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A total of 37 candidates for temporal lobe resection for epilepsy completed the Lateral Dominance Examination, a self-report instrument that measures hand and foot preference. Questionnaire results were compared with speech dominance, which had been determined by Intracarotid Sodium Amytal Procedure. Footedness was as good as handedness as a predictor of language laterality.
The distribution of handedness scores was analysed in 1414 heterosexual, bisexual, and homosexual men and women. Hand preference was assessed by a questionnaire that distinguishes consistently right-handed from partially or completely left-handed individuals, and sexual orientation was measured by the Kinsey scales. As expected from population-based studies, heterosexual men were, on average, more left-handed than heterosexual women. By contrast, gay men were more right-handed than lesbians or heterosexual men, and lesbians were more left-handed than gay men or heterosexual women. This crossover interaction suggests that a common variable influences sex, sexual orientation, and hand preference.
A group of left-handers, approaching the piano for the first time, showed better performance in playing a reversed keyboard (where the pitch decreased from left to right) than a normal keyboard. By testing a separate group of "experienced" left-handers, it was also found that this observed preference that naive left-handers had for the reversed keyboard can disappear with a few years of practice on a normal keyboard. The initial preference for the reversed keyboard shown by left-handers appeared to be specific for this handedness group, as groups of right-handers, regardless of their level of experience with the piano, performed better with the regular keyboard. Finally, based on these results it was hypothesised that left-handers would encounter considerable frustration in learning the "right-handed" piano. However, an informal demographic study of piano students enrolling at a school of music did not reveal a substantially low prevalence of left-handed pianists.
The effects of the variables of hemispheric side of lesion, age at injury and severity of cerebral damage on language performance and hand dominance were investigated in groups of hemiparetic children. Severity of cerebral damage was defined by the degree of structural abnormality shown on computed tomography (CT) scans. Tests of auditory verbal comprehension and object naming were used as indicators of productive and receptive language skills. The responses to a series of questions on a handedness inventory provided a rated measure of hand dominance. The results indicated that language deficits characterize the performance of all patient groups with left cerebral injuries. Impairments are more profound, however, in the case of left hemisphere injuries acquired after the age of 5 years. In addition, prenatal and early postnatal left cerebral lesions consistently result in strong sinistrality. It is concluded that the crucial variable underlying the demonstration of language deficits and left hand dominance is not severity of lesion but age at injury and hemispheric side of lesion.
Experimental data and theoretical work on the inheritance of handedness and cerebral dominance are reviewed. A two-gene, four-allele model, one locus pertaining to left or right hemispheric dominance and the other to contralateral or ipsilateral hand control relative to the dominant hemisphere, is constructed. It is in excellent agreement with all quantitative information regarding this problem. Refinements designed to explain relevant qualitative facts are proposed and discussed.
Calculated circular dichroism spectra are presented for double-stranded polynucleotides of regular sequences in A-RNA, A-DNA, B-DNA, and Z-DNA conformations. Quantum mechanical matrix method calculations were carried out in the near and vacuum ultraviolet regions. In the near UV, the calculated spectra agreed qualitatively with the measured spectra. However in the far and vacuum UV, the calculated CD compared nearly quantitatively with the experimental spectra. The calculations show that the sign of the CD in the vacuum UV, in contrast to that in the near UV, can be correlated with the handedness of the helix.
Polymorphic forms of the DNA duplex with long stretches of structural monotony are known. Several alternating purine-pyrimidine sequences have been shown to adopt left-handed Z-conformation. We report a DNA sequence d(CGCGCGATCGAT)n exhibiting alternating right-handed B and left-handed Z helical conformation after every half a turn. Further, this unusual conformation with change in handedness after every six base pairs was induced at physiological superhelical density.
The etiology of left lateral preference is not well understood, but some studies have suggested that it can be caused by complications at birth. The authors used data from the Child Health and Development Study, a large prospective study of pregnancy and child development conducted 1959-1966 in the San Francisco Bay Area of California, to examine the association between specific birth stressors and hand and foot preference. The study population consisted of 6,968 5-year-olds with no severe congenital abnormalities, and the authors controlled for potential demographic confounders and familial left-handedness. Infants who required resuscitation after delivery or who were twins or triplets were about twice as likely to demonstrate left hand preference at age 5 years (odds ratio (OR) = 1.8, 95% confidence interval (CI) 1.3-2.5, and OR = 2.2, 95% CI 1.2-4.0, respectively). Left-footedness was also significantly associated with the same stressors. No other individual stresses were significantly associated with left-lateral preference, and a composite measure indicated only a weak association. Although males, blacks, and those with left-handed siblings are more likely to show left lateral preference, these variables do not confound the association between birth stress and left lateral preference. These results indicate that specific types of birth stress are strongly associated with left hand and foot preference; however, much of the left laterality in non-clinical populations remains unexplained.
Subjects viewing a rotating screwdriver presented in a motion picture were asked whether it was screwing or unscrewing. A difference emerged in the performance of right- and left-handers. In right-handers, stimulus orientations particularly awkward for a right-hand grip determined higher response times, compared with visually equivalent but more comfortable orientations. When they were also requested to imagine their right hand grasping the screwdriver, similar results were obtained. By imagining the left hand, response times increased and the differences between awkward and comfortable orientations disappeared. In contrast, consistent with their manual dominance, left-handers response times were similar to those obtained when imagining the left but distinct from those obtained when imagining the right hand. We conclude that handedness may guide the interpretation of visual events involving manipulable objects.
This investigation analyzed retrospective normative data from paired-pulse transcranial magnetic stimulation (PP TMS) studies to assess the effects of hemispheric laterality, gender, and handedness on cortical excitability. There were no significant differences between left and right hemisphere responses in either men or women. Likewise, there was no significant difference in findings between men and women, considering each hemisphere separately. There were no significant differences between right-handed individuals and nonright-handed individuals for left or right hemispheric responses in either men or women or for both genders combined. Nevertheless, large intersubject variance and past evidence of cortical excitability modulation by other factors, such as menstrual cycle phase and reproductive hormonal changes in women, suggest a need for further investigations into other potential factors that may contribute to the large variance among healthy individuals.
Twelve right-handed volunteers were asked to judge the laterality of a hand stimulus by pressing a button with one of their toes. Judgements were based on two-dimensional drawings of the back or palm of a right or left hand at various orientations. Suprathreshold single-pulse transcranial magnetic stimulation (TMS) was given to the left primary motor hand area (M1-HAND) at 0, 200, 400, 600, 800 or 1000 ms after stimulus onset to probe the functional involvement of the dominant left M1 at various stages of handedness recognition. We found that mean reaction times and error rates increased with angle of rotation depending on the actual biomechanical constraints of the hand but suprathreshold TMS had no influence on task performance regardless of the timing of TMS. However, the excitability of the corticomotor output from the left M1-HAND was modulated during the reaction. Judging left hand drawings was associated with an attenuation of motor-evoked potentials 300-100 ms before the response, whereas judging right hand drawings facilitated the motor-evoked potentials only immediately before the response. These effects were the same for pictures of backs and palms and were independent of the angle of rotation. The failure of TMS to affect task performance suggests that there is no time window during which the M1-HAND makes a critical contribution to mental rotation of the hand. The modulation of motor-evoked potentials according to the laterality of the stimulus indicates a secondary effect of the task on corticomotor excitability that is not directly related to mental rotation itself.
The hand preferences of Open University (OU) students and their relatives, including children, are described. As in earlier series, estimates of heritability are higher for mothers than fathers. There is no evidence of smaller heritability for paternal than maternal grandparents. The distribution of left-handedness in families is examined in the light of predictions of the right shift theory and on the assumption that the shift depends on a single gene. Good agreement is found between the observed and expected numbers of R x R, L x R and L x L families. Predictions are successful for both strict and generous criteria of sinistrality. Generation differences are found between OU students and their parents and between the students and their children. These are discussed from the viewpoint of a possible heterozygote advantage in intelligence. The higher proportion of sinistral children born to sinistral mothers than fathers can be partly accounted for by supposing that the right shift is more effective in females than males.
A 25-item handedness performance test was administered twice, at a one-month interval, to 85 elementary school children (60 right handers and 25 left handers in two different age groups). The laterality quotient distribution for right handers was more skewed and significantly different in central tendency and shape than the left handers' distribution. Mean point-biserial item-test correlation was 0.85. The test-retest correlation coefficient for the whole group was 0.79.
The authors report the serial neuropsychological evaluations of a patient with acquired left-handedness who had a massive brain tumor that infiltrated the entire temporal and posterior parietal lobes of the left hemisphere. Although the patient had pre-operative impairment of non-verbal memory, follow-up assessment 31 and 66 months after the tumor was resected revealed cognitive functions to be in the high-average to superior range. This case demonstrates the sparing of neuropsychological functions that can be seen with a slowly evolving lesion. The authors suggest that such functional sparing may be due to transfer of function rather than to the residual function of tumor-infiltrated neuronal tissue. Possible mediators of functional preservation include slow lesion growth, the patient's youth at disease onset and the large size of the lesion.
While alpha rhythm asymmetry among normals is thoroughly documented, the significance of this finding in patients is not well known. The occurrences of alpha amplitude asymmetry in 82 clinical referrals of neuropsychiatric patients was studied in this research. Two separate means of quantifying the alpha asymmetry were used: The first by visual inspection; and the second by measurement in a standard manner. A handedness questionaire was administered and indicated that 77 of the sample were right- and five were left-handed patients. By measurement, the mean overall differences in the alpha amplitude between the hemisphere was small (4 per cent) and non-significant. Seventeen patients showed a difference of 15 per cent or greater, and in two the difference reached 33 per cent. It was concluded that alpha asymmetry must be interpreted with care because it was found that there was an association between left-temporal abnormalities and ipsilateral alpha enhancement, and the greater degrees of asymmetry were found in normal EEGs.
Ten healthy subjects aged 20-25 including five right-handed and five left-handed according to the Dellatolas test participated in this functional magnetic resonance imaging (fMRI) study. A 3 Tesla whole-body MR scanner allowed echo planar imaging (EPI)-64 x 64 pixels, repetition time (TR) = 6 s, field of view (FOV) = 20 x 20 cm2--associated to acute anatomical localization of activated foci (256 x 256 pixels). Subjects were bilaterally stimulated with NaCl 85 mM, aspartame 2 mM, quinine hydrochloride 1 mM, glycyrrhizic acid 0.5 mM, guanosine monophosphate 1 mM and D-threonine 250 mM alternating with water. Stimuli and rinse were continuously pushed as bolus of 50 microliters every 3 s to the subject's mouth through microsyringes. We detected brain activated areas by correlation of the MR signal to an on-line perception profile recorded for each experiment and each subject with the finger-span method. We found most activations in the insula and the perisylvian region in agreement with previous electrophysiological studies on monkeys and clinical reports in humans. The superior part of the insula was bilaterally activated, in accordance with a whole-mouth stimulation. A striking lateralization related to handedness was found in a lower part of the insula. This projection in the dominant hemisphere, located in the same coronal plane as the upper insular activation, is the first evidence of a functional lateralization of brain processing involved in taste perception.
State and trait anxiety were found to be unrelated to the handedness categories distinguished by Annett (1970) in a sample of volunteers (N = 385). Furthermore, mean scores for 99 male subjects did not differ significantly from those of 293 females. The mean anxiety levels in this study were much more representative of the general population than those reported in a previous similar study by Beaton & Moseley (1984). A suggestion that subjects classified as mixed-handed might show a tendency to avoid extreme responses was not supported.
1. Motoneurone synchronization as a means of investigating synaptic connectivity was studied in the extensor carpi radialis muscles of the preferred and non-preferred arms of healthy right- and left-handed human subjects. The activities of pairs of motor units recorded during voluntary isometric contractions were analysed by cross-correlation to detect any synchronous motor unit firing in the form of central peaks in the cross-correlation histograms. 2. The synchronization peaks were compared first in the case of 273 motor unit pairs tested in the preferred and non-preferred arms of two left-handed subjects and two right-handed subjects. The percentage of synchronized motor unit pairs was found to be significantly higher in the preferred arm with synchronization peaks significantly larger and broader than in the non-preferred arm. The narrow peaks (< 7.5 ms) likely to reflect the activity of common inputs to motoneurones were also found to be significantly larger in the preferred arm of all four subjects. 3. The handedness-related differences in synchronization were definitely confirmed in a total of 275 pairs of motor units tested in the left extensor carpi radialis muscles of fourteen right-handed subjects using their non-preferred arm and six left-handed subjects using their preferred arm. In order to determine whether the differences in synchronization were dependent on the motor unit type, each motor unit was characterized on the basis of its recruitment threshold and on the basis of the contraction time of its twitch extracted from the overall muscle force using the spike-triggered averaging method. Two populations of motor units were distinguished, namely the 'slow' motor units (recruitment thresholds < 0.4 N, contraction times > 40 ms) and the 'fast' motor units (recruitment thresholds > 0.6 N, contraction times < or = 40 ms). 4. In the non-preferred arm, the synchronization peaks were always fairly narrow, whatever the motor unit's biomechanical properties; whereas in the preferred arm, broad peaks were found to be particularly common among the pairs including one or two fast motor units, which also showed the largest rate of synchronization occurrence. 5. The narrow peaks (< 7.5 ms) were found to be consistently larger in the preferred than the non-preferred arm whatever the categories of motor unit pairs. In both arms, however, the amplitude of the narrow peaks tended to increase as the recruitment threshold of the motor unit decreased and as their contraction time increased.(ABSTRACT TRUNCATED AT 400 WORDS)