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John Hughlings Jackson’s evolutionary neurology: a unifying framework for cognitive neuroscience

Elizabeth A. Franz, Grant Gillett
DOI: http://dx.doi.org/10.1093/brain/awr218 3114-3120 First published online: 16 September 2011

Summary

John Hughlings Jackson was a pioneer in neurology who thought deeply about the structure of the brain and how that manifested itself in the various syndromes that he saw in the clinic. He enunciated a theory of the evolution and dissolution of neural function based on the idea that basic sensorimotor processes become embedded in networks of connections that relate them in successively more complex ways to allow for performance of more and more nuanced and adaptive functions. Hughlings Jackson noted the curious link between human thought, action and speech. He further recognized that disinhibition or release from control and direction marked neurological damage. His integrative framework remains deeply relevant to the plethora of results being produced by the careful and diverse experimentation currently undertaken with the aid of brain imaging techniques of which he could only dream. In celebration of the memory of John Hughlings Jackson, we revisit his concept of neural evolution and development, which led to what eventually became a leading model of brain organization, whereby a new order of behavioural control—the conscious mind—is created out of simpler elements, in a manner similar to Herbert Spencer’s evolutionary theory. By this Hughlings Jackson did not mean anything dualistic but merely that the highest layer of evolution of nervous arrangements was ‘highly complicated’ and that dissolution of that higher level leaves ‘a lower consciousness and a shallower nervous system’.

  • brain behaviour
  • relationships

A historical context

As the second half of the 19th century unfolded, physicians were faced with the need to diagnose neurological disease with no established systematic methods; having only the aid of primitive mechanical devices and diagnostic tools. Scientific studies of biology and psychology soon became open to the influential views of scholars like Herbert Spencer, who is still best known for his belief that higher life forms evolved from lower ones, and perhaps less well known for the related idea that human reasoning and thought evolved from the automatic responses of lower beings (Spencer, 1855). Those evolutionary ideas captured the attention and passion of the young doctor-in-training, John Hughlings Jackson and would shape what began as Hughlings Jackson’s own series of careful examinations of randomly presented patients with myriad symptoms and backgrounds, into what eventually would become ‘a’ if not ‘the’ leading theory of brain organization of the 21st century (and perhaps beyond).

We note here that John ‘Hughlings-Jackson’ preferred the hyphenated version of his name, which joins the surnames of his mother Sarah Hughlings and father Samuel Jackson, and evidence suggests he even used that version when signing medical reports (Swash, 1986, p. 984). However, we have decided in the present article to present his surnames without hyphenation to be consistent with most written accounts in the literature, although we always present both names together (Hughlings Jackson) so as to preserve the link, as he wished.

Hughlings Jackson was born on 4 April 1835 as the youngest son (among three other sons and one daughter) of a farmer and brewer (and was raised without direct influence of his mother, who died when he was only 1 year old: Taylor, 1925, p. 2). At the young age of 15, John Hughlings Jackson already demonstrated hints of what would eventually become his lifelong passion, as he ended his early years of formal education and began informal studies as an apprentice in the household of two physicians, father and son, in a family named Anderson (the elder of whom was also a lecturer at York Medical School) (York and Steinberg, 2006, p. 4). Through the years, Hughlings Jackson began to put together the pieces of the complex puzzle of human nature and thought through his own careful examination, detailed logging and analysis of patients who presented with focal lesions causing epilepsy, hemiplegia, and often loss of speech (aphasia). He began to conceive of such diseases as the result of processes of dissolution, the opposite of evolution, or de-evolution, and it seems clear his views were influenced by the associationist psychology of George Henry Lewis, Alexander Bain and (as already indicated) Herbert Spencer’s evolutionary doctrine (Dewhurst, 1982, pp. 12–13).

With time, Hughlings Jackson’s ideas gained momentum in a broader set of scientific communities, as not only neurologists and other physicians continued to recognize their importance, but also as neuroscientists, psychologists and philosophers around the world increasingly recognized (and continue to recognize) and appreciate Hughlings Jackson for his remarkable insight, foresight and guidance. Those who have read others’ accounts of Hughlings Jackson as a person might also glean something of the humility, integrity and honesty with which he pursued his passion and convictions, in the face of changing social times and often under difficult personal circumstances. As suggested by Taylor (1925), ‘It is difficult to realize the chaotic state of knowledge of nervous diseases which existed before Dr. Jackson’s time’ and ‘how great a part Dr. Jackson’s work and stimulus played in evolving order out of this chaos’ (Taylor, 1925, p. 11).

Evolution and dissolution

Perhaps it was the desperate need for a more systematic method of diagnosis (as one might infer from the writings of York and Steinberg, 2006, p. 10) that set into motion the impetus for Hughlings Jackson to develop a system of diagnosis by extrapolating on the fundamental insight—that the brain’s higher centres elaborate complex processes out of simple forebears (an idea also known to be proposed by Spencer). Hughlings Jackson emphasized the importance of ‘the correspondence of the organism with the environment’ (Hughlings Jackson, 1884, p. 705); therefore, the higher centres are suited to the re-representation of the body and the conditions to which it is responsive. This led to his proposal that the brain evolved with increasingly higher levels of re-representation of basic sensorimotor representations. Hughlings Jackson proposed a three-level system that essentially comprised a sensorimotor machine (the whole brain), with its lower level defined as anterior spinal horns and motor nerve nuclei, its middle level of motor cortex and basal ganglia and highest level, that which ‘re-re-represents the body’, consisting of the premotor (frontal) cortex (York and Steinberg, 2006, p. 19). In his words, ‘the highest centres, through the intermediation of the middle and lowest centres … re-represent all parts of the organism in most intricate combinations’ (Hughlings Jackson, 1884, p. 703). According to this view, sensory impressions and representations of bodily movements are embedded in more complex structures and processes. Hughlings Jackson further held that ‘mentation’ is what we call the highest level so that ‘for every mental state there is a correlative nervous state’ (Hughlings Jackson, 1884. p. 706). What arises is ‘… an organization of many different nervous arrangements of our highest centres, during actual converse with the environment’ (Hughlings Jackson, 1884, p. 706).

Hughlings Jackson’s keen observations and sketch of what would one day become a leading model of brain organization, took place long before modern-day technologies of brain imaging were invented. Hughlings Jackson documented his own use of applying ice to the back of a patient’s neck while examining retinal vessels to measure possible alterations in cerebral blood flow (Hughlings Jackson, 1863; York and Steinberg, 2006, p. 27). Without assuming an overarching theory of mind or brain function ‘his attitude was phenomenal [or phenomenological]’ (Head, 1915) and his hypotheses sprang from ‘clinical fact’ but his conclusions have general and far-reaching implications for current work in many fields including neurology, psychiatry, psychology and more generally, neuroscience. His influence on one of the most famous psychologists in history, William James, was clear in The Principles of Psychology, where James articulated Hughlings Jackson’s views of psychical evolution in terms of the constitution of brain function (and therefore mind) from simple sensory and motor elements (James, 1890/1918, Vol. I, pp. 29–30). James also noted that Hughlings Jackson’s explanation of epileptic seizures ‘involves principles exactly like those which I am bringing forward here’ in that ‘the ‘loss of consciousness’ in epilepsy is due to the most highly organized brain processes being exhausted and thrown out of gear. The less organized (more instinctive) processes, ordinarily inhibited by the others, are then exalted …’ (James, 1890/1918, Vol. II, pp. 125–6). Hughlings Jackson, who was himself strongly influenced by the neuropsychiatry teachings of Thomas Laycock, particularly with regard to the latter’s views on reflex functions in the brain (Dewhurst, pp. 8–9), also had a very strong influence on the field of psychiatry (Head, 1915; Evans, 1972; Fullinwinder, 1983); however, the present article concerns mainly examples rooted in neuroscience.

Hughlings Jackson’s writings expressed his deep convictions about the mind and the brain. His early writings already warned that we should not ‘classify on a mixed method of anatomy, physiology and psychology, any more than we should classify plants on a mixed, general and empirical method as exogens, kitchen herbs, graminaceae and shrubs’ (Hughlings Jackson, 1878, p. 313). These mixed patterns of categorization and description, uninformed by a unifying theoretical structure, were scattered throughout the burgeoning writing on psychology and neurology of his time. Hughlings Jackson emphasized his views that higher nervous processes (mentation) incorporated layers of information patterned by constraints and correlations representing ‘the correspondence of the organism with the environment’ such that the direct relation of a primitive reflex or more automatic response pattern becomes integrated into those higher order patterns. He then illustrated his views with well-chosen examples. Thus, in referring to persons with aphasia, he remarked that ‘phrases, which have a propositional structure, have in the mouths of speechless patients … no propositional function’ (Hughlings Jackson, 1879, p. 209). In recovery, as the speech functions are reorganized, both the relevance of what is said, and normal propositional use of speech, reassert themselves in the control of the words uttered. Hughlings Jackson realized that this higher level of control or ‘propositional function’ whereby a person’s reasoning processes come into play through the to-and-fro of opinion in conversation adds a depth and the essence of complex mental function.

Although recognized predominantly for his insights on neurological disease, Hughlings Jackson’s fundamental idea of brain organization gained little publicity at its conception, and took many years after his death (7 October 1911) to begin to be appreciated for its potential to explain complex brain–behaviour relationships such as those studied in cognitive neuroscience laboratories today. While the scope of the present review focuses primarily on his doctrine of evolution and dissolution, Hughlings Jackson also developed a number of doctrines that have been very influential, and which we touch on here only briefly. Hughlings Jackson’s principle of concomitance, for example, developed in line with his view that there is no need to invoke supernatural agency to explain natural phenomena. His clever idea of weighted ordinal representation was developed to account for the fact that some movements appear to be specially represented, while at the same time others are ‘everywhere represented’ (see York and Steinberg, 2006 p. 18 Tables 1 and 2). Moreover, terms such as ‘Jacksonian epilepsy’ and ‘Jacksonian seizures’ were named (by others) on the basis of his careful and systematic documentation of convulsions of the nervous system, which discharge from one part of the brain and spread to others (Hughlings Jackson, 1867, 1868), providing further evidence of Hughlings Jackson’s proposal of somatotopic representation (and ordinal weighting) (York and Steinberg, 2006, pp. 13–15). His ideas about compensation and neural recovery naturally stemmed from his view of brain organization and accounted for many of the otherwise paradoxical examples of recovery he witnessed in his patients (York and Steinberg, 2006, pp. 25–6). In many ways, Hughlings Jackson boldly went against the current flow of physiology, where the concept of equipotentiality of the brain was rather common (as promulgated by Pierre Flourens, whose primary sources are written in French: York and Steinberg, 2006, p. 13), and against the commonly accepted Cartesian dualism of that era (York and Steinberg, 2006, p. 13).

So far we have highlighted some important insights evident in Hughlings Jackson’s observations of the brain during disease (dissolution). However, just as important are the implications of his ideas about the workings of the human brain during health, reflecting its highest level processes (evolution).

Highest levels of evolution: language and our actions

In hindsight it seems self-evident that ‘humans have a propensity to process information in high-level meaningful units (unified wholes) where possible, reflecting a built-in economy of information processing mechanisms’ (Franz, 2010, p.17). But this requires an appreciation of basic sensorimotor interactions with the world around us, without which we cannot reasonably postulate higher level networks that enable non-automatic, but nevertheless effective, adaptations of human organisms to a complex and ever-changing environment.

Consistent with the framework offered by Hughlings Jackson, recent research on embodied cognition emphasizes pre-existing sensorimotor function as the basis of higher order cognitive (i.e. conceptual) processes which underlie our complex actions (Glenberg and Kaschack, 2002; Franz, 2010; Franz and McCormick, 2010). When we relate language to the use we make of speech in everyday life, we see a doctrine famously associated with Ludwig Wittgenstein—that ‘the meaning of a word is its use in the language’ (Wittgenstein, 1953, #43; references are usually by paragraph number thus: #nn) or ‘an utterance is or is not a proposition according as it is used’ (Hughlings Jackson, 1879, p. 210) apparently making the same claim. Hughlings Jackson formulated the thesis that speech and mentation were closely interrelated through ‘propositional function’ whereby the articulation of language is subsumed to serve communicative needs and is thereby related to a wider context of action and response (Fullinwinder, 1983, p. 153). He remarked ‘words serve us during reasoning; they are necessarily required in all abstract thought’ (Jackson, 1884, p. 704). Therefore, Hughlings Jackson grasped, in nascent form, the insight that was to become associated with the work of Alexandr Luria, one of the greatest neuropsychologists of the 20th century: ‘higher mental processes are formed and take place on the basis of speech activity’ (Luria, 1973, p. 93–4). That idea is here extended in two ways: (i) the thesis that language is involved in facilitating all cognition and therefore also the coordination of action (Glenberg and Kaschak 2002; Franz and McCormick, 2010); and (ii) the binding of higher order re-representations into meaningful packages is used in the processes ‘within conscious activity whose regulation takes place through the intimate participation of speech’(Luria, 1973, p. 94).

The complex integrated functions of the lower levels of sensorimotor networks that often reveal themselves in tasks of higher cognition seem to build on the ‘complex multidimensional matrix of different cues and connections’ that words provide for human agents (Luria, 1973, p. 307). These key thoughts linking speech, propositional function and thought would have warmed the cockles of Hughlings Jackson’s evolutionary heart and would have appealed to his constant search for theoretical integration within the richness of his clinical data, particularly with regard to the importance he placed on findings of aphasia to inform a wider understanding of human psychology.

Contemporary neuroimaging: adapting to our social environment

Extending Hughlings Jackson’s basic model of brain organization to explaining the role of functional brain networks in high-level cognition and social interactions also brings coherent meaning, in our view, to myriad contemporary findings based on brain imaging. Many of these findings ostensibly pose contradictions rather than unified models but we believe they can be usefully informed and integrated by the evolutionary and developmental framework that Hughlings Jackson favoured. It is in that spirit that we explore some of the findings in contemporary brain imaging literature that are seemingly controversial and paradoxical until viewed in light of Hughlings Jackson’s model, which makes them look more explicable. Here we sketch three areas on the brain—(right) temporoparietal junction, superior temporal sulcus, and inferior frontal gyrus—as examples in which an integrating framework of the type Hughlings Jackson offered will greatly enhance ongoing theory and research in cognitive neuropsychology.

Right temporoparietal junction

Research into the neural mechanisms thought to underlie people’s reasoning about mental states and beliefs has recently implicated the temporoparietal junction on the right side of the brain (right temporoparietal junction) [Brodmann area (BA) 39] as an area selective for belief attribution in tasks involving moral judgements (Young and Saxe, 2008, 2009). For example, using functional MRI, Young and Saxe (2009) reported increases in the response of right temporoparietal junction with influences from beliefs relevant to exculpation of an agent who has accidentally caused harm. In related work, Benedetti et al. (2009) asserted that empathy, a high-level process involving affective and cognitive components, can be further ‘dissected’ (p. 154) into component processes, which they suggest involve theory of mind and expectancies of others’ emotional responses. That study pointed to impaired performance in people with schizophrenia on tasks involving theory of mind and empathy, together with neural responses on functional MRI, which differed from normal controls in areas of the right posterior superior temporal lobe (BA 22, 42), left temporoparietal junction and temporal pole (BA 38, 39), along with some structural anomalies in the medial prefrontal areas found to be crucial for social cognition (BA 10). Other researchers implicate these areas in intermodal sensory and perceptual processing where apparent conflict exists (Papeo et al., 2010). Using completely different tasks, other functional MRI research has focused on the right temporoparietal junction in relation to effects of musical improvization (involving the generation of novel musical-motor sequences). Berkowitz and Ansari (2010) demonstrated that, during improvization, musicians showed marked deactivation of the right temporoparietal junction whereas non-musicians did not. The authors implicated the involvement of right temporoparietal junction in an attentional network operating on bottom-up sensory information. In this manner, deactivation might be related to inhibition of bottom-up attention so that top-down and goal-related attention can better operate.

Hughlings Jackson’s model suggests that we should look at integration or evolution whereby higher level representation gathers together information in situations where simple responses will not suffice. In other words, there is high-level responsivity to real-time constraints and complex information processes involving many different inputs, all of which have factored into the ideational representations guiding behaviour. He would plausibly have seen practiced musicians as having evolved higher level patterns and therefore not needing to attend to what they had already produced to initiate ‘novel’ and musical improvizations. Thus, his model potentially integrates the puzzling diversity of roles vested in the relatively circumscribed brain area, right temporoparietal junction (strategically positioned at the junction of visual, sensorimotor, auditory and memory-related brain regions) by noting the need for inclusive re-integration of current contextual material and pre-existing data patterns in responding to a complex situation. In making that inference we are extending Hughlings Jackson’s framework to neurocognitive data that go a long way beyond his own work on aphasia and epilepsy, even though the same evolutionary re-representational (at higher or more integrated and inclusive levels) principles apply. Indeed, many contemporary brain scientists are actively studying evolved systems in the human brain that are specialized for understanding of others and social interactions. Hughlings Jackson’s framework would analyse these in terms of integrative re-representation of sensorimotor and perceptual data from other human beings wherein we use ‘the service of words’ (propositionally but subconsciously) in meaningful interactions (Hughlings Jackson, 1878, p. 323).

Superior temporal sulcus

Within a similar context of theory of mind, one might consider another complicated brain area, often referred to as the region of the superior temporal sulcus, which involves cortex within the sulcus and adjacent surfaces including the middle temporal gyrus. Earlier studies on monkeys with bilateral lesions to this region revealed deficits in discriminating between angles of eye gaze, and right superior temporal sulcus lesions are thought to be the basis of prosopagnosia (Campbell et al., 1990). Later functional MRI studies revealed posterior superior temporal sulcus region activation with passive viewing of gaze shifts (Hoffman and Haxby, 2000). However, Materna et al. (2008) questioned whether activation of the posterior superior temporal sulcus region reflects general processing of directional cues or specifically, eye gaze, reporting that the bilateral areas surrounding and including posterior superior temporal sulcus are activated in response to general direction processing relevant to shared attention, even when the cue was finger pointing without eye gaze. As others have pointed out, there is a segregated representation of the biological motion of body parts in the posterior temporal cortex (including eyes, mouth and hands; Pelphrey et al., 2005), a finding closely related to earlier studies showing cells in the superior temporal sulcus region that are responsive to perceived emotions (Peelen et al., 2010) and moving hands and faces but not to inanimate objects (Frith and Frith, 1999, pp. 1693–4). Hughlings Jackson might have been deeply suspicious of over-localizing or modularizing of the highly complex functions involved given his suggestion that ‘the highest centres – physical basis of mind or consciousness—…represent innumerable different impressions and movements of all parts of the body, although very indirectly’ (Hughlings Jackson, 1884, p. 703).

The collected findings essentially reveal a highly elaborated system that allows the human organism to develop social cognition by drawing on basic sensorimotor processes involved in detecting biological motion and integrating the results with internally originating proprioceptive and motor information. This would make sense of Frith and Frith’s (1999) link between mentalizing and the dorsal action system, if we take account of the need for human beings to locate themselves in a personal and interpersonal space as the ‘where’ of their social being. Here again, Jackson’s model directs us to the levels of evolved integration needed to serve neurocognitive functions intrinsic to our human adaptation to a complex life-world. As a result, the diversity of areas and contributory processes discussed by contemporary researchers can be usefully stitched together.

Inferior frontal gyrus

One of the most influential theories of the neural basis of action recognition is the concept of a mirror neuron system. The theory developed out of findings in monkeys that revealed discharges of neurons within the ventral premotor and rostral inferior parietal lobe both when the monkey performed an action and when it observed a similar action performed by an ‘other’ (Rizzolatti and Craighero, 2004). Human homologues of this mirror neuron system, which usually includes the left inferior frontal gyrus as a primary area (together with other areas such as the inferior parietal lobule) have been identified on the basis of neuroimaging studies, extending the mirror neuron system framework to account for the ability of a human observer to understand ‘what’ actions are being carried out by another person (Keysers and Gazzola, 2006), and even ‘why’ those actions are carried out (Gallese and Goldman, 1998). Earlier studies initially revealed a representation of body parts including face, head and parts of the limbs in the same brain area(s), again reminiscent of Hughlings Jackson’s basic notion that sensorimotor representations become re-represented and re-re-represented in more complex networks underlying real-life processes of social interaction and communication. It would not be surprising if all complex brain networks active during social interactions have, at their basis, simple sensorimotor representations of the human body (and especially the face).

Ramsey and Hamilton (2010), discussing the idea of action perception and the attribution of goals to others, supports the view of an evolved integrated re-representation system that incorporates sensorimotor patterns from both inner and outer perceptual fields into wider adaptive functional assemblies that also use information about object properties, actions and mental state inferences processed in areas beyond those usually included in the mirror neuron system.

Perception and self

Hughlings Jackson’s ideas on the relation between language and thought led to further development of his evolutionary framework. He remarked ‘words are required for thinking, for most of our thinking at least, but the speechless man is not wordless; there is an automatic and unconscious or subconscious service of words … the process of perception in the speechless, not wordless, man may be defective in the sense of being inferior from lack of cooperation of speech: it is not itself in fault, it is left unaided’ (Hughlings Jackson, 1878, p. 323). He expanded these remarks in a footnote: ‘energising of lower, more organised, nervous arrangements, although unattended by any sort of conscious state, is essential for, and leads to, particular energisings of the highest and least organised—the now-organising—nervous arrangements, which last mentioned organising is attended by consciousness’ (Hughlings Jackson, 1878, p. 323).

Taken together, these remarks point towards the thoughts explored by Lev Vygotsky and the neuropsychology of Luria and the work of current theorists of embodied cognition. Vygotsky remarked of language and thought ‘the conception of word meaning as a unit of both generalizing thought and social interchange is of incalculable value for the study of thought and language’ (Vygotsky, 1962. p. 7). To the quotes from Luria above we can perhaps add, ‘the realization that word meaning is the fundamental tool of thinking was crucial to … the description of the psychological structure of thinking as a whole’ (Luria, 1973, p. 326).

Hughlings Jackson also sketched, in outline at least, the complex and mutually facilitatory relationship between thought and language as is shown in his understanding of the use of ‘I’, the first person pronoun. ‘I am awake now but in my sleep I was dreaming. … The I’s and the I’s, the same for a grammarian, symbolize two different persons for the student of mental diseases. I, we may call him B, is I, we may call him A, minus the use of the higher nervous arrangements of the higher centres (dissolution), and plus increased activity of the next lower, Evolution remaining.’ (Hughlings Jackson, 1889, p. 499).

By using ‘I’ and ‘I’ (italicized) Hughlings Jackson was able, in an elegant way, to discuss the varying modes of self-attributive cognitive processes according to their level of integration and sophistication. This idea is ripe for application to the findings in blindsight and other conditions involving partial informational access by the conscious patient and disconnexional defects including the neural disruptions of callosotomy. Hughlings Jackson’s observations about actual multiplicity in the use of ‘I’ prefigures contemporary thinking about the dynamic ‘I’, the multiple components of self-attribution and the sense of self, and the constructed neurocognitive nature of the self (Metzinger, 2004; Northoff and Bamphol, 2004; Gillett, 2008).

Unlike Hughlings Jackson, many human beings (among them some prominent philosophers) have tended naively to regard ‘I’ as a simple reference to a Cartesian inner substance. Hughlings Jackson, however, always reflected on his observations in the clinic and related them to evolutionary and ontogenetic thinking so that they represented far more than mere data; they were insights into human cognition and its neuroscientific underpinnings, carefully integrated according to a theoretical framework that focused on the aspects of our function that we call higher, or mental, or conscious, and these insights enhance our understanding of human neuropsychology. Hughlings Jackson’s integrative approach enables us to consider brain networks as acting in concerted and evolved ways to lift our voluntary activity out of the domain of the mechanistic and automatic.

Finally, we briefly comment on Hughlings Jackson’s discussion of emotion as re-representing ‘the parts of the body concerned in different emotional manifestations’ (Jackson, 1884, p. 704) as a further example of the framework he favoured. It prefigured the somatic, and action-oriented focus of William James’s account of emotion, and also pointed forward to Damasio’s work on the role of emotion and the action system in human consciousness and deliberation (Damasio, 1994). The idea that action is responsive to increasingly integrated patterns of sensorimotor representations, lies at the heart of an informed theory of human and animal cognition.

Conclusions

Hughlings Jackson’s last writings and lectures on neuroscience date from 100 years ago, but truly deserve the adage ‘100 years young’. We have outlined his basic model of evolved brain function that other writers in this issue have linked so ably to Herbert Spencer. We then outlined how Hughlings Jackson’s ideas apparently influenced other more recent researchers and theorists, and we used his concept of evolved brain function to address some contentious areas in contemporary cognitive neuroscience. Hughlings Jackson’s view was that human consciousness brings us to ‘the climax of nervous evolution’ by using the highest levels of integrated information processing to play a pivotal role in action, memory, reason and emotion. That integration fits us uniquely for the demands of life in a world that we have utterly changed from the state of nature in which, as a species, we evolved. Through representation and re-representation, always combining and recombining inputs of various types, and the learning we do as individuals, particularly its condensed forms gained through our ability to ‘propositionalize’ or use language, we have developed what we call mental function of a complexity that vastly outstrips our nearest evolutionary forebears such that some of the philosophers of earlier ages were unable to see any continuity between us and them. Hughlings Jackson saw both the continuities and differences and by carefully observing and reflecting on the dissolution of neural function in those patients that fate and disease put in his way, indicated a direction that, if diligently followed, makes sense of the babel of voices in contemporary theoretical neuroscience.

Abbreviation
BA 
 Brodmann area

References

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