Abstract

John Hughlings Jackson (1835–1911) created a science of brain function that, in scope and profundity, is among the great scientific discoveries of the 19th century. It is interesting that the magnitude of his achievement is not completely recognized even among his ardent admirers. Although thousands of practitioners around the world use the clinical applications of his science every day, the principles from which bedside neurology is derived have broader consequences—for modern and future science—that remain unrecognized and unexploited. This paper summarizes the scientific formalism that created modern neurology, demonstrates how its direct implications affect a current area of neuroscientific research, and indicates how Hughlings Jackson’s ideas form a path toward a novel solution to an important open problem of the brain and mind.

Introduction

The antecedents of most modern medical disciplines—including neurology—can be retrospectively traced for thousands of years to the earliest historical civilizations (Sigerist, 1951; Temkin, 1971). Although it is impossible to know how the originators of these ancient ideas viewed them (Steinberg, 2001), from our present perspective, it is possible to recognize some elements of current notions in these mixed magical/religious, philosophical and empirical structures. Most would agree that the neurological concepts of early Egypt and Mesopotamia were not fully scientific—and modern neurology is—so, at some intervening stage, neurology became a science. The demarcation between pre-scientific and scientific systems can be drawn at any point in this extended development depending solely on a preferred definition of science. As long as the utilized definition is explicit and unambiguous, any such choice is defensible, and can be judged by its heuristic value. For the present purposes, a science will be defined as a circumscribed body of knowledge that is organized by a reproducibly testable and predictive theory containing explicit axioms and methods. This definition is unambiguous and encompasses a commonalty of most modern sciences. By these criteria, the science of neurology began with John Hughlings Jackson—his circumscribed body of knowledge is the human nervous system, his tripartite method is explicit, his axiom is that the nervous system is exclusively sensorimotor, and his reproducibly testable and predictive theory is weighted ordinal representation. This identification does not in any way denigrate nor minimize the contributions of the many whose work preceded—and formed an essential basis—for Hughlings Jackson’s ideas. Classifying the neurological model in which their work occurred as pre-scientific does not reflect on any aspect of their insights or discoveries, but only acknowledges that all elements of a science—as here defined—had not yet coalesced. For example, the accomplishments of Nicholaus Copernicus (1473–1543) and Galileo Galilei (1564–1642) are not diminished in significance, though, according to this definition, the science of physics began with Isaac Newton (1643–1727). It is not the individual’s work that is pre-scientific, it is a retrospective evaluation of the context in which this work transpired. The identical research could occur within either a pre-scientific or scientific model. This type of analysis identifies the origins of modern ideas, and therefore is intrinsically anachronistic. Its utility is scientific and heuristic, not historical.

Hughlings Jackson’s creation of a science of the brain remains one of the great intellectual accomplishments of the 19th century, and one whose implications have even yet been incompletely exploited. This paper will explore the origin of his neuroscience, identify an unrecognized modern consequence, and indicate how his ideas can yield a potential resolution of a currently open question.

The science of neurology

Hughlings Jackson’s tripartite method

Hughlings Jackson began his exclusive focus on diseases of the nervous system in the early 1860s, probably at the suggestion of Charles-Édouard Brown-Séquard (1817–94) (Hutchison, 1911). At this time there was no specialty of neurology, and, as Hughlings Jackson immediately recognized, there was also no conceptual framework for the study of diseases of the nervous system (Hughlings Jackson, 1863a). By June of 1864 he had developed a methodology for investigating neurological disease and along the way he had discovered several important ideas that would form part of his neuroscience (Hughlings Jackson, 1864).

In 1859, Hughlings Jackson joined his fellow Yorkshireman Jonathan Hutchinson (1828–1913) in London, and soon formed a lifelong friendship. First Hutchinson, and then Hughlings Jackson, became reporters for the Medical Times and Gazette—a weekly London medical journal. From the issue of 19 January 1861 the column titled ‘Reports of medical and surgical practice’ carried their joint by-line (Hutchinson and Hughlings Jackson, 1861). As a medical reporter, Hughlings Jackson attended lectures by Brown-Séquard and was familiar with his method of pre- and post-mortem case analysis. This analysis used what may be called the phrenological assumption whereby the nervous system is assumed to consist of anatomically discrete units, each with a specific function. Acknowledging the utility of the phrenological assumption, Hughlings Jackson began collecting cases of what we would now term focal lesions that were restricted to functional units of an anatomic organ (Hughlings Jackson, 1862). A year before his explicit formulation of a complete neurological method, he began to investigate disorders of speech and language (Hughlings Jackson, 1863b). This was a fortuitous choice because it brought immediately into focus the problem of brain functions and mental functions—a relationship whose lack of clarification had prevented a systematic analysis of neurophysiology for millennia. By 1864, Hughlings Jackson had developed his tripartite analysis of neurologic disease consisting of anatomy, pathology and physiology. Specifically he advocated studying every case as presenting: (i) disease of tissue (changes in tissue); (ii) damage of organs; and (iii) disorder of function (Hughlings Jackson, 1864).

Hughlings Jackson’s tripartite methodology, and a study speech and language, led him to the important realization that a consistent and predictable science of the nervous system was possible only if it was seen as an exclusively sensorimotor machine.

Sensorimotor machine—the axiom of Hughlings Jackson’s neurology

Hughlings Jackson came to believe that the nervous system was restricted to only sensory and motor functions. This idea is an essential prerequisite for a science of neurology and is the axiom of Hughlings Jackson’s clinical neurophysiology.

Charles Bell (1774–1842), Francois Magendie (1783–1855) and Marshall Hall (1790–1857), among others, contributed significantly to what became known as the Law of Reflex Action (Bell, 1811; Magendie, 1822; Hall, 1837). Thomas Laycock (1812–76) suggested in 1844 that the law applied to the entire nervous system but did not exclude the possibility that metaphysical agents such as the soul coexisted in the cortex (Laycock, 1845). Finally, in 1884, Hughlings Jackson expunged the metaphysical from neurophysiology by stating that the entire nervous system was an exclusively sensorimotor machine (Hughlings Jackson, 1884). By limiting the study of neurology to observable events of the senses and movement, Hughlings Jackson provided the essential axiom for a science of the nervous system.

Weighted ordinal representation

The restriction of neurophysiology to sensorimotor events is necessary but not sufficient to provide a functional description of the nervous system. For the latter, Hughlings Jackson turned to contemporary ideas of evolution. He was influenced by the applications of elements of Darwinian evolution to diverse systems by Herbert Spencer (1820–1903) (Hughlings Jackson, 1884). Hughlings Jackson adopted the language of evolution and applied it to an organizational hierarchy consisting of four characteristics: increasing complexity, increasing definiteness, increasing integration and increasing interconnections. His clinical neurophysiology consisted of three levels—lowest, middle, and highest—that represent the sensorimotor structure of the body.

Hughlings Jackson’s evolutionary analysis first appeared in 1874 (Hughlings Jackson, 1874–76). In 21 papers—all published in the Medical Press and Circular between 1874 and 1876—Hughlings Jackson presented the simultaneous incremental development of multiple ideas that would form his final evolutionary neurophysiology. At the same time, he was considering the specific nature of the body’s representational hierarchy and the way the different functional units within each level are related.

Hughlings Jackson incorporated and expanded part of William H. Broadbent’s (1835–1907) 1866 hypothesis concerning bilaterally acting muscles (Broadbent, 1866). In particular, he recognized that the representations of the body in the nervous system must have different weightings. In his 1890 Lumleian lectures, Hughlings Jackson revisited his earlier thought processes;

‘Some years ago I inferred … . that both sides of the body are represented in the right half of the brain (I still say ‘right’ for convenience) … and the left and right sides of the body were differently represented in the right half of the brain. (This I have stated seems to me to be but an expansion and modification of the principle of Broadbent’s well-known hypothesis as to the double representation of the bilaterally acting muscles.)’ (Hughlings Jackson, 1890)

Hughlings Jackson theorized that each part of the body was not represented exclusively at one location—as in a homunculus—but rather each must be a heavily weighted element in a complete representation of the body. Maximal plasticity is possible if every functional unit of the nervous system at one level is a weighted copy of the entire next lower level. In other words the somatotopic representation must be ordinal (York and Steinberg, 1994, 1995). Thus, the lower, middle, and highest levels represent, re-represent, and re-re-represent the body, respectively. This representational scheme is shared by the afferent sensory systems (Hughlings Jackson, 1876). Additionally, he realized that if differential weighting was dynamic it could provide an explanation of recovery after brain damage—a well-known clinical phenomenon (Hughlings Jackson, 1884). When one area of the brain is damaged, other units can increase their weighting of the affected region thus compensating for the loss of function (York and Steinberg, 1995).

In 1884 Hughlings Jackson delivered the Croonian lectures to the Royal College of Physicians in which his complete theoretical structure for clinical neurophysiology was presented (Hughlings Jackson, 1884). Weighted ordinal representation provides a consistent and reproducible foundation for a science of neurology and successfully explains neuroscientific discoveries that could not have been imagined in Hughlings Jackson’s time. His restriction of neurology to sensorimotor physiology both made a science possible and also suggested a novel and sophisticated relationship between the brain and mind.

Concomitance

The experiments of a valid science must be reproducible. Consequently, in a clinical science of neurology, the experiments of nature (or neurological testing) require that the physiology of the brain be purely sensorimotor—the inclusion of uncharacterized processes results in the possibility that identical lesions or stimuli will produce inconsistent symptoms or responses. It was the presence of such metaphysical elements that hampered the progress of neurology for millennia. But clearly mental processes do arise from the brain—and they can affect sensorimotor responses—so the inevitable question arises of the relationship between functions of the brain and mind.

In his Croonian lectures Hughlings Jackson addressed this problem (Hughlings Jackson, 1884). He believed brain and mind were related by a doctrine of concomitance—they were like two clocks initially set to the same time, but running independently—in other words, completely correlated but causally unrelated. The term ‘concomitance,’ and the two-clock hypothesis (along with other equivalent analogies), were an invention of Gottfried Leibniz (1646–1716) (Leibniz, 1902). Though exactly how Hughlings Jackson became aware of these ideas is not certain, one possible source was his teacher Thomas Laycock who was familiar with them from the time he spent studying in Göttingen, Germany (Laycock, 1860). Hughlings Jackson believed brain and mind were completely correlated because it seems quite obvious that mental processes accompany brain processes, and he believed they were causally unrelated because he thought that conservation of energy prevented non-physical mental activity from provoking physical action.

Hughlings Jackson expressed an explicit lack of interest in metaphysical questions (Hughlings Jackson, 1887). Though he did have specific reasons for rejecting the other mind–brain hypotheses of which he was aware—now known as Cartesian dualism and the mind–brain identity theory (Hughlings Jackson, 1887)—a particularly attractive feature of the doctrine of concomitance was that it allowed him to completely separate clinical neurology from the difficult metaphysical issues involved in mental processes. Even so, he did discuss implications of concomitance for the ideas of conscious and unconscious thought, and struggled for a decade (from 1878–87) with what he termed the ‘range of concomitance’ (York and Steinberg, 1993). Hughlings Jackson had no doubt that consciousness was the concomitant of the highest level of nervous system evolution, and he therefore sought a structure of the mind consisting of evolutionary levels whose sequential representation resulted in this most complex, most definite, most integrated, and most interconnected mental state (Hughlings Jackson, 1887). He ultimately despaired of this effort (York and Steinberg, 1993), but his ideas form a template for future progress that is the topic of the penultimate section of this investigation.

Hughlings Jackson and cognitive imaging in modern neuroscience

This section presents a four-part argument for the relevance of Hughlings Jackson’s ideas in a focused discipline of modern neuroscience—the specific use of cognitive imaging to understand the nature and content of mental processes. The first part demonstrates how the characteristics of Hughlings Jackson’s concomitance are shared by a sophisticated modern view of the relation of brain and mind—i.e. the mind as an emergent property of the brain. In fact, given the linguistic context of his time, it is difficult to imagine a more accurate statement of these modern principles. Next, the nature of emergence and the rationale for considering the mind as an emergent phenomenon are discussed. Third, the implications of the mind as an emergent property are enumerated. Finally, these implications are used to demonstrate that some aspects of modern cognitive imaging are inconsistent with an emergent description of cognition. The sum of these four linked arguments, in sequence, is that Hughlings Jackson’s ideas of more than a century ago lead to the conclusion that a particular area of modern neuroscience must be modified.

To understand Hughlings Jackson’s contribution to current neuroscience, his ideas must be translated into modern terms. This process is not an attempt to speculate on what Hughlings Jackson may have thought about aspects of contemporary neuroscience, but rather to take his explicit published ideas and place them within the context of an existing scientific formalism. In the language of modern science, Hughlings Jackson’s concept of concomitance is equivalent to a description of the mind as an emergent property of the brain. In Hughlings Jackson’s concomitance, brain activity is correlated with cognitive functions but is causally unrelated—identical to the situation in an emergent system. Though emergence may seem somewhat strange from a biological or neuroscientific perspective, these phenomena are diverse and omnipresent in the natural world and include superconductivity, ferromagnetism and quite possibly the universe itself (Laughlin, 2004). But what exactly is emergence?

The term ‘emergence’ has been applied loosely in philosophy and popular science literature, and can have different meanings even in scientific disciplines. In the present context, emergence has a more restricted definition—a property is emergent if is independent of its substrate, and exhibits divergent (critical) long-range correlations. The defining characteristic of emergent properties is universality, i.e. emergent phenomena are independent of the substrate from which they emerge. An equivalent statement is that an emergent system cannot be understood in terms of a microscopic description of its substrate—a reductive description of an emergent property is not possible. Emergent properties appear at (second-order) phase transitions—criticality, self-organized criticality and scaling behaviour are other terms that are broadly synonymous. The appearance of emergence is experimentally manifest by critical behaviour of long-range correlations within the substrate.

Emergent phenomena are not easy to grasp, and even the simplest examples involve physical properties that are not commonly encountered. A fairly familiar example is superconductivity. In certain metallic and ceramic compounds—near absolute zero—quantized sound waves (quasiparticles called phonons) couple with conduction electrons to form extended two-electron systems—known as Cooper pairs—that can flow with no resistance. Characteristic of all emergent phenomena, superconductivity: (i) is independent of the substrate from which it emerges; (ii) cannot be derived from a microscopic analysis of its substrate—i.e. it has no reductive description; and (iii) demonstrates critical behaviour of long-range correlations at a second-order (superconductor–insulator) phase transition.

But, how do we know that the mind is an emergent phenomenon? We know that cognitive properties are emergent by identification of its experimental hallmarks. Emergent phenomena are recognized by critical behaviour of long-range correlations. In the case of the brain, emergence is identified by correlations of global electrical and/or magnetic activities. Such long-range correlations have been found in many experiments, and sophisticated analysis identifies critical behaviour within the data sets (e.g. Linkenkaer-Hansen et al., 2001; Varela et al., 2001; Berthouze et al., 2010). The correlations and criticality are the experimental signatures of emergent systems. Although long-range correlations and criticality have not been identified in conjunction with specific mental processes, their presence is highly suggestive of emergent behaviour within the brain.

If mental functions are emergent properties of the brain, what can we conclude? The most important conclusion is that brain activity can tell us nothing about the nature of mental processes. No knowledge of brain activity, irrespective of detail and resolution, can advance the understanding of any mental process—i.e. no microscopic description of a substrate can elucidate an emergent property. All that can be determined is the human brain machinery that is used to perform a mental function. Thus, it is impossible to gain an understanding of any aspect of cognition by examining scans of the brain. This fact was elegantly stated by Alan Ropper, a neurologist at Harvard, when he noted, ‘The mind is an emergent property of the brain and cannot be “seen” in images’ (Ropper, 2010).

If Hughlings Jackson’s concomitance of brain and mind is equivalent to a description of mind as an emergent property of the brain, then what does it imply for modern neuroscience? With the advent of high-resolution physiologic imaging technologies such as PET and functional MRI, it has become possible to visualize (presumed) correlates of brain activity—glucose metabolism and blood flow, respectively—in health and disease. Essentially coincident with the appearance of this technology was its use for investigating cognitive, as well as sensorimotor, aspects of the nervous system. Whereas the study of sensorimotor functions—e.g. movement of a finger or recovery from motor stroke—are uncontroversial, there are significant problems with extending imaging to cognitive processes. If there is no causal relation between brain and mind—as indicated by concomitance and emergence—then no information about the mind can be gained by studying the brain.

In essence, this simply reflects the logical asymmetry of cause and effect. It is important to note that this, of course, does not diminish the importance of research programs that ask how the brain performs a particular mental function or that attempt to demonstrate a statistical correlation between cerebral activity and cognitive traits. The problems arise when an attempt is made to use functional imaging to investigate the nature of the tested cognitive function. In some cases, e.g. mental arithmetic, the function—arithmetic—is known and, though nothing new about arithmetic can be learned, the localized brain machinery employed to perform simple problems can be ascertained from imaging results. But in most other cases—such as consciousness, confabulation, moral judgment, creativity and artistic expression—it is a characterization of the function that is of interest. In these circumstances, functional imaging cannot provide any information on the nature or content of the processes involved. Yet, often, modern cognitive imaging proceeds as if this was possible. Even when the authors are careful to explicitly state that they are recording brain correlates of mental functions, the conclusions—or significance—claimed for their results often implicitly demonstrate their belief that some knowledge of the tested process has been achieved. This analysis is usually denoted as the correlation of ‘structure and function’ and has attained a broad consensus in the cognitive imaging community. Though termed a correlation, it indicates a causal relation of brain structures and mental processes (Gazzaniga, 2004).

In addition to interpretive problems in academic research, of greater concern are suggested uses of cognitive imaging in society. There are proposals for the use of functional MRI as a lie detector (Lee et al., 2002), a determinant of awareness in the chronic vegetative state (Owen et al., 2007) and recommendations for applications of functional imaging in the law, economics, and society are increasing (Donaldson, 2004). Though statistical correlations of cerebral activity and observable behaviours are valid, the sample sizes are small relative to comparable data from, e.g. a polygraph, or other forms of psychological testing in these disciplines. Beyond statistics, characterization of a mental process by functional MRI is not possible—recorded activity can provide no information on the content of a thought. The sophisticated technology—and stunning images—provide an apparent scientific imprimatur for the preferred interpretation of the results, but obscure their actual meaning. In these cases—as opposed to sensorimotor imaging—the evidence of our eyes is illusory and must be supplemented by the correct interpretive framework. These particular applications of functional imaging provide only statistical information concerning the experimental query, and their illusion of more profound science may—unintentionally—result in harmful precedents. Phrenology (Rafter, 2005) and eugenics (Dikotter, 1998) are two examples of the potential dangers of the societal institutionalization of incompletely characterized science.

Hughlings Jackson, mental evolution and a future neuroscience

In the previous section, the importance of Hughlings Jackson’s doctrine of concomitance was its implications for the physics of the human mind and brain. In this section it is applied to the details of his specific structure of evolutionary neurophysiology, in a three-step process, to create a novel model of mental evolution. First, concomitance is shown to be equivalent to a complementary duality found in other well-characterized physical systems. Next, using Hughlings Jackson’s structure of nervous system evolution, the nature of the duality implied by concomitance is made explicit. Finally, with the dual character of brain and mind identified, Hughlings Jackson’s ideas again form the basis for creating an evolutionary hierarchy of the mind that parallels exactly his hierarchy of the nervous system. The result is a system for mental evolution that provides unambiguous definition of mental capacities and their relationships to each other, and has testable predictions. No such scientific structure of the mind has been previously proposed. In this manner, a future direction for neuroscience in the field of mental evolution is identified by explicitly following the development of Hughlings Jackson’s ideas. Though the details of the system so generated are beyond the scope of this paper, the point argued here is that Hughlings Jackson’s verbatim comments can provide a path to a novel solution of a currently open question of general interest and importance.

In modern terms, the combination of correlation and acausality that characterizes concomitance defines a type of duality called complementarity. Duality should not be confused with dualism. It is not a philosophical assumption, but a meta-scientific principle that played a prominent role in the quantum revolution of the 1920’s (Bohr, 1928) and does so currently in the most advanced modern physical theories (Maldacena, 1998). Complementarity results from unity at a higher level of abstraction. For example, heads and tails, night and day, and particle and wave, are common examples of acausal correlation due to underlying unity—specifically, the unity is found in the structure of a coin, rotation of the earth, and the formalism of quantum mechanics, respectively. However, simply recognizing that mind and brain are complementary does not provide any information about the nature of their duality. This duality is found in the logic of reflex action and cognition.

As a sensorimotor machine, all nervous system functions are reflex actions, and the logic of reflex action is deduction. This can be seen in many ways, but probably the simplest and most rigorous is the following. A reflex is defined by the following syllogism, ‘If sensory stimulus “x” occurs, then motor response “y” will occur’. Thus, given stimulus ‘x’ we are assured of response ‘y’. Of course, nothing limits the complexity of ‘x’ or ‘y’ and hence this same description applies to spinal reflexes as well as the most complicated and highly integrated action of the highest centres. The above syllogism is an example of modus ponens, the rule of inference defining deduction—if ‘p’ then ‘q’: ‘p’, therefore ‘q’. Thus, a sensorimotor machine is a deductive machine.

Intelligence—a generic term for mental capacity—can be succinctly defined as the facility of induction, i.e. increasing intelligence is manifest by the increasing capacity to identify a general pattern shared by a set of specific observations. The greater the mental capacity, the more rapidly and accurately general laws can be induced from specific occurrences. Thus, the process of the mind is induction and the mind is an inductive machine.

This construction accurately reflects the complementarity of brain and mind as logic can be divided into the dual elements of induction and deduction—like night and day, heads and tails, and particle and wave. Since complementary pairs result from a unity at a higher level of abstraction, it is an interesting exercise to contemplate what logical unity manifests itself as induction and deduction, or mind and brain.

As Hughlings Jackson realized, the brain and mind are completely correlated but entirely distinct. In modern terms, they can be seen as two machines of antipodal character—the former deductive and the latter inductive—acting in concert. Each sensorimotor event is the substrate for a generalization, and each generalization is tested by additional sensorimotor events. For example, a single instance of a complex sensorimotor event such as finding water near a stand of willow trees results in an induction that water can, in general, be found in these circumstances. When water is next required, the induction is tested by looking near a stand of willows. Inductions accompany the reflexes of all levels but are most apparent in the highest centres where their occurrence is responsible for the mental processes that are humanity’s most distinguishing capacities.

Hughlings Jackson’s ideas form a template for the investigation of the currently open question of the origin and nature of the human mind. No claim is made that the future direction of neuroscience, in toto, is a consequence of Hughlings Jackson’s theories, only that his ideas can help resolve this single, currently open, question. Within this context, the value of this development lies not in a comprehensive description of the structure of mental evolution so derived—those details can be found elsewhere (Steinberg and York, 1994; Steinberg, 1999)—but rather in a demonstration that Hughlings Jackson’s ideas, when followed assiduously, have continued relevance for important problems that remain unsettled 100 years after his death.

For a theory of mental evolution to be concomitant with Hughlings Jackson’s theory of brain evolution, it must consist of an ordinal function (concomitant with representation) acting successively on a fundamental substrate (concomitant with the body). If the brain integrates sensory input and by reflex generates a motor response, then the afferent function of the brain can be considered as reconstruction of an increasingly definite, increasingly integrated, and increasingly interconnected sensory map of the external world. In theory, the function of the mind is to interpret these images, and therefore reconstructed images are assumed to be the substrate of mental evolution.

The mind must therefore interpret internal sensory patterns by producing an ordinal hierarchy that will be identified with mental processes, providing their definitions. An important consequence of this structure—contrary to existing cognitive theories—is that the definitions of mental functions so derived are unambiguous and analytic—i.e. each is defined solely in terms of those that precede it. In this manner, an ordinal process of internal interpretation of reconstructed images is concomitant with the brain’s ordinal representations of the body. However, the nature of the ordinal function—concomitant with representation—must still be identified.

Intuitively, increasing mental capacity may be seen as an increasing ability to identify equivalences i.e. to generalize. In this manner, the functional analogue of representation is generalization. That is, as the body is represented and re-represented in the brain, so elements of internal images are generalized and re-generalized in the mind. With the substrate and ordinal function of mental evolution established, the specific levels of evolution—concomitant with the levels of nervous system evolution—can be determined.

The most elementary constituent of an internal image is an object, and thus the analogue of a partition of the body in brain evolution is a partition of internal images into separate objects. Mental evolution then proceeds so that each step represents an equivalence identified in the preceding stage. First categories of similar objects are recognized (categorization). This is concomitant to representation of the body in Hughlings Jackson’s lowest level of brain evolution. Second, the equivalence forming a category is defined (conceptualization). This step is concomitant to the re-representation of the body in Hughlings Jackson’s middle level of brain evolution. Individual definitions must exist somewhere—a place that can be called a concept space. The formation of an abstract concept space is defined as consciousness and corresponds to Hughlings Jackson’s highest level of brain evolution.

The open question of the nature and origin of the human mind has engaged the attention of many disciplines. Among these are studies by anthropologists (Jerison, 1973), philosophers (Jaynes, 1976), and psychiatrists (Ey, 1962; Dewhurst and Beard, 2003). The work of Henri Ey (1900–77) is particularly interesting because it explicitly uses the formulation of Hughlings Jackson’s evolutionary neurophysiology and concomitance to explore mental phenomena. To a significant degree, the present formulation of mental evolution could be seen as an actualization or model for his conceptual vision. However, there is little intersection in content between the current proposal and these investigations other than the common topic of concern. Though the insights are in all cases interesting and perceptive, they do not produce a system that is testable, analytic or predictive.

In summary, a concomitant relation of brain and mind demands that mental evolution be described by three successive actions of an ordinal function on a fundamental substrate. A formal structure for mental evolution can be generated by defining the fundamental substrate of the mind as internally reconstructed images of the external world, and the function acting on this substrate as generalizing the elements of these images. The details of this development, and its explanatory and predictive value for specifics of human mental evolution—e.g. the nature and temporal origin of language and consciousness, and an explanation of Palaeolithic age artefacts—can be found elsewhere (Steinberg, 1997, 1999). This brief overview is meant to demonstrate the relevance of Hughlings Jackson’s ideas—when explicitly followed—as a template that provides a new direction for investigating mental evolution—a currently unresolved problem in neuroscience.

Conclusion

Hughlings Jackson created a new science—a clinical neurophysiology—whose bedside applications have relieved suffering for untold millions. His insights into the brain and mind—though couched in contextual terms of social Darwinism and concomitance that today seem prejudicial and outmoded—are, when closely examined, more sophisticated than current notions and more consistent with current knowledge of the natural world. His ideas are not only manifestly useful 100 years after his death, but, if acknowledged, would transform a specific discipline of modern science and provide heuristic perspectives on the important open question of the origin and nature of the human mind.

The significance of these observations lies not only in the acknowledgment of the perspicacity of a Victorian scientist—and his potential contributions to specific aspects of modern and future neuroscience—but also demonstrate the need for continued vigilance when applying science to society. The complex technology and visually stunning pictures from advanced imaging devices may obscure the crucial step between image and meaning. When confined to the realm of research science the consequences of any misinterpretation are mostly aesthetic. However, as applications extend out of the laboratory, these issues come with a potential cost to individual rights and society. Hughlings Jackson’s scientific legacy is assured, and if his ideas are carefully considered, his humanitarian impact—even if not directly acknowledged—could be of equal importance.

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Author notes

Presented, in part, at the Symposium on the Centennial of the Death of John Hughlings Jackson (1835–1911), Royal Society of Medicine, London, 15 October 2011