Search

Background: Various behavioural indices of brain lateralisation significantly intercorrelate, but current research in this area still focuses on single behavioural asymmetries, such as handedness. Aim: To describe a novel approach, which simultaneously integrates various laterality indices and delineates complex phenotypes. Method Grade of membership (GoM) analysis was used to describe latent, complex lateralisation phenotypes in schizophrenia patients, their siblings and controls. The indices used were: (i) asymmetries of eye, foot and hand ; (ii) hand motor proficiency ; and (iii) handedness of patient’ s first-degree relatives. Results: Three distinct pure types of lateralisation (‘ right’ , ‘ left’ and ‘ mixed’ ) were evident in patients compared to 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.

Bz means of meta-analsys we examined over 40 studies published over the last few decades with reported prevalence data on various handedness subtypes in a schizophrenia population. Each of the three atypical hand dominance patterns (left-, mixed-, and non-right handedness) were significantly greater in schizophrenia patients than in control subjects. The results also showed that the leftward shift in handedness distribution is not entirely due to an increase in mixed-handedness alone.

Although behavioural indices of brain lateralisation are intercorrelated, current research in this area still focuses on isolated behavioural asymmetries, such as shift in handedness. Simultaneous integration of various laterality indices to delineate complex phenotypes might be a more productive research approach. In this study we used a version of latent class analysis - the Grade of Membership model - to describe complex lateralisation phenotypes in schizophrenic patients, their unaffected siblings and controls. The selected indices were: eye, foot and hand asymmetries ; motor proficiency ; and putative genetic indicants (parent’ s handedness, sibling’ s handedness, and familial sinistrality). Three “ pure type” lateralisation patterns were derived from schizophrenia patients and their unaffected siblings, as compared to healthy controls, where only two patterns were found. In the group of schizophrenia patients, lateralisation phenotypes (two leftward and one rightward) showed distinct clinical and behavioural profiles. One of the leftward phenotypes in schizophrenia patients displayed greater clinical severity (lower age at onset, frequent hospital admissions, and more antipsychotic medication) and poorer neurocognitive performance (lower current IQ, poorer sustained attention, and slower speed of information processing). The characterisation of pure lateralisation types in unaffected siblings revealed closer phenotypic similarity to schizophrenia patients, than to controls, thus suggesting a possible genetic effect.

Based on a critical literature review, this study re-examines the claim that mixed-handedness might be a presumed neurodevelopmental marker of both schizophrenia and schizotypy. Handedness was assessed with a standardized handedness questionnaire and schizotypy with the SPQ in a large community sample, in a “ highly healthy” sample, in siblings of schizophrenia, and in patients with schizophrenia. The results did not show a specific relationship between mixed-handedness and features of schizotypy. Only the cognitive-disorganization factor of the SPQ was related to a higher incidence of mixed-handedness, significantly in patients with schizophrenia and as a statistical trend in siblings of patients with schizophrenia. These findings add to the inconsistent observations on reduced laterality along the schizophrenia spectrum, supporting previous notions “ Re-examining handedness in schizophrenia: now you see it-now you don't” (Nelson et al., 1993).

This paper investigates prevalence of atypical lateralisation of hand preferences in schizophrenia patients and their asymptomatic first-degree relatives. The presence of mixed- (OR=3.766 ; 95%CI=1.93-7.35 ; p

Electroconvulsive therapy (ECT) often results in a number of short- and long-time side effects including memory impairment for past and current events, which can last for several months after ECT treatment. It has been suggested that unilateral ECT (uECT) with electrodes placed over the non-dominant (typically right) hemisphere significantly reduces side effects, especially memory disturbances. It is important to note that cerebral dominance equates to speech dominance and avoiding this area of the brain also reduces speech dysfunction after ECT. Traditionally, the routine clinical determination of cerebral dominance has been through the assessment of hand, foot and eye dominance, which is an easy and inexpensive approach that, however, does not ensure accuracy. This review of literature on different methods and techniques for determination of cerebral dominance and provides evidence that functional transcranial Doppler sonography (fTCD) represents a valid and safe alternative to invasive techniques for identifying speech lateralisation. It can be concluded that fTCD, notwithstanding its costs, could be used as a standard procedure prior to uECT treatment to determine cerebral dominance, thereby further reducing cognitive side-effects of ECT and possibly making it more acceptable to both patients and clinicians.