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Handedness: differential specializations for control of trajectory and position.

Handedness is often portrayed as a nonfunctional artifact of cerebral asymmetry. Our data, however, indicate that handedness reflects cerebral specialization for specific control processes. Each hemisphere/limb system is specialized for different but complementary functions: the dominant system for controlling limb trajectory dynamics, and the nondominant system for controlling limb position.

Biomechanical Phenomena↗

Mixed handedness and features of schizotypal personality in a nonclinical sample.

Using a nonclinical, noncollege sample, this study set out to confirm and extend previous findings of a relationship between the cognitive-perceptual features of schizotypal personality and mixed handedness using the Schizotypal Personality Questionnaire (SPQ). Based on previous findings of relationships between nondextrality and thought disorder in schizophrenia, it was predicted that the odd speech subscale of the SPQ would have the strongest relationship with mixed handedness. Mixed-handed adults did have significantly higher scores than right-handed and left-handed adults on the cognitive-perceptual factor and its subscale of odd speech. Similar trends were also observed for the cognitive-perceptual subscales of suspiciousness, eccentric behavior, and unusual perceptual experiences. These results support and extend previous findings, and are broadly consistent with the association between thought disorder and nondextrality in schizophrenia.

Adolescent↗

Side and handedness effects on the cingulum from diffusion tensor imaging.

In order to explore the microstructure of bilateral cingulum bundles associated with side and handedness, fractional anisotropy was extracted from diffusion tensor imaging. Distinguished from the conventional region of interest-based method, a fiber-based analysis method called scale-invariant parameterization method was employed to ascertain the anisotropy along the cingulum bundle in 31 normal right-handers and 14 normal left-handers. The statistical results showed a remarkable left-greater-than-right asymmetry pattern of anisotropy in most segments of cingulum bundles except the most posterior segment, for both right-handers and left-handers. Interestingly, higher anisotropy of the right-hander than the left-hander was found in the bilateral cingulum bundles. No significant handedness-by-side interaction was obtained in the present study, however.

Adult↗

Handedness frequency over more than ten thousand years.

Although there are quite important geographical variations in the frequency of left-handers around the world, nothing is known about its temporal evolution. During the upper Palaeolithic (ca. 35,000-10,000 YBP), humans painted 'negative hands' by blowing pigments with a tube onto one hand applied on the rock in caves in Western Europe, by blowing pigments on their own hand through a tube held in the other hand. The frequency of left-handers prevailing during this period could thus be assessed. For comparison, the handedness of French university students has been observed for the same task. No difference was detected between the two proportions of left-handers, separated by more than 10,000 years. Implications for the evolution of the polymorphism of handedness are discussed.

Adult↗

The handedness of the subunit arrangement of the nicotinic acetylcholine receptor from Torpedo californica.

Cross-linking an alpha-neurotoxin with a known three-dimensional structure and with photoactivatable groups in known positions to native membrane-bound acetylcholine receptor reveals its quaternary structure, including the handedness of its circular subunit arrangement. Photolabelling with alpha-neurotoxin carrying the photoactivatable group at position Lys46 is inhibited by the competitive antagonist (+)-tubocurarine in a biphasic manner, indicating that it reacts with both alpha-subunits that were shown to have different affinities for this antagonist [Neubig, R. R. & Cohen, J. B. (1979) Biochemistry 18, 5464-5475]. Lys46 is located on loop III of the neurotoxin. The other information necessary for the elucidation of the handedness was provided by the recent finding that the central loop of the toxin (loop II) is oriented towards the central pore of the receptor, securing the overall orientation of the bound toxin [Machold, J., Utkin, Y. N., Kirsch, D., Kaufmann, R., Tsetlin, V. & Hucho, F. (1995b) Proc. Natl Acad. Sci. USA 92, 7282-7286]. Looking at the receptor from the synaptic side of the postsynaptic membrane, it was concluded that the clockwise subunit arrangement is alpha H-gamma-alpha L-delta-beta (alpha H and alpha L are the alpha-subunits binding (+)-tubocurarine with high and low affinity, respectively). Its mirror image alpha alpha L-gamma-alpha H-beta-delta could thus be excluded.

Animals↗

Immune disorders and handedness in dyslexic boys and their relatives.

Thirty dyslexic and 30 control boys aged 7-11 years were compared for frequency of immune disorders and handedness as well as for family history of immune disorders and learning disabilities (dyslexia and stuttering). They were also compared for neurological status and for history of speech and language difficulties. There were no significant differences between the two groups in the frequency of immune disorders and in handedness. The results showed significantly more dyslexic boys with soft neurological signs and signs of speech and language disorders. The frequency of dyslexia was significantly higher in the relatives of the dyslexic boys. Also significantly more mothers of the dyslexic boys reported difficulties during pregnancy and complications at delivery. The results are discussed in terms of Geschwind's hypothesis and neuromaturational delay as possible determinants of developmental dyslexia.

Autoimmune Diseases↗

Handedness distribution and figure drawing ability in a deaf school population, with severe learning difficulties: a research note.

The handedness distribution of 71 deaf pupils with severe learning difficulties, was found to be similar to that reported by Soper et al. (1987, American Journal of Mental Deficiency, 92, 94-102) in a mentally handicapped sample, who also found a high incidence of ambiguously handed individuals. Soper's theory, however, that the "acquired" left-handed and the ambiguously-handed are more handicapped and so, we might infer, draw more primitive human figures, was not supported. The left, ambiguously-handed and right-handed had the same scores on human figure drawing. Neither was there a difference in handedness or figure drawing between the "acquired", the "genetic" and the "unknown" cause groups; nor between males and females.

Adolescent↗

Is a maturational lag associated with left-handedness? A research note.

One element of Coren and Halpern's controversial theory [Psychological Bulletin, 109, 90-106 (1991)] that left-handedness is associated with shorter lifespans is the hypothesis that sinistrality is accompanied by a developmental lag. Perinatal traumas could interfere with the normal developmental shift to right-sided lateral preferences during childhood, leading to an association between maturational lag and left-handedness. In a test of this hypothesis, we assessed current stature, predicted adult stature and relative stature, an index of physical maturity, for elementary school-aged children in three separate, large-sample studies. No relations between hand preference and the three measures of physical status were found. Repeated failures to confirm the hypothesis with pre-adolescent samples raise serious doubt about the viability of the left-handed developmental lag hypothesis.

Adult↗

Handedness, clumsiness and cognitive ability.

An unselected group of 170 children aged between eight and nine years was given tests of intelligence, reading ability and manual dexterity. A 'target' group of children was selected on the basis of very poor performance with the non-preferred hand. Using an extension of Satz's pathological left-handedness model, it is argued that there should be a higher proportion of left-handers in the target group than in the remainder of the sample: this prediction was confirmed. It was also predicted that the target group should have a higher incidence of neurological disorder, and that left-handers in the target group should have a lower incidence of familial sinistrality than other left-handers. Partial confirmation of these predictions was obtained. The target group was impaired on cognitive tasks. It is argued that skill with the non-preferred hand may be more meaningful than direction of hand preference as a basis for understanding relationships between handedness and ability.

Birth Order↗

Handedness in very-low-birthweight (VLBW) children at 12 years of age: relation to perinatal and outcome variables.

The authors assessed 137 VLBW children and 162 controls for laterality by observation and questionnaire at 12 years of age. A significantly higher proportion of the VLBW children were either left-handed or mixed-handed. A number of motor cognitive and educational outcome variables were measured. Impaired manual dexterity was found to be significantly more common in VLBW non-right-handers. This group was also found to be more at risk of poor near vision. No cognitive or educational outcomes were associated with handedness. The results seem to support the theory that at least in a proportion of VLBW children, non-right-handedness has a pathological basis, but the relationship to perinatal events remains obscure.

Adolescent↗

Handedness in strabismics. Etiological implications.

The incidence of non right handedness was found to be significantly higher in a group of 228 strabismics when compared with a control group of neurologically normal non strabismic subjects. The difference was still present after elimination of strabismics with known neurological or general health problems, or who were born prematurely. The strabismics showed no inter group differences in handedness in relation to the type of retinal correspondence present or the ability to achieve normal or abnormal binocular single vision. Evidence is reviewed for the presence of a developmental defect leading to strabismus, and results of this survey support a previously proposed idea that a developmental defect leads to strabismus, the type of which reflects the severity of the defect (although external factors may also be an influence).

Adolescent↗

Handedness, anxiety and sex differences.

Anxiety scores of 35 male and 35 female students (28 right-handers, 23 left-handers and 19 mixed-handers) were assessed in relation to the handedness classification of each individual. Females were found to show higher anxiety scores than were males; but in contradiction to previous findings, left-handers and mixed-handers were not found to be more anxious than right-handers. Extremes of handedness, however, were closely related to anxiety scores, with the strongly right-handed and the strongly left-handed both showing higher anxiety scores than those whose hand preferences were less extreme.

Anxiety↗

Anxiety and the measurement of handedness.

University students completed Annett's (1970) Handedness Inventory (n = 254) and the Trait Scale of the Spielberger Anxiety Questionnaire (n = 247). No relationship was found between anxiety and the hand preference classes distinguished by Annett (1970). Discrepancies between these findings and others reported in the literature are attributed to methodological factors concerning the measurement of handedness.

Anxiety↗

Handedness in a Chinese population: biological, social, and pathological factors.

A questionnaire survey of 4143 Chinese was conducted. Social pressure for right-handed writing and eating was effective on these two target skills but showed little indirect influence on hand use in other activities. Neither primiparous birth nor birth to older mothers affected handedness. Twinning, however, seemed to be associated with both decreased right-handedness and lower intelligence.

Birth Order↗

Helix handedness of Leptospira interrogans as determined by scanning electron microscopy.

Representative serovars and strains of the seven genetic groups of Leptospira interrogans, and two previously studied serovars, were all found to form exclusively right-handed helices as determined by scanning electron microscopy. No change in handedness occurred in cells grown in a minimal medium (Tween-80 albumin) compared to cells grown in a rich medium (rabbit serum). The right-handedness of the organisms was related to the evolution, cell wall structure, and the mechanism of motility of L. interrogans.

Culture Media↗

Handedness of the herpes simplex virus capsid and procapsid.

The capsid of herpes simplex virus has an icosahedral surface lattice with a nonskew triangulation number, T=16. Nevertheless, the proteins arrayed on this lattice necessarily have an intrinsic handedness. We have determined the handedness of both the herpes simplex virus type 1 capsid and its precursor procapsid by a cryoelectron microscopic tilting method.

Capsid↗

Handedness and the side on which pharyngeal pouches occur.

Pharyngeal pouches present far more commonly on the left side of the neck than the right. Sixty one patients with a history of pharyngeal pouch were questioned about their handedness and about whether they had had symptoms or signs predominantly on one side of the neck before receiving treatment. There was a highly significant association between handedness and pharyngeal pouches on the opposite side of the neck. It is suggested that this is the reason for the rarity of right sided pouches.

Diverticulum↗

Detection threshold for percutaneous electrical stimuli: asymmetry with respect to handedness.

Sensory strength-duration curves were obtained using percutaneous true square-wave pulses ranging from 0.1 to 20.0 ms produced by an isolated constant current stimulator. In 119 healthy volunteers sensory thresholds were measured bilaterally by stimulating the distal phalange of the little finger. In order to examine the relationship of sensory threshold and handedness the latter was assessed by means of the Edinburgh Inventory. An asymmetry of sensory threshold was found for all the subjects and this was more pronounced with shorter stimuli. Of right-handers tested 73.5% had a lower threshold on the left side while 70.8% of left-handers had a lower threshold on the right side. Although threshold asymmetry is associated with handedness this is not necessarily due to cerebral lateralization.

Adolescent↗