Schizophrenia and rightward bias in line bisection

Behavioral lateralization in bipolar disorders: a systematic review

BACKGROUND

Bipolar disorder (BD) is often seen as a bridge between schizophrenia and depression in terms of symptomatology and etiology. Interestingly, hemispheric asymmetries as well as behavioral lateralization are shifted towards a tendency of left-side or mixed-side bias in schizophrenia whereas no shift is observed in subjects with depression. Given the role of BD with both, (hypo)manic and depressive episodes, investigating hemispheric asymmetries in subjects with BD is an interesting objective.

METHOD

A systematic review of studies including measures of behavioral lateralization in the form of handedness, footedness, eyedness, and language lateralization was performed resulting in 25 suitable studies.

RESULTS

A broad variety of methods was used to assess behavioral lateralization, especially for eyedness, footedness, and language lateralization hindering the integration of results. Additionally, for hand preference, studies frequently used different cut-off scores and classification systems. Overall, studies do not support alteration in side preference in BD subjects. Studies focusing on differences in handedness demonstrate that subjects show equal rates of right- and non-right-handedness as the general population. Few studies focusing on manic episodes point towards increased left-side bias in ear and eye dominance, but the small sample sizes and conflicting results warrant further investigation.

CONCLUSION

The results reinforce that some disorders, such as BD, should not be treated as a homogenous group but sub-groups should be analyzed within the patient's population. Particularly, clinical implications resulting from neuroimaging studies highlight the need to study hemispheric asymmetries given that they may be important to consider for brain stimulation protocols.

Ambiguous handedness and visuospatial pseudoneglect in schizotypy in physical and computer-generated virtual environments

Virtual reality (VR) technology has increased clinical attention in the health care of schizophrenia spectrum disorders in both diagnoses of the symptoms and assessment of schizotypal traits. However, the exact nature of VR-induced positive treatment effect in schizotypy is still unknown. In this study, VR technology was used as a non-invasive neurocognitive trigger to test the asymmetric visuospatial representational instability found in individuals with high schizotypy. The study aimed to reveal the brain functional hemispheric laterality in physical and virtual realities in individuals with schizotypal traits. Fifty-one healthy, right-handed participants (24 males and 27 females) were enrolled through public advertisements. Hemispheric functional asymmetry was measured by the Line Bisection Task (LBT). The results revealed that (a) LBT bias in the physical reality showed a handedness-related leftward pseudoneglect, however, similar handedness-related pseudoneglect in VR has not been found. (b) Comparing LBT bias in physically real and VR environments showed rightward drift in VR environments independently to the degree of handedness. (c) The schizotypy has no association with handedness, however, the cognitive schizotypy is related to the LBT bias. Higher cognitive schizotypy in VR associated with left hemispatial pseudoneglect. In conclusion, schizotypy is associated with ambiguous behavioral and cognitive functional laterality. In individuals with high cognitive schizotypy, the VR environment enhanced the representational articulation of the left hemispace. This effect may be originated from the enhancement of the right hemisphere overactivation and is followed by a lower mental control of the overt behavior.

Exploring the relationship between impaired illness awareness and visuospatial inattention in patients with schizophrenia

Anosognosia, described as impairment in an individual's ability to perceive and understand their illness, and visuospatial inattention commonly co-occur as a result of structural brain lesions in the right posterior parietal area. Anosognosia or impaired illness awareness is a common feature of schizophrenia that contributes to medication nonadherence and poor clinical outcomes. A recent pilot study suggests patients with impaired illness awareness have a rightward visuospatial bias. We aimed to examine this relationship in a large sample of patients. This study consisted of 106 patients with schizophrenia spectrum disorder (henceforth, schizophrenia) and 20 healthy controls. Visuospatial attention was assessed using the line bisection test (LBT). Illness awareness was assessed using the VAGUS self-report version. A Welch's t-test was used to examine differences in LBT scores between patients with schizophrenia and healthy controls. Correlation analyses between LBT and VAGUS scores were performed in patients with schizophrenia. For exploratory purposes, intra-subject reliability of the LBT was also examined using a two-way mixed intra-class correlation coefficient (ICC). There were no differences in LBT scores between patients with schizophrenia and healthy controls. In patients, there were no associations between LBT and VAGUS scores. ICCs between two consecutively acquired LBTs were 0.92 (95% CI: 0.81-0.96) in patients with schizophrenia and 0.93 (95% CI: 0.81-0.97) in healthy controls. Our results, using a reliable measure, did not support our previous preliminary finding that suggested a relationship between impaired illness awareness and visuospatial bias in patients with schizophrenia. Future studies should consider more sensitive visuospatial attention tasks when testing this hypothesis.

Dysfunction of Magnocellular/dorsal Processing Stream in Schizophrenia

Background:

Patients with schizophrenia show not only cognitive, but also perceptual deficits. Perceptual deficits may affect different sensory modalities. Among these, the impairment of visual information processing is of particular relevance as demonstrated by the high incidence of visual disturbances. In recent years, the study of neurophysiological mechanisms that underlie visuo-perceptual, -spatial and -motor disorders in schizophrenia has increasingly attracted the interest of researchers.

Objective:

The study aims to review the existent literature on magnocellular/dorsal (occipitoparietal) visual processing stream impairment in schizophrenia. The impairment of relatively early stages of visual information processing was examined using experimental paradigms such as backward masking, contrast sensitivity, contour detection, and perceptual closure. The deficits of late processing stages were detected by examining visuo-spatial and -motor abilities.

Results:

Neurophysiological and behavioral studies support the existence of deficits in the processing of visual information along the magnocellular/dorsal pathway. These deficits appear to affect both early and late stages of visual information processing.

Conclusion:

The existence of disturbances in the early processing of visual information along the magnocellular/dorsal pathway is strongly supported by neurophysiological and behavioral observations. Early magnocellular dysfunction may provide a substrate for late dorsal processing impairment as well as higher-level cognition deficits.

An evidence for lack of pseudoneglect in patients with schizophrenia: an ERP study

Studies have reported an altered expression of pseudoneglect in patients with schizophrenia, but no study has examined pseudoneglect in schizophrenia at the neural level. We investigated pseudoneglect using the visual P3 event-related potential and the mental number bisection (MNB) task in 21 patients and 25 controls. Using an oddball task, participants were asked to discriminate an infrequent ('one' or 'nine') from a frequent written number ('five'). The P3 ERP components were delayed to the targets on the right of the MNL ('nine') compared to the targets on the left ('one') in controls. The effect of number magnitude on the P3 latency was not observed in the patients. In MNB task, the patients did not show the normal leftward bias observed in healthy individuals. Our findings indicate a lack of pseudoneglect and the presence of an anomalous brain asymmetry in schizophrenia.

Right fronto-parietal dysfunction underlying spatial attention in bipolar disorder

Although the neural underpinning of bipolar disorder (BD) is still unknown, recent research suggests that the right fronto-parietal cortex is particularly affected in BD patients. If this were true, we would expect atypical functional cerebral asymmetries in allocation of visuospatial attention. To test this hypothesis, euthymic BD patients and age- and gender-matched healthy controls were compared on the visual line-bisection task, a reliable measure of visuospatial attention, associated with right parietal function. Line bisection performance (i.e. absolute and directional bias) was compared between groups as a function of response hand and line position. The results showed a typical hand-use effect in healthy controls involving a larger leftward bias (i.e. pseudoneglect) with the left hand than with the right hand. Although euthymic BD patients did not differ from healthy controls in the overall accuracy (i.e. absolute bias), they differed significantly in the directional line bisection bias. In contrast to healthy controls, BD patients did not significantly deviate from the veridical center, regardless of which hand was used to bisect horizontal lines. This finding indicates an atypical functional cerebral asymmetry in visuospatial attention in euthymic BD patients, supporting the idea of a dysfunction especially in the right fronto-parietal cortex.

Negative correlation between leftward bias in line bisection and schizotypal features in healthy subjects

Introduction: Recent studies have found a lack of normal pseudoneglect in schizophrenia patients and in their first degree relatives. Similarly, several contributions have reported that measures of schizotypy in the healthy population may be related to signs of right-sided lateralization, but most of these studies differ greatly in methodology (sample size, choice of schizotypy scales, and laterality tasks) and, consequently, the results cannot be compared and so definitive conclusion cannot be drawn. In this study, our purpose is to investigate whether some tasks of spatial attention may be related to different dimensions of schizotypy not only in a larger sample of healthy subjects (HS), but testing the same people with several supposedly related measures several times.

Materials and Methods: In the first part of the study (Part I), the performance on “paper and pencil” line bisection (LB) tasks in 205 HS was investigated. Each task was repeated three times. In the second part of the study (Part II), a subgroup of 80 subjects performed a computerized version of the LB test and of the mental number line bisection (MNL) test. In both parts of the study, every subject completed the 74-item version of the Schizotypal Personality Questionnaire (SPQ) and the Edinburgh Handedness Inventory (EHI).

Results: In both parts of the study, high scores on the subscale “magical thinking” of SPQ have resulted in being closely linked to a decreased pseudoneglect as assessed by the LB task. On the contrary, right handedness is related to an increased leftward bias at the same task. No association was found between MNL and the other variables.

Discussion: The main finding of this study is that a decreased spatial leftward bias at the LB task correlates with positive schizotypy in the healthy population. This finding supports the hypothesis that a deviation from leftward hemispatial visual preference may be related to the degree of psychosis-like schizotypal signs in non-clinical population and should be investigated as a possible marker of psychosis.

Perceptual pseudoneglect in schizophrenia: candidate endophenotype and the role of the right parietal cortex

Several contributions have reported an altered expression of pseudoneglect in psychiatric disorders, highlighting the existence of an anomalous brain lateralization in affected subjects. Surprisingly, no studies have yet investigated pseudoneglect in first-degree relatives (FdR) of psychiatric patients. We investigated performance on "paper and pencil" line bisection (LB) tasks in 68 schizophrenic patients (SCZ), 42 unaffected FdR, 41 unipolar depressive patients (UP), and 103 healthy subjects (HS). A subgroup of 20 SCZ and 16 HS underwent computerized LB and mental number line bisection (MNL) tasks requiring judgment of prebisected lines and numerical intervals. Moreover, we evaluated, in a subgroup of 15 SCZ, performance on LB and MNL before and after parietal transcranial direct current stimulation (tDCS). In comparison to HS and UP, SCZ showed a systematic rightward bias on LB, partially corrected by selective right posterior parietal tDCS. Interestingly, even FdR showed a lack of pseudoneglect on LB, expressing a mean error lying in the middle between those of HS and SCZ. On the other hand, our results showed no significant difference between the performance of SCZ and HS on MNL. Both groups showed a comparable leftward bias that could not be significantly altered after left or right parietal tDCS. These findings confirm the existence of reduced lateralization in SCZ, suggesting specific impaired functioning of the right parietal lobule. Notably, we report a lack of pseudoneglect not only in SCZ but also in FdR, raising the hypothesis that an inverted laterality pattern may be considered a concrete marker of schizotypal traits.

Differential effects of antipsychotics on lateral bias and social attention in female rats

RATIONALE

Prior research has demonstrated that individuals with schizophrenia may exhibit lateral biases in attention and deficits in social behavior. The use of a noninvasive animal model of attentional impairments in schizophrenia and antipsychotic drugs can help elucidate the biological underpinnings of attentional processes and facilitate the study of novel therapeutics.

OBJECTIVES

The purpose of this study was to compare the effects of three antipsychotic drugs on measures of lateral bias and social attention in healthy, unoperated female rats.

MATERIALS AND METHODS

Female Long-Evans rats selected for a preexisting lateral bias in attention, a right behavioral orientation preference (BOP), were administered clozapine, haloperidol, sulpiride, or vehicle. Lateral bias in attention was assessed by determining which forelimb rats removed a nuisance stimulus from first. Social attention was examined by comparing the latency to remove nuisance stimuli in the presence of a social (inaccessible female rat) versus non-social (blinking clock) distractor.

RESULTS

All antipsychotic drugs eliminated right lateral bias in attention, while control animals retained their initial bias. Clozapine eliminated right lateral bias more rapidly than the other drugs. Animals receiving clozapine also selectively displayed increased attention to another rat.

CONCLUSIONS

The results suggest that the antipsychotic medication clozapine rapidly alters attentional bias and uniquely influences attention to a social stimulus. The right BOP paradigm is a useful animal model for comparing antipsychotic drug effects on lateralized attentional bias and attention to social stimuli.

Hemispatial neglect evaluated by visual line bisection task in schizophrenic patients and their unaffected siblings

Visuospatial attentional asymmetry has been investigated by the line bisection task in patients with schizophrenia, however, those studies are in small number and the results are controversial. The present study aimed to investigate hemispatial neglect in patients with schizophrenia (n=30), their healthy siblings (n=30) and healthy individuals (n=24) by a computerized version of the line bisection task. Deviation from the midline for both hemispaces (mean bisection error-MBE) were calculated and the effects of both hand and line length were controlled. Repeated measures ANOVA yielded a significant hemispace effect for the MBE scores, but no group or group×hemispace interaction effect, i.e., all three groups were inclined to a leftward bias in the left and a rightward bias in the right hemispace. MBEs were significantly different from "zero" only for the right hemispace in siblings and for the left hemispace in controls. Negative symptoms were significantly correlated with the bisection errors in the right hemispace. The results of the present study do not support aberrant hemispheric asymmetry, but bigger bisection errors in schizophrenia.

Visuospatial processing in schizophrenia: does it share common mechanisms with pseudoneglect?

Schizophrenia patients demonstrate behavioural and cerebral lateralised anomalies, prompting some authors to suggest they exhibit a mild form of right unilateral neglect. To better describe and understand lateralised visuospatial anomalies in schizophrenia, three experiments were run using tasks often utilised to study visuospatial processing in healthy individuals and in neglect patients: the Behavioural Inattention Test (BIT), the manual line bisection task with and without a local cueing paradigm, the landmark task (or line bisection judgement), and the number bisection task. Although the schizophrenia patients did not exhibit the full-blown neglect syndrome, they did demonstrate marked spatial biases that differentiated them from controls on all but two tasks. More specifically, schizophrenia patients showed neither a simple perceptual deficit nor an asymmetry, but demonstrated (1) lateralised anomalies on a simple manual line bisection task; (2) unilateral attentional deficits for line bisection within a local cueing paradigm; and (3) a lateralised deficit in the visuospatial representations of numbers. Altogether, these results suggest a right hemineglect-like deficit in schizophrenia in attentional, representational, and motor-intentional processes. Yet it does not appear to be as strong a phenomenon. Indeed, it could be considered as an accentuation of the normal asymmetry in visuospatial processing.

Pathogenetic and therapeutic perspectives on neurocognitive models in psychiatry: A synthesis of behavioral, brain imaging, and biological studies

Neurocognitive assessments are useful to determine the locus of insult as well as functional capacities of patients on treatment. In psychiatry, neurocognitive assessment is useful in the identification of brain lesions, evaluation of cognitive deterioration over time, and advancement of theories regarding the neuroanatomical localization of symptoms. Neurocognitive models provide a bridging link between brain pathology and phenomenology. They provide a useful framework to understand the pathogenesis of psychiatric disorders, bringing together isolated findings in behavioral, neuroimaging, and other neurobiological studies. This review will discuss neurocognitive model of three disorders - schizophrenia, bipolar disorder, and obsessive compulsive disorder - by incorporating findings from neurocognitive, neuroimaging, and other biological studies.

Antithetical asymmetry in schizophrenia and bipolar affective disorder: a line bisection study

OBJECTIVE

Evolutionary theories link the pathogenesis of psychosis with anomalous brain asymmetry. Research shows that aberrant lateralization is linked to schizophrenia with elevated rates of left-handedness and reversal of normal cerebral asymmetries. However, lateralization is underexamined in bipolar affective disorder (BPAD) and the available literature suggests the possibility of greater lateralization, which is diametrically opposite to what is observed in schizophrenia. For the first time, we report concurrent analyses of asymmetry in BPAD and schizophrenia using a line bisection task.

METHODS

We examined 164 subjects (31 patients with BPAD in remission, 30 patients with schizophrenia, and 103 healthy controls) using a two-hand line bisection task with established methodology. Raters with good inter-rater reliability (intraclass correlation coefficient > 0.8) measured deviation from the center. Task performance was compared using analysis of covariance with age, sex, and education as covariates.

RESULTS

Study groups did not differ significantly on age, sex, and handedness (p > 0.06). Patients (both schizophrenia and BPAD) had significantly more errors in identifying the center than controls (p < 0.001). Patients with schizophrenia bisected fewer lines at center than controls and BPAD subjects (p < 0.001). Using their right hand, schizophrenia patients had significant rightward deviation and BPAD patients had leftward deviation (p = 0.001). A significant interaction between diagnosis and direction of deviation (p = 0.01) was noted, with significant rightward deviation in schizophrenia and a trend toward leftward deviation in BPAD.

CONCLUSIONS

Study findings suggest attenuation of normal pseudoneglect in schizophrenia and accentuation of normal pseudoneglect in BPAD, indicating lesser lateralization in schizophrenia and possibly greater lateralization in BPAD. From an evolutionary perspective, schizophrenia and BPAD might have antithetical origins.

Corpus Callosum Maturation and Line Bisection Performance in Healthy Children

Line bisection performance in children has been hypothesized to be a measure of corpus callosum maturation. Several previous studies have shown that normal prepubescent children bisect lines to the right of true center with their right hand and to the left with their left hand (symmetrical neglect). In contrast, children entering puberty reportedly bisect lines to the left with both the right and left hands (pseudoneglect). The shift from symmetrical to pseudoneglect has been hypothesized to reflect corpus callosum maturation and its involvement in the transfer of attention-based visuospatial processes. In the current study, line bisection performance and MR quantitative corpus callosum volumes were examined in 46 healthy children ages 8-18 years. A linear relationship between corpus callosum volume and age was found. However, the expected age-contingent line bisection performance pattern was not observed. In addition to the expected two patterns of line bisection bias, pseudoneglect and symmetric neglect, two additional distinct patterns of line bisection were identified. These findings, and other findings in the literature, raise important questions about the reliability and validity of the line bisection test. No relationship was found between corpus callosum volume and amount or direction of line bisection deviation. Our findings do not support previous hypotheses regarding line bisection-corpus callosum relationship.

Hemispheric asymmetry and callosal integration of visuospatial attention in schizophrenia: a tachistoscopic line bisection study

BACKGROUND

A hallmark of visuospatial neglect syndrome is that patients with lesions to right parietal cortex misbisect horizontal lines far rightward of veridical center. Neurologically normal subjects misbisect lines with a systematic leftward bias (pseudoneglect). Both phenomena, as well as neuroimaging studies, disclose a predominant right-hemisphere control of spatial attention. Numerous studies of patients with schizophrenia have implicated global deficits of either right or left hemisphere function, as well as compromised integrity of the corpus callosum.

METHODS

To better understand the functional implications of schizophrenia we utilized a forced-choice tachistoscopic line bisection task to probe the status of right-hemisphere control of spatial attention, and compared left- versus right-hand unimanual responses to index the degree of callosal transfer of visuospatial information in both patient and control groups.

RESULTS

In contrast to the significant leftward bisection errors of control subjects, patients exhibit no significant leftward error. Whereas control subjects evince a significant correlation between left- and right-hand bisection errors, patients lack a significant intermanual correlation.

CONCLUSIONS

The lack of significant leftward bisection error of patients implies a deficit of right-hemisphere function. The lack of a significant correlation between left- and right-hand bisection errors in patients implies a loss of callosal integrity.

Attention in musicians is more bilateral than in non-musicians

Attention in neurologically intact adults normally errs towards the left side of space, as documented in studies involving tasks of visual attention (i.e., line bisection). The aim of this study was to further investigate lateralisation of attention in musicians and non-musicians. Reaction times and accuracy were recorded to stimuli presented to the left and right of a vertical line in 20 right-handed musicians and 20 matched non-musician controls. While both groups performed more accurately to left-sided stimuli, performance by the musician group was significantly more accurate than the non-musician group for the right-sided stimuli. Musicians also had faster reaction times overall. Consistent with previous research, the results indicate a more balanced attentional capacity in musicians, as well as enhanced visuomotor ability, and are interpreted with reference to extended musical training.

Hemisphere asymmetry in schizophrenia as revealed through line bisection, line trisection, and letter cancellation

Individuals with schizophrenia are known to demonstrate reduced or reversed brain asymmetry. While much is known regarding anatomical brain asymmetry, little is known about how this affects the individual at the functional level. Based on the known leftward bias in normal individuals, the aim of this study was to explore whether any difference in this function would be noted in schizophrenia. This study therefore investigated the phenomenon of functional asymmetry in schizophrenia patients by means of the following tasks: line bisection, line trisection (assessing hemifield spatial neglect) and letter cancellation (assessing contralateral visuospatial exploration). Forty-five schizophrenia inpatients maintained on antipsychotic medication were evaluated. Transections were measured for accuracy, lateralization, and directional bias. In the line bisection task subjects indicated no pseudo-neglect, thus differing from a normal, leftward bias. In the line trisection there was a significant preference to perform the ambiguous instruction on the right side, with no consistent bias in accuracy. Irrespective of conditions, in the letter cancellation task there was always a significant tendency to succeed on the left third compared to the right third. Results may support findings in schizophrenia indicating decreased or altered function of the left hemisphere.