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PubMed1998

Handedness and asymmetry of hand representation in human motor cortex.

The cortical representation of five simple hand and finger movements in the human motor cortex was determined in left- and right-handed people with whole-head magnetoencephalography. Different movements were found to be represented by spatially segregated dipolar sources in primary motor cortex. The spatial arrangement of neuronal sources for digit and wrist movements was nonsomatotopic and varied greatly between subjects. As an estimator of hand area size in primary motor cortex, we determined the smallest cuboid volume enclosing the five dipole sources within the left and right hemisphere of each subject. Interhemispheric comparison revealed a significant increase of this volume in primary motor cortex opposite to the preferred hand. This asymmetry was due to a greater spatial segregation of neuronal dipole generators subserving different hand and finger actions in the dominant hemisphere. Mean Euclidean distances between dipole sources for different movements were 10.7 +/- 3.5 mm in the dominant and 9.4 +/- 3.5 mm in the nondominant hemisphere (mean +/- SD; P = 0. 01, two-tailed t-test). The expansion of hand representation in primary motor cortex could not simply be attributed to a greater number of pyramidal cells devoted to each particular movement as inferred from current source amplitudes. The degree of hemispheric asymmetry of hand area size in the primary motor cortex was correlated highly with the asymmetry of hand performance in a standardized handedness test (r = -0.76, P < 0.01). These results demonstrate for the first time a biological correlate of handedness in human motor cortex. The expansion of hand motor cortex in the dominant hemisphere may provide extra space for the cortical encoding of a greater motor skill repertoire of the preferred hand.

Adult↗
PubMed2001

Hormones and handedness.

BACKGROUND: The Wessex Growth Study has monitored the growth and psychological development of short normal (SN) and average height control subjects since they entered school in 1985/1986. During psychometric testing, we found that 25% SN compared to 9% control subjects wrote with their left hand. The short group also attained significantly lower scores on measures of IQ and attainment and displayed less internalisation of control. Laterality, however, is thought to be influenced by the intrauterine environment and has been associated with pubertal delay. At recruitment, short children had a relatively low birth weight, delayed bone age and were more likely than controls to be short for family. OBJECTIVES: To determine if birth conditions were associated with lateral preference and whether laterality could account for the differences found during the psychometric assessment or predict pubertal timing of SN children. METHODS: Subjects were classified as right- (RH) or left-handed (LH) according to the writing hand and the data were investigated examining the effect of handedness and stature. RESULTS: RH and LH SN children were no more likely to suffer birth complications than those of average height. Psychometric testing did not reveal any significant differences between RH and LH SN children and their patterns of growth appeared to be similar. However, both RH and LH SN children scored less well on tests of cognitive ability and analyses of covariance revealed significant gender/handedness effects for both the timing of puberty and final height. CONCLUSIONS: The increase in left-handedness among SN children did not appear to be related to adverse birth conditions, but it may be that the hormones responsible for growth and development also play some part in brain laterality and cognitive development.

Adolescent↗
PubMed2005

Anatomy of handedness and the laterality of seizure onset: surgical implications of new understandings in motor control.

OBJECTIVES: This article pursues another corollary of the anatomy of handedness, a code for the laterality of motor control. The latter indicates the absence of any motor communication from the minor (right, in the vast majority of population) to the major hemisphere (left, in the vast majority of right handers). It also indicates that all communications between the two hemispheres are excitatory in nature. This arrangement prohibits initiation of seizure within the minor and its propagation to the major hemisphere, via the callosum. METHODS: A comprehensive review of the literature is undertaken regarding theoretical and technical reasons for the failure of seizure surgery in subjects undergoing the same for intractable epilepsy. RESULTS: Whereas the laterality of motor control is heavily biased towards the left hemisphere (approximately 80%), the operation is performed equally on both hemispheres. Failures of surgery in some series were substantially higher among those who had undergone operations on the right hemisphere. Technical reasons for this are traced to the unreliability of tests commonly employed in securing laterality of seizure onset, which is the same as that of motor control. Accordingly, the failure rate of seizure surgery may equal the rate of false lateralization of the major hemisphere in these circumstances. CONCLUSION: Given the dichotomous anatomy of handedness, the most robust test for lateralizing the hemisphere of onset of seizure is that of determining the reaction times of two symmetrically located effectors, one on each side of the body. The side with the shorter reaction time will always be opposite to the major hemisphere. The difference between the two values is commensurate to the inter-hemispheric transfer time.

Brain↗
PubMed1980

Handedness as a determinant of left-right placement in human figure drawings.

Assessed the effects of handedness and eye-dominance on the right-left placement of human figure drawings. Previous studies had reported that right-left placement varied as a function of personality. However, the present findings indicate no significant relationship between the two personality variables in the Thorndike Dimension of Temperament Scale and drawing placement. However, left-right placement did vary significantly as a function of handedness but not eye-dominance. Although all subjects tended to place their drawings left-of-center, right-handed subjects were significantly more extreme in their placement than were left-handed subjects.

Art↗
PubMed2005

Gender differences in handedness and speech lateralization related to early neurologic insults.

Left-handedness is a normal variant but also may result from early-life brain insults. Speech typically resides in the left cerebral hemisphere in normal subjects. In 170 subjects with past brain injuries, bilateral or right hemisphere speech lateralization, determined by the intracarotid amobarbital procedure, was more frequent in females (19 vs 5, p = 0.003) as was left-handedness (26 vs 10, p = 0.004). This could be attributed to greater plasticity or functional symmetry in females.

Age Factors↗
PubMed1984

Left-handedness in early and late onset dementia.

Sixty-five men with the diagnosis of dementia of the Alzheimer type were divided into two groups, according to age at onset of dementia before or after 65 years. A handedness questionnaire was then completed for each patient. There was a significantly higher prevalence of left-handedness in the early, as compared with the late, onset group. Taken together with other data, this finding suggests that presenile dementia (Alzheimer's disease) and senile dementia "of the Alzheimer type " may not be biologically identical.

Age Factors↗
PubMed1989

Non-genic inheritance of cellular handedness.

Ciliates exhibit an asymmetry in arrangement of surface structures around the cell which could be termed handedness. If the usual order of placement of structures defines a 'right-handed' (RH) cell, then a cell with this order reversed would be 'left-handed' (LH). Such LH forms appear to be produced in Tetrahymena thermophila through aberrant reorganization of homopolar doublets back to the singlet condition. Four clones of LH forms were selected and subjected to genetic analysis to test whether this drastic phenotypic alteration resulted from a nuclear genetic change. The results of this analysis indicate that the change in handedness is not due to a genetic change in either the micronucleus or macronucleus. The LH form can, under certain circumstances, revert to the RH form, but typically it propagates itself across both vegetative and sexual generations with similar fidelity. While this analysis does not formally rule out certain possibilities of nuclear genic control involving regulatory elements transmitted through the cytoplasm, when the circumstances of origin and propagation of the LH condition are taken into account direct cortical perpetuation seems far more likely. Here we outline a conceptual framework centred on the idea of longitudinally propagated positional information; the positive evidence supporting this idea as well as further application of the idea itself are presented in the accompanying paper.

Animals↗
PubMed1993

Handedness and sleep apnea.

Left-handedness is associated with shorter life span. Many of the factors contributing to this higher mortality (eg, alcohol consumption, automobile accident, smoking) are the same as in patients with sleep apnea, who also have higher mortality than nonapneic controls. The authors hypothesized that (1) there is a higher prevalence of sinistrality in patients suspected of having sleep apnea than in the general population, and (2) left-handed persons with sleep apnea have a more severe disorder than right-handed ones. These hypotheses were tested in a prospective cohort of 970 patients referred to a sleep disorders center because of suspected sleep apnea. All patients underwent nocturnal polysomnography and measurements of blood pressure. Sixty-one patients were left-handed. The distribution of handedness as a function of age in this cohort was similar to that in the general population. There were 486 patients with an apnea/hypopnea index greater than 10; of these, 34 were left-handed, and 452 were right-handed. Oxygen saturation, blood pressure, age, smoking history, and body mass index were similar in both groups. Left-handed patients with sleep apnea had a significantly higher respiratory disturbance index (RDI) than the right-handed ones (52 +/- 30 vs 38 +/- 35 [p < 0.005]). Right-handed patients were distributed equally among RDI quartiles, but 41 percent of the left-handed patients were within the highest RDI quartile, compared to 12 percent within the lowest quartile. Sinistrality appears to be associated with more severe sleep apnea, which may help to explain the higher mortality seen among the left-handed persons.

Adult↗
PubMed1992

Effects of stimulation intensity, gender and handedness upon auditory evoked potentials.

Left handers and women show less anatomical brain asymmetry, larger corpus callosum and more bilateral representation of specific functions. Sensory and cognitive components of cortical auditory evoked potentials (AEP) have been shown to be asymmetric in right handed males and to be influenced by stimulus intensity. In this study the influence of sex, handedness and stimulus intensity upon AEP components is investigated under basal conditions of passive attention. 14 right handed males, 14 right handed females, 14 left handed males, and 14 left handed females were studied while lying awake and paying passive attention to auditory stimulation (series of 100 binaural clicks, duration 1 msec, rate 1/sec, at four intensities). Cz, C3 and C4 referenced to linked mastoids and right EOG were recorded. Analysis time was 400 msec, average evoked potentials were based on 100 clicks. Stimulus intensity and gender affect early sensory components (P1N1 and N1P2) at central leads, asymmetry is influenced only by handedness, right handers showing larger P1N1 amplitudes over the right hemisphere.

Acoustic Stimulation↗
PubMed1993

Left-handedness and mortality.

We examined mortality associated with handedness in two ways. A simulation using national data suggests that lower mean age at death among left-handed persons, previously offered as evidence of higher mortality, can be explained exclusively by the age distribution of laterality. Second, empiric evidence from a 6-year cohort study of 3774 older adults from East Boston, Massachusetts, demonstrates that left-handedness is not associated with mortality (relative odds = 1.04, 95% confidence interval = 0.79, 1.36).

Age Factors↗
PubMed1999

The association between switching hand preference and the declining prevalence of left-handedness with age.

OBJECTIVES: This study determined the prevalence of left-handedness and of switching hand preference among innately left-handed subjects. METHODS: Subjects of Swiss nationality (n = 1692), participating in a population-based survey in Geneva, Switzerland, completed a questionnaire on innate hand preference and current hand preference for writing. RESULTS: From 35 to 44 years of age to 65 to 74 years of age, the prevalence of innate left-handedness declined from 11.9% to 6.2% (trend P = .007). In these same age groups, the proportion of innately left-handed subjects who switched to the right hand for writing increased from 26.6% to 88.9% (trend P = .0001). CONCLUSIONS: Across generations, we found an increase in the prevalence of switching hand preference among innately left-handed subjects. This phenomenon could be explained by social and parental pressure to use the right hand.

Adult↗
PubMed2005

Differences in handedness and scores of aggressiveness and interpersonal relations of soccer players.

Handedness and differences in interpersonal relations and aggressiveness were studied in 33 right-handed (M age=22.9 yr., SD=4.9) and 18 left-handed (M age=22.5 yr., SD=2.4) male soccer players who played actively in professional soccer leagues of Turkey. Hand preference on the Edinburgh Handedness Inventory and scores for destructiveness, assertiveness, and passive aggressiveness on a Turkish Aggressiveness Inventory, plus scores for sociability, benevolence, tenderheartedness, tolerance, and insistence on the Turkish Interpersonal Relations Inventory were examined. Mean destructive aggressiveness was higher for the left- than the right-handed athletes. Means on tolerance and insistence were higher for the right- than the left-handed athletes. Higher aggressiveness and less tolerance and insistence in the left-handers may be associated with their higher sports performance.

Achievement↗
PubMed1978

Correlation between handedness and birth order: compilation of five studies.

Bakan has suggested that left-handedness is the result of left hemishperic pyramidal motor dysfunction following perinatal hypoxia. To a degree support for the validity of this hypothesis rests on Bakan's (1971, 1977a) findings that left-handed college students were more likely the progeny of birth orders designated as "high-risk" than right-handed students. Attempts by others to replicate Bakan's data have been unsuccessful. To achieve a more powerful test of this relationship than has been provided by any single study, the data from the five studies which have considered it were pooled and tested. The resulting correlation between birth order and handedness was near zero.

Birth Order↗
PubMed1978

Handedness and locus of control.

Groups of 15 left-, 15 mixed-, and 39 right-handers were tested with Rotter's Locus of Control Scale. Contrary to prediction, it was found that both left- and right-handers scored significantly higher, i.e., were more externally controlled, than mixed-handers. Primarily these data suggest a complex relationship between handedness and personality and they serve to reinforce the need to include mixed-handers in research on handedness.

Functional Laterality↗
PubMed1978

Lateral response to suggestion in relation to handedness.

Lateralization of response to the suggestion of a sensation was recorded in 100 psychiatric patients and related to their handedness. Responses showed no over-all preponderance to right or left side. There was, however, a significant association between side of response and handedness.

Adolescent↗
PubMed1980

Salience of handedness in the spontaneous self-concept.

The distinctiveness postulate regarding selective perception implies that an aspect of a complex stimulus is likely to be noticed in direct proportion to its distinctiveness in the environment in which it is perceived. An implied prediction tested in the present study is that handedness is more salient in the self-concepts of left-handers than of right-handers. The spontaneous self-concept was measured in two different populations by open-ended "Tell us about yourself" questions. In each group, a significantly greater proportion of left- than right-handers mentioned their handedness as part of their self-concept.

Adult↗
PubMed1987

Left-handedness in twin families: support of an environmental hypothesis.

Information on handedness, assessed as writing-hand, was collected from 197 MZ twin pairs and 203 DZ twin pairs and from their parents, spouses, and children. Associations for pairs of relatives were studied by 2 X 2 tables, computing chi squared-values and tetrachoric correlations. Correlations of about .3 were obtained for mother-offspring and sibling pairs, while for cousins the correlation was .25 (in a small sample). No other significant associations were found, not even for twins. These results suggest only a small, if any, genetic effect, and only a small environmental between family effect, most of which seems to be a maternal effect. The lack of cotwin correlations and correlations for one of the twins with her/his ordinary brothers/sisters suggest the existence of an effect specific to twins, since the correlation for pairs of ordinary siblings is significant. Conclusions drawn from twin studies alone may be biased. The frequency of left-hand writers has increased from 1% to 10% in the different age groups born during the last century in Norway. This age effect is present mainly in hand writing and not so much in handedness generally, suggesting a decrease in cultural repression against left-hand writing.

Adult↗