minutes

Brain Wave Changes

15-30 minutes

Extended Ionic Imbalance and Energy Depletion, Inflammation and Swelling

30 minutes to several hours

Loss of Brain Function, Flattening of EEG

Several hours to irreversible cessation

Irreversible Cessation

NOTE : Take this timeline just as a rough estimate, not the exact numbers.

Insights from Brain Wave Changes

Recently there were several important observations about brain wave changes (EEG) during the course of dying and I found a good review paper like What happens in the brain when we die? Deciphering the neurophysiology of the final moments in life and many articles listed in reference section. In this sectioin, I will summarize about those findings.

  • Before Death:
    • Decrease in Neuronal Activity: There's often a decrease in overall neuronal activity as the brain approaches death. This includes changes in the frequency of neural oscillations.
    • Alpha Band Activity: Alpha band activity (8–12 Hz), often related to states of relaxation or idling, might change in its functional significance.
    • Gamma Oscillations: Gamma band activity (>40 Hz), associated with consciousness and attention, can show alterations. This high-frequency activity also plays a crucial role in memory processing.
  • At the Moment of Death:
    • Surge of Oscillatory Activity: Right at the onset of death, especially in cases like cardiac arrest, there can be a surge in gamma oscillations, reflecting intense neural activity.
    • Increased Connectivity and Phase-Coupling: This surge is accompanied by increased connectivity across different brain regions and phase-coupling with other frequency bands like theta and alpha.
  • After Death:
    • Isoelectricity (Flat EEG): Following the surge, the EEG eventually flatlines, indicating a cessation of detectable brain activity. This flatline is the traditional marker of brain death.
    • Potential for Resuscitation: Interestingly, the paper discusses the potential for some recovery of brain function if re-oxygenation occurs within a brief window after the onset of isoelectricity.

The process that I mentioned above can be represented in illustration as follows.

Image Source : What happens in the brain when we die? Deciphering the neurophysiology of the final moments in life

Here’s a breakdown of what each stage represents:

  • Oxygen Depletion (A): Initially, as the brain begins to experience a lack of oxygen, there's an increase in beta (15Hz) and gamma (40-80Hz) oscillations. This reflects a heightened state of brain activity despite the onset of oxygen deprivation.
  • Low Frequency Activity (B): As the brain continues to lose oxygen, the high-frequency activity transitions to low-frequency oscillations. This indicates a significant reduction in brain function and could correspond with the loss of consciousness or active thought processes.
  • Isoelectricity (C): This phase shows the brain reaching a state of isoelectricity or a "flat line," where there is no detectable electrical activity. This is commonly associated with brain death, where brain function has ceased.
  • Cytotoxicity and Death (D): Following isoelectricity, cell death occurs due to toxic factors released from damaged cells. This stage represents the point of no return where brain cells have been irreversibly damaged and recovery of brain function is not possible.
  • Wave of Resuscitation (E): Interestingly, the graph shows a "Wave of Resuscitation" following re-oxygenation, suggesting that if oxygen is reintroduced within a critical time window, there may be a potential (though likely limited) for some brain activities to resume.

Neurlogy behind NDE (Near Death Experience)

Near-death experience (NDE) is a phenomenon where people on the brink of death report extraordinary events. They tell of feelings of peace, seeing bright lights, or even watching their life unfold before them. These tales have been told throughout history, but only now are we starting to piece together the puzzle.

Followings are a list of common experiences (NDE) that are reported and possible neurological background :

  • Feelings of Peace: The brain's response to extreme stress may include an endorphin release, which can induce a sense of calm. These naturally occurring opioids are pain-relievers that can create a feeling of euphoria.
  • Out-of-Body Experiences: Such sensations could be due to disruptions in the temporal-parietal junction, the region that integrates sensory information and contributes to body awareness. Anomalies here might lead to a disconnect between the self and the body. These could relate to altered EEG patterns in the temporal-parietal regions, reflecting disrupted body awareness.
  • Tunnel Vision: Oxygen deprivation (hypoxia) affects the visual cortex and can cause tunnel vision or light perceptions, often described in NDEs. Hypoxia can produce characteristic EEG changes, such as slowed or attenuated brain wave patterns, particularly in the visual cortex.
  • Life Review: Serotonin, a neurotransmitter involved in memory and mood, may be released in large quantities during stress, potentially leading to the life review phenomenon where past memories rapidly resurface. Serotonin surges may be detectable as heightened EEG activity due to their role in memory processing.
  • Encountering Bright Lights: Reduced blood flow in the eye can impair the retina's function, possibly leading to the experience of seeing bright lights or tunnel-like visions.