Hierarchical consciousness: the Nested Observer Windows model

Foremost in our experience is the intuition that we possess a unified conscious experience. However, many observations run counter to this intuition: we experience paralyzing indecision when faced with two appealing behavioral choices, we simultaneously hold contradictory beliefs, and the content of our thought is often characterized by an internal debate. Here, we propose the Nested Observer Windows (NOW) Model, a framework for hierarchical consciousness wherein information processed across many spatiotemporal scales of the brain feeds into subjective experience. The model likens the mind to a hierarchy of nested mosaic tiles-where an image is composed of mosaic tiles, and each of these tiles is itself an image composed of mosaic tiles. Unitary consciousness exists at the apex of this nested hierarchy where perceptual constructs become fully integrated and complex behaviors are initiated via abstract commands. We define an observer window as a spatially and temporally constrained system within which information is integrated, e.g. in functional brain regions and neurons. Three principles from the signal analysis of electrical activity describe the nested hierarchy and generate testable predictions. First, nested observer windows disseminate information across spatiotemporal scales with cross-frequency coupling. Second, observer windows are characterized by a high degree of internal synchrony (with zero phase lag). Third, observer windows at the same spatiotemporal level share information with each other through coherence (with non-zero phase lag). The theoretical framework of the NOW Model accounts for a wide range of subjective experiences and a novel approach for integrating prominent theories of consciousness.

Interhemispheric Integration after Callosotomy: A Meta-Analysis of Poffenberger and Redundant-Target Paradigms

The central role of the corpus callosum in integrating perception and cognition across the cerebral hemispheres makes it highly desirable for clinical and basic research to have a repertoire of experimental paradigms assessing callosal functioning. Here, the objective was to assess the validity of two such paradigms (Poffenberger, redundant-target paradigms) by conducting single-step meta-analyses on individual case data of callosotomy patients. Studies were identified by systematic literature search (source: Pubmed and WebOfKnowledge, date: 07.03.2022) and all studies were included that reported callosotomy case data for either paradigm. Twenty-two studies (38 unique cases) provided 116 observations of the crossed-uncrossed difference (CUD) for the Poffenberger paradigm, while ten studies (22 cases, 103 observations) provided bilateral redundancy gain (bRG) measures. Using linear-mixed models with "individual" and "experiment" as random-effects variable, the mean CUD was estimated at 60.6 ms (CI95%: 45.3; 75.9) for commissurotomy, 43.5 ms (26.7; 60.2) for complete callosotomy, and 8.8 ms (1.1; 16.6) for partial anterior-medial callosotomy patients. The estimates of commissurotomy/callosotomy patients differed significantly from patients with partial callosotomy and healthy controls. The mean bRGmin (minimum unilateral reference) was estimated at 42.8 ms (27.1;58.4) for patients with complete and 30.8 ms (16.8; 44.7) for patients with partial callosotomy, both differing significantly from controls. One limitation was that different formulas for bRG were used, making it necessary to split the sample and reducing test power of some analyses. Nevertheless, the present findings suggest that both paradigms assess interhemispheric callosal integration, confirming their construct validity, but likely test distinct callosal functions.

Visual integration across fixation: automatic processes are split but conscious processes remain unified in the split-brain

The classic view holds that when "split-brain" patients are presented with an object in the right visual field, they will correctly identify it verbally and with the right hand. However, when the object is presented in the left visual field, the patient verbally states that he saw nothing but nevertheless identifies it accurately with the left hand. This interaction suggests that perception, recognition and responding are separated in the two isolated hemispheres. However, there is now accumulating evidence that this interaction is not absolute; for instance, split-brain patients are able to detect and localise stimuli anywhere in the visual field verbally and with either hand. In this study we set out to explore this cross-hemifield interaction in more detail with the split-brain patient DDC and carried out two experiments. The aim of these experiments is to unveil the unity of deliberate and automatic processing in the context of visual integration across hemispheres. Experiment 1 suggests that automatic processing is split in this context. In contrast, when the patient is forced to adopt a conscious, deliberate, approach, processing seemed to be unified across visual fields (and thus across hemispheres). First, we looked at the confidence that DDC has in his responses. The experiment involved a simultaneous "same" versus "different" matching task with two shapes presented either within one hemifield or across fixation. The results showed that we replicated the observation that split brain patients cannot match across fixation, but more interesting, that DDC was very confident in the across-fixation condition while performing at chance-level. On the basis of this result, we hypothesised a two-route explanation. In healthy subjects, the visual information from the two hemifields is integrated in an automatic, unconscious fashion via the intact splenium, and this route has been severed in DDC. However, we know from previous experiments that some transfer of information remains possible. We proposed that this second route (perhaps less visual; more symbolic) may become apparent when he is forced to use a deliberate, consciously controlled approach. In an experiment where he is informed, by a second stimulus presented in one hemifield, what to do with the first stimulus that was presented in the same or the opposite hemifield, we showed that there was indeed interhemispheric transfer of information. We suggest that this two-route model may help in clarifying some of the controversial issues in split-brain research.

Entropy and Cross-Level Orderliness in Light of the Interconnection between the Neural System and Consciousness

Despite recent advances, the origin and utility of consciousness remains under debate. Using an evolutionary perspective on the origin of consciousness, this review elaborates on the promising theoretical background suggested in the temporospatial theory of consciousness, which outlines world-brain alignment as a critical predisposition for controlling behavior and adaptation. Such a system can be evolutionarily effective only if it can provide instant cohesion between the subsystems, which is possible only if it performs an intrinsic activity modified in light of the incoming stimulation. One can assume that the world-brain interaction results in a particular interference pattern predetermined by connectome complexity. This is what organisms experience as their exclusive subjective state, allowing the anticipation of regularities in the environment. Thus, an anticipative system can emerge only in a regular environment, which guides natural selection by reinforcing corresponding reactions and decreasing the system entropy. Subsequent evolution requires complicated, layered structures and can be traced from simple organisms to human consciousness and society. This allows us to consider the mode of entropy as a subject of natural evolution rather than an individual entity.

The hard problem of consciousness—A perspective from holistic philosophy

Based on a material view and reductionism, science has achieved great success. These cognitive paradigms treat the external as an objective existence and ignore internal consciousness. However, this cognitive paradigm, which we take for granted, has also led to some dilemmas related to consciousness in biology and physics. Together, these phenomena reveal the interaction and inseparable side of matter and consciousness (or body and mind) rather than the absolute opposition. However, a material view that describes matter and consciousness in opposition cannot explain the underlying principle, which causes a gap in interpretation. For example, consciousness is believed to be the key to influencing wave function collapse (reality), but there is a lack of a scientific model to study how this happens. In this study, we reveal that the theory of scientific cognition exhibits a paradigm shift in terms of perception. This tendency implies that reconciling the relationship between matter and consciousness requires an abstract theoretical model that is not based on physical forms. We propose that the holistic cognitive paradigm offers a potential solution to reconcile the dilemmas and can be scientifically proven. In contrast to the material view, the holistic cognitive paradigm is based on the objective contradictory nature of perception rather than the external physical characteristics. This cognitive paradigm relies on perception and experience (not observation) and summarizes all existence into two abstract contradictory perceptual states (Yin-Yang). Matter and consciousness can be seen as two different states of perception, unified in perception rather than in opposition. This abstract perspective offers a distinction from the material view, which is also the key to falsification, and the occurrence of an event is inseparable from the irrational state of the observer’s conscious perception. Alternatively, from the material view, the event is random and has nothing to do with perception. We hope that this study can provide some new enlightenment for the scientific coordination of the opposing relationship between matter and consciousness.

Disruption of large-scale electrophysiological networks in stroke patients with visuospatial neglect

Stroke frequently produces attentional dysfunctions including symptoms of hemispatial neglect, which is characterized by a breakdown of awareness for the contralesional hemispace. Recent studies with functional MRI (fMRI) suggest that hemineglect patients display abnormal intra- and interhemispheric functional connectivity. However, since stroke is a vascular disorder and fMRI signals remain sensitive to nonneuronal (i.e., vascular) coupling, more direct demonstrations of neural network dysfunction in hemispatial neglect are warranted. Here, we utilize electroencephalogram (EEG) source imaging to uncover differences in resting-state network organization between patients with right hemispheric stroke (N = 15) and age-matched, healthy controls (N = 27), and determine the relationship between hemineglect symptoms and brain network organization. We estimated intra- and interregional differences in cortical communication by calculating the spectral power and amplitude envelope correlations of narrow-band EEG oscillations. We first observed focal frequency-slowing within the right posterior cortical regions, reflected in relative delta/theta power increases and alpha/beta/gamma decreases. Secondly, nodes within the right temporal and parietal cortex consistently displayed anomalous intra- and interhemispheric coupling, stronger in delta and gamma bands, and weaker in theta, alpha, and beta bands. Finally, a significant association was observed between the severity of left-hemispace search deficits (e.g., cancellation test omissions) and reduced functional connectivity within the alpha and beta bands. In sum, our novel results validate the hypothesis of large-scale cortical network disruption following stroke and reinforce the proposal that abnormal brain oscillations may be intimately involved in the pathophysiology of visuospatial neglect.

Stroke patients often exhibit a disabling deficit of visual awareness in the hemifield opposite to their brain lesion, known as hemineglect. Recent studies with functional MRI (fMRI) suggest that hemineglect patients display abnormal functional coupling (i.e., connectivity) within and between brain hemispheres. However, since stroke is a vascular disorder and fMRI measures nonneuronal (i.e., vascular) coupling, we here provide direct evidence of neural network dysfunction in hemineglect by using electroencephalogram (EEG) source imaging, which measures the electrical fluctuations of large neuronal populations. Overall, we observed a breakdown of interhemispheric network connectivity within alpha/beta rhythms, which specifically correlated with the degree of patients’ hemispatial errors. The high temporal resolution and frequency content of EEG signals could lead to more sensitive markers and targeted rehabilitation approaches of hemineglect.

Evolutionary origin and the development of consciousness

This review seeks to combine advances in anthropology and neuroscience to investigate the adaptive value of human consciousness. It uses an interdisciplinary perspective on the origin of consciousness to refute the most common fallacies in considering consciousness, particularly, disregarding the evolutionary origin of the subjective reality in looking for the neural correlates of consciousness and divorcing studies in neuroscience and behavioural sciences. Various explanations linked to consciousness in the field of neuroscience, supplemented with the theoretical explanation of an experience as an ongoing process of overlap between intrinsic neural dynamics and stimulation can be summarised as the stochastic dynamics of one's control system experienced by the individual in the form of subjective reality. This framework elaborates on the world-brain research program and lays foundation for the quantitative description of one's qualitative feelings and naturalistic science of consciousness. Furthermore, this study highlights the philosophical perspective of the inseparability between the physical correlates and the subjective reality contributing to the realistic ontology of conscious processes.

Is There a Causal Link between the Left Lateralization of Language and Other Brain Asymmetries? A Review of Data Gathered in Patients with Focal Brain Lesions

This review evaluated if the hypothesis of a causal link between the left lateralization of language and other brain asymmetries could be supported by a careful review of data gathered in patients with unilateral brain lesions. In a short introduction a distinction was made between brain activities that could: (a) benefit from the shaping influences of language (such as the capacity to solve non-verbal cognitive tasks and the increased levels of consciousness and of intentionality); (b) be incompatible with the properties and the shaping activities of language (e.g., the relations between language and the automatic orienting of visual-spatial attention or between cognition and emotion) and (c) be more represented on the right hemisphere due to competition for cortical space. The correspondence between predictions based on the theoretical impact of language on other brain functions and data obtained in patients with lesions of the right and left hemisphere was then assessed. The reviewed data suggest that different kinds of hemispheric asymmetries observed in patients with unilateral brain lesions could be subsumed by common mechanisms, more or less directly linked to the left lateralization of language.

Can the mind be split? A historical introduction

The idea that the mind might be composed of distinct conscious entities goes back at least to the mid-19th century, and was at first based on the bilateral symmetry of the brain, with each side seemingly a mirror-image replica of the other. This led to early speculation as to whether section of the forebrain commissures might lead to separate, independent consciousnesses. This was not put to the test until the 1960s, first in commissurotomized cats and monkeys, and then in humans who had undergone commissurotomy for the relief of intractable epilepsy. Initial results did indeed suggest independent consciousness in each separated hemisphere, but later findings have also revealed a degree of mental unity, especially in some perceptual functions and in motor control. Some of these findings might be interpreted in terms of subcortical connections or external cross-cuing, and also address questions about the nature of consciousness in a more concrete way.

Lessons from behavioral lateralization in olfaction

Sensory information, sampled by sensory organs positioned on each side of the body may play a crucial role in organizing brain lateralization. This question is of particular interest with regard to the growing evidence of alteration in lateralization in several psychiatric conditions. In this context, the olfactory system, an ancient, mostly ipsilateral and well-conserved system across phylogeny may prove an interesting model system to understand the behavioral significance of brain lateralization. Here, we focused on behavioral data in vertebrates and non-vertebrates, suggesting that the two hemispheres of the brain differentially processed olfactory cues to achieve diverse sensory operations, such as detection, discrimination, identification of behavioral valuable cues or learning. These include reports across different species on best performances with one nostril or the other or odorant active sampling by one nostril or the other, depending on odorants or contexts. In some species, hints from peripheral anatomical or functional asymmetry were proposed to explain these asymmetries in behavior. Instigations of brain activation or more rarely of brain connectivity evoked by odorants revealed a complex picture with regards to asymmetric patterns which is discussed with respect to behavioral data. Along the steps of the discussed literature, we propose avenues for future research.

A Novel Perspective for Examining and Comparing Real and Virtual Test Tasks Performed by the Dominant and Non-Dominant Hand in Healthy Adults

This study presents a novel perspective for the study of functional lateralization in a virtual reality environment. In the model study of handedness, the recognition of the dominant and non-dominant hand in real and virtual conditions was assessed using selected tests, such as a real light exposure test of Piórkowski’s apparatus and classical clinical tests, as well as virtual test tasks, in healthy adults. Statistically significant differences between the dominant and non-dominant hand were observed for tests carried out both in classical conditions and the virtual environment. The results and findings of other studies suggest that the virtual reality approach is a very promising and sensitive tool in the research on functional asymmetries in healthy and disease for motor skills and cognition processes.

Exploring Signatures of Neurodegeneration in Early-Onset Older-Age Bipolar Disorder and Behavioral Variant Frontotemporal Dementia

Introduction: Older-age bipolar disorder (OABD) may involve neurocognitive decline and behavioral disturbances that could share features with the behavioral variant of frontotemporal dementia (bvFTD), making the differential diagnosis difficult in cases of suspected dementia.

Objective: To compare the neuropsychological profile, brain morphometry, and structural connectivity patterns between patients diagnosed with bvFTD, patients classified as OABD with an early onset of the disease (EO-OABD), and healthy controls (HC).

Methods: bvFTD patients (n = 25, age: 66 ± 7, female: 64%, disease duration: 6 ± 4 years), EO-OABD patients (n = 17, age: 65 ± 9, female: 71%, disease duration: 38 ± 8 years), and HC (n = 28, age: 62 ± 7, female: 64%) were evaluated through neuropsychological tests concerning attention, memory, executive function, praxis, and language. Brain morphometry was analyzed through surface-based morphometry (SBM), while structural brain connectivity was assessed through diffusion tensor imaging (DTI).

Results: Both bvFTD and EO-OABD patients showed lower performance in neuropsychological tests of attention, verbal fluency, working memory, verbal memory, and praxis than HC. Comparisons between EO-OABD and bvFTD showed differences limited to cognitive flexibility delayed recall and intrusion errors in the memory test. SBM analysis demonstrated that several frontal, temporal, and parietal regions were altered in both bvFTD and EO-OABD compared to HC. In contrast, comparisons between bvFTD and EO-OABD evidenced differences exclusively in the right temporal pole and the left entorhinal cortex. DTI analysis showed alterations in association and projection fibers in both EO-OABD and bvFTD patients compared to HC. Commissural fibers were found to be particularly affected in EO-OABD. The middle cerebellar peduncle and the pontine crossing tract were exclusively altered in bvFTD. There were no significant differences in DTI analysis between EO-OABD and bvFTD.

Discussion: EO-OABD and bvFTD may share an overlap in cognitive, brain morphometry, and structural connectivity profiles that could reflect common underlying mechanisms, even though the etiology of each disease can be different and multifactorial.

Consciousness after split-brain surgery: The recent challenge to the classical picture

In a recent series of experiments, Pinto and colleagues found that the split-brain patient D.D.C. was able to respond accurately to stimuli in either visual field, whether using his right hand, his left hand, or verbally. Pinto and colleagues argue that this demonstrates that a split-brain patient remains a unitary agent and thus continues to possess a unified consciousness. This paper provides a critical evaluation of that claim. First, we argue that two conceptions of the unity of consciousness need to be distinguished: an agency-based conception and an experience-based conception. Second, we argue that it is an open question whether the data presented by Pinto and colleagues is best understood in terms of the unity of agency. Whether that interpretation is correct depends not only on the mechanisms that produce split-brain behaviour, but also on what is involved in being a single agent. Third, we argue that even if the behavioral data indicated that D.D.C has a unified consciousness in the agency-based sense of the term, it is difficult to reconcile them with the claim that his consciousness is fully unified in the experience-based sense.

Interlimb Transfer of Reach Adaptation Does Not Require an Intact Corpus Callosum: Evidence from Patients with Callosal Lesions and Agenesis

Generalization of sensorimotor adaptation across limbs, known as interlimb transfer, is a well-demonstrated phenomenon in humans, yet the underlying neural mechanisms remain unclear. Theoretical models suggest that interlimb transfer is mediated by interhemispheric transfer of information via the corpus callosum. We thus hypothesized that lesions of the corpus callosum, especially to its midbody connecting motor, supplementary motor, and premotor areas of the two cerebral hemispheres, would impair interlimb transfer of sensorimotor adaptation. To test this hypothesis, we recruited three patients: two rare stroke patients with recent, extensive callosal lesions including the midbody and one patient with complete agenesis. A prismatic adaptation paradigm involving unconstrained arm reaching movements was designed to assess interlimb transfer from the prism-exposed dominant arm (DA) to the unexposed non-dominant arm (NDA) for each participant. Baseline results showed that spatial performance of each patient did not significantly differ from controls, for both limbs. Further, each patient adapted to the prismatic perturbation, with no significant difference in error reduction compared with controls. Crucially, interlimb transfer was found in each patient. The absolute magnitude of each patient’s transfer did not significantly differ from controls. These findings show that sensorimotor adaptation can transfer across limbs despite extensive lesions or complete absence of the corpus callosum. Therefore, callosal pathways connecting homologous motor, premotor, and supplementary motor areas are not necessary for interlimb transfer of prismatic reach adaptation. Such interlimb transfer could be mediated by transcallosal splenium pathways (connecting parietal, temporal and visual areas), ipsilateral cortico-spinal pathways or subcortical structures such as the cerebellum.

Delayed access to conscious processing in multiple sclerosis: Reduced cortical activation and impaired structural connectivity

Although multiple sclerosis (MS) is frequently accompanied by visuo‐cognitive impairment, especially functional brain mechanisms underlying this impairment are still not well understood. Consequently, we used a functional MRI (fMRI) backward masking task to study visual information processing stratifying unconscious and conscious in MS. Specifically, 30 persons with MS (pwMS) and 34 healthy controls (HC) were shown target stimuli followed by a mask presented 8–150 ms later and had to compare the target to a reference stimulus. Retinal integrity (via optical coherence tomography), optic tract integrity (visual evoked potential; VEP) and whole brain structural connectivity (probabilistic tractography) were assessed as complementary structural brain integrity markers. On a psychophysical level, pwMS reached conscious access later than HC (50 vs. 16 ms, p < .001). The delay increased with disease duration (p < .001, β = .37) and disability (p < .001, β = .24), but did not correlate with conscious information processing speed (Symbol digit modality test, β = .07, p = .817). No association was found for VEP and retinal integrity markers. Moreover, pwMS were characterized by decreased brain activation during unconscious processing compared with HC. No group differences were found during conscious processing. Finally, a complementary structural brain integrity analysis showed that a reduced fractional anisotropy in corpus callosum and an impaired connection between right insula and primary visual areas was related to delayed conscious access in pwMS. Our study revealed slowed conscious access to visual stimulus material in MS and a complex pattern of functional and structural alterations coupled to unconscious processing of/delayed conscious access to visual stimulus material in MS.

Growing evidence for separate neural mechanisms for attention and consciousness

Our conscious experience of the world seems to go in lockstep with our attentional focus: We tend to see, hear, taste, and feel what we attend to, and vice versa. This tight coupling between attention and consciousness has given rise to the idea that these two phenomena are indivisible. In the late 1950s, the honoree of this special issue, Charles Eriksen, was among a small group of early pioneers that sought to investigate whether a transient increase in overall level of attention (alertness) in response to a noxious stimulus can be decoupled from conscious perception using experimental techniques. Recent years saw a similar debate regarding whether attention and consciousness are two dissociable processes. Initial evidence that attention and consciousness are two separate processes primarily rested on behavioral data. However, the past couple of years witnessed an explosion of studies aimed at testing this conjecture using neuroscientific techniques. Here we provide an overview of these and related empirical studies on the distinction between the neuronal correlates of attention and consciousness, and detail how advancements in theory and technology can bring about a more detailed understanding of the two. We argue that the most promising approach will combine ever-evolving neurophysiological and interventionist tools with quantitative, empirically testable theories of consciousness that are grounded in a mathematically formalized understanding of phenomenology.

Singularity and consciousness: A neuropsychological contribution

In common sense experience based on introspection, consciousness is singular. There is only one ‘me’ and that is the one that is conscious. This means that ‘singularity’ is a defining aspect of ‘consciousness’. However, the three main theories of consciousness, Integrated Information, Global Workspace and Recurrent Processing theory, are generally not very clear on this issue. These theories have traditionally relied heavily on neuropsychological observations and have interpreted various disorders, such as anosognosia, neglect and split‐brain as impairments in conscious awareness without any reference to ‘the singularity’. In this review, we will re‐examine the theoretical implications of these impairments in conscious awareness and propose a new way how to conceptualize consciousness of singularity. We will argue that the subjective feeling of singularity can coexist with several disunified conscious experiences. Singularity awareness may only come into existence due to environmental response constraints. That is, perceptual, language, memory, attentional and motor processes may largely proceed unintegrated in parallel, whereas a sense of unity only arises when organisms need to respond coherently constrained by the affordances of the environment. Next, we examine from this perspective psychiatric disorders and psycho‐active drugs. Finally, we present a first attempt to test this hypothesis with a resting state imaging experiment in a split‐brain patient. The results suggest that there is substantial coherence of activation across the two hemispheres. These data show that a complete lesioning of the corpus callosum does not, in general, alter the resting state networks of the brain. Thus, we propose that we have separate systems in the brain that generate distributed conscious. The sense of singularity, the experience of a ‘Me‐ness’, emerges in the interaction between the world and response‐planning systems, and this leads to coherent activation in the different functional networks across the cortex.

Higher intelligence may be a risk factor for postoperative transient disturbance of consciousness after corpus callosotomy

INTRODUCTION

Corpus callosotomy (CC) is an established surgical option for palliative treatment of medically intractable epilepsy, especially for seizures with drop attacks. We postulated that specific risk factors for post-CC transient disturbance of consciousness (pCTDC) are associated with CC. The purpose of this study was to review patients with intractable epilepsy who underwent CC and to statistically analyze risk factors for pCTDC.

METHODS

Inclusion criteria for patients who underwent CC between January 2009 and November 2019 were: (1) ≥2 years old and (2) followed up for more than 8 months. The state of consciousness before and after CC was evaluated with the Glasgow coma scale. We statistically assessed predictors for pCTDC as the primary outcome.

RESULTS

Fifty-six patients (19 females, 37 males) were enrolled, and the age range was 2-57 years old. Thirty-seven (66.1%) patients developed pCTDC. The mean period from the beginning of the state of pCTDC to recovery to their baseline conscious level was 4.9 days (range: 2-25 days). All three (100%) normal intelligence level patients, 13 (81%) of 16 patients with a moderately impaired level of intelligence, and 21 (57%) of 37 patients with a severely impaired level of intelligence exhibited pCTDC. Univariate (p = 0.044) and multivariate (p = 0.006) logistic regression analyses for predictors of pCTDC showed that intellectual function was statistically significant.

CONCLUSION

Two-thirds of patients developed pCTDC. One risk factor for pCTDC may be higher intellectual function.

The plasticity of well-being: A training-based framework for the cultivation of human flourishing

Research indicates that core dimensions of psychological well-being can be cultivated through intentional mental training. Despite growing research in this area and an increasing number of interventions designed to improve psychological well-being, the field lacks a unifying framework that clarifies the dimensions of human flourishing that can be cultivated. Here, we integrate evidence from well-being research, cognitive and affective neuroscience, and clinical psychology to highlight four core dimensions of well-being-awareness, connection, insight, and purpose. We discuss the importance of each dimension for psychological well-being, identify mechanisms that underlie their cultivation, and present evidence of their neural and psychological plasticity. This synthesis highlights key insights, as well as important gaps, in the scientific understanding of well-being and how it may be cultivated, thus highlighting future research directions.

Dimensions of Animal Consciousness

How does consciousness vary across the animal kingdom? Are some animals 'more conscious' than others? This article presents a multidimensional framework for understanding interspecies variation in states of consciousness. The framework distinguishes five key dimensions of variation: perceptual richness, evaluative richness, integration at a time, integration across time, and self-consciousness. For each dimension, existing experiments that bear on it are reviewed and future experiments are suggested. By assessing a given species against each dimension, we can construct a consciousness profile for that species. On this framework, there is no single scale along which species can be ranked as more or less conscious. Rather, each species has its own distinctive consciousness profile.

Split-Brain: What We Know Now and Why This is Important for Understanding Consciousness

Recently, the discussion regarding the consequences of cutting the corpus callosum (“split-brain”) has regained momentum (Corballis, Corballis, Berlucchi, & Marzi, Brain, 141(6), e46, 2018; Pinto et al., Brain, 140(5), 1231–1237, 2017a; Pinto, Lamme, & de Haan, Brain, 140(11), e68, 2017; Volz & Gazzaniga, Brain, 140(7), 2051–2060, 2017; Volz, Hillyard, Miller, & Gazzaniga, Brain, 141(3), e15, 2018). This collective review paper aims to summarize the empirical common ground, to delineate the different interpretations, and to identify the remaining questions. In short, callosotomy leads to a broad breakdown of functional integration ranging from perception to attention. However, the breakdown is not absolute as several processes, such as action control, seem to remain unified. Disagreement exists about the responsible mechanisms for this remaining unity. The main issue concerns the first-person perspective of a split-brain patient. Does a split-brain harbor a split consciousness or is consciousness unified? The current consensus is that the body of evidence is insufficient to answer this question, and different suggestions are made with respect to how future studies might address this paucity. In addition, it is suggested that the answers might not be a simple yes or no but that intermediate conceptualizations need to be considered.

Unified tactile detection and localisation in split-brain patients

In 'split-brain' patients, the corpus callosum has been surgically severed to alleviate medically intractable, severe epilepsy. The classic claim is that after removal of the corpus callosum an object presented in the right visual field will be identified correctly verbally and with the right hand but not with the left hand. When the object is presented in the left visual field the patient verbally states that he saw nothing but nevertheless identifies it accurately with the left hand. This interaction suggests that perception, recognition and responding are separated in the two isolated hemispheres. However, there is now accumulating evidence that this interaction is not absolute. Recently, we (Pinto et al., 2017) showed that accurate detection and location of stimuli anywhere in the visual field could be performed with both hands. In this study, we explored detection and localisation of tactile stimulation on the body. In line with our previous results, we observed that split-brain patients can signal detection and localisation with either hand anywhere on the body (be it the arm or the leg) but they remain unable to match positions touched on both arms or legs simultaneously. These results add to the evidence suggesting that the effects of removal of the corpus callosum may be less severe than sometimes claimed.

Asymmetrical Brain Plasticity: Physiology and Pathology

The brain is inherently asymmetrical. How that attribute, manifest both structurally (volumetric, cytological, molecular) as well as functionally, relates to cognitive function, is not fully understood. Since the early descriptions of Paul Broca and Marc Dax it has been known that the processing of language in the brain is fundamentally asymmetrical. Contemporary imaging studies have corroborated early observations, and have also revealed significant functional links to multiple other systems, such as those sub serving memory or emotion. Recent studies have demonstrated that laterality is both plastic and adaptive. Learning and training have shown to affect regional changes in asymmetry, such as that observed in the volume of the planum temporale associated with musical practice. Increasing task complexity has been demonstrated to induce recruitment of contralateral regions, suggesting that laterality is a manifestation of functional reserve. Indeed, in terms of cognitive function, successful aging is often associated with a reduction of asymmetrical activity. The goal of this review is to survey and critically appraise the current literature addressing brain laterality, both morphological and functional, with particular emphasis on the asymmetrical plasticity associated with environmental factors and training. The plastic recruitment of contralateral areas associated with aging and unilateral lesions will be discussed in the context of the loss of asymmetry as a compensatory mechanism, and specific instances of maladaptive plasticity will be explored.

Split-brain patients: Visual biases for faces

Split-brain patients constitute a small subpopulation of epileptic patients who have received the surgical resection of the callosal fibers in an attempt to reduce the spread of epileptic foci between the cerebral hemispheres. The study of callosotomy patients allowed neuropsychologists to investigate the effects of the hemispheric disconnection, shedding more light on the perceptual and cognitive abilities of each hemisphere in isolation. This view that callosotomy completely isolates the hemispheres has now been revised, in favor of the idea of a dynamic functional reorganization of the two sides of the brain; however, the evidence collected from split-brain patients is still a milestone in the neurosciences. The right-hemispheric superiority found in the healthy population concerning face perception has been further supported with split-brains, and it has been shown that the right disconnected hemisphere appears superior to the left hemisphere in recognizing and processing faces with similar characteristics as the observers' (e.g., gender, identity, etc.). Even more controversial is the field of hemispheric asymmetries for processing facial emotion, some evidence suggesting a right-hemispheric superiority for all emotions, some others showing a complementary hemispheric asymmetry depending on the positive or negative emotional valence. Although the practice of callosotomy is mostly abandoned today in favor of pharmacological alternatives, further studies on the remaining split-brain patients could help advance our understanding of hemispheric specialization for social stimuli.