On the futility of using familial sinistrality to subclassify handedness groups

Functional language lateralization during sentence completion in the healthy brain is not associated with the quantitative estimate of familial sinistrality

Familial sinistrality (left-handedness) has been suggested as a proxy for functional language lateralization in the healthy adult brain. Previous studies show that individuals with familial sinistrality tend to have less lateralized language-related brain activation, while individuals without familial sinistrality show greater left-hemispheric lateralization for language. However, familial sinistrality trait has always been treated as a binary categorical variable. In this study a more sensitive quantitative estimate of familial sinistrality (LH load) has been modelled in 39 participants with different direction and degree of handedness by applying a standard genetic multifactorial model. This LH load was tested for an association with functional language lateralization based on an fMRI sentence completion task. Using frequentist and Bayesian statistical frameworks, the association between LH load and language lateralization was not confirmed. The findings of the present research suggest that a quantitative measure of familial sinistrality is not related to individual language representation in the brain measured by a sentence completion fMRI paradigm. However, considering the context of our study and previous research we suggest that familial sinistrality being related to personal handedness could drive functional language lateralization through it.

Handedness and social anxiety: Using Bryden's research as a catalyst to explore the influence of familial sinistrality and degree of handedness

Phil Bryden's work has impacted on many areas of laterality, including degree and measurement of hand preference, as well as influences of familial sinistrality (FS). For example, Bryden[(1977). Measuring handedness with questionnaires. Neuropsychologia, 15, 617-624] is a well-cited and influential paper that remains relevant to this day. Inspired by this we extended our analysis of the relationship between handedness and anxiety in a number of ways. We used familial handedness and strength of handedness to examine their potential influences on anxiety, and extended our research by exploring their relationship to social anxiety, using the Social Phobia Inventory (SPIN). Inconsistent left-handers (ILH) were found to be more socially anxious. In all categories of SPIN except avoidance, ILH were significantly more anxious than consistent right- and left-handers. There were FS differences between ILH with a first degree left-handed relative (FS+) compared to ILH with no first degree left-handed relative (FS-) on all categories of anxiety scores. Within FS+ participants, ILH had significantly higher anxiety scores, compared with consistent handers across all categories. This suggests that ILH's social anxiety may be influenced by a close left-handed relative. Inspired by examining Bryden's work for this special issue, we will continue to add both strength of preference and familial handedness to our work.

Quantifying cerebral asymmetries for language in dextrals and adextrals with random-effects meta analysis

Speech and language-related functions tend to depend on the left hemisphere more than the right in most right-handed (dextral) participants. This relationship is less clear in non-right handed (adextral) people, resulting in surprisingly polarized opinion on whether or not they are as lateralized as right handers. The present analysis investigates this issue by largely ignoring methodological differences between the different neuroscientific approaches to language lateralization, as well as discrepancies in how dextral and adextral participants were recruited or defined. Here we evaluate the tendency for dextrals to be more left hemisphere dominant than adextrals, using random effects meta analyses. In spite of several limitations, including sample size (in the adextrals in particular), missing details on proportions of groups who show directional effects in many experiments, and so on, the different paradigms all point to proportionally increased left hemispheric dominance in the dextrals. These results are analyzed in light of the theoretical importance of these subtle differences for understanding the cognitive neuroscience of language, as well as the unusual asymmetry in most adextrals.

How the development of handedness could contribute to the development of language

We propose a developmental process which may link the development of handedness with the development of hemispheric specialization for speech processing. Using Arbib's proposed sequence of sensorimotor development of manual skills and gestures (that he considers to be the basis of speech gestures and proto-language), we show how the development of hand-use preferences in proto-reaching skills concatenate into object acquisition skills and eventually into role-differentiated bimanual manipulation skills (that reflect interhemispheric communication and coordination). These latter sensorimotor skills might facilitate the development of speech processing via their influence on the development of tool-using and object management abilities.

Nongenetic factors associated with human handedness and footedness in Japanese twin children

OBJECTIVE

The aim of this study is to clarify the factors related to the handedness and footedness of twins using two of the largest databases on Japanese twins available.

METHODS

The first group consisted of 1,131 twin pairs, all school children either 11 or 12 years old (S group), and the second group consisted of 951 twin pairs of different ages (1-15 years) in several maternal associations (M group). All data were gathered using a questionnaire. Factors associated with the handedness or footedness of twin individuals were analyzed by univariate and multivariate logistic analyses.

RESULTS

Multivariate logistic analysis showed that for handedness, birth year (OR=1.02) and neonatal asphyxia (OR=1.62) were selected in the S group, and sex (OR=1.34), the age of twins (OR=1.56), parity (OR=1.31), gestational age (OR=1.58), and family history (OR=1.82) were selected in the M group. for footedness, birth complications (OR=1.37) were selected in the S group, and sex (OR=1.33), the age of twins (OR=1.69), gestational age (OR=1.83), and family history (OR=2.49) were selected in the M group. Factors associated with handedness and footedness specific to twins, such as zygosity, placentation, birth order within twin pairs and the sex of the cotwin, were not found, although being a twin might have some effects.

CONCLUSION

It was concluded that factors that affect handedness or footedness in general, such as sex, birth year, age, parity, neonatal asphyxia, gestational age, birth complications, and family history, seem to have stronger effects on handedness and footedness than being a twin.

Measuring familial sinistrality: Problems with dichotomous classification

Familial sinistrality (FS), or familial left-handedness, is usually measured as a presence/absence dichotomy (FS+/FS-). Measuring FS as a dichotomy is problematic in at least two ways: (1) magnitude data are discarded and (2) there is an increased risk of violating statistical assumptions. We hypothesised that using a non-dichotomised FS measure would allow more sensitive statistical tests than using a dichotomised measure. The non-dichotomised measure examined was proportion of family that is left-handed, or Proportional FS (FSP). FS measures of 60 healthy adults were consistent with our hypothesis: (1) The effect size was 2.3 times larger when FSP was used than when Dichotomised FS (FSD) was used; (2) the observed relationship was statistically significant when FSP was used but not when FSD was used; and (3) statistical assumptions were violated when FSD was used but not when FSP was used. When cases were weighted to account for an increased likelihood of FS in large families, results were similar. Next, bootstrapping methods were used to estimate empirically the long-term differences in power between analyses incorporating FSP and those incorporating FSD. Using FSP was associated with long-term increases in both power and effect size of over 50% relative to using FSD. We conclude that using a proportional rather than a dichotomous measure of FS will enhance the accuracy of observed effect sizes, increase the sensitivity of statistical tests, and reduce the likelihood of violating statistical assumptions.

Mental rotation test performance in four cross-cultural samples (n = 3367): overall sex differences and the role of academic program in performance

Two meta-analyses (Linn and Petersen, 1985; Voyer et al., 1995) discuss variables that affect mental rotation performance but they do not mention a potentially important variable, the Academic Program in which students are enrolled. Sex differences in brain size have been related to sex differences in spatial performance (e.g., Falk et al., 1999) and thus it is important to know whether mental rotation performance shows a significant interaction between Sex and Academic Program. To put our understanding of the Academic Program effect on a firmer empirical footing, we conducted a large scale multicultural study, with samples from Canada, Germany and Japan, using identical test procedures in all studies. Significant main effects for Sex and Academic Program were found in all four studies, with large effect sizes for Sex and medium to large effect sizes for Academic Program (based on Cohen's d). No significant interactions between these variables were found in the four samples. Our demonstration of a reliable Academic Program effect has clear and important pragmatic implications for a broad range of work on spatial ability and its interpretation.

Language and visuospatial impairment in a case of crossed aphasia

Crossed aphasia in dextrals (CAD) constitutes an interesting model for understanding the lateralisation and interaction of language with other cognitive functions in the brain. The authors present a study of a right-handed patient with Wernicke's aphasia following a right hemisphere cerebrovascular accident, who also had impairment in visuospatial skills. Although the patient presented a remarkable improvement in language symptoms on longitudinal follow-up, the combination of linguistic, visuospatial, and attentional impairments ultimately resulted in a persisting inability to perform complex tasks. The study of mild residual disturbances can improve our understanding of the interaction of language with other cognitive functions, going some way towards explaining the particular features found in CAD.

Crossed aphasia: an analysis of the symptoms, their frequency, and a comparison with left-hemisphere aphasia symptomatology

This study presents a thorough analysis of published crossed aphasia (CA) cases, including for the first time the cases published in Japanese. The frequency of specific symptoms was determined, and symptomatology differences based on gender, familial sinistrality, and CA subtype were investigated. Results suggested that the CA population is comparable to the left-hemisphere patient population. However, male were significantly more likely than female CA subjects to show a positive history of familial sinistrality. Typical right-hemisphere (i.e., nonlanguage-dominant) symptoms were frequent but rarely carefully reported or assessed. Results are compared with previous CA reviews and left-hemisphere aphasia. Suggestions for a more systematic assessment of the CA symptomatology are presented.

Differences in language performance in variations of lateralization

Language proficiency was studied in 489 primary-school-aged children classified as extreme left-, extreme right-, mild left-, and mild right-handers on the basis of both hand-preference and hand-skill, using a test battery of seven measures. An ANOVA run on factor scores showed neither significant association of language proficiency with variations of lateralization regarding hand-preference and hand-skill nor differences in factor structure derived from a principal component analysis between extreme vs. mild hand-preference and hand-skill groups. Moreover, low language proficiency was not significantly associated with specific patterns of lateralization in hand-preference subgroups. In contrast, low language performers with poor hand-skill were significantly overrepresented both in the extreme left-handed group alone and when combined with the extreme right-handed, in comparison to mild left- and mild right-handed with respect to population. The data are not consistently accommodated by the theory of balanced polymorphism (mainly Annett, 1978, 1985 Annett & Manning, 1989 ). Alternately, factors such as lag of maturation ( Bishop, 1980, 1984, 1990a, 1990b ), delay of growth ( Geschwind & Galaburda, 1985b ), and developmental instability associated with unique patterns of variations in lateralization ( Yeo, Gangestad, & Daniel, 1993 ) are discussed as possible factors accounting for the present results.

Do the hands talk on mind's behalf? Differences in language ability between left- and right-handed children

Two hundred seventy children of school age, 135 of whom were left-handed and an equivalent number of whom were right-handed, have been examined in the present study using a test battery of nine language ability measures: Vocabulary, Similarities, Comprehension (WISC-R), Deductive Reasoning, Inductive Reasoning, Sentence Completion, Comprehension of Sentential Semantics, Comprehension of Syntax, and Text Processing. The data analysis has indicated that: (1) One-factor solution applies both to the right- and left-handed population according to Standard Error Scree Method (Zoski & Jurs, 1996) with regard to language ability measures. (2) Handedness discriminates between right-handers (superior) and left-handers (inferior) in language ability. (3) There have been subgroups of left-handed children who differ in language ability distribution compared with right-handed children according to Hierarchical Cluster Analysis. (4) Extreme versus mild bias to hand preference and hand skill do not differentiate performance subgroups neither within the left-handed nor within the right-handed main group. (5) Sex and familial sinistrality do not affect performance. The results are discussed in relation to (a) "human balanced polymorphism" theory advocated by Annett (mainly Annett, 1985, 1993a; Annett & Manning, 1989), (b) potential pathology (mainly Bishop, 1984, 1990a; Coren & Halpern, 1991; Satz, Orsini, Saslow & Henry, 1985) and "developmental instability" (Yeo, Gangestad & Daniel, 1993), and delay of left-hemisphere maturation in left-handed individuals (Geschwind & Galaburda, 1985a,b, 1987), by pointing out the strength and weaknesses of these theoretical approaches in accounting for the present data.

Correlations between nonverbal intelligence and peripheral nerve conduction velocity in right-handed subjects: sex-related differences

The speed hypothesis of intelligence was tested in relation to median nerve conduction velocity (NCV) in right-handed subjects. In total, NCV did not significantly correlate with IQ (Cattell's Culture Fair Intelligence test). The motor and sensory median NCVs correlated with IQ positively linearly in men and negatively linearly in women. These results supported the general, unqualified speed hypothesis of intelligence only for men. It was concluded that the conduction speed of the input-output channels of brain as an information processing unit may differentially contribute to nonverbal intelligence, depending upon sex. The male hormone, testosterone, was suggested to be the main factor responsible for sex-related differences in the IQ-NCV relationships.

Interhemispheric cooperation of left- and right-handers in mental calculation tasks

Relations between handedness and interhemispheric processing in cognitive tasks were examined. Thirty six right-handers and thirty left-handers (familial and nonfamilial left-handers) were asked to add two numbers which were presented tachistoscopically. Two numbers were displayed either to one visual field, or one to the left and one to the right visual field simultaneously. In Experiment 1, the numbers were displayed in Arabic numerals, and in Experiment 2 one of the numbers was displayed in Kanji and one in Arabic numerals. The results of Experiment 1 showed a bilateral advantage, however no subject group difference was shown in the performance of the three (left unilateral, right unilateral, and bilateral) presentation conditions. Though familial left-handers showed a weaker tendency to different patterns than right and non-familial left-handers, the results of Experiment 2 were largely similar to those of Experiment 1. These findings suggest that interhemispheric processing may not differ between left- and right-handers.

Handedness trends across age groups in a Japanese sample of 2316

Hand-preference data of 2316 Japanese were analyzed by age groups, sex, and familial sinistrality. Right-hand preference increased across age groups at least up to 30 years for men, while women showed relatively stable and stronger preference for right-hand use. Unlike some Western studies, no linear trends across age groups were found for both sexes. Declining cultural censorship against left-handedness would not be responsible for the trends, since there was no evidence indicating such a decline in Japan. Hypotheses of reduced longevity and life-long adaptation to the right-handed world are not satisfactory either, since both hypotheses assume a linear trend spanning the entire life span. Thus, it seems that a single-factor hypothesis which explains all the results by resorting to a single cause does not account for the complex results found in this and other studies.

Familial sinistrality: the utility of calculating exact genotype probabilities for individuals

Measures of familial sinistrality are frequently used in neuropsychological research. However they suffer from the problem that they are essentially a global measure of phenotypes in the family, whereas they are interpreted as an indicator of the genotype of the individual concerned. In this paper it is shown how to calculate a precise probabilistic estimate of a proband's genotype, given a particular genetic model of handedness, using all of the information available in a family tree. Example calculations are provided for a range of families with one or two sinistral relatives. Genotype probabilities are also calculated for a large population data set (the National Childhood Encephalopathy Study) and it is shown that familial sinistrality does not account for all of the variability present in the genotype probabilities, and that genotype probabilities provide an additional prediction of individual sinistrality after taking familial sinistrality into account, whereas all of the information in familial sinistrality is accounted for by the genotype probabilities. Finally it is shown how genotype probabilities can be used to assess whether there is heterozygote advantage for a characteristic, and using this method it is suggested that there is no support for heterozygotes having higher intellectual ability than homozygotes.

Are families of children with reading difficulties at risk for immune disorders and nonrighthandedness?

This study used questionnaire data to examine immune disorders and nonrighthandedness in the families of children enrolled in a learning disabilities school and children attending regular classrooms in public schools. Groups were organized according to their performance on a standardized test of reading comprehension to avoid overlap. In total, 468 questionnaires were returned, from which we were able to derive a final sample of carefully matched subjects: 55 subjects undergoing remediation for reading problems and 55 age- and sex-matched control subjects. The results indicated that children with reading problems and their families more frequently suffered from some immune and autoimmune disorders, particularly those involving the gastrointestinal tract and the thyroid gland. In addition, symptoms of attention deficit hyperactivity disorder were associated with Crohn's disease and migraine headache in the families. There was no evidence of an elevated prevalence of nonrighthandedness in the children with reading problems and their families.

Right-handers and left-handers show differences and important similarities in task integration when performing manual and vocal tasks concurrently

For a sample of 73 consistent left-handers, 46 inconsistent left-handers and 65 right-handers, reciprocal interactions between unimanual or bimanual tasks and concurrent reading tasks were shown to be a complex function of task characteristics and sample composition. The suggestion that subgrouping of left-handers [Hellige and Key, Cerebral Control of Speech and Limb Movements, North Holland, Amsterdam, 1990] influences task interactions in left-handers was borne out. Both manual and vocal performance were measured. The effects of the vocal task on the manual task were variable for groups and conditions, but an important common trend emerged: all handedness groups showed the same robust effect: vocal task performance was better when the right hand performed the manual task. Finally, speaking rate increased and tapping rate decreased during concurrent single hand tapping [cf. Hiscock, Brain Cognit. 1, 119-131, 1982]; and there was an opposite effect with concurrent bimanual tapping. The results favour a task integration model rather than an interference in cerebral functions space model.

Childhood hemiplegia: is the side of lesion influenced by a family history of left-handedness?

Family histories of left-handedness were obtained for 396 children with congenital or acquired hemiplegia. As in other studies, right-sided hemiplegia was substantially more common than left-sided hemiplegia. The excess of right hemiplegia was entirely accounted for by children with left-handed relatives. This is contrary to what would be expected if the preponderance of right hemiplegia reflected a greater vulnerability of the dominant hemisphere to early damage. Though the observed association between right hemiplegia and a family history of left-handedness may well have occurred by chance, it could potentially reflect some heritable aspect of cerebral asymmetry (such as slow development of the left hemisphere) that predisposes an individual both to left-handedness and to left-hemisphere injury.

Motor preference, major depression and psychosocial dysfunction among children with attention deficit hyperactivity disorder

Since left motor preference has been hypothesized to lead to increased risk for psychopathology and cognitive deficits, it is possible that it may confer greater vulnerability for these problems to attention deficit hyperactivity disorder (ADHD) children. Subjects were 6-17 year-old boys with DSM-III-R ADHD (N = 140) and normal controls (N = 120) and their first-degree relatives. Information on motor preference was obtained in a standardized manner blind to the proband's clinical status. Although no excess of non-right motor preference was identified in ADHD probands compared with normal controls, the non-right motor preference observed in ADHD probands was partly familial and was associated with significantly increased risk for major depressive disorder and impaired psychosocial functioning. Non-right motor preference in ADHD probands significantly increases the risk for major depression and impaired psychosocial functioning. These findings raise the possibility of alterations in cerebral dominance which may be implicated in the expression of specific problems in some patients with ADHD. Further research is needed to replicate these findings and to directly assess cerebral functioning in ADHD.

Does motor cerebral dominance develop secondary to sensory dominance?

Current research and theoretical frameworks for understanding motor dominance assume that motor dominance is primary. Various developmental clues, however, suggest that the maturation of proprioceptive sensory processing predates that of motor control. We hypothesized that the observed adult pattern of lateralized motor dominance may develop as a consequence of preexisting lateralized "sensory" or "proprioceptive dominance." To test whether motor preference could develop in response to sensory dominance, we investigated sighting eye dominance, eye lid winking, and handedness in 164 individuals. Subjects winked the nondominant eye significantly more frequently than the dominant eye and independently of their handedness, lending partial support to the idea that motor function can develop in response to sensory function. Specific investigation of the development of the proprioceptive system would be needed to evaluate whether lateralization of motor handedness develops as a consequence of "proprioceptive" lateralization.

Handedness, sex, and familial sinistrality effects on spatial tasks

Left-handed (N = 109) and right-handed (N = 115) undergraduates (99 males, 125 females) received the SIBT (a "mental rotation" test), the 3DD (3-dimensional drawing test), and a family sinistrality (FS) questionnaire. Left-handers were further separated into consistent left-handed (CLH) and inconsistent left-handed (ILH) subgroups, based on consistency of hand preference. On the spatial tests, males outperformed females, with no overall handedness effects. Also, for males, CLH's (but not ILH's) performed significantly worse than right-handers on the SIBT, but this difference was not found on the 3DD. For females, no handedness subgroup differences were found on either spatial tasks. Familial sinistrality was twice as common in left-handers as in right-handers. Among males, the incidence of FS+ in the CLH subgroup also was over twice that for ILH's. Thus, where left-handers report a greater incidence of FS+, and are inferior to right-handers in mental rotation skill, it is CLH's (particularly males) who contribute mostly to these effects. The results suggest that previous discrepant findings reported in studies of the cognitive correlates of left-handedness may be due in part to the mixing of two distinct left-handed subgroups. An understanding of the differences between them may be crucial for better understanding the genetic and neurobiological mechanisms underlying handedness.

Pathological left-handedness revisited: dichotic listening in children with left vs right congenital hemiplegia

Thirty-one children with right (n = 18) and left (n = 13) congenital hemiplegia were compared for incidence of hand- and foot-preference, eye-dominance, and familial sinistrality. In addition, they were tested with dichotic listening for correct reports of consonant-vowel syllables. The two groups of children were closely matched on IQ and sensory functioning. Children with mental retardation, or epileptic seizures were not included. The results showed that 89% of the left hemisphere impaired (LHI) children were left-handed, all of them preferred the left foot, and 72% were left eye-dominant. In the right hemisphere impaired (RHI) group, everyone (100%) preferred the right hand and foot, and 62% were right eye dominant. The dichotic listening results showed a significant right ear advantage (REA) in the RHI-group, and a significant left ear advantage (LEA) in the LHI-group. The results are discussed in the framework of pathological handedness and shifts in hemisphere control of language in children with early brain injury. It is argued that the homogeneous samples, except for the site of lesion, provides an interesting possibility to compare cognitive effects of left and right hemisphere impairment in children.

A simple dual-task study of laterality, sex-differences and handedness

Nine-hundred and eighty-one right-handed and 55 left-handed subjects were required to tap with a pen for 10 secs between targets 6 cm apart whilst either saying nothing, reciting a tongue-twister or saying la-la. The numbers of dots produced in 10 secs in each condition were analysed. The right-handed group demonstrated the usually found degradation in their right-hand performance whilst reciting the meaningful words, but showed a lesser effect when saying la-la. Their left-handed performance was essentially unaffected. Absolutely no evidence for the presence of a sex difference in lateralization of language was found. The much smaller sample of left-handed subjects presented a complex picture of no significant effects, whether they were the sole left-handers in their family, or had other left-handed close relations.