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At least 703 records · Page 39Linked to original sources
PubMed1996

Effects of perinatal testosterone on handedness of gerbils: support for part of the Geschwind-Galaburda hypothesis.

When assuming their species-typical tripodal stance, male Mongolian gerbils (Meriones unguiculatus) use their right forepaw for support more frequently than do females. This experiment determined whether, as N. Geschwind and A. M. Galaburda (1987) have proposed, the direction of such sexually dimorphic lateral asymmetry of forelimb use is affected by perinatal exposure to testosterone (TP). It was found that male gerbils injected with TP when 4 days old were significantly less likely to rest on their right forepaw when in a tripodal stance than were their oil-injected siblings. Female gerbils injected with TP when 6 days old were more likely than oil-injected controls to use their right forepaws for support. The findings demonstrate effects of perinatal exposure to TP on handedness in gerbils and suggest that the relationship between TP exposure and asymmetrical forelimb use is not always as direct as Geschwind and Galaburda's model suggests.

Animals↗
PubMed1997

Individual differences in lateralization: effects of gender and handedness.

Male and female left- and right-handers participated in 3 experiments designed to investigate 3 components of performance asymmetry in lateralized tasks. Experiment 1 used a consonant-vowel-consonant (CVC) identification task measuring quantitative differences in hemispheric abilities and hemispheric control and qualitative differences in hemispheric strategies. The quantitative data revealed that left-handers have a smaller performance asymmetry than do right-handers and that both groups have the same degree of increased accuracy when stimuli are presented bilaterally. Handedness affected the qualitative measures of men, not of women. Experiment 2 used nominal and physical letter-matching tasks with bilateral presentations and measured the flexibility of callosal function. The results suggest that left-handers have less flexible interhemispheric communication than do right-handers and show no effect of gender. Experiment 3 used a chair identification task indexing hemispheric arousal bias. Left-handers tended to have more aroused right than left hemispheres, whereas the distribution of right-handers was centered around 0 arousal bias. Intertask analyses revealed a relationship between arousal bias and metacontrol, where individuals with more aroused right hemispheres tended to use a right-hemisphere strategy in the bilateral condition of the CVC experiment. Intercorrelations between measures from the experiments revealed only a limited relationship between metacontrol patterns in the CVC task and a measure of callosal flexibility in the physical letter-matching task. The results are discussed in the context of the relationships between dimensions of hemispheric asymmetry.

Adult↗
PubMed1998

Multitask analysis of cerebral hemisphere specialization in monozygotic twins discordant for handedness.

This study constitutes a multitask appraisal of cerebral hemisphere specialization with 13 monozygotic (MZ) twin pairs discordant for handedness. Tasks included dichotic listening, finger tapping with concurrent loads, two tachistoscopic visual half-field tests, and a free-vision face test. Overall, MZ twins showed similar performance asymmetries on most tasks. Different asymmetries, however, were observed on the finger tapping with anagram load and visual half-field with chair stimuli. In these instances, asymmetries for left- and right-handed MZ twins were more similar to patterns reported in the literature for left- and right-handed singletons, respectively, than for opposite-handed co-twins.

Adolescent↗
PubMed1991

Manual laterality in nonhuman primates: a distinction between handedness and manual specialization.

This article examines individual and group manual lateralization in nonhuman primates as a function of task's demands. It is suggested to distinguish low- from high-level manual activities with respect to the novelty variable and to the spatiotemporal scale of the movements. This review shows that low-level tasks lead to (a) symmetrical distributions of hand biases for the group and (b) manual preferences that are not indicative of the specialization of the contralateral hemisphere. In contrast, behaviors expressed in high-level tasks (a) show asymmetrical distribution of hand biases for the group and (b) seem to be related to a specialization of the contralateral hemisphere. Two types of lateralization, handedness and manual specialization, correspond to the 2 levels of tasks that are distinguished.

Animals↗
PubMed1993

Do left-handers die sooner than right-handers? Commentary on Coren and Halpern's (1991) "Left-handedness: a marker for decreased survival fitness".

Cross-sectional life span studies of handedness typically show decreasing percentages of left-handers in older age groups. In an article in Psychological Bulletin, S. Coren and D. F. Halpern (1991) argued that this age trend reflects the shorter life span of left-handers than right-handers. They presented 2 studies of their own providing what they regard to be direct evidence that left-handers, on average, die sooner than right-handers. They also proposed a variety of reasons for what they called left-handers' "decreased survival fitness." I discuss Coren and Halpern's reasons for rejecting a more conventional explanation of the life span data; the 2 studies that they offered in support of their argument; their analysis of other evidence they invoked to account for left-handers' putative decreased survival fitness; and, finally, new studies in which the longevity explanation was tested by more direct means than have been used thus far. I conclude that the case for the "decreased survival fitness" hypothesis cannot be sustained.

Adolescent↗
PubMed2000

Birth order and hand preference in chimpanzees (Pan troglodytes): implications for pathological models of handedness in humans.

The effect of birth order on hand preference was assessed in a sample of 154 captive-born chimpanzees. Subjects were classified as first, middle, or latter born using 2 classification criteria based on their birth order. Hand preference was measured using a task that elicited coordinated bimanual actions. Significant birth-order effects were found for both classification criteria, with first- and latter-born subjects exhibiting a lesser degree of right-handedness compared with middle-born subjects. These data suggest that biological rather than sociological factors play a greater role in explaining the observed birth-order effects on hand preference in humans.

Analysis of Variance↗
PubMedDate not supplied

Determination of the absolute handedness of knots and catenanes of DNA.

DNA winds about itself in a right-handed or left-handed fashion at several structural levels. The double helix is generally right-handed and is given a (+) sign by convention, whereas supercoiling of the helix axis is always (-) in the cell. The winding in higher -order forms such as knots and catenanes is unknown, and this has impeded elucidation of the mechanisms of their formation and resolution by replication, recombination and topoisomerase action. We introduce here a procedure for determining the handedness of DNA winding by inspection of electron micrographs of DNA molecules coated with Escherichia coli RecA protein. We demonstrate the validity of the method and show that DNA topoisomerase I of E. coli generates an equal mixture of (+) and (-) duplex DNA knots, and that one product of recombination by resolvase of transposon Tn3 (refs 8, 9) is a catenane of uniquely (+) sign.

Bacterial Proteins↗
PubMed2005

Attending to local form while ignoring global aspects depends on handedness: evidence from TMS.

Our perceptions of the whole and of the parts of a visual stimulus are mediated by different brain regions. We used low-frequency transcranial magnetic stimulation (TMS) to show for the first time that opposite, homologous regions in the two hemispheres are involved in attending to local parts for left- and right-handed individuals. The brain regions that focus on the 'trees' while ignoring the 'forest' are switched as a function of handedness.

Analysis of Variance↗
PubMed2000

Exercise-induced sympathetic activation is correlated with cerebral hemisphere laterality, but not handedness.

To investigate whether sympathetic responses are correlated with central laterality or handedness, muscle sympathetic nerve activity (MSNA), heart rate (HR) and blood pressure (BP) were compared between right (RA) and left arm (LA) grip exercise with volitional maximum effort (MVHG) for 2 min and post-exercise arterial occlusion (PEAO) in right- and left-handed volunteers. MVHG and PEAO led to a greater increase in MSNA in RA than in LA exercise (180 vs. 150%, P=0.004; 140 vs. 85%, P=0.005). MVHG elevated HR to a significantly lesser extent in RA than in LA (35 vs. 46%, P=0.030), and the difference was maintained during PEAO. The BP rise during MVHG and PEAO was the same in RA and in LA. Muscle sympathetic nerve activity, HR and BP responses during MVHG and PEAO showed no difference between the dominant and non-dominant arm. These results suggested that the effects of central motor command and metaboreflex on sympathetic outflow to the vasculature and the heart may be selectively modulated partly by hemispherical laterality.

Adult↗
PubMed2001

Sighting dominance, handedness, and visual acuity preference: three mutually exclusive modalities?

It is tempting, even perhaps for the clinician, to assume prima facie that an individual's handedness is indicative of other lateral asymmetries, including ocular (sighting) dominance and preferred monocular acuity. An analysis of new data relating to these three modalities, as collated from counter-balanced groups of normally sighted male and female children and adults examined in optometric practice, confirms the general fallacy of this assumption and considers why it is such a persistent misconception. The degree of association between the three modalities in right-preferent individuals is revealed as statistically no greater than chance. On the basis of this study, estimates of right-sided hand, eye and/or acuity congruency are derived for the information of the clinician in the prescribing environment of the consulting room.

Adolescent↗
PubMed1976

Handedness of crossover connections in beta sheets.

In a crossover connection, the polypeptide chain leaves one end of a beta sheet, forms a loop of any length and any conformation, and reenters the same beta sheet from the opposite end. Of the 85 examples of crossover connections which occur in the known protein structures, 83 are righthanded and only two are lefthanded. It is proposed that consistent handedness, even in long irregular loops, could be produced by the preferred twist direction of extended chain and the righthandedness of alpha-helices, provided certain conditions hold during the protein folding process.

Carboxypeptidases↗
PubMed2003

Sex and handedness differences in hearing durations of the right and left ears in healthy young adults.

The aim of this work was to study the sex and handedness differences in hearing durations of the right and left ears in healthy young adults. The hearing durations were assessed using a modified Rinne test. The hearing durations of both the right and left ears were longer in males than females. In right-handers, the hearing duration of the right ear was longer than that of the left ear; in left-handers, the hearing duration of the left ear was longer than that of the right ear. These results suggest a male superiority in auditory perceptual acuity; a left-ear advantage in left-handers may result in the superiority of non-right-handers in musical tasks.

Acoustic Stimulation↗
PubMed2003

Sex and handedness differences in eye-hand visual reaction times in handball players.

Sex and handedness differences in the eye-dominant hand, the right eye-right hand and the left eye-left hand visual reaction times were studied in 270 right-handed and 56 left -handed young handball players. Reaction time was assessed by a software package. All visual reaction times were longer in women than in men. In the eye-dominant hand and the left eye- left hand visual reaction times, the left-handers had a superiority over the right handers, but there was no difference between the right eye-right hand visual reaction times of the right- and left-handers. In right-handers, all visual reaction times were longer in women than in men, but there was no sex difference in left-handers. The results suggest that left-handed players have probably an intrinsic neurological advantage.

Adolescent↗
PubMed1979

Sex differences and the incidence of left-handedness.

The higher incidence of left-handedness among males still remains a manifest and interesting phenomenon. For instance, Clark indicated that 7.84% of her male respondents were left-handed compared to 3.91% of the females. A study in South Africa among 882 students (mean age 13 years) yielded similar results: 11.13% of the males were left-handed compared to 7.69% of the females.

Adolescent↗
PubMed1984

A developmental study of the relationship between handedness and eyedness as applied to disappearing visual targets.

This study investigated differences between adult and children's perception of a disappearing, lateralized stimulus. In 20 trials, 23 first graders and 22 college students viewed a luminous target of parallel lines subtending a visual angle of 11 degrees 30' and reported whether a stimulus disappeared on either side of fixation or all at once. Both groups, regardless of handedness and eye dominance, had stronger right-field stability, therefore more left-field fragmentation.

Adult↗
PubMed1984

Dichotic listening and tactual mental rotation in females as a function of familial sinistrality and strength of handedness.

In this study the effects of familial sinistrality and strength of handedness on dichotic listening and tactual mental rotation were investigated. Nonfamilial left-handers were inferior to familial left-handers, particularly in right-ear performance. The decrement in right-ear performance is interpreted as indicative of a pathologically functioning left hemisphere in nonfamilial left-handers. The direction of ear asymmetry tends to be more predictable in strong left-handers than in weak left-handers, with nonfamilial strong left-handers showing a significant left-ear superiority and familial strong left-handers a nonsignificant right-ear superiority. In the tactual mental rotation task, the results suggest a preference of left-handers for a verbal encoding strategy, especially in the right hemisphere. This preferential strategy is particularly manifest in familial weak left-handers and nonfamilial strong left-handers. The results are discussed in terms of their implications for underlying patterns of cerebral organization in the left-handers.

Adult↗
PubMed1987

Birth stress, autoimmune diseases, and handedness.

A large nonclinical sample of left-handed and right-handed subjects completed laterality and medical health questionnaires. The group of left-handed subjects showed a raised incidence of birth complications and learning disorders whereas no differences were found for birth order and maternal age. Left-handed and right-handed subjects showed similar incidences of autoimmune diseases, allergies, migraine, and stuttering. These results suggest that an association between early pathology and left-handedness may be found in a subset of the nonclinical left-handed population. The underlying pathological influence seems to manifest itself in pregnancy and birth complications rather than in immune disorders.

Adult↗