Disembodiment and Language in Schizophrenia: An Integrated Psychopathological and Evolutionary Perspective

Abstract

Different hypotheses have flourished to explain the evolutionary paradox of schizophrenia. In this contribution, we sought to illustrate how, in the schizophrenia spectrum, the concept of embodiment may underpin the phylogenetic and developmental pathways linking sensorimotor processes, the origin of human language, and the construction of a basic sense of the self. In particular, according to an embodied model of language, we suggest that the reuse of basic sensorimotor loops for language, while enabling the development of fully symbolic thought, has pushed the human brain close to the threshold of a severe disruption of self-embodiment processes, which are at the core of schizophrenia psychopathology. We adopted an inter-disciplinary approach (psychopathology, neuroscience, developmental biology) within an evolutionary framework, to gain an integrated, multi-perspectival model on the origin of schizophrenia vulnerability. A maladaptive over-expression of evolutionary-developmental trajectories toward language at the expense of embodiment processes would have led to the evolutionary “trade-off” of a hyper-symbolic activity to the detriment of a disembodied self. Therefore, schizophrenia psychopathology might be the cost of long-term co-evolutive interactions between brain and language.

“No longer can man confront reality immediately, as it were, face to face. Physical reality seems to recede in proportion as man’s symbolic activity advances”.

Cassirer, E. 1974. An essay on man: an introduction to a philosophy of human culture.¹

Introduction

Schizophrenia is a severe neuro-developmental disorder with a notably stable 1% prevalence, regardless of epochs and cultures.^2,3 Remarkably, schizophrenia is a uniquely human condition, being absent in other close species, like great apes.^2,4 This has led to connect the disorder to a recent selection for species-specific human traits.⁵ Actually, during evolution, an abrupt cognitive re-configuration marked the separation of Homo sapiens from its ancestors.^6,7 Since language is one of the most distinctive features of humans, its acquisition is the principal candidate for that radical transformation.⁸

Timothy Crow was the first to point out the relationship between the evolution of language and schizophrenia, linking the disorder to a reduced inter-hemispheric asymmetry: in particular, language and schizophrenia would share a common origin in a saltational genetic event that defined the human species, allowing the two hemispheres to develop with a degree of independence.⁹ Since then, several investigators focused on language disconnectivity as core feature of schizophrenia¹⁰ reporting specific language impairments even in the prodromal stage,^11–14 whereas neuro-imaging findings,^11,15–17 have confirmed reduced functional and structural laterality in regions for language processing.

What is missing is an evolutionary approach to schizophrenia primarily oriented by psychopathology. Psychopathological research regards schizophrenia as a disturbance of self-embodiment,^18,19 with motor²⁰ and language²¹ disturbances as early markers of the disorder. Therefore, the present review attempts to find a connection between these three main dimensions of schizophrenia; in particular, we suggest that the evolutionary-developmental reuse of basic sensorimotor loops for language pushed the human brain close to the threshold of a severe disruption of self-embodiment processes, which are based on the same sensorimotor substrate.

Finally, this contribution strongly emphasizes an inter-disciplinary approach. Only at the intersection of different fields while simultaneously interfacing with an evolutionary framework, we may search for the phylogenetic and developmental pathways underlying such an “elusive disorder”.²²

The Disembodied Self in Schizophrenia

Despite the clinical heterogeneity of schizophrenia, a core feature of the disorder has been posited in a specific disruption of the implicit consciousness of one’s body, also referred to as bodily self.²³ The bodily self is the basis for higher levels of the self, through the incorporation of affective, cognitive and socio-cultural features within a hierarchical organization.²⁴ A disturbance of the bodily self (or disembodiment of the self) encompasses the whole schizophrenia spectrum,²⁵ manifesting as weakening of the basic sense of the self, disruption of implicit bodily functioning, and hyper-reflective distancing from others and worldly objects.^26,27 Patients subjectively feel a diminished sense of existing as embodied subjects, vitally immersed in the world and authors of their own actions.²⁴ Cenestopathic sensations often accompany such a pervasive lack of presence, caused by a detachment of self and the body.²⁶

The bodily scaffoldings of the self, in terms of agency and ownership, with fixed and solid boundaries, are shaped by an integrated network of multisensory inputs, constrained by the motor potentialities of our own body.^23,28,29 Therefore, self-embodiment processes are multi-sensorial, dynamic, and relational in nature.^30,31 In this connection, corollary discharge (CD) systems exert a crucial role.^32,33 CD is an evolutionarily conserved neural mechanism aimed at distinguishing between sensations coming from external sources and self-generated sensations. In essence, during actions, a copy of motor signals is transmitted to sensory regions to modulate sensory processing and perception.³⁴ CD represents the scaffolding for different processes at many levels, from fine calibration of the motor action flow and sensory analysis to self-monitoring and agency.^35–37

Qin and colleagues³⁸ have recently proposed a three-level organization of the self from the internal body to the external environment, through the integration of interoceptive, exteroceptive and mental-self processing. Such a hierarchical self-model permits to link together different facets of the self, from sensorimotor/bodily level to higher cognitive, affective and social features. The connections between the different levels of self-processing are underpinned by differential temporo-spatial dynamics of brain’s spontaneous activity^39,40 (figure 1). In this regard, there is evidence for a global disruption in the spatial (eg, functional connectivity) and temporal (eg, coupling between different frequency fluctuations) properties of brain rhythmicity in schizophrenia.⁴⁰ In particular, schizophrenia patients show a prolonged temporal integration, with abnormally strong integration of stimuli across different time points, disrupting a continuous sense of the self.⁴¹

Fig. 1.

The hierarchical structure of self-processing, underpinned by sensorimotor integration and orchestrated by the dynamics of brain’s spontaneous activity.

Altogether, schizophrenia disembodiment lies on a missing integration and adjustment of sensorimotor loops at different levels, with a cascading effect on somatosensory perception, fluidity, grace of movements, and sense of agency.¹⁹ In this connection, there is evidence for an association between subjective disembodiment experiences (eg, loss of body integrity, cohesion, and demarcation) and impaired postural and gait patterns in schizophrenia.⁴²

Motor and Language Disturbances in Schizophrenia

Motor disturbances are detectable in the entire schizophrenia spectrum,^43,44 including high-risk individuals and drug-naïve patients.⁴⁵ Particularly, gait and balance deficits, delayed gross motor milestones and dyscoordination would reflect vulnerability from the first 2 years of life, thus representing early markers of the disorder.^46,47

There is neuro-radiological and neuro-physiological evidence that early motor disturbances lie on extensive deficits in sensorimotor integration systems,⁴⁸ involving frontoparietal, basal ganglia and cerebellar connections,^49,50 as well as aberrant structural connectivity of the pre-motor and motor cortices.²⁰ Such a widespread structural and functional disconnection strongly suggests an early impairment in motor development and maturation.²⁰

Similar to motor symptoms, language anomalies are present in the majority of schizophrenia patients and their relatives and are viewed as reliable “linguistic biomarkers” of psychotic proneness.¹⁴ They concern various areas of linguistics, including phonetics, semantics, syntax and pragmatics.^51–53 In particular, the structure of language, at different levels, is used in a peculiar or awkward way, moving away from the normal pragmatic context⁵⁴ towards a progressive impoverishment of meaning (concretism) or a decontextualized semantic hyper-proliferation.

Cohort studies confirm an association between language and neuromotor impairments^55–58: in early-onset schizophrenia motor disturbances are associated with impairment in both receptive and expressive language,^56,57 whereas in at-risk adolescents, a disruption in receptive language (but not expressive language) co-occurs with deficits in motor functioning and processing speed.⁵⁸ In schizophrenia, an association has been found between abnormal movements and thought and language disorganization.^59,60 Schizophrenia patients also exhibit an impaired integration of abstract speech-gesture combinations.^61,62 Its neural basis lie in a disrupted connectivity involving the left inferior frontal gyrus (IFG), the supplementary motor area (SMA) and the anterior cingulate cortex (ACC), due to their role in movement control, gestural and speech processing.⁶³

The Bodily Roots of Language: An Evolutionary and Developmental Perspective

An embodied approach to language may provide the pathophysiological link between the motor and language domains.⁶⁴ Regardless of strong or weak embodied-language models, the central assumption is that sensory and motor information is a necessary part of language processing at different levels (from syntax to semantics).⁶⁵

From a developmental perspective, sensorimotor interactions with the environment have a pivotal role in shaping language processing in childhood. Both the sensorimotor experiences obtained from objects manipulation as well as proprioceptive information about body posture influence how these objects are categorized during language learning.⁶⁴ A large number of studies has provided evidence that during language processing, the meaning implied in words and sentences has to be simulated.^66–68 For example, when children interact with an object, the sensorimotor experience creates a mental representation of the object based on the action performed⁶⁹; this motor information is later simulated when the children view novel objects and have to make a categorization decision. In such a way, words and concept learning are grounded in sensorimotor experience.^64,69,70 Accordingly, thought disorders have been found to be associated with body image disturbances in individuals at-risk for schizophrenia.^23,71 Formal thought disorders, which include disordered verbalization and concretism, would reflect “an anomalous relationship between words and their referents”.²³ Difficulties with figurative expressions, such as irony and metaphors, suggest diminished embodiment, highlighting the role of embodiment processes in communication.^23,72

These findings are consistent with neurolinguistic and neurophysiological evidence that areas traditionally regarded as purely motor (eg, primary motor or the pre-motor cortices), as well as areas traditionally assigned to the processing of language (eg, Broca’s region), are functionally and structurally connected in a unique integrated system.^73,74 In particular, language processes rely on a diffuse sensorimotor system,^75–78 anatomically organized at different levels (from sub-cortical to cortical areas), along a gradient from concrete sensorimotor functions to abstract, domain-general processing.⁷⁷ Strik and colleagues⁷⁹ have recently proposed a hierarchical sensorimotor organization, specialized for human communication, allowing partially distinct corticobasal loops (affective, language, and motor loops) to be orchestrated as an integrated neuro-functional system. These loops overlap with important sensorimotor connections of the cerebral cortex, via basal ganglia and thalamic pathways. A higher-order integration would be mediated by fiber nodes or hubs, which convey convergent information from the subordinate sensorimotor systems and interoceptive information from the body.⁸⁰

Many of the sensorimotor structures involved in language processes have a long evolutionary history. For example, CD signalling serves the function of reflex inhibition and sensory filtration in invertebrates, sensorimotor planning and learning in vertebrates,⁸¹ fluent vocal and speech production and control in humans.^34,82,83 The cerebellum, evolved in early vertebrates for sensorimotor synchronization,^84,85 was adjusted to serve higher cognitive functions,⁸⁶ including the timing and synchronization of linguistic processes.⁸⁷ The basal ganglia, also highly conserved across vertebrate phylogeny with the function of selecting context-dependent motor programs,^88,89 are actively recruited in human language with a role in word fluency and sentence construction.⁹⁰ Accordingly, many language impairments in schizophrenia (eg, neologistic speech, loosening of association, word-finding difficulties) depend on a diffuse disturbed sub-cortical-cortical fine-tuning, centered in the basal ganglia and the thalamus nodes. These neural pathways, far to be restricted to motor functions, have a gating function in processing contextual information for language, modulating the activity of several language-related cortex areas (eg, superior frontal, temporal, and cingulate gyrus).⁹¹ A large-scale distributed network disconnectivity would ultimately disrupt the normal pattern of left hemisphere dominance of language processing (particularly in regions of auditory-conceptual and auditory-motor integration (Brodmann’s area 40) and of motor planning/articulation systems (areas 44, 45),⁹¹ as demonstrated in functional and structural imaging studies in both schizophrenia and at-risk individuals.⁹²

Therefore, the origin of language appears as an incremental process, with a gradual adjustment of connectivity patterns originally shaped by evolutionary pressures for other purposes. This global connectivity rearrangement is paralleled by a global re-configuration of human brain’s rhythmicity.⁴ In this respect, according to the concept of spatiotemporal psychopathology,^39,40 an impairment in the dynamics of spontaneous neural activity might bridge the gap between the sensorimotor substrate with higher-order domains, including language, with a cascading effect on different levels of self-processing.³⁹ The synergistic interaction of widespread and diverse neural systems in language processes strongly suggest that there has been long-term brain-language coevolution, involving a very broad suite of genetic loci and many levels of intra-evolutionary mechanisms.⁹³

• 1. The gestural origin of language

The strong link between sensorimotor functions and speech in humans as well as the available evidence gathered in nonhuman primates’ communication support a gestural origin of language, ie, the development of language from a bodily-visual communication.⁹⁴ In this connection, it has been postulated a pivotal role of the mirror system in the Broca’s area, which, in humans, participates in both speech production and hand movements.⁹⁵ Interestingly, its homologous area in monkeys (pre-motor F5) is involved in the production of gestural communicative signals.⁹⁶ Broca’s area presents a somatotopic organization, with distinct mirror neurons specifically activated by the observation/execution of hand/mouth and food-related acts.^97,98 Therefore, the hand/mouth integrated motor system, primarily involved for the bringing-to-the-mouth actions (eg, food manipulation), may have facilitated the phylogenetic shift from a primitive hand-gesture communication system to speech.⁹⁵

Different selection pressures may have been at work in the shift from a manuo-visual system to a vocal-acoustic one, probably promoting learned behavioral adaptations subsequently genetically channeled.⁹⁹ In this regard, a circular relationship occurred, within constructed eco-cultural niches, among brain expansion, social complexity, novel cognitive demands and technological elaboration in the emergence of language^76–78 (figure 2). In particular, the evolution of tool-making abilities, requiring an increasingly complex control of the human hand (using Broca’s area), may have had a pivotal role to the evolution of gestural communication¹⁰⁰ as well as to enhanced articulatory control,¹⁰¹ both of which are central to human language evolution. As confirmation, apparently separate processes such as tool-making, communicative gestures and language processing insist on the very same sensorimotor pathways.^77,102

Fig. 2.

Circular relationship, within constructed eco-cultural niches, among brain expansion, social complexity, novel cognitive demands, and technological elaboration in the emergence of language.

Therefore, the language processing and production system gradually originated from a series of pre-existent sensorimotor circuits at different levels, functionally exploited for communicative behavior, while retaining their original function as well.^103–105 Existing neural structures are normally reused/recycled/redeployed as new brain functions develop, to the extent that “neural reuse” has been proposed as a fundamental organizing principle of the brain.¹⁰⁶ The principle of reuse is channeled by the functional characteristics of the pre-existing structures and the functional requirements of the emergent capacity; that is, a novel function finds its “neural niche”.¹⁰⁷ So for example, sensorimotor functions were recruited because they were more suitable for the emergent properties of language during long-term coevolutionary plastic processes in which brain had to adapt to language and language to brain.⁹³

• 2. Developmental pathways towards symbolic communication

Developmental processes of fine-tuning connectivity are essential for the functional adjustment of neural pathways for novel functions, including language.¹⁰⁸ Neural connectivity refinement generally relies on selection-like processes, driven by signal-mediated activity-dependent competition.^93,109 Therefore, evolutionary-developmental mechanisms of neural reuse for human-evolved phenotypes, like language, largely depend on unconstrained plastic and epigenetic processes at work on evolutionarily constrained pre-existing structures. Human neocortex, relatively unconstrained in its connectivity,¹¹⁰ late developing¹¹¹ and phylogenetically recent,¹¹² is highly dependent on such developmental neuroepigenetic and plastic processes, and thus particularly suitable to be exploited for new demands.¹¹³ In this connection, during human speciation the rapid and disproportionate expansion of the cortical mantle untethered large portions of the cortex from strong neuro-chemical constraints with the emergence of non-canonical association networks primarily connected with each other rather than strictly constrained by sensorimotor systems.¹¹⁰

The increased plasticity of sensorimotor pathways, underpinned by a new, long-distance and unconstrained neural connectivity, may represent the neurobiological basis for a fully developed symbolic communication, so specific to human language.¹¹⁴ Human language is in fact composed of symbols, which bear little or no physical relation to the objects, actions or properties they represent.^115,116 For example, along a gradual abstraction process, the involvement of sensorimotor system in concept understanding moves from fully detailed to less detailed simulation as familiarity with metaphoric action increases.¹¹⁷ This gradient of abstraction of semantic processing, whilst retaining a link to sensorimotor circuits, requires the involvement of additional “convergent” zones, in which higher-order conjunctions and correlations are captured and neurally stored.¹¹⁸ Thereby, along a fundamental continuity from sensorimotor to symbolic interaction with the environment,¹¹⁹ words and things gradually lose their univocal and unambiguous character to open up to a polysemic (symbolic) system of signification with a high degree of plurality.^120,121

The human predisposition to symbol-making is dramatically represented in the precursor stages of schizophrenia delusion (often referred to as “delusional atmosphere”^122,123), in which, within a radical alienation of the environment, objects lose their familiar, pragmatic meaning to acquire an indefinite, uncanny quality, opening up to any potential meaning, in a sort of polysemic diffusion.

Discussion

Our language-readiness resulted from the emergence of a novel, widespread neuronal rearrangement, which entailed new patterns of brain rhythmicity, long-distance connections among distributed neurons, and a global remodeling of brain development and function.⁴ Randolph Nesse has suggested that the “very rapid selection for language and cognitive ability over the past 100 000 years has pushed some aspect of brain development close to a threshold which, if exceeded, causes psychosis in a few unfortunate people”.¹²⁴ In other words, language represents one of the traits for which selection has driven the mean to a “fitness cliff”, beyond which the system falls off precipitously.¹²⁵

Remarkably, the human species (the “symbolic animal” according to Cassirer¹; the “symbolic species” as Deacon⁷⁶ puts it) has the unique possibility to move freely from a bodily immersion to reality to a complete disengagement, giving access to a cultural world of symbolic self-creation.^126,127 In contrast, in schizophrenia a disembodied self is an inherent, persistent condition,^27,128 often coupled with a hyper-symbolic attitude.^129,130 Schizophrenia patients in fact manifest a radical alienation from pragmatic concerns with a solipsistic orientation toward an empty philosophizing and pseudo-abstract reasoning.¹²⁹ Delusion itself in schizophrenia acquires a peculiar, ontological feature, typically concerning general metaphysic ideas about the fundamental nature of reality.^129,131

Schizophrenia disembodiment has been brought back to an early disruption of basic processes of sensorimotor integration and organization.^23,33 Noteworthy, during the human lineage split, the very same sensorimotor pathways were extensively exploited for the development of language. In particular, language processes rely on basic mechanisms of sensorimotor integration, dispersed along a constellation of cortical and sub-cortical systems with a long phylogenetic history and very different original functions. Such long-term evolutionary-developmental processes irreversibly shaped the functional connectivity and the spontaneous activity of our brain,⁴ allowing the incorporation of the embodied level with higher-order levels, including a fully developed symbolic activity. Nevertheless, the same evolutionary mechanism of neural reuse of sensorimotor pathways for language, while leading to symbolic communication, exposed humans to a catastrophic failure of self-embodiment processes (figure 3). In fact, it introduced the vulnerability, uniquely human, to an excessive functional displacement of sensorimotor circuits towards the symbolic-conceptual level with overly unconstrained association networks, that end up weakening the bodily-motor substrate in which the bodily self is rooted.^33,38 In particular, self-embodiment processes (including agency and self-others demarcation) lie on fundamental multisensory/sensorimotor mechanisms which also offer an embodied basis for the development of language. Therefore, a disbalance towards abstraction, which exceeds the threshold of sensorimotor constraints, risks eroding the sensorimotor looping of self-embodiment and untethering language from its bodily ground. The result is a disembodied self and a hyper-symbolic language (figure 4).

Fig. 3.

Evolutionary-developmental mechanisms of neural reuse of sensorimotor pathways for language, while leading to fully developed symbolic communication, exposed humans to a failure of embodiment processes.

Fig. 4.

A disbalance towards abstraction, which crosses the threshold of sensorimotor constraints, eventually leads to a disembodied self and a hyper-symbolic language.

During ontogeny, many complex developmental (pre- and perinatal, psychosocial, bio-cultural) mechanisms,¹³² acting on fine-tuning processes of neural circuitry, contribute calibrating, or alternatively decompensating such an integrated sensorimotor and language system into a full-blown psychosis. An asymmetry towards symbolic language early manifest in motor symptoms, which are significantly associated with both language^55–58 and self-embodiment⁴² disturbances, as expression of intertwined developmental pathways. Noteworthy, psychopathology has repeatedly emphasized a failure of integrative processes in schizophrenia pathophysiology,¹³³ from Chaslin’s “discordance”,¹³⁴ Bleuler’s “splitting” (spaltung)¹³⁵ to Meehl’s schizotaxia.¹³⁶ According to our model, such a splitting would deal with a maladaptive over-expression of evolutionary-developmental trajectories toward language at the expense of embodiment processes, leading to a hyper-symbolic activity to the detriment of a disembodied self. This model fits well with the evolutionary notion of “tradeoff”, ie, a process through which a trait increases in fitness at the expense of the decreased fitness in another trait.¹³⁷ In this regard, there is evidence that schizophrenia involves extremes of tradeoffs for human recently evolved cognitive traits, evolutionarily selected for their benefits near the mean, at the cost of their catastrophic effects if expressed in the tails of the normal distribution.¹³⁸

Schizophrenia patients in fact, typically hyper-reflective and embedded in ontological concerns, have loosened to the maximum or definitely lost the bodily, practical immersion in the environment in favor of an inflated and hyper-symbolic thought, thus overcoming the cliff edge beyond which fitness crashes. A weakening of the bodily grasp on reality implies a disengagement from the immediate attunement with the world, with a failing sense of what others consider self-evident.¹³¹ The “loss of the vital contact”,¹³⁹ or of the “natural self-evidence”,¹⁴⁰ as well as the “oddness”¹⁴¹ or the “praecox feeling”¹⁴² we perceive whenever we interact with schizophrenia patients, all reflect an underlying perturbation of the bodily/motor substrate. On the other hand, language, unanchored from bodily self-knowledge, declines to a hyper-charged and insubstantial propositional and referential potentiality,¹⁴³ becoming “dereistic”¹³⁵ or empty philosophizing.¹⁴⁴

A disruption in embodiment processes reverberates in all dimensions of schizophrenia psychopathology^23,27:

• 1) Abnormal bodily experiences (cenesthopathic symptoms): the body is no longer an integral part of patients’ subjective experience but it turns into a de-animated object, with a tendency to hyper-reflect on it, which sometimes takes the form of an incessant self-monitoring.^27,119

• 2) Abnormal permeability of ego-boundaries (“Transitivism”¹³⁵; “First Rank Symptoms”¹⁴⁵): The fading of the implicit awareness of one’s own body as a unified entity, and a disrupted agency blur the boundaries that allow us to distinguish the self from the environment, leading to external misattributions of self-generated actions.^23,33 This might have implications for the emergence of passivity delusions (experiencing one’s own thoughts, feelings, or actions as under external control) and auditory verbal hallucinations (eg, hearing one’s thoughts spoken aloud or externalized commenting “voices”).

• 3) Disruption of self-others attunement (inter-subjectivity): An impaired embodied synchronization with others is at the basis of schizophrenic autism, as defective form of coexistence, and more generally of the behavioral and mental attitude of distancing from and disinterest towards practical reality and social life.^27,146

• 4) “Destructuration”¹⁴⁴ of the experiential process (meaning bestowing): Since the process of constructing meaning is rooted in our own bodily enactment, a language untethered from its sensorimotor basis fails to order our experience within a common frame of reference, exposing schizophrenia patients to lose “the natural perceptual context”,¹⁴⁷ ie, the pre-reflective, meaningful grasp on worldly objects. Objects may then evoke novel idiosyncratic meanings, sometimes passively imposed on the subject in the form of revelation (delusional perception).¹⁴⁵

• 5) Thought/ speech disorganization. A disembodied thought and language is by its nature a-pragmatic,¹⁴⁸ moving in-between the opposite ends of rigid concretism or extreme elusiveness. Detached from an embodied framework, single words may be used in an idiosyncratic or bizarre manner or patients may even produce new words (neologisms).¹⁴⁹

Our model differs from previous language-based evolutionary approaches in the following points:

• 1) It does not postulate a single, all-or-nothing (“big bang”⁹) event, abruptly marking the human split lineage together with the origin of language and schizophrenia. The widespread connectivity adjustment for language at different levels (basic sensorimotor processes; cortical-sub-cortical integration; global brain rhythmicity) rather indicates long-term coevolutionary brain-language mechanisms at work within eco-cultural niches of increasing tool-making and social abilities, in accordance with current evolutionary-developmental approaches.^78,93

• 2) It reaffirms the relevance of language in schizophrenia, while emphasizing an embodied approach to the disorder, in line with psychopathological tradition and recent research.¹⁵⁰

This is not to say that our hypothesis is in contrast with other evolutionary theories of schizophrenia, particularly with the view of the disorder as a pathology of the social brain.^151,152 Nevertheless, we suggest that in schizophrenia impairments in higher-order levels (including social cognition) lie on the more basic level of self-embodiment processing, perturbed by a permanent disbalance between the bodily-motor and the symbolic language systems. Rather, our hypothesis fits well with the concept of “Spatiotemporal Neuroscience”¹⁵³ and “oscillopathic” approaches.⁴ According to these models, abnormal dynamics of brain rhythmicity undermine those basic mechanisms of sensorimotor integration, that underlie the incorporation of different levels of the self, and thus the developmental pathways of self-processing.¹⁵³

Future research should be addressed to investigate language disturbances in schizophrenia within an embodied framework, for example focusing on potential speech-motor biomarkers of psychosis risk.

As a main limitation, this work is not a comprehensive review of all available evidence for an evolutionary approach to schizophrenia, but it cites selected papers that the authors considered as conducive to address the main hypothesis presented. Moreover, for the reasons of brevity our account of psychopathological symptoms was limited. This has left out many other symptoms, such as specific formal thought disorders, to name but a few. Similarly, different subtypes of schizophrenia were not considered.

Concluding, as part of a long-term coevolutionary process, the emergence of language has given humans the unique possibility of finely calibrating our detachment from the primitive, embodied adhesion to reality, opening up to a novel symbolic-mediated world. Sass¹²⁹ defined schizophrenia as a metaphysical disease, referring to the hyper-symbolic consciousness of schizophrenia patients. In this respect, the fact that what makes us specifically human (ie, a complex symbolic language) derives from the very same structures involved in our motor enactment, has created the unique vulnerability (also specifically human) for a symbolic proliferation untethered from its bodily ground.

Funding

This research received no specific grant from any funding agency, commercial or not-for-profit sectors. VL was supported by the doctoral grant “Young Talents in Psychiatry 2021” funded by the Fondation FondaMental and the Fondation Bettencourt Schueller. These funding agencies had no further role in the study, in the analyses or in the decision to submit the article for publication.

Conflict of Interest

None.

Authors’ Contribution

M.T. wrote the draft manuscript, which was repeatedly revised and supplemented by all authors.

Data, Materials and/or Code Availability

Not applicable.