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At least 613 records · Page 34Linked to original sources
PubMed1986

A syndrome of pathological left-handedness. Correlates of early left hemisphere injury.

A pattern of correlative changes in lateralization in individuals with known or suspected brain injury recently has been advanced as the syndrome of pathological left-handedness (PLH). This syndrome, which is believed to be caused by an early left-sided cerebral lesion, may include asymmetric motor and/or trophic changes on the right side of a body part in addition to changes in higher-level cognitive processing abilities. Several clinical case studies have provided support for such a syndrome. Despite their clinical subject to inherent biases of selection. The present study was therefore designed to evaluate the PLH syndrome in a systematic fashion by using a large number of brain-injured and normal subjects. The incidence of each of the putative elements of the PLH syndrome was investigated. The results suggest that traits such as atypical cerebral speech representation, motor impairment of the nondominant hand, and hypoplasia of the right foot are salient features of the syndrome. The results are discussed with reference to clinical diagnostic implications.

Adolescent↗
PubMed1986

Quantitative analysis of cerebral asymmetries. Fronto-occipital correlation, sexual dimorphism and association with handedness.

To investigate the biological and functional significance of cerebral asymmetries, we measured lateral differences of the frontal and occipital poles on computed tomographic scans of 66 adult outpatients with no diagnosed abnormalities. In addition to confirming the greater average sizes of the right frontal and left occipital poles, we found a significant linear correlation relating anterior and posterior difference measures. Men showed greater degrees of frontal and occipital asymmetries than women; reversals of the typical asymmetries were more common among women. Reduction or reversal of the usual left occipital predominance in the presence of typical right frontal predominance was associated with non-right-handedness. These findings clarify and extend prior qualitative observations and relate to the possible role of testosterone in modulation of cortical asymmetries. Reduced structural asymmetries among women and non-right-handers may provide an anatomical basis for clinical and laboratory findings of lessened functional lateralization in these groups.

Adult↗
PubMed2004

Mirror writing, left-handedness, and leftward scripts.

This minireview concerns a new observation on mirror writing. An uncommon form of writing, mirror writing is seen among healthy individuals, but it can also follow a variety of neurological diseases; it is nearly always carried out with the left hand and is more easily undertaken by left-handers. We have found that a particularly high prevalence of left-handed mirror writing has been reported among those whose native languages are traditionally written in a leftward direction, including Chinese, Japanese, and Hebrew. Innate left-handers and those whose languages are written leftward thus share an unusual facility for left-handed mirror writing, an observation that may have implications for understanding hemisphere specialization in relation to handedness.

Dominance, Cerebral↗
PubMed2000

Handedness and cortisol in tufted capuchin monkey infants.

In this research, we examined the relationship between handedness and levels of plasma cortisol in infant monkeys (Cebus apella). Specifically, we sought to test the hypothesis that stress functioning is related to hemispheric specialization and is manifested in a positive correlation between cortisol levels and the frequency of right- versus left-hand use. We found a significant relationship between stress cortisol at age 6 months and lateral bias towards greater use of the right versus left hand at ages 6 and 12 months. These data suggest an early developmental influence of stress reactivity on the emergence of hemispheric specialization for manual control in infant monkeys through the 1st year of postnatal life.

Age Factors↗
PubMed1987

Strength of handedness as an indicant of delinquent's behavior.

In a sample of incarcerated male delinquents (N = 254), dichotomous and continuous measures of handedness were compared in concurrent prediction of delinquent behavior and correlation with past delinquency. The continuous measures proved to be more sensitive indicants of scores on a rating scale of conduct disorder than was the simple dichotomy of left- vs. right-handed. This superiority of continuous measures was not seen on other indicants of delinquency, where sinistrality did not relate to delinquency. Sinistrality was related to the ratings of conduct disorder. No differences on measures of delinquency appeared when strongly and weakly lateralized groups of right- and left-handers were compared.

Adolescent↗
PubMed2001

Plasma cortisol is associated with handedness in infant rhesus monkeys.

In this research we examined the relationship between plasma cortisol and handedness in infant rhesus macaques (Macaca mulatta). Specifically, we tested the hypothesis that stress functioning is related to hemispheric specialization and manifested in a positive correlation between cortisol levels and the frequency of right- versus left- hand use. We found a significant positive relationship between cortisol levels sampled at ages 1 and 3 months and lateral bias toward greater use of the right hand versus left hand sampled between ages 4 and 11 months. Further, we found a significant negative relationship between cortisol sampled at age 5 months and strength of lateral bias (independent of direction). These data suggest an early developmental influence of stress functioning on hemispheric specialization for manual control in infant monkeys.

Age Factors↗
PubMed1991

Origins of the handedness of biological molecules.

Pasteur (1860) showed that many organic molecules form enantiomeric pairs with non-superposable mirror-image shapes, characterized by their oppositely signed optical rotation but otherwise apparently identical. Equal numbers of left-handed and right-handed molecules resulted from laboratory synthesis, whereas biosynthetic processes afforded only one of the two enantiomers, leading Pasteur to conclude that biosynthesis involves a chiral force. Fischer demonstrated (1890-1919) that functional biomolecules are composed specifically of the D-sugars and the L-amino acids and that the laboratory synthetic reactions of such molecules propagate with chiral stereoselectivity. Given a primordial enantiomer, biomolecular homochirality follows without the intervention of a chiral natural force, except prebiotically. Chiral forces known at the time were found to be even handed on a time and space average, exemplifying parity conservation (1927). The weak nuclear force, shown to violate parity (1956), was unified with electro-magnetism in the electroweak force (1970). Ab initio estimations including the chiral electroweak force indicate that the L-amino acids and the D-sugars are more stable than the corresponding enantiomers. The small energy difference between these enantiomeric pairs, with Darwinian reaction kinetics in a flow reactor, account for the choice of biomolecular handedness made when life began.

Amino Acids↗
PubMed2004

Sex difference in chimpanzee handedness.

Chimpanzees at Mahale, Tanzania, show strong individual hand preferences when they use bimanual actions in processing the fruit of Saba florida and Citrus lemon. The direction of hand preference differs between the sexes: most males are left-handed, whereas most females are right-handed. Monkeys and apes are considered to lack "handedness," in the sense of a population mode of left- or right-hand preference; they are normally ambidextrous. Indeed, strong individual preferences were previously seldom found in natural tasks. We propose that lateralization of manual actions becomes advantageous in bimanual tasks, which involve role differentiation between the hands and a need to combine power and precision. If the pattern of lateralization found here reflects the ancestral state, common to chimpanzees and humans, this may explain why, in modern humans, women tend more strongly to be right-handed than men, who include a larger minority of left-handers.

Animals↗
PubMed2006

Handedness control of peptide helices by amino acid side-chain chirality: Ile/aIle peptides.

A set of four hexapeptide sequences, each characterized by four strongly helicogenic Aib residues and all combinations of two isomeric Ile/aIle residues at positions 2 and 5, was synthesized by solution methods and fully characterized. A detailed solution (by FT-IR absorption, NMR, and CD techniques) and solid/crystalline state (by X-ray diffraction) conformational investigation allowed us to validate our assumption that all four peptides are folded in well-developed 3(10)-helical structures. However, the most relevant conformational conclusion extracted from the present 3D-analysis is that the handedness of the 3(10)-helical structures formed does not seem to be sensitive to the configurational change at the beta-carbon atom of the constituent Ile versus the diastereomeric aIle residues (in other words, the dominant control on this important structural parameter appears to be exerted by the chirality of the amino acid alpha-carbon atom). These results complement published findings on the diverging relative stabilities of the intermolecularly H-bonded beta-sheet structures generated by Ile versus aIle homo-oligopeptides.

Isoleucine↗
PubMed2003

Homochiral oligopeptides by chiral amplification within two-dimensional crystalline self-assemblies at the air-water interface; relevance to biomolecular handedness.

A possible role that might have been played by ordered clusters at interfaces for the generation of homochiral oligopeptides under prebiotic conditions has been probed by a catalyzed polymerization of amphiphilic activated alpha-amino acids, in racemic and chiral non-racemic forms, which had self-assembled into two-dimensional (2D) ordered crystallites at the air-aqueous solution interface. As model systems we studied N(epsilon)-stearoyl-lysine thioethyl ester (C(18)-TE-Lys), gamma-stearyl-glutamic thioethyl ester (C(18)-TE-Glu), N(alpha)-carboxyanhydride of gamma-stearyl-glutamic acid (C(18)-Glu NCA) and gamma-stearyl-glutamic thioacid (C(18)-thio-Glu). According to in-situ grazing incidence X-ray diffraction measurements on the water surface, (R,S)-C(18)-TE-Lys, (R,S)-C(18)-TE-Glu, and (R,S)-C(18)-Glu-NCA amphiphiles self-assembled into ordered racemic 2D crystallites. Oligopeptides 2-12 units long were obtained at the air-aqueous solution interface after injection of appropriate catalysts into the water subphase. The experimental relative abundance of oligopeptides with homochiral sequence generated from (R,S)-C(18)-TE-Lys and (R,S)-C(18)-TE-Glu, as determined by mass spectrometry on enantioselectively deuterium-labeled samples, was found to be significantly larger than that obtained from (R,S) C(18)-thio-Glu which polymerizes randomly. An efficient chiral amplification was obtained in the polymerization of non-racemic mixtures of C(18)-Glu-NCA since the monomer molecules in the racemic 2D crystallites are oriented such that the reaction occurs between heterochiral molecules related by glide symmetry to yield heterochiral oligopeptides whereas the enantiomer in excess, in the enantiomorphous crystallites, yield oligopeptides of a single handedness.

Air↗
PubMed2005

Lysine-based peptide nucleic acids (PNAs) with strong chiral constraint: control of helix handedness and DNA binding by chirality.

Two enantiomeric chiral PNAs bearing three adjacent D- or L-lysine-based residues in the middle of the strand ("chiral box" PNAs, sequence H-GTAGA(Lys)T(Lys)C(Lys)ACT-NH2) have been used as models in order to comprehensively study the effects of the stereogenic centers on PNA conformation and on PNA binding properties to complementary PNA and DNA strands. The binding properties of the two enantiomeric PNAs and of their homologous achiral PNA have been extensively studied by UV and CD spectroscopy and by mass spectrometry, both in the antiparallel and in the parallel mode with complementary PNA and DNA strands. In the antiparallel PNA:PNA duplexes, L-Lys PNA were found to form left-handed, and D-Lys PNA right handed helices, while in parallel duplexes, the reversed helicities were observed. Correspondingly, the preferred mode of binding and the best mismatch recognition of the D-Lys containing PNA with (right handed) DNA was found to be in the antiparallel orientation, while that of L-Lys PNA was found to be in the parallel mode. A rationale which correlates the preferred handedness of the PNA-PNA duplexes to the directionality of the binding to complementary DNA duplexes has been devised according to structural data and considering the "retro-inverso" concept widely used for peptides.

Base Pair Mismatch↗
PubMed1992

Sylvian fissure morphology and asymmetry in men and women: bilateral differences in relation to handedness in men.

The anatomy of the sylvian fissure in the human brain was studied to develop reliable criteria for anatomical landmarks of the posterior part of the fissure for use in its definition and measurement; to quantify right-left asymmetries in segments of the sylvian fissure; to assess whether any anatomical features are associated with hand preference (selected as one index of hemispheric functional asymmetry); and whether structure-function relationships are similar in men and women. A sample of 67 brain specimens (24 men and 43 women, mean age = 53 years) was studied postmortem (with the aid of dissection) from people who had been tested before death for detailed hand preference. Sylvian fissure anatomy in the human brain is very variable and no agreement exists as to the point of its posterior termination. The posterior ascending ramus, originating at the posterior bifurcation of the fissure, was found to be the continuation of the main limb of the sylvian fissure. Three segments of the sylvian fissure were defined and measured: anterior, horizontal, and vertical. The anterior segment showed no asymmetry; the horizontal segment was twice as large on the left side as on the right; and the vertical segment twice as large on the right. The two asymmetries counterbalanced each other, and overall asymmetry in the posterior region (horizontal plus vertical) was minimal. The basic asymmetry is in the position at which the fissure turns up, resulting in the different extent and position of the surrounding right and left parietal and temporal gyri and associated cytoarchitectonic regions. The possible embryological course of the asymmetry is discussed. Handedness correlated with anatomy of the sylvian fissure in men. In contrast to general expectation, hand preference was associated with a bilateral feature of morphology, and not with less asymmetry in non-right-handers. Men having consistent-right-hand preference had longer horizontal segments in both hemispheres compared to men not having consistent-right-hand preference. The direction and magnitude of asymmetry did not differ between the two male hand-preference groups. Since hand preference is an index of other motor and perceptual functions which are asymmetrically represented in the two hemispheres in gyri surrounding the sylvian fissure, it is suggested that anatomy of the sylvian fissure is related to functional asymmetries in men. A sex difference in structure-function relationship was observed. No association was found between hand preference and sylvian fissure anatomy in women.(ABSTRACT TRUNCATED AT 400 WORDS)

Brain↗
PubMed1986

Postural and lateral asymmetries in the ontogeny of handedness during infancy.

Ten newborn infants who preferred to lie with their heads turned rightward and ten who preferred to lie with their heads turned leftward had their hand-use preferences for reaching assessed at 8 different ages during the period 12-74 weeks postpartum. Eighteen infants maintained stable hand-use preferences throughout this period and the direction of their neonatal head orientation preference predicted the hand they preferred to use. The neonatal head-turn preference was maintained through the first 2 months and induced lateral asymmetries in visual regard and motor control of the hands. These lateral asymmetries are plausible contributors to mechanisms linking neonatal headturn preference to infant hand-use preference. Thus, the dextral bias in handedness may be derived, in part, from the rightward bias in neonatal head-turn preference.

Child Development↗
PubMed1995

Talents and disorders: relationships among handedness, sex, and college major.

One-hundred and nine consistent left- and right-handers participated in an experiment investigating the role of Handedness, Sex, and College Major in predicting spatial talents, verbal problems, immune disorders, allergies, and myopia. Left-handers had poor verbal ability. Males in spatial majors (requiring extensive math) had high spatial ability and poor verbal ability. Left-handed males in spatial majors had high spatial ability, poor verbal ability, an elevated incidence of asthma, and a marginally higher incidence of myopia. No trade-off between spatial and verbal ability was found. Results provide qualified support for Geschwind and Galaburda's (1987) hypothesis of the "Pathology of Superiority."

Adolescent↗
PubMed2000

Ratings of emotion in laterally presented faces: sex and handedness effects.

Sixteen right-handed participants (8 male and 8 female students) and 16 left-handed participants (8 male and 8 female students) were presented with cartoon faces expressing emotions ranging from extremely positive to extremely negative. A forced-choice paradigm was used in which the participants were asked to rate the faces as either positive or negative. Compared to men, women rated faces more positively, especially in response to right visual field presentations. Women rated neutral and mildly positive faces more positively in the right than in the left visual field, whereas men rated these faces consistently across visual fields. Handedness did not affect the ratings of emotion. The data suggest a positive emotional bias of the left hemisphere in women.

Adult↗
PubMed1999

Left-handedness and achievements in foreign language studies.

Studies of brain lateralization lend support to the hypothesis that language-motor functions in left-handers are differently organized from those in right-handers. However, the implications of these differences regarding cognitive functioning are as yet subject to controversy. This concerns all hypotheses raised and empirical data collected over the years. Although it was suggested that left-handers are at higher risk of having language and reading deficits, empirical data from clinical and nonclinical populations are inconclusive at the present time. No effort, however, has been invested in examining possible differences in academic studies of foreign languages according to handedness. Here we report data indicating inferior achievements of left-handed native Hebrew speakers in studies of English as a foreign language. Left-handed pupils significantly more than right-handers were placed in lower level English classes and had more difficulties in applying orthographic-phonological mapping rules in reading English words and pseudowords. However, left-handers' difficulties in this task were not correlated with their performance in a word recognition task. It is thus suggested that the "common symptom" of poor word reading in left-handers indicates different processing failures in different left-handers, some of which impede the buildup of an internal representational system of mapping orthography to phonology and some of which concern mainly the precision of word production.

Achievement↗
PubMed2001

Familial handedness and access to words, meaning, and syntax during sentence comprehension.

We compared right-handed familial dextral (FS-) and familial sinistral (FS+) participants who were aged either 10-13 years (children) or 18-23 years (adults). In word probe and associative probe tasks, FS+ adults responded faster than all other groups and FS+ children responded more slowly than all other groups. In the word probe task, only the FS- adults showed a significant effect of the serial position of the target word. We interpret these differences to support an analysis-by-synthesis model of comprehension in which individuals who differ in familial handedness and age emphasize different linguistic representations during comprehension. In general, FS+ individuals focus on words and meaning, while FS- individuals focus on syntactic representations. In FS+ individuals, age-related experiences with language produce a shift in responding from compositional meaning to words and their associations. In FS- individuals, age-related experiences with language produce a shift toward responding based more on detailed syntactic representations, including the serial order of words and possibly the structural roles of clauses.

Adolescent↗
PubMed2001

Tripedal knuckle-walking: a proposal for the evolution of human locomotion and handedness.

A comparative morphological analysis of human and non-human hominoids was conducted in an attempt to determine the mode of locomotion of the protohominid. Although the generalized hominoid anatomy permits variation of locomotion: brachiation, knuckle-walking, etc., minor variations in structure determine which behavior is favored. Arboreal arm swinging requires a flexible forelimb while terrestrial fist or knuckle-walking demands more rigidity of the hand and wrist. It is demonstrated that the large human thumb accompanied by the strong adduction of the thenar, hypothenar, and palmar interosseous muscles offer powerful rigidity to the hand, while fusion of the os centrale with the scaphoid during gestation permits the formation of an arch of carpals which imbue the wrist with the stability necessary for weight bearing. Fascialization of the contrahentes and dorsiepitrochlearis muscles in the human as well as depilation of the middle phalanges; the webbing (syndactyly) of the palm; the direction of the fibers of the interosseous membrane of the forearm; the shape of the puerile annular ligament, and the direction of the human glenoid fossa strongly suggest that the ancestor of man used a knuckle-walking form of locomotion prior to becoming bipedal. A model is presented that suggests that bipedalism was attained through an intermediate stage of tripedalism. The model is based on the fact that man's anatomy is much more asymmetric than that of the great apes. A presumption is made that due to the absence of trees for climbing in the transition from forest to open plain, the protohominid needed to carry tools (stones) at all times for protection. Stones could be carried for long distances on the posterior iliac crest since the weight would be shifted posteriorly over the legs. Pick up, medial rotation and adduction of the stone would employ a two-muscle chain of biceps brachii and latissimus dorsi. On the iliac crest, the stone is posterior to the coronal plane of the glenohumeral joint, and with the contraction of this two-muscle chain, the shoulder on one side is moved posteriorly effecting a semi-erect posture. It is proposed that tripedalism of the protohominid may be an explanation for the handedness unique to hominids.

Animals↗