Science in Christian Perspective
Some Recent Findings in the Neurosciences and their Relevance to
C. DANIEL GEISLER
Professor of Neurophysiology Professor of Electrical and Computer Engineering
University of Wisconsin-Madison
From: JASA 28 (December 1976: 156-164
The basic building block of the vertebrate nervous system is the nerve cell. Interactions among nerve cells are accomplished by several means, chief among which are electrical pulses sent along each cell's enclosing membrane, These pulses cause the release of chemicals, called neurotransmitters, which affect neighboring cells. These neurotransmitters can influence conscious experience, as shown by the close connection between antipsychotic drugs and the neurotransmitter dopamine. As knowledge of brain function and the accompanying powers to control people accumulate, many questions are underscored. Who will control the new powers? Can the human brain be considered a computer? The answer to the last question is unknown. The organization of the brain, with its array of 1O° interconnected nerve cells, is far too complex for complete analysis by present methods. Moreover, it appears that a random component exists in the pulse patterns generated by all known nerve cells. Although not conclusive, this randomness suggests that any deterministic model of the brain would, in principle, be inaccurate. Thus, scientists may never be able to describe fully the reasons why a particular brain behaves as it does.
Modern scientific study of the brain is raising issues that are being taken seriously by an increasing number of people. With recent successes in measuring and manipulating various brain processes and in devising mathematical and computer models for them, brain scientists are currently gaining much deeper insights into the structures and functions of the brain. A few workers in several different areas of brain research have even concluded that enough is known about the functioning of the brain to show that it is a completely mechanistic machine."1,2 As it is difficult to visualize how such a machine could have free will and dignity, characteristics which most Christians believe to be intrinsic attributes of a human personality, these conclusions have been strenuously resisted. Others, fearful of the growing power of scientists to manipulate the human brain, have given warnings about the possible abuse of these powers.3,4 Thus, modem attempts to unravel the mysteries surrounding the nature of the human brain have become of considerable interest to Christianity. It is the purpose of this paper to describe a few of the newly discovered characteristics of brain function and to discuss some of their implications for Christian thought.
As in many fields of science, the study of brain mechanisms has tended to he concentrated according to various levels of complexity. Some scientists are investigating the behavior of single molecules or groups of molecules, while others investigate the structure and function of single nerve cells or of particular neural subsystems. Still others study the behavior of whole organisms. New findings in all of these areas are relevant to our purposes, but attention is focused here on the recently discovered properties of single nerve cells, particularly the mechanisms by which they communicate rapidly with each other.
The basic building block of the vertebrate nervous system is the nerve cell, called a neuron. Neurons come in many shapes and sizes, but there are certain features common to all of them. As an example, a schematic drawing of a common neuron found in the cat's spinal cord is shown in Fig. 1. This neuron looks somewhat like a tree, with root-like dendrites, a long slender trunk callel the axon, and branch-like axon terminations. There is also a roughly spherical cell body which contains the cell nucleus and is concerned with maintaining the overall health of the cell. Attention should be drawn to the outline of the cell. The lines in Fig. 1 delineating it represent a very thin skin-like membrane which completely surrounds the neuron. This membrane, which is approximately 10-5 mm (10-8 meters) in thickness, is itself an active part of the neuron and separates the inside of the cell, with its unique properties, from its surroundings. An electrical voltage of roughly 60 mV (0.06 volts) exists across the membrane.
This may seem like a tiny voltage, but remember that it exists across a very thin membrane. At those submicroscopic dimensions, it produces quite a strong electrical effect, comparable to those in existence in modern electronic devices.
Shown in Fig. 2 is a plot of how changes in this membrane voltage might look as
a function of time. For the first 2 msec (0.002 seconds) of the
graph, the voltage
is observed to vary rather randomly about an average value of zero. At 2 msec,
a slow increase in the voltage begins so that at 3 msec the voltage has risen
to 10 mV. Once the cell voltage has passed that value, a remarkable
A short voltage pulse of almost 100 my is generated. Moreover, once
has had a chance to reset itself, it will generate a similar pulse
again and again,
whenever this critical voltage level, called the threshold level, is
at 7 msee in Fig. 2). Notice that the height and shape of the two pulses shown
in the figure are almost identical. The pulse height is determined by
in ion concentrations within and without the cell. Because these concentrations
are similar for all neurons, all neuronal pulses have about the same size.
The voltage trace shown in Fig. 2 represents the voltage across a patch of membrane located near the junction of the cell body and the axon. For the type of neuron shown, this particular region has the lowest threshold level, and neuronal pulses are generated there before anywhere alse. Once generated in the junction region, the neuronal pulse has a strong influence on neighboring regions of membrane. The positive nature of the pulse raises the voltage across the adjacent patch of membrane, causing that voltage to cross its own threshold level. A neuronal pulse is then generated by this second patch of membrane and causes, in turn, the third section of membrane to generate a pulse. The first section is meanwhile resetting itself and is not affected by the pulse on the second section. The process continues on down the axon, each section generating a pulse which causes a pulse in the succeeding section. The process is very much like the burning of a firecracker fuse, where the heat of the burning section of the fuse ignites the next section. In both eases, a signal is transmitted from one end to the other, a heat pulse in one ease and a voltage pulse in the other. Moreover, in both cases the length of the signal path does not matter. Once started, the pulse propagates at a constant speed to the end of the line. Unlike the firecracker fuse which burns but once, the axon resets itself in a msec or so and is ready to conduct another pulse. It will conduct many millions of pulses over the course of its lifetime. The utility of such a mechanism is clear: pulses can be sent over arbitrarily long distances without any loss of signal. Thus, although only 102 mm in diameter, the axon of the neuron depicted in Fig. 1 conducts its pulses from the cell body which lies in the spinal cord to a muscle located, let us say, in the foot, a distance of approximately one meter. There is a price paid for this "lossless" transmission of pulses over long distances. Not only does it involve an expenditure of energy to keep the axon in readiness to gencrate pulses, but the only type of signals that can be sent along the axon are pulses. Subthreshold voltages, such as characterize the first 3 msec of the membrane voltage shown in Fig. 2, fade away within a few mm.
Before the neuronal pulse reaches the end of the axon, we must pause and briefly consider just how the axons terminate. Work with the electron microscope has revealed that, even to its very tip, each axon is totally surrounded by the cell membrane, but that very close, specialized connections are made with a certain number of other cells.6 In the brain, these connections are made to other neurons, but axons leaving the brain may also make connections with muscle fibers and other types of cells.
Figure 3 shows schematically a neuron-to-neuron connection, which is
known as a synapse. On the left or delivering side of the synapse in
Fig. 3, the
cell membrane is thickened a hit and there are a number of small
known as vesicles located in the immediate vicinity. Just opposite,
on the right side, which may be a patch located on a dendrite or the cell body
or even in rare cases on the axon of the receiving neuron, is also
presumably specially adapted for its synaptic role. Although only one synapse
is shown in Fig. 3, a single axon usually makes many synaptic connections along
the course of its termination.
Let us return now to the neuronal pulse as it reaches the end of the axon terminations. Just as the purpose of igniting a firecracker fuse is to deliver heat to the firecracker itself, so the purpose of the neuronal pulse is to deliver a voltage change to the membrane of the synaptic region at the end of the axon. That purpose accomplished, the neuronal pulse vanishes, without having any direct effect on the receiving neuron.
The next stage in the process is a chemical one.7 Upon arrival of the voltage change in the synaptic region, minute packets of a chemical compound are emitted from the axon into the gap between the two neurons. Although not absolutely certain, there is strong evidence that the total contents of one of the spherical vesicles clustered in the synaptic region make up one packet. Upon arrival in the narrow synaptic cleft, the molecules of the chemical compound are bounced around by other molecules and quickly arrive at the membrane of the receiving neuron. There, the emitted molecules form linkages with special sites on the receiving membrane that are very precisely constructed for the reception of that type of molecule. After a brief linkage, the emitted molecules break free and most of them, by various processes, are absorbed back into the emitting neuron for recycling.
During its brief existence, the linkage between the receptor site and the emitted molecule causes a change to occur in the properties of the receiving neuron's membrane. This structural change in turn causes a small voltage change to appear in the receiving neuron. If enough emitted molecules link up with the receiving membrane in a short time, the sum of all their voltage changes might be enough to carry the voltage of the trigger zone of the receiving cell past the threshold level, and a neuronal pulse would be generated on the axon of the receiving cell.8 Thus, through the use of a chemical intermediate, a voltage change is produced in the receiving neuron by the neuronal pulse on the emitting axon. As a recognition of its message-carrying nature, the chemical used as the intermediate is known as a neurotransmitter.
Not all of the interactions between neurons are carried on by means of nerve pulses, the only known method of rapid interoeuron communication over long distances. Other modes are used when neurons lie near each other. For example, dendrites of neighboring neurons may form close contacts having all of the signs of chemical transmission: vesicles localized in one dendrite and thickened cell membranes existing on both sides of the synaptic cleft.9 Thus, the transmission of information between these dendrites appears to be by means of neurotransmitters. In this case, however, the release of the chemical is not necessarily triggered by a neural impulse, but may be released by the smaller sub-threshold voltages that exist across the cell membrane in that region. It has been estimated that up to 50% of the brain may be composed of locally interacting circuits,10 where transmitter release is governed by these sub-threshold cell potentials and by neural pulses conducted on very short axons. There is evidence that some of these neighborhood interactions may even be by direct electrical means, without the use of chemical transmitters.11
Some of the most exciting recent discoveries in the neural sciences have been concerned with oeurotransmitters.7 The use of the plural form of the word is deliberate, for it is well established that not all neurons use the same neurotransmitter chemical, Two compounds, acetylcholine and noradrenaline, have been positively identified as neurotransmitters. That is, both compounds possess the complete set of specific characteristics that neurochemists have established as essential for a neurotransmitter. Nine other compounds present in the brain have been identified as possible neurotransmitters, but as yet they have not been shown to possess all of the needed properties. Although each of these compounds merits extensive discussion, we will consider only dopamine, one of the nine partially proven neurotransmitters. Effects attributed to its presence are very impressive and are closely tied into conscious human experience.
Dopamine seems to serve several purposes in the brain. Its clearest role is in connection with the proper functioning of the muscular nervous system. Not long ago, it was discovered that the brains of some patients who had died of Parkinsonism, a disease which produces uncontrollable shaking in its victims, had an abnormal dopamine content. In these brains, a particular region that is normally rich in dopamine, due to dopamine-containing axons which terminate there, was found to have virtually no dopamine. In attempts to
The excellent correlation of the data is indeed strong evidence that the powerful therapeutic effect of the antipsychotic drugs is related to the reduction of the flow of dopamine between neurons.
supply the missing dopamine, it was further discovered that injecting a closely related compound, dopa, into the blood of Parkinson's disease patients, dramatically helped to relieve their symptoms. Apparently, the dopa molecules had been able to cross into the brain, and there they had been changed into the needed dopamine by a brain enzyme known to promote this transformation. Thus, although the precise roles of dopamine. releasing axons in the neural circuits involving muscular control are unknown at present, it seems clear that these roles are of major importance.
Another role for dopamine is in the process of being established. Since their initial appearance in the 1950's, there have been a number of drugs developed for the treatment of schizophrenia. Many of these drugs are quite different from each other, but all have antipsyehotie
effects. Research involving these drugs has shown that they also have in common the ability to block the transmission of dopamine between neurons. Although the precise mechanisms of this blockage are still in debate,12,13 there is evidence which suggests that the drugs inhibit the release of the dopamine from the ends of the emitting axons. Figure 4, a drawing taken directly from a recent report,13 shows the doses of the different antipsychotic drugs needed to reduce by 50% the amount of dopamine released by electrical stimulation of excised brain slices, compared to the average clinical doses used for controlling schizophrenia. The correlation between the two measures is really remarkable. Although the different clinical doses vary by more than 10,0000-to-i, they can be used to predict with extreme accuracy the dopamine-inhibiting effect. It can be seen, for example, that quite high doses of chlorpromazine are prescribed for controlling schizophrenia, and that quite high doses of that drug are also needed to inhibit the release of dopamine from brain slices. Only the few points at the extreme top and bottom of the figure deviate significantly from the relationship shown by the straight line. Although the brains of rats, from which the electrically excited samples were obtained, are obviously very different from human brains, they have many biochemical similarities. Thus, the excellent correlation of the data in Fig. 4 is indeed strong evidence that the powerful therapeutic effect of the antipsyehotie drugs is related to the reduction of the flow of dopamine between neurons. However, even if this particular relationship were to be confirmed, much would remain mysterious. For example, it is not even
clear which of the several kinds of dopamine-containing neurons are involved in the tranquilizing reactions evoked by the antipsyehotie drugs. More fundamentally, the relationships which exist between neural activity and conscious experience of any kind are almost completely unknown.
For the last two decades, neuronal pulses have been directly observable by means of microeleetrodes. These devices, which in principle amount to small wires sharpened to a very fine point, have minute tips that can be positioned either just inside or just outside a single neuron. With that positioning, each pulse generated by that neuron causes a very small electrical signal to flow through the mieroeleetrode. Electronic amplifiers increase the size of the signals up to the level needed by the pulse analyzing equipment used, principally the computer. This combination of the mieroeleetrode to record neuronal signals and the computer to analyze them has been a very productive one. Using them, brain scientists have been able to investigate pulse patterns generated by neurons in many different regions of the brain. As an example of the kind of information being gathered, let us consider the pattern of pulses which has been recorded from neurons of the ear. These patterns are among the simplest in the vertebrate nervous system, and extensive studies have revealed the main outlines of their behavior.14
There are approximately 50,000 neurons that send information from each ear into the brain of the eat, a common experimental animal. These neurons have cell
bodies and single dendrites situated in the bony parts of the ear, and their axons extend to just inside the brain of the animal. The obvious purpose of these neurons is to carry information into the brain concerning the sound signals striking the ear. Figure 5 shows an example of how these neurons respond when a pure tone, say middle C, is sounded in the ear. The top line of the figure shows the waveform of the air pressure changes caused by the tone, and the middle line shows the neuronal pulse pattern that would typically be observed on a single one of the axons leading into the brains. At first glance, the pattern is not impressive. There are relatively few pulses and they seem to occur rather randomly. Sometimes a long interval separates two adjacent pulses and sometimes they occur in quick succession. On further investigation, however, it is found that there is a great deal of orderliness in the pattern. Either a single pulse or none at all is generated during any one cycle of the sound stimulus. Moreover, if a pulse does occur during a particular cycle, its time of occurrence is restricted to that part of the cycle near the pressure peak. A study of the intervals between pulses would reveal that although the sequence of long and short intervals is unpredictable, the probable numbers of short ones and long ones that will occur in the future can be estimated from the corresponding numbers in these data.
It might be wondered at this stage just how the brain could make sense of such a signal. If the pulse patterns of neuron 1 were the only information that the brain received about the sound signal, its interpretation would indeed be difficult. Remember, however, that thousands of these axons exist. Many of them are known to produce pulse patterns that, although not identical to the pattern of neuron 1, have nearly the same general description. Thus, the second pulse pattern shown in Fig. 5 shares all of the characteristics given for the pattern of pulses generated by neuron 1, but the two patterns are not identical. Imagine summing 100 such pulse patterns. On any one particular pressure peak, some neurons, say 20 on the average, would generate a pulse; few neurons would generate a pulse in any of the pressure valleys. Thus, every time about 20 pulses occurred within a short time period, a pressure peak would most probably have occurred. If only one or two pulses occurred in that period, a pressure valley most likely occurred then. Simply observing how the total number of pulses occurring on those 100 axons varied with time would give the observer a rather accurate indication of the pressure waveform.
The uncertainty concerning just when a neuron is going to generate the next pulse is not confined to the neurons leading from the ear. All neurons which respond to tones, even those located in the brain's farthest reaches15, do so by generating pulse patterns which contain a considerable measure of uncertainty. It seems clear from this neuronal variability that the same tone will be represented differently in the brain at different times. Data showing unpredictable aspects could also be presented for the responses produced by other types of sensory stimuli. Neurons in the brain responding to flashes of light generate different pulse trains in response to identical repetitions of the same flash.16 Moreover, uncertainties are not confined to the sensory systems of the brain. Neurons such as that depicted in Fig. 1, which send pulses out of the spinal cord to control the muscles of the body also display variability in their discharge patterns, although those pulse patterns are much more nearly predictable than the ones shown in Fig. 5. In general, it appears that all neurons have some degree of unpredictability connected with the generation of their axon pulses.
The Neuron as a Computing Element
Some of the information-transferring functions of the single neuron are now fairly well understood, at least in general principles. Although the details of the generation of the nerve pulses and the release of chemical transmitters by the different kinds of neurons are not yet known, there is no longer any real disagreement about the reality of these basic neuronal processes themselves. One neuron does not, however, make a brain. It takes many of them working together to make up the simplest kind of brain. It is this very area of interconnections and interactions between neurons that brain scientists are now just beginning to investigate.9 Unfortunately, the research is so new and the complexides of the brain so great that not much can be said yet of a positive nature. Although a considerable amount is known about where the axons of individual neurons begin and end and about which parts of the brain are related to which functions, the particular interactions between neurons by which the brain processes and stores the vast amount of information it receives are almost wholly unknown. In view of this ignorance, it is clearly impossible to state whether or not the brain is constructed like a digital computer, or anything else for that matter. However, because of the similarities in their overall information processing abilities, the brain and the digital computer have been considered by some to he the same type of mechanism.2 To appreciate just how computer processes might he considered models of brain processes, it will he useful at this point to compare certain aspects of the two systems.
The basic budding blocks of the digital computer are called logic elements. Each of these elements is an electronic device that has a single output terminal which can have only one of two possible voltage levels on it. If the sum of the input voltage is more positive than a certain threshold level, say for convenience 10
The wonder is that the brain is able to achieve such highly reliable results with basic building blocks whose characteristics are describable only in probabilistic terms.
mV, the output is set to one level, say 100 mV. When the input voltage is below
the threshold level, the output voltage assumes its other level, say
Thus, the output level of the device is either zero or 100 mV, and
level which exists at any one time depends on whether or not the input voltage
exceeds the threshold level, 10 mV. Aside from the fact that its output voltage
level does not automatically reset itself to zero upon reaching the
100 mV level,
a property which could be easily added, the behavior of the logic
element is strikingly
reminiscent of the neuron membrane (cf. Fig. 2). This resemblance is
for the first logic element was in fact developed as a model for a
patch of neuron membrane.17 The communication of one element with another is also
similar to the
communication between neurons. Although no chemical intermediates are involved,
the output of one logic element is conveyed via wires to the inputs
of other elements,
where it causes voltage changes to appear.
There are differences, however, which do exist between the neuron and the logic element. For one, the particular way in which these input voltage levels are handled by a modern digital computer's logic elements is different from the way in which neurons handle incoming pulses. To put it simply, a logic element generates pulses on its output lines in response to single input pulses, whereas the neuron generally needs many pulses before it can produce a pulse. But this difference should not be considered an essential one, for it is possible to build computers from a different type of logic element, one which, like a neuron, requires the summation of many input pulses before an output pulse is generated. In fact this summing type of logic element is a more powerful computing element than the type operating by means of single pulses."18
There is a second and apparently more fundamental difference that exists between the neuron and any type of logic element now in use. On the one hand, the logic element is a completely deterministic device that, if working properly, always generates an output pulse when the proper input pulse or pulses have been received. Any uncertainty in the timing or size of the pulses is considered a cause for concern and steps are taken to make these uncertainties as small as possible. On the other hand, uncertainty seems to he a basic property of a neuron. Consider, for example, the situation shown in Fig. 5. It is impossible to predict, by any known methods, whether neuron 1 will emit an output pulse during any particular cycle of the sound wave. It cannot be argued that this uncertainty is simply a matter of particularly unfavorable conditions. For no matter how loud or soft the sound is made, the pattern of output pulses can still he described only in probabilities and not certainties. Furthermore, as was already pointed out, these uncertainties are not con
Present scientific evidence does not prove or disprove the existence of the soul nor prove or disprove that humans are only biological machines.
fined to neurons handling sound information, but are characteristic,
to some extent,
of all neurons studied. It should therefore come as no surprise to learn that
most of the mathematical descriptions of neural pulse trains use
As so little is known about detailed interneuronal functioning, it is exceedingly difficult to try to contrast the operation of the brain at any level of organization other than that of the basic building blocks. It would appear, however, based on the differing characteristics of their basic building blocks, that the brain and the computer will prove to be very different. The modern digital computer is a completely deterministic machine, dependent for proper functioning on the unfailing operation of every single electronic component. By contrast, the brain can apparently tolerate considerable variability in the response characteristics of all of its neurons. Moreover, experiments have failed to show that the brain is dependent in its operations on any one neuron.20 The wonder is that the brain is able to achieve such highly reliable results with basic building blocks whose characteristics are describable only in probabilistic terms.
IMPLICATIONS FOR CHRISTIANS
Lessons describing the characteristics of single neurons or chemical transmitters are not scheduled for inclusion in the educational curricula of the Christian Church. Yet modern scientific study of the brain is of importance to Christians because of the intimate relationship which exists between the brain and the mind. ("Brain" is here used to mean the physical organ. "Mind" is used in the psychological sense to mean "the totality of conscious and unconscious mental processes and activities21 of a person.) For it cannot be denied that altering and controlling the human brain has proven capable of altering the most intimate and personal aspects of human experience.7 The use of antipsychotic drugs to control schizophrenia is but one example of the many ways in which drugs can be used to change fundamental aspects of human personality. There are also electrical22 and surgical23 means of altering the brain which greatly change human experience. In short, in its rapid development of ways in which to exert direct control over the brain, the neuroscienees are also learning to control the human mind.
Many of the practical implications for Christians, and for other ethically minded people, of the new types of biomedical control have been clearly stated by others and do not need to he completely restated here.24 However, it would be well to consider briefly one area of ethical concern which has particular relevance to brain research. This area concerns questions on the use and abuse of power.
Perhaps the most important point to he raised regarding the exercise of the new powers that neuroscience is creating is the one raised many years ago by C. S. Lewis.2,3 In eloquent language, he pointed out that the powers created by science are never wielded by humanity as a whole, but by the small minority of people who happen to be in control at the time. It must be granted that so far, in this country, the powers of brain control have been used mostly for beneficial purposes, such as controlling schizophrenia and relieving the symptoms of Parkinson's disease. Indeed, it is with the long range hope of learning how to prevent and alleviate diseases and malfunctions of the brain that the large amount of federal support for brain research is granted. Yet, regardless of original motives, new powers of control are being created, and once created, these powers will be available to future controllers, Whoever they may he.
As an example of the possible mischief that could be accomplished, consider the method recently suggested by two brain scientists for the control of violent crimes. Under this method, parolees, high risk ex-convicts, and people on bail would be required to wear physiological monitoring equipment connected by tiny two-way radios to a computer.25 The computer's programs would continually monitor the signals telemetered to it by each radio. Whenever the programs detected an excited physiological state in a subject located in a suspicious place, an impending crime would be diagnosed. Police would be dispatched to the scene or an electrical shock would be applied to certain of the subject's brain centers, causing him to forget or abandon the project. Such a system is technically feasible now, but would be of little or no value, because only the crudest of estimates of the state of mind of a person can currently be constructed from physiological data, including brain signals. Even so, the subject, with constant surveillance of both his external and internal worlds and with the continual threat of instantaneous outside intervention, would stiffer a much more profound loss of privacy and free will than in prison. These potential losses will no doubt become greater as the years go by, for brain scientists will be able to make increasingly accurate judgments about a subject's mental state and be able to influence it more exactly. Some may argue that though regrettable, such effects would be tolerable, for they would be confined to a small criminal segment of the population. However, history, including that of some countries during this very year, teaches us that anyone, irrespective of his actual offenses, can be declared a lawbreaker by the powerful. Moreover, many governments have demonstrated that the number of oppressed need not be a small number nor only a small segment of the population. Science is forging unique tools of great power. To believe that these tools may not someday be used ruthlessly against powerless people is to ignore the lessons of history. It is also to ignore the Biblical lesson that the kingdom of God is not yet established on the earth,26 and that evil still exists.
There are several other ethical aspects of brain research that have been raised24 that must be at least mentioned here. On the one hand, it is possible that some people without outside coercion will voluntarily use the fruits of brain research for self-degradation and dehumanization. The contemporary drug culture has graphically pointed out just how far this process can go. On the other hand, much of the truly beneficial knowledge that is being developed will, for a long time to come, be readily available only to those limited segments of our country's and the world's populations that are able to obtain adequate medical care. Like all inequities, this distribution presents serious ethical problems. Taken together, all of these concerns indicate that further brain studies should he approached with great caution. It will require great wisdom to plan future research so as to obtain the maximum of beneficial results and at the same time to develop adequate safeguards against the misuse of the resulting powers. Christians, with the fear of the Lord which is the beginning of wisdom,27 have important roles to play in this planning.
The increasing ability of brain scientists to understand and manipulate the human brain and mind by using the techniques of the physical sciences has goaded some people to the belief that the brain must operate totally according to the same basic physical and chemical priciples that govern inanimate objects.1,2 Implicit in this belief is a conviction that the mind is some aspect of the brain's functioning, with no existence apart from the brain. For it is without question that the brain controls the muscles of speaking and acting (cf. Fig. 1). If the brain's activities, and hence the person's words and deeds, were to be totally explainable by physical and chemical principles, then neither the brain itself nor anything acting on it would be exempt from following these principles. In short, the mind would have to be a manifestation of the activity of the brain, totally explainable by scientific principles, or it would have to be a totally passive spectator.
Although mechanistic interpretations of human behavior are not new,28 there now seems to be fresh evidence to support these positions. What should we think of such hypotheses? Is a belief that the brain and the mind are just parts of a biological machine compatible with Christian beliefs?
Most Christians through the centuries have answered the last question with a resounding, "No". They believed that the essence of every person is a non-material immortal soul. Orthodox Christians still believe that the soul goes immediately to its reward upon the death of the body. There, they believe, the soul will remain, independent of a body, until it is joined to a new and different kind of body at the final resurrection. 29
It should be clear by this point in the paper that scientific evidence is not
capable of deciding this basic disagreement between most Christians
and the mechanists.
The human brain's array of more than 1010 neurons, interconnected by means of
neuronal pulses and other mechanisms, is of a complexity far beyond the ability
of modern science to analyze and describe completely. The point was well summed
up by Dr. H. Davis, a distinguished senior neurophysinlogist. At a
of the Society for Neuroscience, he referred to the relationship
between the brain
and the mind as the neuroscienees' toughest unsolved problem.30 He
that neuroscientists have learned not even to use physiological and
terms in the same sentence, because of the mysterious gap that exists between
them. Some scientists even go so far as to say that the scientific tools needed
to tackle that gap have not even been developed yet.20 In short, understanding of the
neural principles governing the brain's "higher" functions,
the soul and the mind are associated, is much too rudimentary in nature either
to support or to attack the traditional Christian position at this
time. The first
conclusion to be reached, therefore, is that present scientific evidence does
not prove or disprove the existence of the soul nor prove or disprove
are only biological machines.
As brain research continues, however, knowledge of the workings of the brain will undoubtedly continue to grow. Increasingly complex models of neurons and neuronal interactions will be developed and some would see no barriers to eventually achieving arbitrarily detailed explanations of the brain. If that happened, there would be no need to talk about the soul, for all human actions would be predictable by scientific principles. It appears, however, that there may be naturally imposed limits to the ability of science to describe brain behavior. As we have seen, the present study of neurons has indicated that the uncertainties connected with the times of occurrence of the neuronal pulses are beyond current deterministic explanation. Thus, even if future scientific advances would make it possible to construct mechanistic models of each neuron in a particular brain and of all of their interconnections, it would seem unlikely that the actions of the brain model would be exactly those of the brain itself. For, as far as we can see now, the model of each neuron and perhaps each neural conection would have to include elements of uncertainty. Some models of the neurons represent these uncertainties by means of random variations in the threshold voltage level.31 Others include uncertainties in the times at which the packets of chemical transmitters are discharged into the synaptic cleft.32 By these and other means, most neuron models now incorporate an element of random behavior.19
Ever since the inception of quantum theory, scientists have suggested that the uncertainties of position and movement assigned by the theory to elementary particles might be important in the functioning of the brain.33 As these uncertainties on the atomic scale are very small, various schemes have been suggested for amplifying their size33 so as to produce effects at higher levels of organization. It would appear that the neuron is just such an amplification device. For, if the neuron models are accurate, uncertainties in the threshold level or in the times of transmitter release are events caused by uncertainties in the motion of a relatively few atoms and molecules. The unpredictabilities of these few particles would thus be reflected in the uncertain timing of the neuronal pulse, an event which controls the flow of many thousands of atoms and molecules. In any ease, uncertainties, originally thought to hold only for atomic and molecular events, appear to be a fundamental characteristic of pulse events occurring in the neuron. And as the neuron is the basic building block of the brain, uncertainty is thereby introduced into the highest levels of its organization.
Science may never be able to decide whether or not human beings have free will or a soul.
A word of caution must he inserted here. The uncertainties observed in neural
behavior might possibly be removed by future studies. One possibility is that
investigations pushed to molecular levels of organization might yield
descriptions of the emission of neurotransmitters by the vesicles.
eventuality seems very unlikely, for current investigations show that the times
of neurotransmitter packet release do indeed seem to have random distributions.34
Another possibility is that groups of neurons may be found which together have
deterministic behavior. A logic element is an example of such a
device. Its deterministic
electrical output is made up of many electrons and other charge carriers, each
of which can be described only in probabilistic terms. So far, however, there
is no evidence of any groupings of neurons which produce completely
outputs. Thus it would appear that some degree of uncertainty is
indeed a fundamental
characteristic of the triggering of neuronal pulses.
The theological implications of uncertainties in the functioning of individual neurons are unclear. Some have argued that unpredictable events in the brain would reduce the control that an individual has over his own thoughts and actions.35 Others feel that uncertainty connected with brain events would provide a mechanism for free will to act that would not disturb the predictability of physical events.33 Under this scheme, the will would be able to alter the individual brain events which happened at particular instants without changing the statistical properties of the events, which would be under the control of physical principles. Whatever the merits of these speculations, the existence of fundamental uncertainties in the timing of neuronal events would mean, subject to the qualifications given in the preceding paragraph, that science would never be able to construct a completely deterministic explanation of the functioning of the brain. The uncertainties in this explanation could very well he large enough to produce uncertainties in the basic decision-making processes of the brain, processes commonly associated with the will and the soul. Thus, a second conclusion can be drawn; science may never he able to decide whether or not human beings have free will or, by implication, a soul. In any ease, the decision is a very long way off.
It would he irreverent to end this section and this paper without reporting the feeling of awe and wonder that often steals over neuroscientists as we contemplate the workings of the brain. Everything is so complex, yet, when understood, all of the parts prove to he beautifully fitted for the functions that they fulfill. Surely we are fearfully and wonderfully made.36
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