Prevalence and correlates of mixed-handedness in schizophrenia

Phenotyping in clinical laterality research: a comparison of commonly used methods to determine mixed-handedness and ambidexterity

An increased prevalence of mixed-handedness has been reported in several neurodevelopmental and psychiatric disorders. Unfortunately, there is high between-study variability in the definition of mixed-handedness, leading to a major methodological problem in clinical laterality research and endangering replicability and comparability of research findings. Adding to this challenge is the fact that sometimes researchers use the concepts of mixed-handedness and ambidexterity interchangeably. Therefore, having a consensus on how to determine mixed-handedness and how to distinguish it from ambidexterity is crucial for clinical laterality research. To this end, hand preference and hand performance data from more than 600 participants from the Dortmund Vital Study (Trial registration: ClinicalTrials.gov NCT05155397), a population-based study in Germany, was analyzed to ascertain an optimal classification to determine mixed-handedness and ambidexterity. Using a combination of latent class analyses, effect size determination, and comparisons with the existing literature, we establish that an LQ cut-off criterion of +/-60 for mixed-handedness is optimal for future clinical laterality studies. Moreover, we show that mixed-handedness and ambidexterity are not identical and that the terms should not be used interchangeably. We further highlight the need for a consensus on how to mathematically determine ambidexterity as results of existing categorization schemes largely differ.Trial registration: ClinicalTrials.gov NCT05155397; https://clinicaltrials.gov/ct2/show/NCT05155397.

Handedness as a neurodevelopmental marker in schizophrenia: Results from the FACE-SZ cohort

OBJECTIVES

High rates of non-right-handedness (NRH) including mixed-handedness have been reported in neurodevelopmental disorders. In schizophrenia (SZ), atypical handedness has been inconsistently related to impaired features. We aimed to determine whether SZ subjects with NRH and mixed-handedness had poorer clinical and cognitive outcomes compared to their counterparts.

METHODS

667 participants were tested with a battery of neuropsychological tests, and assessed for laterality using the Edinburg Handedness Inventory. Clinical symptomatology was assessed. Learning disorders and obstetrical complications were recorded. Biological parameters were explored.

RESULTS

The prevalence of NRH and mixed-handedness was high (respectively, 42.4% and 34.1%). In the multivariable analyses, NRH was associated with cannabis use disorder (p = 0.045). Mixed-handedness was associated with positive symptoms (p = 0.041), current depressive disorder (p = 0.005)), current cannabis use (p = 0.024) and less akathisia (p = 0.019). A history of learning disorder was associated with NRH. No association was found with cognition, trauma history, obstetrical complications, psychotic symptoms, peripheral inflammation.

CONCLUSIONS

Non-right and mixed-handedness are very high in patients with SZ, possibly reflecting a neurodevelopmental origin. NRH is associated with learning disorders and cannabis use. Mixed-handedness is associated with positive symptoms, current depressive disorder, cannabis use and less akathisia. However, this study did not confirm greater cognitive impairment in these patients.

Comparative Analysis of Lateral Preferences in Patients With Resistant Schizophrenia

BACKGROUND

Schizophrenia is a chronic brain disorder of diverse etiology and clinical presentation. Despite the expansion of treatment methods, between 30 and 50% of cases remain resistant to treatment. In patients with schizophrenia, specifics in the dominant lateralization in the brain function have been discovered. This gave a reason to seek the relation between functional lateralization and the effect of treatment.

METHODS

Of the 105 people observed with schizophrenia, 45 (42.9%) were treatment resistant, and 60 (57.1%) were considered responders. We compared functional lateralization (hand, foot, and eye) between the two groups. Handedness was ascertained by using the Edinburgh Handedness Inventory. The assessment was made at 12 weeks of treatment.

RESULTS

Of all patients with schizophrenia, 41.89% have mixed lateralization, 53.34% are right winged, and 4.76% of the patients are left winged. Resistance of the symptoms shows that 26 (57.78%) are cross-dominated, 18 (40%) are right winged, and 1 (2.22%) is left winged. In patients with clinical remission, 18 (30%) are of mixed dominance, 38 (63.33%) are right winged, and 4 (6.66%) are left winged. From the results for the separate lateralization of the hand, foot, and eye, we found a significant difference only in terms of the dominance of the eye. In 44 (41.9%) of the patients, we found dominance of the left eye. In patients with resistance, the percentage established by us is higher-at 26 (57.8%). These results indicate that the increased percentage of mixed dominance in patients with schizophrenia is mainly due to left-sided lateralization of the eye, especially in those with resistance to treatment.

CONCLUSION

We find an increased number of patients with cross-dominance left eye dominance in patients with schizophrenia. Cross-dominance and left eye dominance are associated with a higher probability of symptom resistance than other forms of lateralization (left-handed or right-handed). The high percentage of cross-dominance is due to the high percentage of left-sided dominance of the eye.

Translation, cultural adaption, and test-retest reliability of Chinese versions of the Edinburgh Handedness Inventory and Waterloo Footedness Questionnaire

Quantitative assessments of handedness and footedness are often required in studies of human cognition and behaviour, yet no reliable Chinese versions of commonly used handedness and footedness questionnaires are available. Accordingly, the objective of the present study was to translate the Edinburgh Handedness Inventory (EHI) and the Waterloo Footedness Questionnaire-Revised (WFQ-R) into Mandarin Chinese and to evaluate the reliability and validity of these translated versions in healthy Chinese people. In the first stage of the study, Chinese versions of the EHI and WFQ-R were produced from a process of translation, back translation and examination, with necessary cultural adaptations. The second stage involved determining the reliability and validity of the translated EHI and WFQ-R for the Chinese population. One hundred and ten Chinese participants were tested online, and the results showed that the Cronbach's alpha coefficient of internal consistency was 0.877 for the translated EHI and 0.855 for the translated WFQ-R. Another 170 Chinese participants were tested and re-tested after a 30-day interval. The intra-class correlation coefficients showed high reliability, 0.898 for the translated EHI and 0.869 for the translated WFQ-R. This preliminary validation study found the translated versions to be reliable and valid tools for assessing handedness and footedness in this population.

Left handedness: Facts and Figures across Cultures

Approximately 10% of human beings are left handed, although the incidence rate dif fers as a function of sex, age, and culturelgeographical locations. Studies reveal that (a) the incidence of left handedness is more common in Euro-American than in Orien tal ( India, Japan, China) cultures, (b) the prevalence of left handedness throughout the historical era is best explained by genetic models, (c) left handedness is associated more with immune and psychopathological disorders, and (d) sanctions against left hand use are rooted to the belief system and social construction in a given culture. These obser vations were made in this article to ascertain the issues related to left handedness, espe cially in socio-cultural contexts.

Pain perception in schizophrenia: influence of neuropeptides, cognitive disorders, and negative symptoms

OBJECTIVES

The causes and nature of insensitivity to pain in schizophrenia remain unknown. The role of endorphins and the association of cognitive dysfunction and negative symptoms are postulated.

METHODS

In this study, 43 patients with schizophrenia, five first-degree relatives, and 34 healthy controls were examined. Participants' plasma concentrations of substance P, β-endorphin, and calcitonin gene-related peptide (CGRP) were assessed. In patients, the Trail-Making Test, the Color Reading Interference Test (Stroop test), and the Positive and Negative Syndrome Scale Negative Syndrome subscale (PANSS N) test were performed. We also evaluated pain threshold using nociceptive reflex (RTIII) testing.

RESULTS

The mean β-endorphin concentration was about 20% higher in patients than in healthy controls (P<0.05). CGRP concentrations were significantly higher in patients than in controls (5.34 ng/mL versus 4.16 ng/mL; P<0.01). Subjects treated with antipsychotic polytherapy had higher concentrations of CGRP than did patients treated with second-generation antipsychotic monotherapy (5.92 ng/mL versus 5.02 ng/mL; P<0.05). There were no correlations between any biochemical parameters and Trail-Making Test, Stroop test, and PANSS N scores. There were no differences in RTIII among study groups. Strong negative correlation (P<0.001) was found between PANSS N scores and subjective pain threshold on the right lower limb.

CONCLUSION

The insensitivity to pain in schizophrenia is a complex phenomenon that is probably not related to changes in nociceptive pathways. Increase in β-endorphin level may be related to this issue, but it is uncertain if such concentration ensures analgesic effect. It is unknown if patients with schizophrenia in fact experience less pain. Cognitive impairment and excess negative symptoms may strongly influence the patient's expression of pain.

Excess of non-right-handedness in schizophrenia: meta-analysis of gender effects and potential biases in handedness assessment

BACKGROUND

The notion that schizophrenia is characterised by increased non-right-handedness is a cornerstone of the theory that schizophrenia arises from, and is genetically linked to, abnormal brain lateralisation. Reviews and meta-analyses have reported higher rates of non-right-handers in patients with schizophrenia. However, this was suggested to be the result of a gender artefact or a hidden bias in self-report handedness questionnaires.

AIMS

To investigate using a meta-analytical approach whether the excess of non-right-handedness is seen in both females and males, and also when handedness is assessed behaviourally.

METHOD

Electronic databases were searched for studies that reported (a) the rate of female and male non-right-handers in schizophrenia compared with controls and (b) the rate of non-right-handers in schizophrenia (regardless of gender) based on behavioural handedness assessment.

RESULTS

The odds ratios (ORs) for females (OR = 1.63; based on 621 patients, 3747 controls) and males (OR = 1.50; based on 1213 patients, 3800 controls) differed significantly from 1.0, indicating both female and male patients were more often non-right-handed than controls. Moreover, there was an excess of non-right-handedness in patients with schizophrenia when handedness was assessed behaviourally: OR = 1.84 (1255 patients, 6260 controls). Even when both gender and behavioural handedness assessment were controlled for simultaneously, the excess of non-right-handedness persisted.

CONCLUSIONS

The findings clearly demonstrate that the excess of non-right-handedness in schizophrenia does not result from a gender artefact or from biased handedness questionnaires. It is a true empirical effect and may indeed reflect a genetic link between schizophrenia and brain lateralisation.

A psychometric approach to the relationship between hand-foot preference and auditory hallucinations in the general population: atypical cerebral lateralization may cause an abnormal sense of agency

The present study examined the relationship between the atypical cerebral lateralization pattern represented in hand and foot preferences and schizotypal personality traits, especially proneness to auditory hallucinations as related to a sense of agency. A sense of agency, measured with questionnaires in the present study, is the sense that "I am the one who causes the actions." Although atypical lateralization and an abnormal sense of agency may be related to schizophrenia or schizotypal personality, the connection between them has remained unclear. The present study used cluster analysis to categorize the handedness-footedness combinations. The results indicated that people with right-handedness and left-footedness may have more schizotypal traits and that their abnormal sense of agency may cause schizotypal personality traits. Although the reasons for crossed lateral preference remain unclear, we discuss this in terms of early switching in handedness, which may underlie atypical lateralization and lead to the experience of auditory hallucinations deriving from an abnormal sense of agency.

Familial sinistrality and handedness in patients with first episode schizophrenia: the EUFEST study

The population with schizophrenia is characterised by a leftward shift in handedness-sinistrality. However, findings are inconsistent in chronic patients, and familial sinistrality (FS), defined as the presence of left-handed close relatives, might contribute to the discrepancies. Therefore the aim of this study was to investigate the strength of manual lateralisation in patients with first episode schizophrenia, taking into account familial sinistrality. The Edinburgh Inventory (EI) allowed us to categorise 179 patients from the EUFEST study and 189 controls presenting "strong handedness" (SH: EI absolute value between ∣81∣ and ∣100∣) or "weak-handedness" (WH: EI value between -80 and +80). The nominal logistic regression did not show an FS effect, but a nearly significant interaction between illness and FS (p =.07). There were fewer participants without FS presenting SH among patients (99/151: 65.6%) than among controls (134/164: 81.7%, p =.001). In contrast, the number of participants with FS presenting SH was similar between controls (68%) and patients (75%, p =.57). The presence of left-handed relatives (FS + ) tended to reduce manual lateralisation, but only in controls. This supports the notion that reduced manual lateralisation in schizophrenia is related to the illness rather than to familial left-handedness.

Hand preference and hand skill in families with schizophrenia

Direction and degree of handedness in humans are variable between individuals and thought to be in part inherited. Several studies have shown an increase in non-right handedness among patients with schizophrenia, and some have included unaffected relatives. The present study was designed to determine whether reduced right handedness is more frequent among individuals with schizophrenia as compared with their well relatives and whether it clusters within families having multiple ill members. A total of 259 families comprising 418 individuals diagnosed with schizophrenia or schizoaffective disorder, 54 individuals with other psychoses, 145 family members with depression and other minor diagnoses, and 288 unaffected individuals were included. Hand preference was assessed by the Annett Scale and right relative to left hand skill measured using the Tapley-Bryden test. For all assessments of hand preference and hand skill, females were significantly more lateralised towards the right than males. Those individuals with schizophrenia or schizoaffective disorder had significantly less right hand preference than their unaffected relatives when measured as a quantitative index of items from the Annett Scale (p = .019), but not categorically (right, left or mixed). In contrast, there was no difference in hand skill between diagnostic groups. Hand preference was significantly correlated among male-male affected sibling pairs (p = .01) and similar results were found for hand skill among the total group of affected pairs (p = .001). Although these results only partially support a relationship between handedness and schizophrenia, they nevertheless draw attention to sex differences in hand preference and the familial aspects of hand preference in this disorder. More direct approaches to the genetics of cerebral dominance and psychosis are required.

Handedness and schizotypal features in healthy subjects

BACKGROUND

An excess of mixed-handedness has been repeatedly reported in schizophrenia and schizotypy. Handedness is a measure of atypical cerebral lateralization, which is considered as a risk factor for schizophrenia. Several studies have attempted to identify correlations between handedness and dimensions of psychosis but the results obtained so far remain inconclusive.

OBJECTIVE

To explore a possible link between mixed-handedness and the three classical dimensions of psychosis. As speech and language disorders may be associated with cerebral lateralization, we predicted a correlation between mixed-handedness and disorganized dimension.

METHODS

We used the Schizotypal Personality Questionnaire (SPQ) and the Edinburgh Handedness Inventory (EHI) to study the correlation between mixed-handedness scores and positive, negative or disorganized dimensions in a sample of 62 healthy subjects.

RESULTS

We found a negative correlation between mixed-handedness and the disorganized dimension of schizotypy, as individuals with prominent mixed-handedness showed more severe disorganization.

CONCLUSION

We have identified a link between mixed-handedness and the disorganized dimension that may help to identify genetic vulnerability factors involved in psychosis.

Mixed-handedness is associated with the reporting of psychotic-like beliefs in a non-clinical Italian sample

Atypical handedness has been repeatedly reported in schizophrenia, with quantitative review of evidence showing an increase of non-right-handedness in patients diagnosed with schizophrenia. Mixed-handedness is also higher among non-clinical people scoring high on questionnaires aimed at measuring psychosis-proneness. However, the greatest part of information on non-clinical samples came from samples collected in North America or in the UK: differences by countries in the socio-cultural pressure to use the right hand could influence the results. In this study 604 Italian non-clinical participants (248 males, 41.1%; 356 females, 58.9%; mean age=34.5+/-11.9) completed the Annett Hand Preference Questionnaire (HPQ), the General Health Questionnaire (GHQ), and the Peters et al. Delusions Inventory (PDI). In the sample, 527 subjects (87.3%) were classified on the HPQ as right-handed, 53 (8.8%) were classified as mixed-handed, and 24 (4.0%) were classified as left-handed. Mixed-handed scored statistically higher on the PDI than the right-handed and left-handed, but right-handed and left-handed did not differ from each other on a statistical ground. The difference by handedness was specific for PDI, since scores on the GHQ-12 did not differ by handedness group. The links between mixed-handedness and psychosis-proneness in non-clinical samples are a reliable finding, deserving further investigation as a model for the risk of schizophrenia.

Verbal creativity and schizotypal personality in relation to prefrontal hemispheric laterality: a behavioral and near-infrared optical imaging study

Although anecdotal and correlational results have suggested a reliable relationship between creativity and psychosis, few studies have examined this relationship using empirical methods. In addition, little is known about the neural substrates of creative thinking. We investigated the creative thinking process in relation to schizotypal personality, schizophrenia and prefrontal hemispheric laterality using behavioral and near-infrared optical spectroscopy (NIRS) methods. Schizophrenic, psychometrically ascertained schizotypal, and healthy control subjects (all right-handed) participated in a novel "alternate uses" task designed to assess divergent thinking (DT) ability. The DT task required subjects to generate "uses" for conventional and ambiguous objects. Prefrontal activity was measured using NIRS while subjects were engaged in DT vs. a cognitive control task in a subset of the subjects. Behavioral data indicated that schizotypes had enhanced DT ability compared with schizophrenic and control subjects, who showed similar performance overall. NIRS data showed that DT was associated with bilateral prefrontal cortex (PFC) activation, but the right PFC particularly contributed to the enhanced creative thinking in psychometric schizotypes compared with the other two groups. Thus, creative thinking seems to robustly recruit bilateral PFC, but it is the right PFC that is preferentially activated in schizotypes in relation to their enhanced DT.

Magical ideation and its relation to lateral preference

Schizophrenia and schizotypal personality have been linked to sinistrality as well as ambidextrality. The current study clarifies the relation between laterality and schizotypal personality by administering a battery of laterality questionnaires to measure hand, eye, ear, and foot preference in a group of 933 university students. To determine whether the relationship between schizotypy and laterality is limited to self-report measures, performance asymmetries between the hands were measured with tapping rate. There was no difference between dextrals and sinistrals in schizotypal personality, as indexed by the Magical Ideation (MI) scale. MI was higher, however, for individuals with a weak preference for either hand or eye compared to those with a strong dominance. In addition, individuals inconsistent in their lateral preference across modalities showed higher MI scores. Performance asymmetries had no effect on MI scores. This lack of effect was attributed to the inability of performance measures, such as tapping rate, to identify ambidextrals. The results support research linking schizotypal personality to ambidextrality and weak cerebral dominance and demonstrate that the association extends to modalities other than hand preference.

Handedness in children of schizophrenic parents: data from three high-risk studies

This is the first report of data analyses from a consortium of longitudinal genetic-risk studies on offspring of schizophrenic parents (CLOSSER) who were followed from birth or mid-childhood to their early 20's or considerably older ages. Three of the CLOSSER studies provide data to enable us to address long-persisting questions in the schizophrenia literature concerning possible atypicality of hand dominance associated with the illness. Handedness, used as a proxy for cerebral lateralization, is a topic of considerable importance because of its potential to reveal mechanisms in the underlying pathophysiology of schizophrenia. We examine agreement among the CLOSSER studies with respect to possible deviance in handedness in subjects with schizophrenic parents (high-risk individuals) and specifically in those who have gone on to develop adult schizophrenia, compared with other subjects of these studies. Possible developmental delay in age at lateralization is also considered.

Laterality phenotypes in patients with schizophrenia, their siblings and controls: associations with clinical and cognitive variables

BACKGROUND

Various behavioural indices of brain lateralisation significantly intercorrelate, but current research in this area still focuses on single behavioural asymmetries, such as handedness.

AIMS

To describe a novel approach, which simultaneously integrates various laterality indices and delineates complex phenotypes.

METHOD

Grade of membership analysis was used to describe latent, complex lateralisation phenotypes in patients with schizophrenia (n=157), their siblings (n=74) and controls (n=77). The indices used were asymmetries of eye, foot and hand; hand motor proficiency; and handedness of patient's first-degree relatives.

RESULTS

Three distinct pure types of lateralisation ('right', 'left' and 'mixed') were evident in patients compared with two ('right' and 'left') in siblings and controls. The 'mixed' type in patients featured absence of eye and foot lateralisation and presence of familial sinistrality, despite a right-hand dominance for writing. Patients with schizophrenia expressing the 'left' phenotype had a more severe course of illness, significantly increased scores on two schizotypy factors and poorer neurocognitive performance. The pure types in the siblings were similar to those in healthy controls.

CONCLUSIONS

The findings suggest that a leftward reversal, rather than a reduction in lateralisation, is associated with clinical severity and neurocognitive deficits in patients with schizophrenia.

Handedness in schizophrenia: a quantitative review of evidence

OBJECTIVE

The prevalence of various anomalous handedness subtypes in schizophrenia patients remains ambiguous. Although current literature favours the notion that the shift in lateral preferences seen is because of an increase of mixed-handedness, several studies suggest that exclusive left handedness is more prevalent than in the general population.

METHOD

Over 40 studies with reported prevalence data on various handedness subtypes in a schizophrenia population were evaluated by meta-analysis. Combined odds ratios for the three common handedness subtypes (left, mixed, and right) were separately calculated.

RESULTS

Each of the three atypical hand dominance patterns were significantly greater in schizophrenia patients than in control subjects, showing that the leftward shift in handedness distribution is not entirely because of an increase in mixed-handedness alone.

CONCLUSION

An increase of exclusive left-handedness is at variance with the prevailing assertion that the handedness shift in schizophrenia patients is because of a diffuse and bilateral hemispheric insult.

Childhood laterality and adult schizophrenia spectrum disorders: a prospective investigation

Left or mixed-handedness, footedness, and eye dominance are thought to indicate abnormalities in lateralization related to schizophrenia. Increased left or mixed-dominance in schizophrenia suggests possible hemispheric abnormalities associated with the disorder. A related body of research suggests that some indications of lateralization abnormalities may be evident prior to the onset of schizophrenia, suggesting that disruptions in lateralization are inherent to the developmental course of the disorder. We attempted to replicate and extend upon findings indicating differences in lateralization between children who later developed a schizophrenia spectrum disorder (n = 26) and those who did not develop a schizophrenia spectrum disorder (n = 216), among a high-risk and control, longitudinal sample. The rate of left or mixed-footedness, eye dominance, and any anomalous lateralization, but not handedness, discriminated between those who developed schizophrenia spectrum disorders and those who did not. Left or mixed-laterality appears to signal neurological disruption relevant to the development of schizophrenia spectrum disorders.

Strong mixed-handedness in schizophrenia

There is still considerable discussion of whether schizophrenia is a lateralized brain disorder. In fact, schizophrenic patients appear to exhibit a shift away from dexterity, as confirmed by the majority of the 23 publications dealing with this question (14 positive, seven null, two paradoxical). However, quite a few of these positive studies have distinguished between left-handedness and mixed-handedness (MH), thus lacking specificity. Whereas prior studies failed to specify schizophrenic MH, we could observe a significant relationship between strong MH and schizophrenia in male patients in a relatively small group due to sex differentiation and accurate application of Annett's hand preference questionnaire.

Categorization and validation of handedness using latent class analysis

BACKGROUND

A view that handedness is not a dichotomous, i.e. left-right, phenomenon is shared by majority of researchers. However, there are different opinions about the exact number of hand-preference categories and criteria that should be used for their classification.

OBJECTIVES

This study examined hand-preference categories using the latent class analysis (LCA) and validated them against two external criteria (i.e. hand demonstration test and a series of arbitrary cut-off points).

METHOD

The Edinburgh Handedness Inventory was applied to 354 individuals randomly selected from the general population, and the obtained data were analysed using the LatentGOLD software.

RESULTS

Three discrete hand-preference clusters were identified, i.e. left-, right- and mixed-handed category. Further subdivision of hand-preference clusters resulted in a non-parsimonious subcategorization of individuals. There was a good agreement between the LCA-based classification and classification based on hand-preference demonstration tests. The highest agreement between the LCA model and the different types of arbitrary classification criteria ranged between 0 ± 50 and 0 ± 70 of the laterality quotient.

CONCLUSIONS

The study findings supported the view that handedness is not a bimodal phenomenon. However, definitions and subcategorizations of mixed-handedness using the cut-off points that are outside of the recommended range may lead to misclassification of cases. It is hoped that the categorization and validation of handedness developed in the context of this study will make future research in this area less dependent on arbitrary values and criteria.

Eye-Hand Preference in Schizophrenia: Sex Differences and Significance for Hand Function

Hand preference and eye dominance were investigated in 73 (30 women, 43 men) schizophrenic patients and 71 (30 women, 41 men) healthy controls. There were significantly more schizophrenic patients and normal controls who were significantly right-hand dominant. However, schizophrenic patients showed a significant excess of left-eye dominance relative to controls (65.8% vs 29.6%; Odds Ratio = 4.75, p < .001). In addition, female schizophrenic patients showed a higher rate of non-right (either left or inconsistent) eye dominance (80%) than male schizophrenic patients (55.8%) and controls (33.3%). Analysis of hand performance on the Purdue Pegboard Test indicated that schizophrenic patients who showed crossed eye-hand dominance scored higher than did patients without crossed eye-hand dominance.

Is lateral bias anomalous in early-onset schizophrenia? Selected comparisons with normal populations

The aim of this study was to investigate lateral bias in patients with early-onset schizophrenia. Hand, eye, and foot preferences and relative hand skill were examined in early-onset patients (n=44) and matched controls (n=39), and were compared with population estimates. Patients demonstrated a significant excess in mixed handedness (20.5% vs. 8.5%) relative to population estimates and reduced relative hand skill on a pegboard task compared with controls. Left eye preference was significantly less common in schizophrenic patients relative to population estimates. Crossed eye-hand and eye-foot preferences were not significantly increased in the patient group as a whole but were present, respectively, in four of nine and five of nine mixed-handed patients but in none of five mixed-handed controls. These findings are consistent with the view that lateralisation is anomalous in schizophrenia early in the course of illness.

Crossed hand-eye dominance in male psychiatric patients

Increased incidence of left-eye and crossed hand-eye dominance have been considered as indicating left hemispheric dysfunction in many neuropsychiatric disorders. This study investigates the incidence of left-eye and crossed hand-eye dominance in patience with schizophrenia (n = 68), panic disorder (n = 62), personality disorder (n = 35), heroin addiction (n = 54), and mental retardation (n = 33), in comparison with controls (n = 944). All psychiatric groups, except the group with panic disorder, had significantly greater frequency of left-eye dominance than the control group. Furthermore, all psychiatric groups, except the personality-disordered group, had significantly greater frequency of crossed hand-eye dominance than the control group. These findings further support the evidence of an anomaly in hemispheric lateralization among different psychiatric populations, particularly among those with psychotic symptoms and cognitive deficits.

Neurological soft signs in first-episode psychosis: a systematic review

BACKGROUND

Neurological soft signs (NSS) are minor neurological signs indicating non-specific cerebral dysfunction. Their presence has been documented extensively in schizophrenia but not during the first psychotic episode.

AIMS

To review studies that have specifically investigated NSS at the time of the first psychotic episode.

METHOD

A review of studies investigating neurological function in first-episode psychosis, using a clinical examination.

RESULTS

Patients with first-episode psychosis show an excess of NSS, particularly in the areas of motor coordination and sequencing, sensory integration and in developmental reflexes. Furthermore, NSS may be associated with a specific laterality pattern.

CONCLUSIONS

More studies on first-onset schizophrenia are needed, evaluating both sensory and motor neurological domains (scoring separately for the two sides of the body), integrating this knowledge with neuroimaging findings and clarifying the role of NSS as markers of cognitive dysfunction.

Sinistrality in subtypes of schizophrenia

Sinistrality, characterized by an excess of non-right-handedness, has been reported in schizophrenic patients, but the findings are controversial.

AIM

As sinistrality could be linked to a failure of hemisphere specialization in schizophrenia that would translate into language disorders, sinistrality was found out in disorganized and positive schizophrenic patients characterized by language disorders.

METHODS

Seventy-three schizophrenic patients (DSM IV) and 81 controls were evaluated with the Edinburgh Handedness Inventory (EHI). Patients were evaluated and classified into five subtypes (deficit, positive, disorganized, mixed and residual) with the Positive and Negative Syndrome Scale and the Schedule for the Deficit Syndrome.

RESULTS

Disorganized patients had a significantly more severe sinistrality in comparison to the deficit, residual and mixed subtypes and controls. A negative correlation was found between the disorganization and the EHI scores (r = - 0.34; P < 0.01). A significantly more severe sinistrality was also observed in the positive subtype in comparison to controls, but there was no correlation between hallucinatory and EHI scores (r = 0.06).

CONCLUSION

The findings provided further evidence that the defects in the normal process of lateralization observed in schizophrenia affects primarily disorganized patients.

Sinistrality in schizophrenia

Sinistrality characterized by an excess of non-right handedness has been reported in schizophrenic patients. Two factors, sex and kind of evaluation of handedness have contributed to major discrepancies across studies.

AIM

The hypothesis tested was that schizophrenic patients show a sinistral shift in handedness compared to controls taking into account the sex and using a continuum scoring system for evaluating handedness.

METHODS

Seventy-three (73.1% males) schizophrenic patients (DSMIV) and 81 (64.2% males) controls were evaluated with the Edinburgh Handedness Inventory (EHI [Neuropsychologia, 9 (1971) 97]).

RESULTS

The EHI score mean difference between patients with schizophrenia and control group was not significant when sex was taken into account.

CONCLUSION

Schizophrenic patients taken as a whole did not show a sinistral shift in handedness even if the sex and the continuum score for handedness were considered.

Narrow and broad definition of mixed-handedness in male psychiatric patients

Differences in assessment and classification procedures of many mixed-handedness studies have made comparison of findings difficult. In the present study, "narrow" and "broad" definitions of mixed-handedness were investigated using the Annett Handedness Questionnaire in patients with schizophrenia (n=68), panic disorder (n=62), borderline personality disorder (n=35), heroin addiction (n=54), and mental retardation (n=33) in comparison with 944 controls. According to the "narrow" definition of mixed-handedness, an excess of mixed-handedness was observed in patients with borderline personality disorder and mental retardation. An excess of nonmixed-handedness was found in patients with panic disorder. According to the "broad" definition of mixed-handedness, an excess of mixed-handedness was observed in patients with mental retardation, in the total sample of psychiatric patients (n=252), and in the schizophrenic patients. Thus, we can conclude that different mixed-handedness definitions can be associated with different results. Furthermore, we suggest that the neurotic part of the present psychopathology spectrum tends to be related to an excess of normal or nonmixed-handedness, and the psychotic as well as the organic portion is associated with an excess of mixed-handedness, regardless of the definition of mixed-handedness used.

Dermatoglyphic fluctuating asymmetry and atypical handedness in schizophrenia

Atypical handedness and dermatoglyphic abnormalities are hypothesized to reflect a neurodevelopmental disturbance in schizophrenia. Developmental instability, indexed by dermatoglyphic fluctuating asymmetry (FA), reflects the degree to which an individual's ontogenetic program is maintained and provides a useful framework in which to consider atypical handedness in schizophrenia. Thirty patients diagnosed with schizophrenia were compared with 37 matched healthy controls on levels of dermatoglyphic FA, a demonstration task determining hand preference and a test of relative hand skill. Multivariate analyses established that patients demonstrated greater FA and more atypical hand skill compared with controls. In patients, but not in controls, there was a strong positive association between a measure of FA and a measure of atypical hand skill, suggesting that these markers of neurodevelopmental disturbance are related in schizophrenia. On a measure of hand preference, patients were more likely than controls to be classified as mixed handed than either right or left handed. Results from the present study support the conjecture of greater developmental instability in schizophrenia affecting neurodevelopmental processes, including those conferring manual dominance.

Handedness, language lateralisation and anatomical asymmetry in schizophrenia: meta-analysis

BACKGROUND

Cerebral lateralisation appears to be decreased in schizophrenia. Results of studies investigating this, however, are equivocal.

AIMS

To review quantitatively the literature on decreased lateralisation in schizophrenia.

METHOD

Meta-analyses were conducted on 19 studies on handedness, 10 dichotic listening studies and 39 studies investigating anatomical asymmetry in schizophrenia.

RESULTS

The prevalence of mixed- and left-handedness ('non-right-handedness') was significantly higher in patients with schizophrenia as compared to healthy controls, and also as compared to psychiatric controls. The analysis of dichotic listening studies revealed no significant difference in lateralisation in schizophrenia. However, when analysis was restricted to studies using consonant-vowel or fused word tasks, significantly decreased lateralisation in schizophrenia emerged. Asymmetry of the planum temporale and the Sylvian fissure was significantly decreased in schizophrenia, while asymmetry of the temporal horn of the lateral ventricle was not.

CONCLUSION

Strong evidence is provided for decreased cerebral lateralisation in schizophrenia.

Epidemiology and pathobiology of bipolar disorder, and their exploration within a complete catchment area population

Epidemiological and pathobiological findings in bipolar disorder [BP] have often been limited by selection bias and lack of epidemiological representativeness. In a rural, circumscribed catchment area, 'all' patients with BP were identified and assessed. On preliminary analysis, morbid risk [MR] for BP over the area as a whole was 5.0 ± 0.6/1000. The distribution of MR for BP over geographical subregions showed no significant deviation from a statistical model for random occurrences in space by place at birth, in contrast to schizophrenia [SZ], and varied only modestly among males by place at onset. These results imply different etiological factors acting in BP in comparison with SZ, particularly with regard to the role of early versus later life events. In preliminary analyses of psychotic and cognitive features, current severity of positive symptoms was predicted in BP only by increasing dominance of the left hand; negative symptoms by duration of illness and current anticholinergic exposure; poorer general and frontal cognitive function by older age at onset of illness, increasing duration of illness, and current anticholinergic exposure. The finding on handedness suggests disturbance of cerebral asymmetry associated with positive symptoms in BP, while both negative symptoms and cognitive impairment may involve progressive processes. Further analysis of this epidemiologically complete population, including systematic comparisons of BP with schizoaffective disorder and SZ, continues.

Schizophrenic patients and their first-degree relatives show an excess of mixed-handedness

An excess of mixed-handedness in schizophrenia has been reported. However, it is not established whether this excess is manifest in non-schizophrenic psychoses, nor whether the underlying etiology is genetic or environmental. We investigated these issues in a group of patients with schizophrenia (n=94), affective psychosis (n=63), other psychosis (n=26); their respective first-degree relatives (total n=183) and a control group (n=85). A narrow definition of mixed-handedness was used corresponding to groups 5 and 6 as defined by the Annett Handedness Questionnaire. We found an excess of mixed-handedness in the schizophrenic group compared with controls (OR=5.2, 1.4-18.6, p<0.006). There was no difference between the other psychotic groups and controls. There was a trend for an excess of mixed-handedness in the first-degree relatives (n=99) of schizophrenic patients (p=0.055), but not in the relatives of affective or other psychotic patients. There was a striking linear trend in the proportion of mixed-handedness between controls, the relatives and the schizophrenic patients (chi2=7.0, p=0.008). There was no association between mixed-handedness and a history of pregnancy or birth complications in the schizophrenic group. There was some evidence for impaired sociability in the mixed-handed schizophrenic patients. Our results indicate that the excess of mixed-handedness in schizophrenia may have a genetic basis.

Early age of onset, brain morphological changes and non-consistent motor asymmetry in schizophrenic patients

Previous data suggest abnormalities in the consistence of motor dominance in schizophrenia (e.g. mixed-handedness, poor correlation between hand, eye and foot preferences and an increase of hand-eye crossed dominance). The aim of this work is to examine the clinical significance of hand-eye and hand-foot crossed dominance in a sample of 61 right-handed schizophrenic patients. The application of multivariate analysis revealed that 23 right-handed and non-right-eyed patients (crossed hand-eye dominant group) had a significant earlier clinical onset and smaller brain size, global and frontal area, than 38 right-handed and right-eyed schizophrenics (consistent hand-eye dominance group). These findings are discussed within the context of neurodevelopmental disorders.

Schizophrenia Risk and Handedness: A Mixed Picture

Numerous previous studies have reported on handedness differences among schizophrenics, as well as in normal subjects who are high in ''schizotypal'' traits, and hence putatively at risk for schizophrenia. Results have varied, but there is evidence of a shift away from dextrality, especially consistent among schizotypal individuals. Using both a conventional three-category and Annett's seven-category classification of handedness, we re-examined the question in 681 general population subjects assessed for schizotypy. The three-category analysis confirmed previous findings of increased schizotypy in mixed-handers. However, the more fine-grained analysis showed that, although mild degrees of mixed handedness were indeed associated with increased schizotypy, this trend was reversed in the most mixed-handed subjects whose schizotypy scores did not differ significantly from right-handers. Independently of our work, this subgroup of mixed-handers are also reported to show superior intellectual function, especially on some spatial tasks. We concluded that previous studies of schizophrenia and schizotypy have failed to distinguish different reasons for shifts from dextrality. It is argued that the latter's association with schizophrenia might come about through exogenous, neurodevelopmental, influences, whereas some-possibly genetically basedforms of mixed handedness could reflect a variety of cerebral organisation that protects against, rather than enhances, the risk for mental disorder.

Childhood laterality and later risk of schizophrenia in the 1946 British birth cohort

An increased rate on non-righthandedness and other abnormalities of lateralization have been reported in schizophrenia. We investigated childhood hand preference and eye dominance as risk factors for adult schizophrenia among a general population birth cohort. Pre-schizophrenic children showed a significant excess of left-eye dominance at age 11 when compared with controls (OR 2.5, 1.0-5.8, p = 0.03), but there was no significant difference in hand preference between pre-schizophrenic children and controls.

Mixed-handedness in patients with functional psychosis

BACKGROUND

An excess of non-right-handedness has been shown among patients with schizophrenia. However it is not clear whether this finding can be accounted for by an increase in left-handedness, mixed-handedness or both. It is not known whether atypical patterns of hand preferences occur in other functional psychotic illnesses.

METHOD

The Annett hand preference questionnaire was administered to patients with schizophrenia (n = 120); affective psychosis (n = 55); schizoaffective psychosis (n = 41), and control subjects (n = 86). Handedness was classified into three categories: right, mixed and left-handedness.

RESULTS

The hand preference patterns of patients with functional psychotic illnesses were not significantly different from controls. Patients with schizophrenia showed a non-significant excess of mixed-handedness compared with controls. Patients with schizophrenia and affective psychosis showed a non-significant decrease in left-handedness compared with controls.

CONCLUSIONS

Although our results showed a trend in the hypothesised direction, we failed to demonstrate that patients with psychotic illness differed from controls on self-reported hand preference patterns.