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PubMed2003

fMRI of emotional responses to odors: influence of hedonic valence and judgment, handedness, and gender.

Previous positron emission tomography studies of right-handed individuals show that the left orbitofrontal cortex is dominant during emotional processing of odors. We collected functional magnetic resonance imaging data from 28 subjects to study this network as a function of odor hedonic valence (pleasant vs. unpleasant), active hedonic judgments versus passive sensation of hedonically charged odors, handedness, and gender. Two functional runs were performed, with pleasant and unpleasant odors presented in different epochs. In the first run, subjects passively smelled odorants, whereas in the second run they rated degree of odor pleasantness or unpleasantness by using a "finger-span" technique that simulated a visual rating scale. Electrodermal and plethysmography responses were simultaneously recorded to control for covert, physiological manifestations of the emotional response. The piriform-amygdala area and ventral insula were activated more for unpleasant than pleasant odors. More extreme ratings were also associated with higher electrodermal amplitude, suggesting that activation stemmed more from emotional or hedonic intensity than valence, and that unpleasant odors induced more arousal than pleasant odors. Unpleasant odors activated the left ventral insula in right-handers and the right ventral insula in left-handers, suggesting lateralized processing of emotional odors as a function of handedness. Active decisions about odor pleasantness induced specific left orbitofrontal cortex activation, implicating the role of this area in the conscious assessment of the emotional quality of odors. Finally, left orbitofrontal cortex was more active in women than men, potentially in relation to women's well-documented advantage in odor identification.

Adult↗
PubMed1979

Association of handedness and birth order in monozygotic twins.

In a random sample of 104 pairs of middle-class Caucasian, handedness-discordant twins six years of age or older, a significant relationship has been found between birth order and handedness in monozygotic twins, there being an excess of left-handed among first-born twins (P less than 0.01). No such relation has been found in dizygotic twins.

Birth Order↗
PubMed1975

Mid-phalangeal hair, hand clasping and handedness among Khatris and Baniyas of Patiala, India.

Mid-phalangeal hair, hand clasping and handedness have been examined in 425 adult subjects from two endogamous groups of Patiala, Hindu Khatris (230) and Baniyas (195). In a majority of subjects (53.73% in males and 46.35% in females) mid-phalangeal hair appears to be completely absent. The highest frequency of this trait is found in the combination III-IV and, when considering individual digits, on IV (around 50%). As for hand clasping, R-type appears to be more frequent in Khatris and L-type in Baniyas. Right handedness appears to be by large more frequent in both groups and sexes.

Female↗
PubMed1982

Speech dominance, handedness and electro-convulsions.

This paper discusses methods for assessing speech dominance in cases for unilateral ECT. The use of formal laterality tests has been strongly advocated in the literature, but is seldom adopted in clinical practice. Assessment of handwriting type (left/right, inverted/non-inverted) has been put forward as an alternative, but is not valid. Consideration of handedness alone is the most common practice, but is of little value. From current evidence on the relation of handedness to speech dominance, the paper evaluates the likely outcomes of always administering right-sided ECT, and of giving formal tests to left-handers only.

Dominance, Cerebral↗
PubMed1998

P300 and handedness: on the possible contribution of corpus callosal size to ERPs.

The P300 event-related potential (ERP) was elicited in left- and right-handed young adult male and female participants (n = 20/group) with both auditory and visual stimulus discrimination tasks that varied systematically in difficulty. P300 amplitude was larger across all task conditions for left- than for right-handed participants at anterior and central electrode sites. P300 latency was shorter across all task conditions for left- than for right-handers. Task difficulty did not affect the ERP handedness differences. Male and female subjects demonstrated comparable ERP handedness effects, although smaller P300 components were obtained for males than for females. When considered in the context of corpus callosal size differences for left-versus right-handed and male versus female participants, the findings suggest that the P300 reflects callosal size and interhemispheric transmission efficacy.

Acoustic Stimulation↗
PubMed1975

Frequency of left-handedness among the Andhra Pradesh people.

The percentages of left-handed people among the males and females of Andhra Pradesh tribals in India were found to be 15.49 and 7.79, and in Hindus 6.9 and 4.65. The difference between the sexes among tribals is significant. The tribal people studied were Koya Doras, Sugalis (or Lambadis), and Konda Reddis. It is suggested that similar quantitative studies of left-handedness should be made in other tribal and aboriginal populations before they are culturally comditioned to right-handedness.

Ethnicity↗
PubMed2003

Self-assembly of spherical colloids into helical chains with well-controlled handedness.

Physical constraint and capillary force have been combined to provide a generic approach to assemble achiral building blocks such as monodisperse spherical colloids into helical mesostructures. The key component of this process is an array of V-shaped grooves anisotropically etched in the surface of a Si(100) wafer. The structural arrangement among the spherical colloids is determined by the ratio between the width of the V-grooves and the diameter of the colloids. Double-layered structures with a helical morphology will be formed when this ratio falls between 2.70 and 2.85. The exact handedness of these helical structures could be controlled by varying the relative orientation of capillary force with respect to the longitudinal axis of the spirals. The processing of an achiral material into helical mesostructures having well-controlled handedness should allow us to explore new properties that this material otherwise does not exhibit. The self-assembly process may also provide valuable insights to improve our understanding on the mechanism(s) by which pure enantiomers with a particular sense of rotation evolved in nature.

Colloids↗
PubMed2007

The role of domain-specific practice, handedness, and starting age in chess.

The respective roles of the environment and innate talent have been a recurrent question for research into expertise. The authors investigated markers of talent, environment, and critical period for the acquisition of expert performance in chess. Argentinian chess players (N = 104), ranging from weak amateurs to grandmasters, completed a questionnaire measuring variables including individual and group practice, starting age, and handedness. The study reaffirms the importance of practice for reaching high levels of performance, but it also indicates a large variability: The slower player needed 8 times as much practice to reach master level than the faster player. Additional results show a correlation between skill and starting age and indicate that players are more likely to be mixed-handed than individuals in the general population; however, there was no correlation between handedness and skill within the sample of chess players. Together, these results suggest that practice is a necessary but not sufficient condition for the acquisition of expertise, that some additional factors may differentiate chessplayers and nonchessplayers, and that starting age of practice is important.

Achievement↗
PubMed1991

Left-handedness: a marker for decreased survival fitness.

Life span studies have shown that the population percentage of left-handers diminishes steadily, so that they are drastically underrepresented in the oldest age groups. Data are reviewed that indicate that this population trend is due to the reduced longevity of left-handers. Some of the elevated risk for sinistrals is apparently due to environmental factors that elevate their accident susceptibility. Further evidence suggests that left-handedness may be a marker for birth stress related neuropathy, developmental delays and irregularities, and deficiencies in the immune system due to the intrauterine hormonal environment. Some statistical and physiological factors that may cause left-handedness to be selectively associated with earlier mortality are also presented.

Functional Laterality↗
PubMed1997

Handedness and speech: a critical reappraisal of the role of genetic and environmental factors in the cerebral lateralization of function.

Functional predominance of the left cerebral hemisphere with regard to both handedness and speech has usually been assumed to be due to some underlying neural specialization that is predetermined and inborn. However, data from left-handed individuals and animal experiments, together with a consideration of the effects of natural selection on brain and behaviour during hominid evolution, are incompatible with such an explanation. A critical reexamination of the relevant nonhuman and human evidence suggests that although the development of a cerebral lateralization for speech and handedness is dependent on both genetic and environmental factors, the specific role of inborn and postnatal influences is very different. This has significant implications for a fundamental revision of current theory and research orientation.

Animals↗
PubMed1997

The genetics and evolution of handedness.

At some point in hominid evolution, a mutation may have produced a "dextral" (D) allele, strongly biasing handedness in favor of the right hand and control of speech toward the left cerebral hemisphere. An alternative (chance [C]) allele is presumed directionally neutral, although there are probably other genes that influence asymmetries and that may create a weak bias toward right-handedness (and other asymmetries). Simulations show that the D allele could have spread quite quickly through a population, given even a minuscule advantage of CD heterozygotes over CC and DD homozygotes in terms of reproductive fitness. This heterozygotic advantage would also explain the apparent stability in the relative proportions of left-handers and right-handers. This putative, uniquely human allele may have emerged with the evolution of Homo sapiens in Africa some 150,000 to 200,000 years ago.

Adaptation, Biological↗
PubMed2005

Is handedness recognition automatic? A study using a Simon-like paradigm.

The authors used a modified Simon task (J. R. Simon, 1969) to assess the automatic recognition of handedness. Participants responded to the color of a circle in the center of the photograph of a right or a left hand, displayed in the center of the computer screen. A regular Simon effect was found for back views, whereas a reverse Simon effect was found for palm views. This pattern of results was found when the forearm was present (Experiment 2), when 1 finger at a time was rendered invisible (Experiment 3), and when the hands were connected to a body image (Experiment 4). When the hands were cut at the wrist, no effect emerged (Experiment 1). These findings suggest an automatic encoding of the relative position of the hand in relation to the body (imaginary or real) rather than the automatic encoding of handedness.

Automatism↗
PubMed2003

Opposite turning behavior in right-handers and non-right-handers suggests a link between handedness and cerebral dopamine asymmetries.

The strong right hand preference in humans remains a riddle; no lateralized behavior other than fine finger dexterity relates to it. The relation between handedness and language dominance may be far weaker than currently judged; after all, both right-handers and non-right-handers utilize the left brain for speech. There is, however, a lateralized motor preference in animals, turning behavior, that is strongly associated with hemispheric dopamine (DA) asymmetries. Turning consistently occurs towards the side with less DA. The authors tested 69 right-handers and 24 non-right-handers with a device recording spontaneous turning behavior for 20 hr within 3 days. Findings indicate that right-handers preferred left-sided turning and non-right-handers preferred right-sided turning. This result suggests a link between handedness and DA asymmetries.

Adult↗
PubMed2005

Primary motor cortex asymmetry is correlated with handedness in capuchin monkeys (Cebus apella).

Humans exhibit a population-wide tendency toward right-handedness, and structural asymmetries of the primary motor cortex are associated with hand preference. Reported are similar asymmetries correlated with hand preference in a New World monkey (Cebus apella) that does not display population-level handedness. Asymmetry of central sulcus depth is significantly different between left-handed and right-handed individuals as determined by a coordinated bimanual task. Left-handed individuals have a deeper central sulcus in the contralateral hemisphere; right-handed individuals have a more symmetrical central sulcus depth. Cerebral hemispheric specialization for hand preference is not uniquely human and may be more common among primates in general.

Animals↗
PubMed2004

Intelligence, memory, and handedness in pedophilia.

A sample of 473 male patients with pedophilia (assessed by the patients' sexual history and penile response in the laboratory to standardized, erotic stimuli) or other problematic sexual interests or behaviors received brief neuropsychological assessments. Neuropsychological measures included a short form of the Wechsler Adult Intelligence Scale--Revised (D. Wechsler, 1981), the Hopkins Verbal Learning Test--Revised (R. H. B. Benedict, D. Schretlen. L. Groninger. & J. Brandt, 1998), the Brief Visuospatial Memory Test--Revised (R. H. B. Benedict, 1997), and the Edinburgh Handedness Inventory (S. M. Williams, 1986). Pedophilia showed significant negative correlations with IQ and immediate and delayed recall memory. Pedophilia was also related to non-right-handedness even after covarying age and IQ. These results suggest that pedophilia is linked to early neurodevelopmental perturbations.

Adult↗
PubMed1995

Age and handedness: patterns of change in the population and sex differences become visible with increased statistical power.

In a sample of 12,030 subjects, ranging in age from 8 to 99 years, significant decreases in both mixed and consistent left-handedness were found as age increased. There were also significant sex differences, with males more likely to be left- or mixed-handed. These age and sex differences were reported as non-significant in Porac's (1993) smaller sample of 654. Methodological issues associated with asserting the null hypothesis in handedness studies when statistical power is low are also discussed.

Adolescent↗
PubMed1991

Occupation and handedness: an examination of architects and mail survey biases.

Handedness among architects was determined by mail survey. Contrary to previous reports, no evidence was found of an excess of left-handers among a sample of 236 fully qualified male architects and 78 male architectural students. A second study examined whether the use of mail surveys systematically biases the returns of handedness questionnaires. For this, questionnaires were sent to 1,017 university students. No evidence was found for a bias amongst those who did and did not reply to the initial questionnaire. These results strengthen the findings of the first study.

Architecture↗
PubMed1991

Evidence from reversal of handedness in C. elegans embryos for early cell interactions determining cell fates.

Many animals with overall bilateral symmetry also exhibit some left-right asymmetries with generally invariant handedness. Therefore, the left-right embryonic axis must have a consistent polarity, whose origins and subsequent effects on development are not understood. Caenorhabditis elegans exhibits such left-right asymmetries at all developmental stages. The embryonic cell lineage is asymmetric as well: although the animal is generally bilaterally symmetric, many of its contralaterally analogous cells arise from different lineages on the two sides of the embryo. I accomplished reversal of embryonic handedness by micromanipulation at the 6-cell stage, which resulted in mirror-image but otherwise normal development into healthy, fertile animals with all the usual left-right asymmetries reversed. This result demonstrates that in the 6-cell embryo the pair of anterior (AB) blastomeres on the right is equivalent to the pair on the left, and that the extensive differences in fates between lineally homologous derivatives of these cells on the two sides of the animal must be dictated by cell interactions, most of which are likely to occur early in embryogenesis.

Animals↗