Consciousness after death
Consciousness after death is a common theme in society and culture in the context of life after death. Scientific research has established that the mind and normal waking consciousness are closely connected with the physiological functioning of the brain, the cessation of which defines brain death. However, many people believe in some form of life after death, which is a feature of many religions.
Neuroscience is a large interdisciplinary field founded on the premise that all of behavior and all of the cognitive processes that constitute the mind have their origin in the structure and function of the nervous system, especially in the brain. According to this view, the mind can be regarded as a set of operations carried out by the brain.
There are multiple lines of evidence that support this view. They are here briefly summarized along with some examples.
- Neuroanatomical correlates: In the field of neuroimaging, neuroscientists can use various functional neuroimaging methods to measure an aspect of brain function that correlates with a particular mental state or process.
- Experimental manipulations: Neuroimaging (correlational) studies cannot determine whether neural activity plays a causal role in the occurrence of mental processes (correlation does not imply causation) and they cannot determine if the neural activity is either necessary and sufficient for such processes to occur. Identification of causation and necessary and sufficient conditions requires explicit experimental manipulation of that activity. If manipulation of brain activity changes consciousness, then a causal role for that brain activity can be inferred. Two of the most common types of manipulation experiments are loss-of-function and gain-of-function experiments. In a loss-of-function (also called "necessity") experiment, a part of the nervous system is diminished or removed in an attempt to determine if it is necessary for a certain process to occur, and in a gain-of-function (also called "sufficiency") experiment, an aspect of the nervous system is increased relative to normal. Manipulations of brain activity can be performed in several ways:
- Pharmacological manipulation using various drugs which alter neural activity by interfering with neurotransmission, resulting in alterations in perception, mood, consciousness, cognition, and behavior. Psychoactive drugs are divided into different groups according to their pharmacological effects; euphoriants which tend to induce feelings of euphoria, stimulants that induce temporary improvements in either mental or physical functions, depressants that depress or reduce arousal or stimulation and hallucinogens which can cause hallucinations, perception anomalies, and other substantial subjective changes in thoughts, emotion, and consciousness.
- Electrical and magnetical stimulations using various electrical methods and techniques like transcranial magnetic stimulation. In a comprehensive review of electrical brain stimulation (EBS) results obtained from the last 100 years neuroscientist Aslihan Selimbeyoglu and neurologist Josef Parvizi compiled a list of many different subjective experiential phenomena and behavioral changes that can be caused by electrical stimulation of the cerebral cortex or subcortical nuclei in awake and conscious human subjects.
- Optogenetic manipulation where light is used to control neurons which have been genetically sensitised to light.
- Symptoms of brain damage: Examining case studies (like the case of Phineas Gage) and lesion studies are the only sources of knowledge regarding what happens to the mind when the brain is damaged. Various symptoms have been documented.
- Mental development/brain development correlation: The brain grows and develops in an intricately orchestrated sequence of stages, and this development is correlated with the development of various mental capabilities. Impairments in the growth and development of the brain also result in various neurodevelopmental disorders.
Death was once defined as the cessation of heartbeat (cardiac arrest) and of breathing, but the development of CPR and prompt defibrillation have rendered that definition inadequate because breathing and heartbeat can sometimes be restarted. Events which were causally linked to death in the past no longer kill in all circumstances; without a functioning heart or lungs, life can sometimes be sustained with a combination of life support devices, organ transplants and artificial pacemakers.
Today, where a definition of the moment of death is required, doctors and coroners usually turn to "brain death" or "biological death" to define a person as being dead; brain death being defined as the complete and irreversible loss of brain function (including involuntary activity necessary to sustain life).
Near-death experiences (NDEs)
A near-death experience (NDE) refers to a personal experience associated with impending death, encompassing multiple possible sensations including detachment from the body, feelings of levitation, total serenity, security, warmth, the experience of absolute dissolution, and the presence of a light.
Explanatory models for the NDE can be divided into several broad categories, including psychological, physiological, and transcendental explanations. Research from neuroscience considers the NDE to be a hallucination caused by various physiological and psychological factors, while some NDE researchers in the field of near-death studies, notably Pim van Lommel, Sam Parnia, Peter Fenwick and Bruce Greyson have argued that the NDE cannot be adequately explained by physiological and psychological causes and that the experience poses a major challenge to current materialistic thinking regarding the relationship between consciousness and the brain. The major premise behind the argument that NDEs present such a challenge is that the experience represents a case of a heightened lucid consciousness happening while the brain either no longer functions or while being too severely impaired to support such a lucid consciousness.
According to neuroscientist Jason J. Braithwaite,
Where neuroscience and the paranormalist part intellectual company is primarily over the existence of objective cases where lucid experience occurs in the co-presence of objective, verifiable evidence of total and complete brain inactivity or brain activity insufficient to support consciousness. In many ways this gets to the crux of the theoretical divide between neuroscientific accounts of the NDE and those ideas consistent with paranormal/dualistic interpretations of the NDE. The paranormalist makes a number of sweeping assumptions about the existence of certain evidence, about the brain, about psychology, and then from this muddy premise, argues that certain observations demand explanation from mainstream science. However, the neuroscientist does not accept that these cases, as presented by paranormalists, have ever really been established or actually represent the type of evidence the paranormalist presumes. As such, the need for this type of explanation becomes redundant. The theoretical divide then can be seen as one of sufficiency, where the paranormalist thinks a sufficient case has been made to demand explanation, and the neuroscientist views the case to be insufficient to warrant one."
The "heightened lucid consciousness" of NDErs is according to Braithwaite compatible with the predictions of the dying-brain hypothesis, "...the dying-brain hypothesis predicts that more vivid, profound, and meaningful NDEs are likely to be associated with greater degrees of disinhibition. Thus, NDEs reported when people truly are nearer to death (and hence the level of disinhibition would conceivably be greater), should be more vivid, profound, detailed and meaningful, relative to those reported when people only believed themselves to be so. This is exactly what has been found."
In contrast to the hypothesis that NDEs occur during the supposed period of no brain activity or brain activity insufficient to support consciousness, Braithwaite (2014), as well as psychologist Chris French argued that the NDE could easily have occurred well before brain activity ceased, or well after during recovery. Parnia and Fenwick (2001) had rejected the idea that the NDE may have occurred just prior to or just after the loss of consciousness. They argued that LOC happens too quickly and that events that occur just prior (or just after) would not be expected to be recalled, and that the period of recovery is characterized by delirium and not by the lucid consciousness reported by NDErs. In a summary of these arguments, Braithwaite (2014) concluded that "all claims about the phenomenology being different between NDEs and syncope, or the time periods in cases of cardiac arrest being 'too quick' are irrelevant as neither pertain to the actual arguments from the syncopal model. As a consequence, these specific dualist arguments against syncope as a comparative model of NDEs can be legitimately ignored."
Parnia and Fenwick (2001) also argued that the occurrence of anecdotal reports of patients being able to see and recall detailed events occurring during the cardiac arrest that are afterwards verified by hospital staff supports the argument that such perception sometimes do occur during periods of clinical death. NDE researcher Janice Miner Holden found 107 such anecdotal reports in the NDE literature as of 2009, out of which approximately 91% were accurate.
According to French (2005) and Blackmore (1993), when serious attempts at corroboration are attempted, the evidence often turns out to be nowhere near as impressive as it initially appeared. And such cases can possibly (since they had not been ruled out) be accounted for in terms of non-paranormal factors including, "information available at the time, prior knowledge, fantasy or dreams, lucky guesses, and information from the remaining senses. Then there is selective memory for correct details, incorporation of details learned between the end of the NDE and giving an account of it, and the tendency to tell a good story.”
NDE researchers have also been criticized by scientists of placing undue confidence in EEG measures. French (2005) and Braithwaite (2008, 2014) claimed that survivalists generally appear to assume that a flat EEG is indicative of total brain inactivity. Even assuming that NDEs actually occur during such periods, the assumption that isoelectric surface EEG recordings are always indicative of total brain inactivity is according to Braithwaite and French wrong. Braithwaite (2008) noted that "unless surgically implanted into the brain directly, the EEG principally measures surface cortical activity. The waveforms seen in cortical EEG are largely regarded to come from the synchronistic firing of cortical pyramidal neurons. As such, it is entirely conceivable that deep sub-cortical brain structures could be firing, and even in seizure, in the absence of any cortical signs of this activity."
According to French (2005) future research in the near-death experience should focus on devising ways to distinguish between the two main hypotheses relating to when the NDE is occurring. If it really is occurring when some NDE researchers claim that it is, during a period of flat EEG with no cortical activity, then modern neuroscience would require serious revision. This would also be the case if the OBE, either within the NDE or not, could be shown to be veridical. Attempts to test the veridicality of OBEs using hidden targets (e.g., Parnia and Fenwick (2001) should be welcomed.
- Biogerontology, the science of biological aging
- Death anxiety (psychology)
- Disorders of consciousness, including brain death
- Dualism (philosophy of mind)
- Eternal oblivion
- Life extension
- Neural correlates of consciousness
- Senescence, biological aging
- Thanatophobia, fear of death
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