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PubMed1976

Handedness and the cerebral representation of speech.

Hand preferences vary not discretely but continuously and the continuum of preference is closely and reliably linked with a continuous roughly Normal distribution of differences between the hands in skill. Questions about handedness can be usefully formulated in terms of the distribution of differences in skill and in terms of the theshold or criterion which divided those likely to be classified as right handers from those likely to be classified as left handers. A theory of the origin of hand preferences suggests that three factors are involved. The first in non-genetic accidental variation in the development of the two sides of the body in all bilaterally symmetrical species showing limb preferences. The second in a systematic bias to the right hand in man, probably linked with the tendency for the left hemisphere to serve speech. The third is socio-cultural factors affecting the expression of sinistrality. An explanation of the relation between hand preference and cerebral speech laterality requires the assumption that in some individuals the factor biasing speech to the left hemisphere is absent. This would imply that the bias is not a universal species character but that it is subject to genetic variation. Making the simplest possible further assumptions that in the absence of bias, the laterality of handedness and of cerebral speech are independent and each governed by chance, it is possible to account for the distribution of right and left handers with dysphasias following right and left unilateral cerebral lesions.

Aphasia↗
PubMed1984

Proflavine binding to poly(rC-rA) inverts the CD spectrum but not the helix handedness.

The interaction of proflavine hemisulfate with the sodium salt of poly(rC-rA) in solution (unbuffered) yields an inverted (mirror-like) circular dichroism (CD) spectrum to that of the free poly(rC-rA). Simultaneously, an induced negative Cotton effect appears in the proflavine band region with a maximum at 467 nm and a slight shoulder at 420 nm. This observation may be explained as resulting from the formation of a poly(rC-rA).proflavine complex with the polynucleotide existing as a right-handed parallel chain duplex with the proflavine intercalated between the CpA sequence and not the ApC sequence. The intercalation geometry here is expected to be analogous to that found in the crystal structure of the dinucleotide CpA.proflavine complex (Westhof et al. J. Mol. Biol., 1981) which forms a miniature right-handed helix. Although normally an inverted spectra could be attributed to a reversal in the helix handedness, the similarity in the 31P nuclear magnetic resonance spectra between the free and proflavine bound poly(rC-rA) indicates that their handedness is the same. The inverted CD spectrum may be a result of the different stacking orientation between the intercalated proflavine and the A-A base-pair on one hand and the triply hydrogen bonded protonated C-C base-pair on the other.

Acridines↗
PubMed1993

Reverse relationship between alpha-carbon chirality and helix handedness in (alpha Me)Phe peptides.

The crystal-state preferred conformations of two tripeptides, one tetrapeptide, and one pentapeptide, each containing a single residue of the chiral, C alpha, alpha-disubstituted glycine C alpha-methyl, C alpha-benzylglycine [(alpha Me)Phe], have been determined by X-ray diffraction. The tripeptides are Z-L-(alpha Me)Phe-(Aib)2-OH dihydrate and Z-Aib-D-(alpha Me)Phe-Aib-OtBu, the tetrapeptide is Z-(Aib)2-D-(alpha Me)Phe-Aib-OtBu, and the pentapeptide is pBrBz-(Aib)2-DL-(alpha Me)Phe-(Aib)2-OtBu. While the two tripeptides are folded in a beta-bend conformation, two such conformations are consecutively formed by the tetrapeptide. The pentapeptide adopts a regular 3(10)-helix promoted by three consecutive beta-bends. This study confirms the strong propensity of short peptides containing C alpha-methylated alpha-aminoacids to fold into beta-bends and 3(10)-helical structures. Since Aib is achiral, the handedness of the observed bends and helices is dictated by the presence of the (alpha Me)Phe residue. In general, we have found that the relationship between (alpha Me)Phe chirality and helix handedness is opposite to that exhibited by protein aminoacids. A comparison with the preferred conformation of other extensively investigated C alpha-methylated aminoacids is made.

Models, Molecular↗
PubMed1999

Proprioceptive control of wrist extensor motor units in humans: dependence on handedness.

The effectiveness of the monosynaptic proprioceptive assistance to the wrist extensor motoneurone activity was investigated during voluntary contraction in relation to the subjects' handedness. The reflex responses of 411 single motor units to homonymous tendon taps were recorded in the wrist extensor carpi radialis muscles in both arms of five right-handed and five left-handed subjects. In the right-handed subjects, the motor unit reflex responses were clearly lateralized in favour of their right arm, whereas no side-related differences were observed in the left-handed subjects, whatever the motor units' mechanical properties and firing rates. When the muscle spindle sensitivity was by-passed by electrically stimulating the primary afferents in both arms of three right-handed and three left-handed subjects, no side-related differences were observed in the Hoffmann reflex (H-reflex) amplitude in either of the two lateralization groups. The effectiveness of the primary afferent synapses on to the motoneurones therefore does not seem to depend on the subject's handedness. Without excluding the possibility of structural changes being involved at the periphery, the comparisons carried out on the data obtained using electrical vs mechanical stimulation suggest that the asymmetrical effectiveness of the proprioceptive assistance observed in favour of the right arm in the right-handed subjects might result from either the gamma or beta drive being more efficient. This asymmetry might result from the preferential use of the right hand in skilled movements. In a predominantly right-handed world, however, left-handed people might tend to develop the ability to use their right arm almost as skillfully as their preferred left arm, which could explain the symmetrical effectiveness of the proprioceptive assistance observed here in the left-handers' wrist extensor muscles.

Action Potentials↗
PubMed2006

Lateralised vestibular hypofunction: canal paresis and handedness.

In this retrospective study it was found that 549 out of 1175 patients seen for vestibular assessment within an 8-year period within a district hospital service showed lateralised canal paresis as determined by caloric testing. It was found that there was a tendency for canal paresis, indicative of vestibular hypofunction, to be on the side of handedness. This bias showed statistical significance, (chi-squared, p < .005), for the patients overall, as well as for the 65 left-handers considered separately, (p < .05). Surprisingly, this form of bias does not appear to have been reported previously. The bias was shown most clearly in the largest of the groups defined by sex and handedness, namely that of female right-handers. In this group the prevalence of associated hearing loss was similar for canal paresis on either side. This allowed speculation as to the particular type of disorder to which those cases of canal paresis that were associated with the bias might be due, from which it seemed that migraine, rather than Menière's disease or vestibular neuronitis, was likely.

Aged↗
PubMedDate not supplied

On the relationship between handedness and longevity.

During the past five years, there have been numerous studies of the relationship between handedness and longevity. In this report, I review previous contributions and use methods of survival analysis on a set of 4,448 males to determine the strength of the relationship between handedness and longevity. The results indicate that left-handers have small, yet significant, declines in survival probabilities between the ages of 65 and 85.

Adolescent↗
PubMed1996

Left-handedness and age: comparing writing/ drawing and other manual activities.

The percentage of individuals who use the left hand for writing/drawing, brushing teeth, and throwing a ball was compared in 3229 subjects ranging in age from 8 to 96 years. The "elimination" versus "modification" hypotheses were tested as explanations of prior observations that there are fewer left-handers among the elderly. These hypotheses predict different numbers of left-handed elderly individuals when measured by activities not influenced by social pressure. The results suggest that there are age-related patterns among different measures of left-handedness. However, a significant decline in left-handedness among the elderly was also found when measured by less culturally determined activities.

Journal Article↗
PubMed1998

Description and validation of a flexible and broadly usable handedness questionnaire.

Empirical evidence is provided which shows that handedness questionnaires should: (a) comprise items that cover skilled and unskilled activities; (b) be sufficiently long to capture a ''mass effect'' of variability in lateral preferences over a range of items; and (c) allow graded answer options for individual items rather than forced left/right choices. When using questionnaires that meet these criteria, it is possible to establish significant correlations between hand preference and performance even within a group of right-handers. In addition, such questionnaires are flexible enough to accommodate a great variety of handedness classification schemes.

Journal Article↗
PubMed1999

Handedness in the NAS/NRC twin study.

In 1985, a hand preference survey was completed by 973 dizygotic and 1158 monozygotic male twin pairs, all veterans of World War II. This is the largest single twin study of handedness on record. As in state-of-the-art animal research, the laterality criterion was sensitive to both direction and consistency (degree, strong or weak) of handedness. Significant pairwise concordance was shown for the total group, and for consistency and directional factors separately. However, no zygosity differences were demonstrated.

Journal Article↗
PubMed2001

Handedness in Colombia: some associated conditions.

As part of a national neuroepidemiological study a population-based sample of 6941 subjects, 10 years of age or older, was selected in five different regions in Colombia (South America). Overall, 91.65% of the participants (90.6%) of the males; 92.7% of the females) considered themselves as right-handers. Handedness was significantly correlated with education in men but not in women. Handedness was not associated with age. Prevalence of history of loss of consciousness, tremors, difficulties with speech, and traumatic head injury was observed to be higher in non-handers than in right-handers. This finding was particularly evident in men. Implications of current results are analysed.

Journal Article↗
PubMed1992

The influence of handedness on the distribution of muscular weakness of the arm in facioscapulohumeral muscular dystrophy.

The strength of 10 muscle groups in both arms was measured using hand-held myometry to determine the influence of handedness on left-right differences of muscle strength in facioscapulohumeral muscular dystrophy (FSHD). Two groups of subjects were studied: 24 healthy volunteers (19 right-handed), and 53 patients (42 right-handed) with autosomal dominant FSHD. An opposite left-right difference of strength of shoulder and arm muscles was found: right-handed volunteers were stronger on the right side, right-handed patients were stronger on the left side. This opposite left-right difference was statistically significant for the supraspinatus muscle, the wrist extensors and the shoulder internal rotators. The number of left-handed subjects was too small for statistical analysis. The relation between handedness and increased muscle weakness in right-handed FSHD patients suggests that mechanical factors may play a distinct role in the progression of muscle weakness in FSHD.

Adolescent↗
PubMed2006

Handedness is associated with asymmetries in gyrification of the cerebral cortex of chimpanzees.

Gyrification of the cerebral cortex reflects complexity in cortical folding during development of the brain. In this paper, we evaluated whether chimpanzees show asymmetries in gyrification and if variation in gyrification asymmetries were associated with handedness. Magnetic resonance images were obtained in a sample of 76 chimpanzees, and gyrification measures were obtained from 10 equally spaced slices of the cortex. Asymmetry quotients (AQs) in gyrification were compared for 4 measures of handedness including reaching, coordinated bimanual actions, manual gestures, and throwing. Overall, the chimpanzees showed significant differences between the right and left hemispheres that were region specific. Significant differences in AQ's were found in right- and nonright-handed chimpanzees for throwing and, to a lesser degree, for manual gestures. Increasing age was associated with increasing gyrification in the prefrontal regions, particularly in female chimpanzees. The results indicate that variation in gyrification between hemispheres is associated with functional measures of laterality in chimpanzees.

Aging↗
PubMed2006

The Association between handedness, brain asymmetries, and corpus callosum size in chimpanzees (Pan troglodytes).

It has been suggested from studies in human subjects that sex, handedness, and brain asymmetries influence variation in corpus callosum (CC) size and these differences reflect the degree of connectivity between homotopic regions of the left and right cerebral hemispheres. Here we report that handedness is associated with variation in the size of the CC in chimpanzees. We further report that variation in brain asymmetries in a cortical region homologous to Broca's area is associated with the size of the CC but differs for right- and left-handed individuals. Collectively, the results suggest that individual differences in functional and neuroanatomical asymmetries are associated with CC variation not just in humans but also in chimpanzees and therefore may reflect a common neural basis for laterality in these 2 species.

Aging↗
PubMed1998

Handedness is a determining factor in lateralized olfactory discrimination.

The study aimed to re-investigate differences in olfactory thresholds and odor discrimination between the left and right sides in relation to the handedness of healthy subjects. Twenty left- and 20 right-handers participated; all were in excellent health with no indication of any major nasal or health problems, and all were non-smokers. The two groups were comparable in terms of sex and age (left-handers: 11 women, 9 men, median age 25 years; right-handers: 9 women, 11 men, median age 26 years). Odor thresholds did not differ in relation to handedness. However, in the odor discrimination task the left-handers performed significantly better at the left side compared with the right nostril; this pattern was reversed in the right-handers. The data indicate that, similar to other sensory systems, higher olfactory functions exhibit a certain degree of lateralization.

Adult↗
PubMed2003

Parent-of-origin effects on handedness and schizophrenia susceptibility on chromosome 2p12-q11.

Schizophrenia and non-right-handedness are moderately associated, and both traits are often accompanied by abnormalities of asymmetrical brain morphology or function. We have found linkage previously of chromosome 2p12-q11 to a quantitative measure of handedness, and we have also found linkage of schizophrenia/schizoaffective disorder to this same chromosomal region in a separate study. Now, we have found that in one of our samples (191 reading-disabled sibling pairs), the relative hand skill of siblings was correlated more strongly with paternal than maternal relative hand skill. This led us to re-analyse 2p12-q11 under parent-of-origin linkage models. We found linkage of relative hand skill in the RD siblings to 2p12-q11 with P=0.0000037 for paternal identity-by-descent sharing, whereas the maternally inherited locus was not linked to the trait (P>0.2). Similarly, in affected-sib-pair analysis of our schizophrenia dataset (241 sibling pairs), we found linkage to schizophrenia for paternal sharing with LOD=4.72, P=0.0000016, within 3 cM of the peak linkage to relative hand skill. Maternal linkage across the region was weak or non-significant. These similar paternal-specific linkages suggest that the causative genetic effects on 2p12-q11 are related. The linkages may be due to a single maternally imprinted influence on lateralized brain development that contains common functional polymorphisms.

Chromosome Mapping↗
PubMed1994

Risk factors for wrist fracture: effect of age, cigarettes, alcohol, body height, relative weight, and handedness on the risk for distal forearm fractures in men.

Fractures of the distal forearm (wrist) are among the most common of all fractures. While evidence exists concerning risk factors for wrist fracture among women, little is known about risk factors among men. This study examines the relation of lifestyle characteristics (cigarette smoking, alcohol consumption, relative weight) as well as body height and handedness to the risk for fracture in a male population that has been followed up for 6 years. The 51,529 men, who were between the ages of 40 and 75 years in 1986, were participants in the Health Professionals Follow-up Study, a national prospective cohort study. In 271,552 person-years of follow-up, 271 respondents reported a wrist fracture. The risk for wrist fracture in this population did not vary with age. Cigarette smoking, alcohol consumption, body height, and relative weight also were not related to risk for wrist fracture. Handedness, which was divided into four mutually exclusive categories (right-handed, left-handed, forced to change, and ambidextrous), was significantly associated with wrist fracture. Left-handers had a multivariate relative risk for wrist fracture 1.56 times that of right-handers (95% confidence interval 1.02-2.37), and men who reported they had been forced to change from left-handed to right-handed had a multivariate relative risk 2.47 times greater than right-handers (95 percent confidence interval 1.21-5.04).

Adult↗
PubMed1996

The factorial structure of schizotypy: Part II. Cognitive asymmetry, arousal, handedness, and sex.

We replicate relations between factors of schizotypy and cognitive asymmetry patterns assessed with recognition memory for words versus faces, and with arousal levels assessed with self-report scales. The withdrawn factor or subscales of loneliness and constricted affect were associated as before with a right hemisphere, face advantage asymmetry, as was physical anhedonia in males. Subjects with the opposite asymmetry and those high on the active factor--eccentricity and odd speech--had high self-report activation scores. These relations better characterized males who also had higher scores on the asymmetry-related factors. Females had higher scores on the third unreality factor--unusual perceptions and odd beliefs--which showed inconsistent relations with cognitive asymmetry. Non-right-handedness was associated with both hemisphere asymmetry patterns suggesting that the structural mechanism responsible for non-right-handedness is associated with bidirectional hemispheric functional imbalance. The results support the importance of patterns of functional asymmetry in underpinning different aspects of schizotypy.

Adult↗
PubMed2000

Handedness and mortality: a follow-up study of Danish twins born between 1900 and 1910.

The declining prevalence of left-handed individuals with increasing age has led to two main avenues of hypotheses; the association is due either (1) to a birth cohort effect and/or an age effect caused by a switch to right-handedness with advancing age or (2) to mortality selection that reduces survival in left-handed individuals, or both. It is uncertain whether a cohort or age effect can explain the decline in age-related prevalence, and conflicting evidence exists in favor of the mortality hypothesis. We compared mortality in a subgroup of 118 opposite-handed twin pairs by counting in how many instances the right-handed twin died first. There was no evidence of differential survival between right-handed and non-right-handed individuals in the entire 1900-1910 cohort. With respect to the number of right-handed twins who died first, there was no material disadvantage among those who were not right-handed. In 60% (95% confidence interval = 49.0-71.5%) of dizygotic pairs, the right-handed twins died first. In 50% of monozygotic pairs, right-handed twins died first. The prevalence of not being right-handed was higher among males (9.2%) than females (6.5%); there was a similar frequency of non-right-handedness in monozygotic (8.0%) and dizygotic (7.8%) twins. We did not find evidence of excess mortality among non-right-handed adult twins in this follow-up study.

Cause of Death↗