Body-environment integration: Temporal processing of tactile and auditory inputs along the schizophrenia continuum

The Evolution of Symbolic Thought: At the Intersection of Schizophrenia Psychopathology, Ethnoarchaeology, and Neuroscience

The human capacity for symbolic representation arises, evolutionarily and developmentally, from the exploitation of a widespread sensorimotor network, along a fundamental continuity between embodied and symbolic modes of experience. In this regard, the fine balancing between constrained sensorimotor connections (responsible for self-embodiment processing) and more untethered neural associations (responsible for abstract and symbolic processing) is context dependent and plastically neuromodulated, thus intersubjectively constructed within a specific socio-cultural milieu. Instead, in the schizophrenia spectrum this system falls off catastrophically, due to an unbalance toward too unconstrained sensorimotor connectivity, leading to a profound distortion of self/world relation with a symbolic activity detached from its embodied ground. For this very reason, however, schizophrenia psychopathology may contribute to unveil, in a distorted or magnified way, ubiquitous structural features of human symbolic activity, beneath the various, historically determined cultural systems. In this respect, a comparative approach, linking psychopathology and ethnoarchaeology, allows highlight the following invariant formal characteristics of symbolic processing: (1) Emergence of salient perceptive fragments, which stand out from the perceptual field. (2) Spreading of a multiplicity of new significances with suspension of common-sense meaning. (3) Dynamic and passive character through which meaning proliferation is experienced. This study emphasizes the importance of fine-grained psychopathology to elucidate, within a cross-disciplinary framework, the evolutionarily and developmental pathways that shape the basic structures of human symbolization.

Bi-directional and multi-modal effects of dexamphetamine on spatial binding windows in healthy individuals

OBJECTIVES

Stimuli that are separated by a short window of space or time, known as spatial and temporal binding windows (SBW/TBWs), may be perceived as separate. Widened TBWs are evidenced in schizophrenia, although it is unclear if the SBW is similarly affected. The current study aimed to assess if dexamphetamine (DEX) may increase SBWs in a multimodal visuo-tactile illusion, potentially validating usefulness as an experimental model for multimodal visuo-tactile hallucinations in schizophrenia, and to examine a possible association between altered binding windows (BWs) and working memory (WM) suggested by previous research.

METHODS

A placebo-controlled, double-blinded, and counter-balanced crossover design was employed. Permuted block randomisation was used for drug order. Healthy participants received DEX (0.45 mg/kg, PO, b.i.d.) or placebo (glucose powder) in capsules. The Rubber Hand Illusion (RHI) and Wechsler Adult Intelligence Scale Spatial Span was employed to determine whether DEX would alter SBWs and WM, respectively. Schizotypy was assessed with a variety of psychological scales.

RESULTS

Most participants did not experience the RHI even under normal circumstances. Bi-directional and multimodal effects of DEX on individual SBWs and schizotypy were observed, but not on WM.

CONCLUSIONS

Bidirectional multimodal effects of DEX on the RHI and SBWs were observed in individuals, although not associated with alterations in WM.

Synchrony perception across senses: A systematic review of temporal binding window changes from infancy to adolescence in typical and atypical development

Sensory integration is increasingly acknowledged as being crucial for the development of cognitive and social abilities. However, its developmental trajectory is still little understood. This systematic review delves into the topic by investigating the literature about the developmental changes from infancy through adolescence of the Temporal Binding Window (TBW) - the epoch of time within which sensory inputs are perceived as simultaneous and therefore integrated. Following comprehensive searches across PubMed, Elsevier, and PsycInfo databases, only experimental, behavioral, English-language, peer-reviewed studies on multisensory temporal processing in 0-17-year-olds have been included. Non-behavioral, non-multisensory, and non-human studies have been excluded as those that did not directly focus on the TBW. The selection process was independently performed by two Authors. The 39 selected studies involved 2859 participants in total. Findings indicate a predisposition towards cross-modal asynchrony sensitivity and a composite, still unclear, developmental trajectory, with atypical development associated to increased asynchrony tolerance. These results highlight the need for consistent and thorough research into TBW development to inform potential interventions.

Schizophrenia and the bodily self

Despite the historically consolidated psychopathological perspective, on the one hand, contemporary organicistic psychiatry often highlights abnormalities in neurotransmitter systems like dysregulation of dopamine transmission, neural circuitry, and genetic factors as key contributors to schizophrenia. Neuroscience, on the other, has so far almost entirely neglected the first-person experiential dimension of this syndrome, mainly focusing on high-order cognitive functions, such as executive function, working memory, theory of mind, and the like. An alternative view posits that schizophrenia is a self-disorder characterized by anomalous self-experience and awareness. This view may not only shed new light on the psychopathological features of psychosis but also inspire empirical research targeting the bodily and neurobiological changes underpinning this disorder. Cognitive neuroscience can today address classic topics of phenomenological psychopathology by adding a new level of description, finally enabling the correlation between the first-person experiential aspects of psychiatric diseases and their neurobiological roots. Recent empirical evidence on the neurobiological basis of a minimal notion of the self, the bodily self, is presented. The relationship between the body, its motor potentialities and the notion of minimal self is illustrated. Evidence on the neural mechanisms underpinning the bodily self, its plasticity, and the blurring of self-other distinction in schizophrenic patients is introduced and discussed. It is concluded that brain-body function anomalies of multisensory integration, differential processing of self- and other-related bodily information mediating self-experience, might be at the basis of the disruption of the self disorders characterizing schizophrenia.

Sense of agency and its disturbances: A systematic review targeting the intentional binding effect in neuropsychiatric disorders

Sense of agency (SoA) indicates a person's ability to perceive her/his own motor acts as actually being her/his and, through them, to exert control over the course of external events. Disruptions in SoA may profoundly affect the individual's functioning, as observed in several neuropsychiatric disorders. This is the first article to systematically review studies that investigated intentional binding (IB), a quantitative proxy for SoA measurement, in neurological and psychiatric patients. Eligible were studies of IB involving patients with neurological and/or psychiatric disorders. We included 15 studies involving 692 individuals. Risk of bias was low throughout studies. Abnormally increased action-outcome binding was found in schizophrenia and in patients with Parkinson's disease taking dopaminergic medications or reporting impulsive-compulsive behaviors. A decreased IB effect was observed in Tourette's disorder and functional movement disorders, whereas increased action-outcome binding was found in patients with the cortico-basal syndrome. The extent of IB deviation from healthy control values correlated with the severity of symptoms in several disorders. Inconsistent effects were found for autism spectrum disorders, anorexia nervosa, and borderline personality disorder. Findings pave the way for treatments specifically targeting SoA in neuropsychiatric disorders where IB is altered.

Time processing in neurological and psychiatric conditions

A central question in understanding cognition and pathology-related cognitive changes is how we process time. However, time processing difficulties across several neurological and psychiatric conditions remain seldom investigated. The aim of this review is to develop a unifying taxonomy of time processing, and a neuropsychological perspective on temporal difficulties. Four main temporal judgments are discussed: duration processing, simultaneity and synchrony, passage of time, and mental time travel. We present an integrated theoretical framework of timing difficulties across psychiatric and neurological conditions based on selected patient populations. This framework provides new mechanistic insights on both (a) the processes involved in each temporal judgement, and (b) temporal difficulties across pathologies. By identifying underlying transdiagnostic time-processing mechanisms, this framework opens fruitful avenues for future research.

The impact of cardiac phases on multisensory integration

The brain continuously processes information coming from both the external environment and visceral signals generated by the body. This constant information exchange between the body and the brain allows signals originating from the oscillatory activity of the heart, among others, to influence perception. Here, we investigated how the cardiac phase modulates multisensory integration, which is the process that allows information from multiple senses to combine non-linearly to reduce environmental uncertainty. Forty healthy participants completed a Simple Detection Task with unimodal (Auditory, Visual, Tactile) and bimodal (Audio-Tactile, Audio-Visual, Visuo-Tactile) stimuli presented 250 ms and 500 ms after the R-peak of the electrocardiogram, that is, systole and diastole, respectively. First, we found a nonspecific effect of the cardiac cycle phases on detection of both unimodal and bimodal stimuli. Reaction times were faster for stimuli presented during diastole, compared to systole. Then, applying the Race Model Inequality approach to quantify multisensory integration, Audio-Tactile and Visuo-Tactile, but not Audio-Visual stimuli, showed higher integration when presented during diastole than during systole. These findings indicate that the impact of the cardiac phase on multisensory integration may be specific for stimuli including somatosensory (i.e., tactile) inputs. This suggests that the heartbeat-related noise, which according to the interoceptive predictive coding theory suppresses somatosensory inputs, also affects multisensory integration during systole. In conclusion, our data extend the interoceptive predictive coding theory to the multisensory domain. From a more mechanistic view, they may reflect a reduced optimization of neural oscillations orchestrating multisensory integration during systole.

Enhanced temporal resolution of vision in action video game players

Video game play has been suggested to improve visual and attention processing. Nevertheless, while action video game play is highly dynamic, there is scarce research on how information is temporally discriminated at the millisecond level. This cross-sectional study investigates whether temporal discrimination at the millisecond level in vision varies across action video game players (VGPs; N = 23) and non-video game players (NVGPs; N = 23). Participants discriminated synchronous from asynchronous onsets of two visual targets in virtual reality, while their EEG and oculomotor movements were recorded. Results show an increased sensitivity to short asynchronies (11, 33 and 66 ms) in VGPs compared with NVGPs, which was especially marked at the start of the task, suggesting better temporal discrimination abilities. Pre-targets oculomotor freezing - the inhibition of small fixational saccades - was associated with correct temporal discrimination, probably revealing attentional preparation. However, this parameter did not differ between groups. EEG and reconstruction analyses suggest that the enhancement of temporal discrimination in VGPs during temporal discrimination is related to parieto-occipital processing, and a reduction of alpha-band (8-14 Hz) power and inter-trial phase coherence. Overall, the study reveals an enhanced ability in action video game players to discriminate in time visual events in close temporal proximity combined with reduced alpha-band oscillatory activities. Consequently, playing action video games is associated with an improved temporal resolution of vision.

Perceptual Functioning

Perceptual disorders are not part of the diagnosis criteria for schizophrenia. Yet, a considerable amount of work has been conducted, especially on visual perception abnormalities, and there is little doubt that visual perception is altered in patients. There are several reasons why such perturbations are of interest in this pathology. They are observed during the prodromal phase of psychosis, they are related to the pathophysiology (clinical disorganization, disorders of the sense of self), and they are associated with neuronal connectivity disorders. Perturbations occur at different levels of processing and likely affect how patients interact and adapt to their surroundings. The literature has become very large, and here we try to summarize different models that have guided the exploration of perception in patients. We also illustrate several lines of research by showing how perception has been investigated and by discussing the interpretation of the results. In addition to discussing domains such as contrast sensitivity, masking, and visual grouping, we develop more recent fields like processing at the level of the retina, and the timing of perception.

Temporal Order Judgments in Schizophrenia and Bipolar Disorders – Explicit and Implicit Measures

Ordering events in time is essential for the understanding of causal relationships between successive events. Incorrect causal links can lead to false beliefs and an altered perception of reality. These symptoms belong to psychosis, which is present in schizophrenia (SZ) spectrum and bipolar (BP) disorder. Experimental results show that patients with SZ have an altered perception of temporal order, while there are no data in patients with BP. We investigated the ability of patients with SZ, BP, and controls to judge the order of stimuli with a 100-ms Stimulus Onset Asynchrony (SOA), and how such large asynchronies facilitate temporal order judgments for small asynchronies. Explicit temporal order effects suggest that patients with SZ perform worse at a long SOA (100 ms) as compared to controls, whereas patients with BP show no difference compared to controls or to patients with SZ. Implicit order effects reveal improved performances in case of identical as compared to different relative order between two successive trials for all groups, with no differences between the groups. We replicated explicit order impairments in patients with SZ compared to controls, while implicit effects appear to be preserved. This difficulty for patients to consciously order stimuli in time might be understood under the light of the loosening-of-associations phenomenon well described in SZ. Further, we showed that patients with BP do not reveal such an explicit order impairment which is consistent with phenomenological descriptions, suggesting a difference in time experience in patients with SZ and BP.

Timing and schizophrenia: Time to get abstract?

In this commentary I summarize why I started to study timing in schizophrenia, and why I got interested in non-conscious mechanisms. I emphasize the contrast between the multitude of tiny sensory characteristics that need to be processed, mostly non-consciously, and the stability and continuity we experience subjectively. My work suggests this to be true also for timing. Our studies unveiled some of the mechanisms helping us to ignore the tiny signals that may otherwise disrupt our sense of time continuity, and suggest such disruption may occur in individuals with schizophrenia. Given the link between timing and the sense of self, I propose that further studies on timing may help to connect neurobiology, cognitive and clinical disorders in individuals with schizophrenia, thus helping to develop innovative therapeutics.

Influence of E/I balance and pruning in peri-personal space differences in schizophrenia: A computational approach

The encoding of the space close to the body, named peri-personal space (PPS), is thought to play a crucial role in the unusual experiences of the self observed in schizophrenia (SCZ). However, it is unclear why SCZ patients and high schizotypal (H-SPQ) individuals present a narrower PPS and why the boundaries of the PPS are more sharply defined in patients. We hypothesise that the unusual PPS representation observed in SCZ is caused by an imbalance of excitation and inhibition (E/I) in recurrent synapses of unisensory neurons or an impairment of bottom-up and top-down connectivity between unisensory and multisensory neurons. These hypotheses were tested computationally by manipulating the effects of E/I imbalance, feedback weights and synaptic density in the network. Using simulations we explored the effects of such impairments in the PPS representation generated by the network and fitted the model to behavioural data. We found that increased excitation of sensory neurons could account for the smaller PPS observed in SCZ and H-SPQ, whereas a decrease of synaptic density caused the sharp definition of the PPS observed in SCZ. We propose a novel conceptual model of PPS representation in the SCZ spectrum that can account for alterations in self-world demarcation, failures in tactile discrimination and symptoms observed in patients.

Time in schizophrenia: a link between psychopathology, psychophysics and technology

It has been widely demonstrated that time processing is altered in patients with schizophrenia. This perspective review delves into such temporal deficit and highlights its link to low-level sensory alterations, which are often overlooked in rehabilitation protocols for psychosis. However, if temporal impairment at the sensory level is inherent to the disease, new interventions should focus on this dimension. Beyond more traditional types of intervention, here we review the most recent digital technologies for rehabilitation and the most promising ones for sensory training. The overall aim is to synthesise existing literature on time in schizophrenia linking psychopathology, psychophysics, and technology to help future developments.

Maladaptive reorganization following SCI: The role of body representation and multisensory integration

In this review we focus on maladaptive brain reorganization after spinal cord injury (SCI), including the development of neuropathic pain, and its relationship with impairments in body representation and multisensory integration. We will discuss the implications of altered sensorimotor interactions after SCI with and without neuropathic pain and possible deficits in multisensory integration and body representation. Within this framework we will examine published research findings focused on the use of bodily illusions to manipulate multisensory body representation to induce analgesic effects in heterogeneous chronic pain populations and in SCI-related neuropathic pain. We propose that the development and intensification of neuropathic pain after SCI is partly dependent on brain reorganization associated with dysfunctional multisensory integration processes and distorted body representation. We conclude this review by suggesting future research avenues that may lead to a better understanding of the complex mechanisms underlying the sense of the body after SCI, with a focus on cortical changes.

Striatal GABA level is associated with sensory integration ability in individuals with low levels of negative schizotypy

Recent studies suggest that altered gamma-aminobutyric acidergic (GABAergic) function may result in multisensory integration deficits in schizophrenia. However, it is unclear whether the GABA level is abnormal in individuals with high levels of schizotypal traits and how it would correlate with sensory integration ability in these individuals. This study aimed to compare the GABA level between individuals with high and low levels of negative schizotypy, and examine the relationship between GABA levels and sensory integration ability in each group. In vivo GABA+ and N-acetylaspartate (NAA) levels in the striatum were measured using proton magnetic resonance imaging in 19 participants with high levels of negative schizotypy and 21 participants with low levels of negative schizotypy. The Sensory Integration subscale of the abridged version of the Cambridge Neurological Inventory was used. We examined the group differences in GABA+/NAA levels, and the correlation between striatal GABA+/NAA levels and sensory integration ability in each group. The two groups showed comparable levels of in-vivo GABA+/NAA. In-vivo GABA+/NAA levels were negatively correlated with sensory integration score in participants with low levels of negative schizotypy, but not in participants with high levels of negative schizotypy. Our findings indicate that the increased GABA level is correlated with better sensory integration ability in individuals with low levels of negative schizotypy, implicating the role of GABAergic function in multisensory integration. Unlike schizophrenia patients, individuals with high levels of schizotypy do not exhibit any abnormality in their GABAergic system and sensory integration ability.