Making Waves: The Neural Activity of the Dying Brain

Anoushka Bhatt

Illustrations by Jane Stempien

Death is an inescapable part of life. But what really happens as we die? Although everyone eventually dies, very little is actually known about the brain activity associated with death. In the past, death was defined as the termination of cardiac activity and lung functioning; however, this definition has since evolved. A person is now considered dead — both clinically and legally — when blood flow to the brain stops and neural activity ceases, which is known as brain death [1]. While brain death is sometimes preceded by a halt in cardiac activity, a person is not considered officially dead until their brain activity ceases completely [2]. Since previous neurological data had shown a decrease in brain activity after cardiac arrest, it was widely accepted that brain activity typically decreased as a person is dying [3, 4]. However, a 2022 case study — in which a man’s brain activity was monitored as his heart stopped beating — displayed a relative increase in certain brain waves leading up to and following the cardiac arrest that led to his death [5]. This case lends us a new perspective into the inner workings of a person’s brain as they approach death [5, 6]. Although the neural activity of the dying brain has been monitored before, this case study was the first time that any heightened activity was observed leading up to death, raising new questions about the experience of dying [6].

Setting the Scene: John Doe Arrives in the ER

An 87-year-old man — John Doe — arrives at the emergency room after a fall [5]. He has sustained a head injury, but his neurological status appears to be normal. He passes the basic tests of neurological functioning and demonstrates intact reflexes as well as a normal pupillary response to light [5]. Suddenly, his neurological status deteriorates: his pupil sizes distort and his eyes no longer respond to light, a sign of neurological damage [7]. Random bursts of electricity in John’s brain disrupt normal electrical patterns and cause epileptic seizures, during which his movements, sensations, and consciousness are impaired [8]. During each seizure, which can last from a few seconds to a couple of minutes, John temporarily loses control of his body [9]. His complex network of brain cells, or neurons, begins to glitch like a malfunctioning computer. Billions of neurons in the brain comprise this complex network and send electrical messages throughout the body and allow a person to do everything from breathing to thinking [10]. When neurons fire, they produce electrical signals that can be picked up by a machine called an electroencephalogram, or EEG [11]. To monitor his seizures, John’s doctors hook him up to an EEG by placing small electrodes on his head [5]. Each electrode measures electrical activity in different regions of John’s brain and the EEG generates a corresponding image that depicts brain waves as multiple lines on a screen [12]. The frequency of brain waves, measured by the number of wave peaks per second, denotes the type of wave [13]. Each type of brain wave contributes to different states of brain activity, like sleeping or problem-solving. [13, 14]. As John experiences intermittent seizures, his doctors observe shifts in electrical activity on the EEG [5]. 

Directly Preceding Cardiac Arrest: John Doe In Critical Condition

John Doe’s condition deteriorates further as blood begins pooling on the surface of his brain, pressing against and damaging brain tissue [5, 15]. Unexpectedly, John goes into cardiac arrest: his heart stops pumping blood [5, 16]. As blood flow to John’s brain and the rest of his body comes to a standstill, the EEG continues to collect data on the ongoing electrical patterns in his brain [5]. The machine detects two distinct types of brain waves: gamma and alpha. On the EEG, gamma wave activity increases directly before John’s cardiac arrest [5]. Typically associated with complex mental processes like attention, language, learning, and memory, gamma waves are recognized by their high frequency and are primarily observed during periods of high alertness and consciousness [17, 18]. Therefore, the increase in gamma waves just before John’s cardiac arrest was highly perplexing, considering he had lost consciousness. Alpha waves, which were also observed on the EEG, have a lower frequency than gamma waves and are generally observed when people feel relaxed: when the brain is in an idle state [13, 19]. Thus, it is surprising that both alpha and gamma waves were simultaneously observed in John’s brain activity. The case study proposes cross-frequency coupling as a possible mechanism to elucidate the puzzling presence of two contradictory waves. Through cross-frequency coupling, alpha waves are able to modulate the activity of gamma waves [5]. Alpha waves are typically inhibitory, meaning that they can regulate other brain waves by suppressing their activity [20]. Since the activity of alpha waves is decreasing in this particular study, they fail to inhibit gamma activity, leading to an increase in gamma waves [20]. However, it is not quite possible to discern whether cross-frequency coupling is responsible for the increase in gamma wave activity. Overall, the most prominent activity seen in John’s brain is gamma activity. Gamma waves are often correlated with activity in the visual cortex — the part of the brain that processes visual information — and are also involved in memory recall [5, 21, 22]. The observed increase in gamma wave activity before cardiac arrest invites inquiry into what, if anything, is experienced visually in the moments leading up to death.

After Cardiac Arrest: Questions and Concerns

After John goes into cardiac arrest, blood flow to his brain decreases and his brain exhibits less overall activity [5]. However, this case showed both an increase in gamma activity leading up to cardiac arrest and a relative increase in gamma activity in the moments following cardiac arrest. Although John’s brain activity decreased overall due to reduced blood flow, the relative levels of gamma activity — in comparison to the levels of other brain waves — were higher in the moments following cardiac arrest than during the time between seizures, the interictal period [5]. A common method of approximating normal brain activity during seizures, the interictal period was used as a baseline for comparison in this case, as it was the closest representation of resting brain activity for John Doe [5, 6, 23]. 

The relative increase of gamma waves in John’s brain following cardiac arrest is not consistent with the generally accepted idea that brain activity slows in the moments leading up to death [5, 6]. In prior cases, EEGs from four patients were collected during the withdrawal of life support, subsequent brain death, and for 30 minutes after death [4]. Leading up to brain death, the four EEGs showed varying levels of activity; however, they demonstrated complete inactivity for at least one and a half minutes directly preceding the stopping of the heart and no activity afterward. These findings are at odds with what was observed in John’s case, and may be explained by the fact that John’s death was a natural result of cardiac arrest, whereas the other four deaths were ‘slower,’ a consequence of withdrawing life support [4]. These findings raise many questions. Is the observed activity indicative of consciousness or merely a random firing of neurons? What do these findings mean in relation to the various cultural definitions of death [24]? Should doctors change the way they treat people in their last moments before death? As more questions arise, these findings may shape our understanding of what occurs during our final moments. While more information is necessary to paint a more comprehensive picture of brain activity during death, there are ethical concerns when it comes to conducting research on a dying person [4, 25, 26]. Attaching electrodes to the heads of people who are dying, for instance, may compromise their end-of-life comfort [25]. Another concern with end-of-life research is the issue of obtaining informed consent from people who are already incapacitated and unable to provide consent [26]. As this area of research grows, ethical considerations will be of continued importance. 

Filling the Gaps: Where Research Can Take Us

Despite its impact, John Doe's case study has been criticized due to concerns with the study’s data analysis methods [6]. A primary concern in John Doe’s case study is the lack of healthy baseline activity recorded in John’s brain, since a baseline of normal neural activity was not recorded when John arrived at the ER with head trauma [1, 6]. As a result, interictal period activity between John’s seizures was compared to the observed brain activity preceding his death, which failed to provide a clear picture of John’s brain activity under normal circumstances [1]. Therefore, we cannot be certain that the observed brain activity is unusual, as it may appear. It is also important to note that muscle contractions — such as those corresponding with John’s seizures — produce electrical signals themselves and are known to contaminate EEG readings [1, 27]. Therefore, John’s true level of brain activity may have been misrepresented due to muscle contractions [1]. While John Doe’s case study offers novel insight into brain activity at the end of life, it is still only one case study, and additional studies should be conducted to better understand the brain activity associated with cardiac arrest and traumatic brain injury [4]. Continued awareness of the variability in brain activity in each instance of death is vital, as each person exhibits physiological and neurological differences which can influence the way that end-of-life treatment is carried out. While death cannot be examined in a lab under controlled conditions, further research can provide us with a greater understanding of brain activity during our final moments.

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