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Displacement and Evolution: A Neurocognitive and Comparative Perspective

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Abstract

By re-evaluating Crow (2000)'s claim that "Schizophrenia [is] the price that Homo sapiens pays for language", we suggest that displacement, the ability to refer to things and situations outside from here and now, partly realized through syntactic operation, could be related to the symptoms of schizophrenia. Mainly supported by episodic memory, displacement has been found in nonhuman animals, but more limited than that in humans. As a conserved subcortical region, the hippocampus plays a key role in episodic memory across species. Evidence in humans suggests that the parietal lobe and basal ganglia are also involved in episodic Memory. We propose that what makes human displacement more developed could rely on the better coordination between the hippocampus and the parietal lobe and basal ganglia. Given that all these areas taking part in language processing, displacement could have served as an interface between episodic memory and language.
UC Merced
Proceedings of the Annual Meeting of the Cognitive Science
Society
Title
Displacement and Evolution: A Neurocognitive and Comparative Perspective
Permalink
https://escholarship.org/uc/item/2hv2f27d
Journal
Proceedings of the Annual Meeting of the Cognitive Science Society, 43(43)
ISSN
1069-7977
Authors
Shi, Edward Ruoyang
Zhang, Qing
Publication Date
2021
Peer reviewed
eScholarship.org Powered by the California Digital Library
University of California
Displacement and Evolution: A Neurocognitive and Comparative Perspective
Edward Ruoyang Shi (edwardshiruoyangend@gmail.com)
Department of Catalan Philology and General Linguistics, University of Barcelona, Gran Via de Les Corts
Catalanes, 585, 08007 Barcelona, Spain
Qing Zhang (zhangqing3@mail.sysu.edu.cn)
Department of Psychology, Sun Yat-Sen Universtiy, Waihuan East Road, No. 132, Guangzhou 510006, China
Abstract
By re-evaluating Crow (2000)’s claim that “Schizophrenia [is] the
price that Homo sapiens pays for language”, we suggest that
displacement, the ability to refer to things and situations outside
from here and now, partly realized through syntactic operation,
could be related to the symptoms of schizophrenia. Mainly
supported by episodic memory, displacement has been found in
nonhuman animals, but more limited than that in humans. As a
conserved subcortical region, the hippocampus plays a key role in
episodic memory across species. Evidence in humans suggests that
the parietal lobe and basal ganglia are also involved in episodic
Memory. We propose that what makes human displacement more
developed could rely on the better coordination between the
hippocampus and the parietal lobe and basal ganglia. Given that all
these areas taking part in language processing, displacement could
have served as an interface between episodic memory and
language.
Keywords: displacement; schizophrenia; episodic memory;
hippocampus; comparative cognition
Introduction: the central paradox
Despite the substantial disadvantage in survival, the
genetic predisposition of schizophrenia has not been
eliminated from population within a few generations. This is
the central paradox concerning schizophrenia raised in
Huxley et al. (1964). In order to resolve this paradox, Crow
(2000) approached this issue from the evolutionary
perspective and claimed that “schizophrenia [is] the price
that Homo sapiens pays for language”. To be more specific,
he proposed that language, the most characteristically
human capacity, was the balancing advantage for the Homo
sapiens-specific predisposition to schizophrenia (not always
pathologically expressed). However, with the advancement
in cognitive neuroscience and accumulating evidence from
comparative biology, it gets clear that some of the claims in
Crow (2000) seem to be hardly maintained and need to be
updated.
In the present work, through the lens of episodic memory
deficits of schizophrenia and evidence from comparative
biology, we focus on the capacity of displacement and how
it relates to the evolution of language. Displacement enables
humans to refer to things and situations outside from here
and now (Bickerton, 2009), and it is traditionally assumed
to be one of the design features that distinguishes human
language from nonhuman animal communicative signals
(Hockett, 1960). However, it is not necessarily a feature of
language. In the following sections, we will first explain
how displacement could be realized by, but beyond the
mechanism of episodic memory. Data from behavioral
studies in comparative biology have revealed that animals
also have episodic-like memory but very limited in terms of
displacement.
Secondly, at the brain level, as a major long-term memory
hub, the hippocampus is assumed to be the basis for
episodic memory. Further, since the hippocampus is a
highly conserved brain structure, its functions could shed
light on comparative studies from evolutionary perspective.
Going into the details of neural basis of displacement,
existing evidence has shown that displacement is not
human- or language-specific but a domain-general property
closely linked to episodic memory in both temporal and
spatial dimensions. We propose that what makes humans
superior to animals in terms of displacement is the better
coordination between the hippocampus and basal ganglia as
well as the parietal lobe, with the evidence in humans that
the basal ganglia and parietal lobe both contribute to
episodic memory in different ways. Furthermore, findings of
all three brain areas involved in language processing suggest
displacement could be an interface between episodic
memory and language.
Finally, we come back to schizophrenia and relate its core
symptoms to the functions of the hippocampus, basal
ganglia and parietal lobe. Schizophrenia patients exhibit not
only cognitive problems related to episodic memory, but
also language problems, both of which could be related to
displacement.
“Schizophrenia as the price that Homo sapiens
pays for language”?
To evaluate Crow’s claim that “schizophrenia [is] the
price that Homo sapiens pays for language”, we need to
have a better understanding of how language evolved, and
which parts of language that have distinguished humans
from other nonhuman animals could have contributed to the
emergence of schizophrenia. To this end, two basic
questions from a bottom-up perspective will be revealing.
First, which property of language is the most
characteristically human capacity? Second, is/are the
component(s) human unique or shared with nonhuman
animals? Beyond behavioral level, we aim to emphasize that
the neural basis of such component(s) could provide more
straightforward insights to the questions above.
Crow (2000) claimed that “arbitrariness”, the absence of
any relationship between a word's form and its meaning, is
the distinctive characteristics of human language. However,
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from evolutionary perspective, Bickerton (2009) argued that
“arbitrariness” is also a feature of some animal
communication system, for instance, the vervets’ alarm calls
for eagles, leopards and snakes. These calls function
differently from words in human language system. Take the
eagle call as an example. it does not translate as “eagle” nor
evokes the image of eagle or anything that eagle could do. It
just draws attentions to the predators from air. It seems more
efficient and functional to translate the call as "Look out, an
eagle is coming!" or "Danger from the air!" or "Quick, find
the nearest bush and hide in it!" (Bickerton2009:44)
At the brain level, lateralization has been proposed as the
critical change giving rise to the emergence of language
Crow, 2008; Corballis, 2003). Literature suggested that
lateral asymmetry is unique in our species (Harrington,
1989). Crichton-Browne (1879) first related mental disorder
with brain asymmetry from the perspective of evolution.
Other studies provided further evidence on asymmetries and
some suggested anatomical asymmetries at the cortical level
contribute to speciation event (Geschwind & Levitsky 1991).
Further, it is assumed that asymmetry at the brain level has
genetic endowment and gives rise to the phenomena of
handedness which is specific to Homo sapiens (Harris,
1991).
However, with the accumulating evidence from
comparative studies (see Fitch and Braccini, 2013 for a
review), the central position of lateralization in
distinguishing Homo sapiens as a species has been
challenged, so that it is inconclusive to explain the
emergence of language. One of the basic features of the
vertebrate brain is neural asymmetry (Vallortigara & Rogers,
2005), and species-typical patterns of left-hemispheric
dominance provided neural basis for conspecific
communication in chimpanzees (Taglialatela et al., 2008)
and rhesus monkeys (Hauser & Andersson, 1994). Going
beyond the primates, left-hemispheric dominance effect
concerning language evolution has been found in birds. For
instance, vocal learning in zebra finches (Moorman et al.,
2012), song discrimination in Bengalese finches (Okanoya
et al., 2001) and hypoglossal functions in canaries
(Nottebohm, 1971).
Hence, the claims in Crow (2000) seem not to be
maintained. In the next section, we will focus on the
property of language that is different from animal calls,
namely displacement. The key difference is that language
makes human beings escape from the limitation of here and
now while animal calls are confined to current situations.
Displacement and episodic memory
Displacement, the ability to talk about things and event
outside from here and now (Bickerton, 2009), heavily relies
on episodic memory, which enables one to revisit the past
event and imagine possible future scenarios (Tulving,
2001). It is worth noting that displacement involves both
temporal and spatial information, which are important for
episodic memory formation and retrieval in both time and
space scales. Tulving (2002) claimed that episodic memory
is human-unique, indicating that displacement may also be
human-unique. Hockett (1960) also posited that
displacement is one of the design features of human
language which is distinct from animal communication
signals. It thus seems that displacement could be both
language- and human-specific from the theoretical
perspective. However, as we have access to more data of
nonhuman animal behavior, episodic-like memory has been
argued to be detected in nonhuman animals, but inferior to
that found in humans in terms of time interval and space
distance.
Clayton & Dickinson (2010) have argued that in
nonverbal animals, it is impossible to take advantage of
their verbal output, so ethological criteria for episodic
memory in nonhuman animals need to be established.
Observations in the wild and lab have demonstrated that
nonhuman animals possess episodic-like memory with
reference to the criteria of “what-where-when”. Examples
include food caching birds (Clayton & Dickinson, 1998),
rodents (Crystal & Smith, 2014), and nonhuman primates
(Martin-Ordas et al., 2010), but it is limited by the length of
time interval of the two measured incidents (Cook et al.,
1985). Furthermore, displacement as a whole has been
reported to be detected in invertebrates: waggle dance of
honeybees (Root-Bernstein, 2010), and food navigation
(Schwarz et al., 2017) and recruitment systems in ants
(Holldobler & Wilson, 1978), but still within the limit of
distance (Yule, 2010). These data suggest that although
short-distance (time and space) displacement has been found
in nonhuman animals, long-distance displacement could be
specific to humans. We suggest that such human-specific
long-distance displacement can be explained from both
neurological and theoretical perspectives.
Hippocampal contribution to episodic memory
in humans and nonhuman animals
The hippocampus is assumed to be involved in explicit
long-term memory and episodic memory (Graf & Schacter,
1985; Voss et al. 2017). To be more specific, it is well
established that the hippocampus is involved in spatial
information (Eichenbaum, 2017; Schiller et al., 2015) and
encoding of time (Eichenbaum, 2015). The hippocampus is
also assumed to store information of when, where and what
(Tsao et al., 2018).
In addition to the function of information storage from
multisensory input, the hippocampus was also proposed to
be engaged in dynamic process like conjunctions of
complex elements including items, context, and temporal
information (Cowell et al., 2019: 5; Shimamura, 2010).
When experience unfolds overtime, interrelated stimuli are
processed and bound together to form coherent memory
(Eichenbaum & Cohen 2004). This actually anchors the
mechanism of relational binding of the hippocampus which
referred to as the function of “rapidly, continuously, and
obligatorily form associations among disparate elements
across space and time, and further to enable the comparison
of internal representations with current perceptual input”
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(Olsen et al., 2012). Such functions of the hippocampus
seem to form the essential basis for displacement.
Comparative data also suggest the role of the
hippocampus in episodic memory. In avian species, as we
have stated in the previous section, food-caching behavior to
some extent reflects episodic-like memory. Investigation
from the brain level reveals that the hippocampus plays a
crucial role in food-storing. Black-capped chickadees and
dark-eyed juncos with hippocampal lesions show memory
impairment for location (Hampton & Shettleworth, 1996;
Sherry & Duff, 1996), suggesting that the functions of avian
hippocampus could be homologous to mammalian
hippocampus (Colombo & Broadbent, 2000; Sherry &
Vaccarino, 1989). Hippocampal lesions also impacted the
performance of spatial learning in Japanese quails (Lormant
et al., 2020). The size of the hippocampus relative to
telencephalon in food-storing passerines is considerably
larger than that in non-food-storing ones (Sherry & Duff,
1996). This enlargement of the hippocampus relative to
other brain areas indicated that memory for food caches
could drive the increase of the hippocampal neurons for
survival (Clayton, 1998). Indeed, it has been found that the
seasonal change in caching is correlated with the seasonal
change in hippocampal size in food-storing birds (Sherry &
Hoshooley, 2010).
Studies on rodents have shown that different subregions
of the hippocampus are involved in episodic memory which
can be decomposed into components, recognition, temporal
order and spatial memories (Aggleton & Pearce 2001). The
novel object recognition (NOR) task for the purpose of
investigating nonspatial memory in rodents has shown that
the hippocampus is not only taking part in object
recognition, but also sensitive to the time delay between the
sample and test sessions (Cohen & Stackman, 2015),
suggesting that the recognition role of the hippocampus may
depend on temporal information. Temporal order has been
explored using odors in rodents (Fortin et al., 2002; Kesner
et al., 2002). The data suggested that the hippocampus is
involved in remembering events in sequence. Besides, the
result of the visual object presentations in rats with lesion in
the dorsal CA1 and CA3 of the hippocampus further
suggested that only CA1 is critical for temporal information
processing (Hoge & Kesner, 2007), whereas the temporal
order of the spatial information was reported to be processed
by ventral hippocampus (Howland et al., 2008). With
respect to spatial memory, early studies have demonstrated
that hippocampal lesions in rats exhibit impaired spatial
learning (Jarrard, 1993). The discovery of “place cell”
(O’Keefe & Nadel, 1978) also suggested the important role
of the hippocampus in spatial cognition.
In nonhuman primates, sub-components of episodic
memory were also examined separately as well as in
combination. The what-where association was investigated
in macaques by recording single hippocampal formation
neurons, and the results showed that both separation and
combination of representations of objects and where they
locate involved the hippocampus, which is a required
property in an episodic memory system (Rolls et al., 2005).
Recording 644 neurons from the hippocampus, and
entorhinal and perirhinal cortex in the medial temporal lobe
in two macaques, Naya & Suzuki (2011) found that the
most prominent “time cells” signals were observed in the
hippocampus, suggesting that the hippocampus is sensitive
to time scale. Lesion studies also suggested the role of the
hippocampus in episodic memory in nonhuman primates.
For instance, conducting delayed nonmatching to sample
task on cynomolgus monkeys, Zola et al. (2000) found that
object recognition memory was impaired in hippocampal
lesion group. Taken together, comparative evidence
indicated that the hippocampus is involved in episodic(-like)
memory in nonhuman animals, homologous to the functions
of human hippocampus.
What makes human displacement highly
developed?
In humans, apart from the fact that the hippocampus is
responsible for episodic memory, the parietal cortex is
equally important to be mentioned. The parietal lobe is
evidenced to play a role in integrating multisensory inputs,
which is essential for the formation of episodic memory.
Neuroimaging studies indeed address the role of the parietal
lobe in episodic memory. Both time and space travel tasks
elicit activation of the inferior parietal lobe (Gauthier & van
Wassenhove, 2014). The angular gyrus, a region lying at the
ventral posterior parietal cortex, was shown to be involved
in both encoding and retrieval episodic memory (Tibon et
al., 2019). The left lateral parietal cortex was also reported
to be activated in time travel of past, present and future
(Nyberg et al., 2010). On the other hand, although it is
generally assumed that the basal ganglia are the neural basis
for procedural memory while the hippocampus supports
long-term memory, evidence has shown that these functions
are actually distributed in the brain (Schreiweis et al., 2014).
Neuroimaging and neuropsychological evidence suggests
that the basal ganglia are also involved in encoding and
retrieval of long-term memory (Han et al., 2010; Shohamy
& Adcock, 2010). Scimeca & Badre (2012) also proposed
that the function of cognitive control of the basal ganglia
enhances the likelihood of the success of retrieval.
On the coordination between the hippocampus and the
parietal lobe and basal ganglia, evidence has shown that the
hippocampus is involved in the network including medial
temporal lobe and posterior parietal cortex (Szczepanski &
Saalmann, 2013). Further, anterior hippocampus is
connected with dorsal parietal cortex which related to items
consistent with retrieval goals, and posterior hippocampus is
functionally connected with ventral parietal cortex which
processes unexpected items (Ciaramelli et al., 2020).
Resting state Functional Magnetic Resonance Imaging
(fMRI) scanning on normal subjects showed robust
connection between the hippocampal formation and various
subregions of the parietal cortex including precuneus,
posterior cingulate, retrosplenial cortex, and bilateral
inferior parietal lobule (Vincent et al., 2006). In the case of
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the basal ganglia, evidence has shown that humanized
FOXP2 inserted in mice enhances the information
transformation between the basal ganglia and hippocampus
(Schreiweis et al., 2014), suggesting a human specific basal
ganglia-hippocampal coordination. These data suggest that
the hippocampus works with the parietal lobe and basal
ganglia to serve the functions of encoding and retrieval of
episodic memory, and thus displacement in humans could
be obtained by better coordination between the
hippocampus and the parietal lobe and basal ganglia
respectively.
Displacement as an interface between episodic
memory and language
In addition to the aforementioned contributions to
episodic memory, the hippocampus, basal ganglia, and
parietal lobe have also been shown to be involved in
different aspects of language processing. In this sense,
displacement could serve as an interface between episodic
memory and language.
The hippocampus has been implicated in new grammar
learning (Opitz & Friederici, 2003; Kepinska et al., 2018),
syntactic integration in language comprehension (Meyer et
al., 2005), and naming ability (Davies et al., 1998;
Matthews, 2015). The results of Glikmann-Johnston et al.
(2015) suggested that the hippocampus is involved in brain
network which selectively supports verbal semantic fluency.
Further, Liégeois et al. (2004) showed that lesions at the left
language area did not associate with the activation in the
analogous regions in the right hemisphere, while in patients
with hippocampal lesion, right-lateralized, or bilateral
language related regions, activation were detected. This
indicates that the hippocampus may be implicated in
language lateralization. Using blank filling tasks, Piai et al.
(2016) have found that the theta-oscillatory activity
supported by the hippocampus is stronger in the condition
of semantically associated sentences than semantically
neutral sentences. Such direct evidence of involvement of
the hippocampus in language online processing encouraged
Covington & Duff (2016) to propose a domain general
prediction role of the hippocampus in language-memory
interface.
Parietal lobe has been implicated in contributing to
language evolution and development. In the dual-stream
hypothesis for language processing, the dorsal pathway II
connecting the superior temporal gyrus (STG) to inferior
frontal gyrus (IFG, BA 44) via the arcuate fasciculus (AF)
going through the parietal cortex has been proposed to be
involved in complex sentence processing (Friederici, 2012).
The enlargement of the parietal lobe has been detected in
evolution in humans (Boeckx & Benítez-Burraco, 2014),
which could have provided humans with enough space
(Deacon, 1989) for the maturation and emergence of the
dorsal pathway II in development and evolution.
Furthermore, Boeckx (2016) has hypothesized that the two-
dimensional recursive structure of syntactic computation
could have been formed by paring two existing one-
dimensional sequences supported by frontal-parietal and
fronto-temporal connection which already present in
nonhuman primates, emphasizing the important role of the
parietal cortex of humans. Moreover, comparing human AF
with that of chimpanzees and macaques, Rilling et al. (2008)
found that human AF is more strongly enhanced and widely
connected.
Evidence has shown that the basal ganglia are also
involved in language processing. In Event-Related
Potential (ERP) studies, syntactic inconsistency elicits P600
wave. In a series of event-related fMRI studies, patients
with basal ganglia lesion and Parkinson’s disease were
asked to process the syntactic incorrect sentences and the
modulations of P600 wave were detected (Kotz et al. 2003).
Further, results show that the basal ganglia are involved in
syntactic processing (Friederici & Kotz, 2003). In an fMRI
study, the authors found increased activation in both right
and left basal ganglia when the participants process
sentences with complicated syntactic structures (Progovac et
al., 2018). From clinical perspective, Shi & Zhang (2020)
propose that the basal ganglia are involved in the process
where hierarchical syntactic structures are transferred into
linearized structures.
Having established that displacement could serve as an
interface between memory system and language. Let’s take
a closer look at how this interface is captured in both
clinical and linguistic terms and how linguistic theories
could map onto brain functions. Besides, the question of
why human beings has superior displacement will also be
discussed.
Cognitive deficits and corresponding
biomarkers of Schizophrenia
Dating back to 1950s, Bleuler (1950) has maintained that
the cognitive deficits associated with schizophrenia is partly
due to inability to organize or associate ideas in memory.
Impairment of episodic memory has also been well
documented in schizophrenia (Leavitt & Goldberg, 2009),
leading to the distortion of the subjective experience of
space (Jaspers, 1963), time (Fuchs, 2013) and person (Crow,
2000). The absence of subjectivity in schizophrenia involves
experiences of fragmentation, meaninglessness, and
ineffable strangeness (Sass & Pienkos, 2013). This
symptom is related to the malfunction of displacement and
manifested as the anomalous use of deixis in patient's
speech. Deixis is the use of words or phrases referring to
specific time, place or person. There are various attempts to
capture this symptom in linguistic terms and no consensus
has been achieved as for whether there are lexical or
syntactic deficits. For example, it has been proposed that the
semantic memory of schizophrenic patients is impaired (see
McKenna and Oh 2005 for a review), accordingly lexical
accessing including deixis is malfunctioned. On the other
hand, Hinzen & Sheehan (2013) proposed that this symptom
is related to grammatical deficits which is manifested as
building the deictic frame of reference. Since lexical
items consists of deixis, the deficits of using deixis could be
1882
related to the process of lexical accessing (Pomarol-Clotet et
al. 2008 among others). Moreover, Boeckx (2015) has
proposed that the formation of lexical items involved
syntactic operation. Furthermore, syntax is an essential
aspect of human language (Chomsky et al. 2019), without
which we cannot express full-fledged meaning. Hence, as a
subcomponent of language, syntax might be related to
displacement and the symptoms of schizophrenia. The
neurological deficits of schizophrenia suggest that this
might be the case.
Although there are very few studies addressing the
correlation between these symptoms related to language and
brain function or structural changes, a lot of which focused
on memory and other cognitive deficits of schizophrenia
patients. Both the structure and function of the hippocampus
have been found to be deviant in schizophrenia patients
(Harrison, 2004). Structural Magnetic Resonance Imaging
(MRI) studies have shown reduced volume and altered
shape of the hippocampus in prodromal and first episode
patients (Velakoulis et al., 1999). The neuropsychological
deficits attributed by the hippocampus were reported to be
correlated to the hippocampal volume and activation (Jessen
et al., 2003). For example, related to our proposal,
deactivation of the hippocampus in episodic memory task—
conscious recollection of the words—was detected in
schizophrenia patients compared to controls (Heckers et al.,
1998). Positron emission tomography (PET) studies
provided evidence of positive correlation between the
symptoms and hippocampal metabolic activity (Medoff et
al., 2001).
Schizophrenia patients with lesions at the inferior parietal
lobule, exhibit diverse cognitive deficits. Using spatial
cueing paradigm, Maruff et al. (1998) found that patients
with schizophrenia had difficulties in directing visual spatial
attention, and processed linguistic cues more slowly relative
to spatial cues (Posner et al., 1988). The patients also
showed deficits in both gestural perception (recognition)
and production (performance) (Walther et al., 2015). Gray
matter reduction was observed in the inferior parietal lobe
predominantly in patients with schizophrenia (Dutschke et
al., 2018). Compared to controls, patients with
schizophrenia performed worse in auditory 2-back task
which tests phonological working memory, and
neuroimaging data show a hypo-activation in dorsolateral
prefrontal cortex, supramarginal gyrus, inferior parietal
lobule, and superior parietal areas (Menon, Anagnoson,
Mathalon, et al., 2001; Schneider et al., 2007).
Gunduz et al. (2002) conducted a structural MRI study
comparing the volume of the basal ganglia structures and
the limbic forebrain in first episode schizophrenia to healthy
subjects, and the results showed no difference between two
groups. However, increased volume and shape change of the
basal ganglia were reported by Mamah et al. (2007). The
enlarged volumes of the total basal ganglia and subregions,
especially the caudates, are associated with worse
performance of finger tapping and Hebb’s Recurring Digits
(Hokama et al., 1995), suggesting the abnormal volume is
reflected in dysfunction of the basal ganglia in
schizophrenia patients. In addition, using a motor
sequencing task, Menon et al. (2001) investigated the
activation difference of the basal ganglia regions and the
thalamus between schizophrenia patients and healthy
controls. Significant bilateral deficits in the posterior
putamen, globus pallidus, and thalamus were found in
schizophrenia subjects.
Both functional and structural anomalies were detected in
the hippocampus, basal ganglia and parietal lobe in
individuals with schizophrenia. And these regions underlie
language processing, especially syntax. Since syntactic
operation is domain-general and cross-modular, and
displacement possibly serves as the interface between
episodic memory and language, we propose that
schizophrenia is the price that Homo sapiens pays for syntax.
Conclusion
In this paper, by re-evaluating Crow’s (2000) statement
that “schizophrenia [is] the price that Homo sapiens pay for
language”, we propose that displacement, which is
supported by syntactic operation, is the key factor that
distinguishes humans from nonhuman animals, the
disruption of which could be a possible candidate giving
rise to symptoms of schizophrenia. Through illustrating the
relation between episodic memory and displacement, we
provide evidence of episodic-like memory present in
nonhuman animals, yet more limited than in humans. At the
brain level, we highlight that the functions of the
hippocampus in episodic memory play a crucial role in
displacement. With the evidence that the parietal lobe and
basal ganglia are both involved in episodic memory, we
further propose that what makes human displacement more
developed than nonhuman animals could be the better
coordination between the hippocampus, basal ganglia and
parietal lobe. The involvement of these three areas in
language processing indicates that displacement might be an
interface between episodic memory and language.
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