Consciousness Beyond Life: The Science of the Near-Death Experience (27 page)
Read Consciousness Beyond Life: The Science of the Near-Death Experience Online
Authors: Pim van Lommel
Unproven Hypotheses
So far we can locate no single region in which the neural activity corresponds exactly to the vivid picture of the world we see in front of our eyes.
—F
RANCIS
H. C. C
RICK
The hypothesis that consciousness and memory are produced and stored exclusively in the brain remains unproven. For decades, scientists have tried unsuccessfully to localize memories and consciousness in the brain. It is doubtful whether they will ever succeed. At present science cannot explain how certain neural networks produce the subjective essence of thoughts and feelings because so far no neurophysiological study has identified any exact correspondence between specific neural activities and the specific content of memories, experiences, feelings, or thoughts. The assumption was that an activity in specific neural networks would always result in the same thoughts and feelings. Some studies spoke of a “matching content doctrine” because it was thought that the sight of certain images would always prompt the same visual perception with associated thoughts and emotions on account of this perception triggering activity in specific neural visual networks. These days scientists simply speak of neural correlates of consciousness, which means that there is a correlation (a relationship or connection) between registered activities in the brain and experiences in consciousness, and various imaging techniques (EEG, MEG, fMRI, or PET scan) have shown that a specific conscious experience can activate many, sometimes quite remote, brain centers.
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But a connection says nothing about cause or effect. A conscious experience can be the result of brain activity, but a brain activity can also be the result of consciousness. Likewise, a connection says nothing about the content of a subjective experience. An exact match between measurable brain activity and the subjective content of conscious experiences seems highly unlikely because neural activity is no more than neural activity: a way of coding information. Evidence of neural activity only means the presence of active structures. You might think of it as a radio: somebody can activate a radio by switching it on and then search for a certain wavelength to receive a particular station, but doing this does not affect the content of the broadcast. In other words, tuning in to a radio station has no influence on program content. Equally, switching on your computer, connecting to the Internet, and navigating to a Web site does not determine the content of this Web site.
The activation of certain areas of the brain cannot explain the content of thoughts and emotions. A correlation between activities in certain areas of the brain and certain conscious experiences fails to explain the origins of either consciousness or the subjective content of consciousness. The explanatory gap between the brain and consciousness has never been bridged because a certain neuronal state is not the same as a certain state of consciousness. It looks as if scientific research methods are not accurate enough for studying the neural processes underlying our conscious experiences or for demonstrating how neurons or neural networks might produce the essence of our private thoughts and feelings because, as I have explained before, what we can measure is only a correlation between registered activities in the brain and experiences in consciousness. It seems fair to conclude that current knowledge does not permit us to reduce consciousness only to activities and processes in the brain.
Interestingly, this view is fundamentally in agreement with the ideas of the philosopher and neuroscientist Alva Noë, who, based on entirely different neuroscientific research, writes in his recent book:
All scientific theories rest on assumptions. It is important that these assumptions be true. I will try to convince the reader that this startling assumption of consciousness research that consciousness is a neuroscientific phenomenon and that it happens in the brain is badly mistaken…. Contemporary research on consciousness in neuroscience rests on unquestioned but highly questionable foundations. Consciousness does not happen in the brain…. What determines and controls the character of conscious experience is not the associated neural activity. It is misguided to search for neural correlates of consciousness: There are no such neural structures. That is why we have been unable to come up with a good explanation of its neural basis…. The idea that we are our brains is not something scientists have learned; it is rather a preconception. That consciousness arises in the brain goes unquestioned. It is an unargued-for starting assumption…. It is just prejudice. We are not entitled to conclude that consciousness depends only on actions of the brain itself. And in fact we have every reason to reject it now…. Experience and cognition are not bodily by-products. It is a hard conclusion, but one that is hard to avoid…. Moreover, the mere absence of the normal behavioural markers of consciousness does not entail the absence of consciousness.
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Noë proposes that consciousness is not a by-product of the brain but that the brain’s job is that of facilitating a dynamic pattern of interaction among brain, body, and world.
Neuroscience has so far been unable to explain how neuronal behavior might account for the cause and content of thoughts and emotions, but still most scientists continue to support the view that cerebral processes underpin all aspects of consciousness. An article by Jeffrey Saver and John Rabin about the neural substrate of religious experience illustrates just how extreme this view is: “All human experience is brain-based, including scientific reasoning, mathematical deduction, moral judgment, and artistic creation, as well as religious states of mind…. There are no exceptions to this rule.”
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Neuropsychiatrist Jeffrey Schwartz writes, “Mainstream philosophical and scientific discussions may remain strongly biased toward a materialistic perspective, because one restricts one’s questions to the domain where materialism is unchallenged.”
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For decades, scientists have tried unsuccessfully to localize memories and consciousness in the brain, and it seems doubtful that they will ever succeed. So despite the fact that a majority of contemporary scientists specializing in consciousness research still espouse a materialist and reductionist explanation for consciousness, the hypothesis that consciousness and memory are produced and stored exclusively in the brain remains unproven.
Neurons and Electromagnetic Fields
The brain consists of a hundred billion neurons, twenty billion of which are located in the cerebral cortex.
Several thousand neurons die every day, but in the course of days and weeks the fats and proteins that constitute the neurons’ cell membrane undergo constant regeneration.
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The composition and cohesion of all cerebral structures, from molecules to neurons, are in constant flux, which raises a question about long-term memory. Neurons process and transmit information through electrical charges across their cell membranes, and each neuron has at least a thousand and sometimes up to ten thousand synapses, which can both excite and inhibit other neurons. Synapses are the junctions between neurons (see figure).
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A neuron with dendrites and synapses.
A neuron with dendrites and synapses. Illustration by Maura Zimmer.
Neurons work together in a highly complex network. Complexity involves a high level of integration (mutual cooperation) and differentiation (mutual differences). It means that there is a system of different neural networks (subsystems) that are both dynamically connected and differentiated.
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The result is “organized chaos.” Such processes are known as a self-organizing system, producing patterns and structures that interact with their environment but are not directly caused by external factors. A good example of self-organization is a vortex in flowing water, in which the shape of the vortex is determined by the rate of flow and the quantity of water, but the vortex itself is spontaneous and self-regulating.
We also find such self-organization in the electrical phenomena in the brain. Neurons communicate through changes in voltage, which release neurotransmitters in the synapses, or junctions between cells. The sum total of all the voltage changes produces constantly changing electrical fields.
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This also results in constantly fluctuating magnetic fields along the simultaneously activated dendrites, as the branched projections of the neurons are called. During each activity in the brain, all the electrical and magnetic patterns of millions or billions of neurons change every millisecond. Yet neither the number of neurons nor the exact shape of the dendrites nor the individual electrical pattern of individual neurons appears to play a decisive role in the information exchange. Instead the exchange is determined by the constantly changing patterns—caused by self-organization—of the electromagnetic fields that form along the dendrites in specialized neural networks.
The Influence of Electromagnetic Activity on Brain Function
The constantly fluctuating electromagnetic field in and around the brain is registered by the EEG, and from the EEG even the electrical activity of the heart can be deduced (ECG). The question now is what role the electromagnetic activity of neural networks might play in the working of the brain and in the experience of consciousness. Interfering with the brain’s electromagnetic field appears to have an effect on brain function because several studies have shown a clear change in the function of neural networks when external magnetic or electrical fields were aimed at the brain. Stimulating or inhibiting neural networks through electrical or magnetic stimulation makes it possible to study the function of these networks, while it can also trigger certain experiences in the mind and can offer a therapeutic potential.
Magnetic Stimulation
When magnetic fields are aimed at the brain, as in transcranial magnetic stimulation or TMS (see figure), this can, depending on the duration and intensity of the administered magnetic energy, either inhibit or excite certain parts of the brain. Targeted magnetic fields are thus capable of temporarily exciting or inhibiting local brain function by influencing the neurons’ constantly changing electromagnetic fields, sometimes beyond the time of stimulation, but apparently without any lasting effect.
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Transcranial magnetic stimulation thus makes it possible to map the function of certain areas of the cerebral cortex. The function of small areas in the cortex can be studied to within milliseconds, enabling scientists to research the contribution of neural networks in the cerebral cortex to specific cognitive functions.
Transcranial Magnetic Stimulation (TMS).
Transcranial Magnetic Stimulation (TMS). Illustration by Maura Zimmer.
But at a higher intensity TMS can also cause temporary impairment of brain function. Interrupting the electromagnetic processes in the cerebral cortex can momentarily disrupt vision or the experience of physical movement. Stimulating the occipital lobes, the visual processing center, can cause temporary blindness. There appears to be a direct link between the presence of an electromagnetic field and the function of neural networks. The loss of this field causes the loss of function.
Electrical Stimulation
Electrical stimulation of local neuronal networks also disrupts normal brain function, as described in 1958 by neurosurgeon Wilder Penfield and in 2004 by neurologist Olaf Blanke. Local electrical stimulation of epilepsy patients sometimes triggers images from the past (but never a panoramic life review), flashes of light, sounds, and (very rarely) a sense of detachment from the body. These artificially induced experiences are never identical to a typical NDE or to an out-of-body experience with verifiable components, nor are they life-changing. The use of low levels of electrical energy would occasionally produce either no effect or a stimulating effect, for example in the case of stimulation of the motor cortex, which causes patients’ limbs to move involuntarily. But during stimulation with higher levels of energy, the patient’s own electromagnetic fields are wiped out, resulting in the loss of function of the stimulated area in the cerebral cortex. Again, the loss of the electromagnetic field leads to a loss of function.
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