|Year : 2008 | Volume
| Issue : 3 | Page : 7
Is there only one way to make a brain?
|Date of Web Publication||17-Nov-2008|
The philosopher John Z. Young once wrote that the brain 'contains the record of all our aims and ambitions and is essential for the experience of all pleasures and pains, all loves and hates'. The functions of the brain are so extensive that the primary difficulty of making a brain is defining the desired product. While the human brain constitutes a physical structure of neurons and glia, its function is of greater significance, and indeed, the definition of a bodily organ can only be legitimately founded upon its role in preserving the organism.
As 'the coordinating centre of sensation and intellectual and nervous activity', the brain is an integral element of the nervous system controlling both internal homeostasis and the interactions of the organism with its environment, from the trivial maintenance of breathing to the finer mechanisms of rational thought and consciousness in humans. The characterisation of every duty performed by the brain appears as yet impossible, for there is an inherent paradox in employing the brain to understand itself; William C. Corning in The Mind: Biological Approaches to its Functions (1968) laments thus:
'In the study of brain functions we rely upon a biased, poorly understood, and frequently unpredictable organ in order to study the properties of another such organ; we have to use a brain to study a brain.'
While humanity has yet to discover the full range of capabilities afforded by the brain, Nature in the guise of the blind watchmaker of evolution does comprehend the true complexity of the brain, for it is the architect of this organ. Thus, to facilitate our understanding of the processes behind the making of a brain, it is useful firstly to examine the natural evolution of the organ. Thereafter, one must discuss the development of the brain from birth using the template created by evolution, and the interaction between Nature and Nurture. Having engaged in the natural production of the brain, one will be adequately prepared to analyse the potential to make an artificial brain using human technology, and to subsequently evaluate the plausibility of these arguments. Therefore, we begin with evolution developing the human brain, a process which has required 'all the forces of nature, forces which, for thousands of years, have been expending themselves upon it and impressing on it a slow and continuous motion of evolution'.[Additional file 1]
| Evolution of the brain|| |
At some distant point in history, certain creatures in the Animalia kingdom evolved to develop the brain, a 'complex web of adaptations built into the nervous system'. From the simplest system of an undifferentiated nerve net, in jellyfish for example, Nature made an arrangement resembling the brain with the evolutionary creation of insects, where a collection of ganglia cells function as a coordinating centre. The true brain has developed only in vertebrates, in which evolution has incrementally and accumulatively produced an effective coordination centre encased in bone, thus allowing the development of a complex nervous system with reduced risk from damage. This process of evolution incessantly perfecting the nervous system appears to be continuing even today; researcher Bruce T. Lahn at the University of Chicago recently discovered that two genes determining brain size emerged a mere six thousand years ago. Thus, while 'we tend to think that we have reached the pinnacle of evolution...the human brain is still changing'.[Additional file 2]
Although we have determined the evolutionary pathway towards the human brain, the reasons for this process have yet to be discussed. In Unweaving the Rainbow (1998), Richard Dawkins uses the numerical growth of the human population to justify the evolutionary advantage inherent in a more developed hominid brain. An increased population size necessitated linguistic communication for the effective distribution of manpower during hunting and foraging expeditions, which also required representational maps of the environment to be designed; the use of projectiles in the hunt itself called for improved nervous coordination between the hand and the eye. All these processes needed a bigger and more sophisticated brain, for Harry J. Jerison's 'principle of proper mass' states that the size of a species' brain is approximately proportional to the intricacy of the movement it undertakes. Therefore, Nature made the human brain because the pressures of community cohabitation rendered it an evolutionary necessity.
| Development of the human brain|| |
Through evolution, Nature has created the instructions for the making of the brain structure. As a corollary of our treasured status as human beings, we are able to make a brain by employing these processes of Nature through sexual intercourse. After the initial act of fertilisation, the physical mechanism by which Nature makes a human brain can be observed in the development of the organ, a process one must understand in our attempt to make a brain. In the embryo, a mesoderm layer of cells residing between the primitive ectoderm and endoderm forms a long cylindrical structure known as the notochord. The release of chemicals from the notochord induces rapid division of cells in the ectoderm, resulting in a neural plate. A crease - the neural groove - subsequently appears in the plate. This neural groove deepens until closure at the top of the groove creates a neural tube, the basis for the spinal cord and brain. Roofs develop at the ends of the tube, causing complete closure, whereupon vesicles form at the anterior end, which will eventually become the convoluted lobes of the brain. Subsequent migration of cells, produced at a rate of 250,000 per minute, from the ectoderm to their assigned positions in the brain occurs with the help of chemicals released by developing target organs, resulting in the precise architecture of the neuronal network. These nerve cells then develop dendrites and axons, undergo myelinization, and begin to establish synaptic connections with other cells.
Thus far the development of the human brain discussed has been the consequence of Nature expressed through inherited genes. However, the plastic brain responds to the environment to further its development. Matt Ridley states in Nature via Nurture (2003) that genes 'may direct the construction of the body and the brain in the womb, but then they set about dismantling and rebuilding what they have made almost at once - in response to experience'. Indeed the reliance of genes on the environment to sanction the expression of its potential has resulted in 'windows of opportunity' whereby a skill can only be acquired during a specific period, subject to the provision of sufficient stimuli. The importance of adequate stimulation on the growth of the brain cannot be stressed more emphatically, as exemplified by the lamentable case of Genie, who aptly demonstrates the problems of neglect during childhood.
At the tender age of twenty months, Genie was pronounced by her doctor as developmentally disabled. As a result of this consultation, she was cruelly locked up in a bedroom and severely beaten by her father whenever she endeavoured to speak. The doctor's diagnosis became a self-fulfilling prophecy when Genie was found by the Californian authorities at the age of thirteen, mute and unable to communicate by language. Subsequent attempts to acquire language through education were successful only to a certain extent. Susan Curtiss notes that 'in the most fundamental and critical aspects, Genie has language', for she was able to communicate using rudimentary vocabulary, albeit combined with faulty syntax. As Russ Rymer observes:
'Despite trying, she never mastered the rules of grammar, never could use the little pieces - the word endings, for instance. She had a clear semantic ability but could not learn syntax.'
Genie's inability to comprehend the technicalities of grammar has made her the exemplar of the critical period hypothesis proposed by Eric H. Lenneberg in his Biological Foundations for Language (1967), which was published before the discovery of Genie. He states that language acquisition has a critical period lasting from birth to puberty, so that a child who fails to learn language during this time will never achieve full linguistic competence. Genie's failure to communicate using conventional grammar and syntax supports Lenneberg's theory, yet Peter E. Jones has disputed the wisdom of justifying the concept of critical periods using the cases of Genie and other 'feral children'. Evaluating the current psycholinguistic evidence, Jones concludes that the emotional and physical trauma impressed upon Genie by her father irreparably affected her ability to acquire language. Not only was she deprived of linguistic stimuli, but the environment in which she was raised scarcely constituted the perfect nurturing ground for development; John Bowlby claims that 'mother love in infancy and childhood is as important for mental health as are vitamins and proteins for physical health'. Therefore, Genie's forced withdrawal from nurture of any manner certainly contributed to her failure to acquire language. Whilst a brain unable to comprehend language is nonetheless a brain, it is in the majority of circumstances an avoidable aspect which responsible parents would surely wish to avert. Barring medical reasons, to make the brain a parent would wish their child to possess, Nurture is as important as Nature.
| Artificial Intelligence|| |
Having observed the way a human brain is created by Nature via Nurture, one is now better equipped to engage the task of making a brain. When creating an object with a precedent template, it is wise to attempt a replication of that blueprint. Looking to the example of Nature to seek inspiration for alternative ways to make a brain can be done through simulation of Nature in artificial intelligence or through manipulation of natural processes to produce synthetic brains.
The creation of robots with pathways based on the structure of the brain has represented a significant advance in both robotics and neuroscience. Jeffrey L. Krichmar and his team at the Neurosciences Institute in California have constructed Darwin VII, a robot whose brain architecture contains 18 neural areas, 19556 neuronal units and a staggering 450000 synaptic connections. The most fascinating aspect of the design is that 'the simulation was based on the anatomy and physiology of vertebrate nervous systems'. Using experimental values obtained from rats and apes, Krichmar was able to simulate a taste system inspired by the operant conditioning advocated by Burrhus F. Skinner. As Darwin VII explores its surroundings, it senses the presence of blocks scattered by the researchers. On lifting these blocks, the robot discovers that certain blocks conduct electricity while other blocks are insulators. If the block is a conductor, the Value System is triggered, adjusting the algorithm so that the synaptic connection is enhanced; accordingly, if the block fails to conduct, an aversive mechanism occurs, thereby strengthening the robot's disapproval of insulator blocks. In this way, the researchers are able to reinforce Darwin VII's preferences and dislikes. Similarly, Junyang Weng at Michigan State University has assembled SAIL, the Self-Organising Autonomous Incremental Learner. An initial period of guided activity with feedback induced by the researcher develops SAIL's disinclination to certain conditions, and thereafter the robot can be left to its own devices to perform specified tasks.[Additional file 3]
Darwin VII and SAIL are both exceptional demonstrations of artificial intelligence founded upon the natural design of the brain, yet one wonders how far the analogy comparing the brain to a computing machine actually holds: is making a computer equivalent to making a brain? In purely biological terms, the brain acts as a processor which receives a stimulus and provides a response; equally, a programmable computer gives output values based on the input and designated algorithm. However, the comparison becomes significantly weaker when one takes into account the detail that a computer is programmable, set to implement a certain algorithm without realising the significance of the action. The brain however is able to perform a variety of tasks, and indeed understands the meaning of the deed. This is the basis of John R. Searle's Chinese Room Argument: despite the ability of computers to simulate 'the formal structure of the sequence of neuron firings' required to master the Chinese language, the semantics of that language would nonetheless be unfamiliar to the computer, for the definition of semantic meaning, the currency in which the brain deals, lies not in the physical principles building the computer, but in the meaning arbitrarily assigned by a nurturing society. Thus, Searle concludes that the comparison between the brain and a digital computer is meaningless: 'Even getting this close to the operation of the brain is still not sufficient to produce understanding.'
In its ability to undertake such a great variety of tasks, the brain certainly outperforms the computer, for it is the human brain which specifies the algorithms a synthetic computer can perform, yet the brain does not know the full extent of its abilities. Thus the computer is by definition paradoxically limited by the brain's inadequacies in understanding its own expertise. Moreover, certain processes accomplished by the brain cannot be defined as algorithms and one cannot hope to design a computer to feign that process. John Z. Young remarks that 'consciousness is such a dominating feature of one's existence that it is very hard to characterise or analyse it'. Such is the status of the mind, 'the faculty of consciousness and thought', about whose relationship with the body entire philosophies exist, ranging from the overtly scientific to the unashamedly religious. As the basis of Gestalt psychology holistically states, the whole is greater than the sum of its parts: the brain is not merely the sum of its individual processes. Therefore, building a computer capable of simulating neurological functions is not tantamount to making a brain; we must look elsewhere for a different approach to successfully executing our problem.
| Stem Cells|| |
If the computer cannot satisfactorily be likened to a brain on account of its lack of semantic ability and absence of mind, it follows that the few possibilities for making a brain lie in the ethically precarious realm of manipulating Nature itself, for a derivative of Nature acquires semantic understanding in the same way as a human does. Stem cells have been a fundamental source of moral ammunition in the Republican War on Science, and the potential inherent in recent research suggests that they could prove to be a way of making a brain. In 2002, Charles F. Stevens and colleagues at the Salk Institute showed that neural stem cells extracted from the hippocampus of a rat brain developed to 'show the same key properties as do mature CNS neurons', and indeed formed synaptic connections to adjacent adult neurons. Since the neuron is the basic unit of brain architecture, it is not inconceivable that an effective method of creating neurons could theoretically make a brain. As Harvard neuroscientist E. Snyder states:
'If we can further understand brain-cell regeneration and harness the process intelligently, then re-creating the brain, or at least parts of the brain, may lie within our grasp.'
Even brain implantation might one day become a possibility, rather than a harrowing myth reminiscent of Mary Shelley's Frankenstein (1831). In 2001, embryonic neurons capable of producing the neurotransmitter dopamine were implanted in twenty patients with severe Parkinson's disease, with seventeen successes, whereby synaptic connections were made between the implanted neuron and adjacent neurons. However, Snyder maintains that at present to implant a brain, 'the connections required are just too complex'.[Additional file 4]
| Educating the brain|| |
Robots and stem cells have both demonstrated physical potential to become brains, yet the question of Nurture remains unanswered: if one were presented with the tabula rasa surmised by Jean-Jacques Rousseau with the full potential to become a brain, what would be the aims of education in the creation of the desired product, and how would one make a mind? Evidently, one must be cautious of the dangers associated with distinguishing brains on account of their desirability, for one can easily be accused of facilitating a slippery-slope towards Huxley's dystopia of Brave New World (1932). However, educational theorists throughout history have sought to discover the ideal purposes of education: Johann F. Herbart champions Morality, John Locke Virtue and Wisdom, yet the majority agree that education must bequeath to the child qualities necessary for life as an abiding member of society, namely 'belief in the 'common good', equality and liberty...impartiality and respect for persons.'
For the behaviourist John B. Watson, a child provided with regulated conditioning and censorship of environment could be made to behave in any defined manner. Thus, he famously declared that he could make a brain as he desired:
'Give me a dozen healthy infants, well-formed, and my own specified world to bring them up in and I'll guarantee to take any one of them at random and train him to become any type of specialist I might select...regardless of his talents, penchants, tendencies, abilities, vocations and race of his ancestors.'
Nevertheless free will - unpredictable and so often irrational - appears to contradict the notion of deterministic behaviour established as a result of conditioning. Indeed Alfred J. Ayer notes that 'it is unlikely that such psychological correlations would be nearly so stringent as the laws of physics.' However, one could argue that even free will is a function of Nurture, for the conscience which motivates the expression of the will is a product of social upbringing. Therefore, one is drawn towards the demise of an universal intuitive morality, a direction which inevitably leads to the Emotivist meta-ethic derived by Ayer.[Additional file 5]
Yet Watson is nonetheless disillusioned in rooting his behaviourism so deeply in conditioning stimuli causing a certain effect, for he overemphasises a scientific approach and thereby misses the point about humanity: that we are all fundamentally different and our minds cannot be accordingly manipulated by the same scientific techniques. The repulsive horror of frontal lobotomies championed by Walter Freeman in the United States testifies to the hope that medicine will not strive to seek only a physical solution for the psychological problems faced by modern society. It is true that Freeman's patients improved with respect to their psychological condition and thereby adhered closer to the vision of a 'normal' brain, but they simultaneously became incapacitated, unable to exhibit the personality they had hitherto expressed. Only when the situation is alarmingly dire should the brain be physically changed in the hope of inducing a corresponding change in psychological behaviour, albeit a change which can never be precisely predicted. Today a physical treatment for epilepsy is cerebral commisurotomy, the severing of the corpus callosum which joins the two hemispheres of the brain. This operation has provided experimental evidence that multiple states of mind and consciousness can exist, as inferred by Thomas Nagel, for one hemisphere of the brain remains oblivious of sensory information received by the other hemisphere.
| Making the conscious mind|| |
Regarding the formation of the mind and consciousness, distinctive components of the human brain, the difficulty of applying scientific methodology is again evident; as Daniel C. Dennett maintains: 'science has revealed the secrets of many initially mysterious natural phenomena…but consciousness seems utterly unlike these'. Consciousness is known to be a definite feature of the human brain, so it is constructive to contrast our brains with those of animals. The fundamental difference between the brain of other vertebrates and that of the human is that the cerebellum and cerebral hemispheres of humans are comparatively developed, as Charles Darwin observed in The Descent of Man (1871): 'the difference in mind between man and the higher animals, great as it is, certainly is one of degree and not of kind'. According to Alison Hills, author of Do animals have rights? (2005), this difference in brain structure is responsible for the status of humans as conscious moral agents, who are able autonomously to reflect on their actions, a gift which separates us from other animals and allows for the creation of societies founded upon a communal recognition of moral justice, thus providing 'the basis for our whole elaborate social, ethical and moral system'. Hills' argument suggests that the creation of the mind complements brain development through evolution, thereby implying that a specific means of mind formation is not required in the making of a brain, for the complex brain itself generates the conscious mind. Indeed Jonathan Glover states that consciousness might possibly be a trait developing through evolution, noting that it 'is a matter of degree, not stopping abruptly, but fading away slowly as one descends the evolutionary scale'.
| Conclusions|| |
There is more than one way to make a brain, for a centre of nervous coordination is achieved within a diverse range of organisms in the natural world, suggesting that the mechanisms behind the formation of each one are different. To make a human brain, however, encompasses only one definite route, namely human sexual intercourse, which utilises the evolutionary production of a template inherited in genetic material. While possibilities for the making of a human brain lie in artificial intelligence and stem cells, significant difficulties - both practical and ethical - restrict our current understanding of these potential techniques, so that the only way of making a human brain remains as yet the natural process. The challenge to make the human brain, an organ which behaves as specifically desired, poses a further problem, for one cannot be absolutely sure that physical manipulation or conditioning will result in a specified pattern of behaviour. It is simply beyond the scope of human technology to predict the end product of brain fabrication. It seems that Nature alone operating symbiotically with Nurture holds monopoly over the ability to create the brains which make us autonomous individuals: I am I because Nature taking its course via Nurture has made me, me, an analysis aptly reflected by an inversion of the Cartesian dictum: Sum, ergo cogito. I am, therefore I think.
|How to cite this article:|
Leung T. Is there only one way to make a brain?. Young Scientists J 2008;1:7