Zur hemispha¨rendominanz fu¨r sprache und rechnen: Elektrophysiologische korrelate einer linksdominanz bei linksha¨ndern

Slow brain potentials were recorded in left-handers and right-handers during: (i) processing of language and mental arithmetic tasks, without vocalization, and (ii) subsequent writing down of the answers with either the right or left hand. Left-sided laterality of negative potentials was taken as evidence of hemispheric dominance. It appeared during the processing of words and numbers in 26 of the 30 left-handers and was localized mainly in the left frontal and temporal parietal regions. Similar results were found with the right-handers. This electrophysiological evidence indicates that the left hemisphere is dominant for language and calculation in the vast majority of left-handers. Only when writing with either their left or right hand do left-handers show less left-sided laterality than right-handers.     

Reaction time differences between left- and right-handers during mental rotation of hand pictures

During mental rotation tasks using hand pictures, right-handers make left–right judgements by mentally rotating their own hand to an orientation of the presented hand image. Although strategy difference for the tasks between left- and right-handers has been suggested, the strategy of left-handers has been incompletely understood. In the present study we compared differences in reaction times between 15 left-handed and 16 right-handed normal individuals during a mental rotation task using simple hand pictures. Participants were required to identify pictures of a hand presented in four orientations (upright, counterclockwise rotated, clockwise rotated, and inverted) as either a right or a left hand. Right-handers recognised a right hand faster than a left hand, whereas no significant difference was seen for left-handers. Both left- and right-handers recognised a right hand faster than a left hand in counterclockwise-rotated images, and recognised a left hand faster than a right hand in clockwise-rotated images. The findings suggest that the differences in the reaction times between left- and right-handers depend on a laterality balance of hand motor skills. During mental rotation task using simple hand pictures, left-handers may mentally simulate their own hand to match the stimulus image as similar to right-handers.     

Premotor programming and cortical processing in the cerebral cortex. Electrophysiological correlates of hemispheric dominance

Slow brain potentials were averaged from 12-15 EEG records (t = DC or 5 s) before and during voluntary hand movements and writing, spatial vision, language, and calculation tasks without vocalization and with visual fixation. EOG and writing pressure or EMG were recorded simultaneously. Skilled actions caused largest negative potentials in the contralateral sensorimotor hand area. Left-sided lateralization or bilaterally equal surface-negative potential shifts appeared during language and calculation tasks in 90% of the right-handers and in 75% of the left-handers. Right-sided lateralizations occurred during the viewing of perspective Necker figures or random-dot stereograms in the large majority of all subjects.     

Hand preference and performance in 20 pairs of monozygotic twins with discordant handedness

The differences between right (RH) and left (LH) handers reported in the literature on fine motor tasks, has traditionally been interpreted relative to purported functioning of the cerebral hemispheres. However, conclusive evidence for performance differences which are intrinsic to handedness per se is difficult to obtain unless left and right handers are compared who are similar in their genetic and environmental background. The present study therefore, employed a monozygotic (MZ) twin design which minimizes differences in genetic variation between the two groups. Forty female monozygotic twins (20 pairs) were selected on the basis of discordance of writing hand. Their laterality preferences were assessed and they were tested for differences on hand performance tasks (dot filling, finger tapping, and peg moving). The results revealed that on the hand and foot preference inventories, the right-handers were more strongly lateralized than their left-handed sisters, and that the left-handers had greater variation in their laterality scores. There were substantial correlations between preference and performance scores. The analyses not only revealed the obvious strong main effects of writing hand on performance tasks, but interaction effects of handedness on the peg-moving task. The dot filling task differentiated the writing versus non-writing hand considerably better than either of the other two performance tasks. However, no evidence was found to indicate that twins who wrote with their left hands showed poorer performance than their right-handed twin sisters.     

Hand dominance for signing: clues to brain lateralization of language

Virtually all right-handed individuals are left hemisphere dominant for language. Sign languages of the deaf provide an unusual vehicle for exploring the link between handedness and hemispheric specialization for language since in sign language the hands themselves are the language articulators. Performance of the right and left hand was examined in deaf native users of American Sign Language (ASL) for speeded production of one-handed signs and for shadowing of signed discourse. Opposite patterns of asymmetries in hand performance were found in right- and left-handers. However, left-handers were more flexible than right-handers in signing with their non-preferred hand. Furthermore, unusual patterns of hand use for sign were found in a deaf signer with a left hemisphere lesion, possibly indexing increased mediation of the intact hemisphere. Implications for brain organization of language in a visual-gestural mode are discussed.     

Determination of cortical language dominance using functional transcranial Doppler sonography in left-handers.

OBJECTIVE: Verbal analytical functions are primarily related to the left hemisphere in right-handers, but there is yet no agreement about cortical language dominance in left-handers. Also, there are some contradictory reports about sex differences in cortical language lateralization. The aim of this study is to investigate cortical language dominance in left-handers and to explore gender influence on cortical language representation. METHODS: We performed functional transcranial Doppler sonography (previous validated for determination of cerebral language lateralization) during a word generation task, measuring changes in mean cerebral blood flow velocity (BFVmean) in both middle cerebral arteries (MCA) in 150 healthy subjects (75 left-handers and 75 right-handers). In left-handers we observed significant increase BFVmean in right MCA in 58 (77.3%) subjects. Bilateral increase was observed in 11 (14.7%) subjects and increase in left MCA in 6 (8%) subjects. In right-handed group 93.3% subjects showed left cortical dominance, while 6.7% showed bilateral language representation. RESULTS: Current results showed significant (P<0.0001) right hemispheric language dominance in healthy left-handed subjects. CONCLUSIONS: Our results showed significant difference in hemispheric dominance for verbal function between righthanders and lefthanders. Also there is statistically insignificant female gender tendency for bilateral hemispheric language representation in both handedness.     

Eye-dominance, writing hand, and throwing hand

Handedness and eye-dominance are undoubtedly associated statistically, although a previous meta-analysis has found that the precise relationship is difficult to explain, with about 35% of right-handers and 57% of left-handers being left eye dominant. Of particular difficulty to genetic or other models is that the proportions are distributed asymmetrically around 50%. The present study asked whether this complicated pattern of association occurred because, following Peters, it is necessary to divide right-and left-handers into consistent handers (who write and throw with the same hand) and inconsistent handers (who write and throw with opposite hands). In an analysis of 10,635 subjects from questionnaire studies, 28.8% of left-handers and 1.6% of right-handers by writing were inconsistent for throwing. Our results also showed that writing hand and throwing hand both relate independently to eyedness, that throwing hand is somewhat more strongly associated with eyedness, and that the awkward asymmetry around 50% is now removed, 24.2% of consistent right-handers being left eye dominant compared with 72.3% of consistent left-handers, and 55.4% of inconsistent right-handers compared with 47.0% of inconsistent left-handers. We conclude that eyedness is phenotypically secondary to writing and throwing handedness. In our discussion we note that eyedness runs in families, we present new data suggesting that writing hand and throwing hand are co-inherited, and we argue that further data are now required to model properly the associations of writing hand, throwing hand, and eyedness, as well as probably also footedness and language dominance.     

Subject Variables and Cerebral Organization for Language

The present study investigated the usefulness of a variety of subject variables that have been proposed as having predictive value for determining cerebral organization for language. To accomplish this, a total of 373 subjects (117 left-handers and 256 right-handers) were given 240 trials of a consonant-vowel dichotic listening task to assess direction and degree of language lateralization. Each subject was also classified on the basis of eight subject variables (handedness, strength of handedness, familial sinistrality, writing hand posture, sex, sighting dominance, preferred footedness, and overall laterality). The results of the study indicated that left hemisphere language processing is very pervasive and that most of the subject variables examined were not very useful predictors of language lateralization. In addition, surprisingly, footedness and not handedness was the single best predictor of cerebral organization for language.     

Hemispheric dominance for language: quantitative aspects

Data extracted from 29 reported series of cases were analyzed for the purpose of assessing the contribution of each hemisphere to the handling of language in left-handers (including ambidexters), impure right-handers (right-handers with personal or familial traits of left-handedness) and pure right-handers (right-handers without such traits). It was concluded that the representation of language in the two hemispheres varies over a continuous spectrum, from strict left-brainedness, through various degrees of ambilaterality (favoring one or the other hemisphere), to strict right-brainedness. Calculations based on the data led to estimates of (a) the percentage of subjects that will become aphasic following lesions of the left, the right or either hemisphere, and (b) the percentage of subjects that will be able to compensate, partially or completely, with the remaining hemisphere. All numerical results obtained were accounted for by a simple anatomical model based on estimates of (a) the frequency distribution of the subjects with regard to the percentage of a language area occupying each hemisphere, according to handedness, and (b) the percentage of a language area that must be destroyed so that aphasia will appear, and the percentage that must be spared so that partial improvement or total recovery will ensue.     

Cortical DC-potentials as electrophysiological correlates of hemispheric dominance of higher cognitive functions

Cortical activation during cognitive processing was assessed with a new, noninvasive electrophysiological method: Cortical DC-potentials were recorded from frontal, central, temporal and parietal electrode positions on the scalps of 150 normal adult subjects while they performed cognitive tasks involving language, calculation, music and spatial vision. During the 10-s registration period, shifts in DC-potentials were analyzed with reference to a baseline 3-s preperiod. 15-30 trials were averaged. A lateralized preponderance of negativity by more than 3 microV was used as the criterion of hemispheric dominance. Language tasks caused left-sided lateralization in 76% of the right-handers (n = 80), bilaterally equal surface negativity in 15% and right-sided lateralization in 9%. During the same tasks, 22% of the left-handers (n = 45) had right-sided lateralization. Calculation tasks produced left-sided lateralization in 65% of the right-handers and left-handers. Music tasks caused more right-sided (53%) than left-sided (39%) lateralization dependent on musical training. Visuospatial processing yielded a right temporoparietal lateralization in 77%.     

Patterns of hand preference and unintentional injuries among Indian attempted hand switchers and hand non-switchers

This study examines the patterns of hand preference and unintentional injuries of attempted hand switchers and hand non-switchers. Data were collected from 3698 participants in Kharagpur, India, on measures of hand preference, hand switching, and unintentional injuries. The direction of left- or right-handedness was on the basis of hand used for the item “writing on paper” and the degree of handedness was based on the average score of remaining items in the handedness inventory. Results reveal that, among attempted hand-switchers, learned right-handers were not right-sided in hand continuum as the natural right-handers, but left-handers were left-sided as natural left-handers. With increasing age the learned right-handers become less right-sided and natural right-handers become more right-sided. Females (males) are found to be more right-handed than males (females) among learned right-handers (natural right-handers). On the direction of handedness, the learned right-handers have more than twice the risk of unintentional injuries than the natural right- and left-handers. On degree of handedness, the use of inconsistent left and both hands among natural left-handers, the use of inconsistent right and both hands among natural right-handers, and the use of weak right hand among learned right-handers increase their vulnerability to unintentional injuries. Any deviation from the genetic make-up in hand use elevates the risk of unintentional injuries, suggesting that one should not change the biological hand.     

Influence of handedness on peripheral auditory asymmetry

It is well established that in humans many differences between right- and left-handers, anatomical, physiological and functional, exist. Left- and mixed-handedness is associated with greater bihemispheric representation of cognitive functions than in right-handers. Several studies indicate a left–right asymmetry in the function of hearing pathways between cochlea and auditory cortex, and furthermore, that this asymmetry is associated with handedness. Our investigation focuses on the medial olivo-cochlear system, which has been demonstrated to be more effective in the right than left ear in right-handers. The aim of the study was to investigate this auditory efferent system asymmetry according to handedness, gender, eyedness, footedness and the presence of spontaneous otoacoustic emissions. The medial efferent system has been found to be more effective in the right than left ear in right-handers, while functioning symmetrically in left-handers. Furthermore, the olivo-cochlear system, assumed to be involved in basic language processing, shows an asymmetrical pattern of functioning influenced by handedness as well as by hemispheric language representation. Reverse medial efferent system asymmetry was observed in left-handers compared to that in right-handers, on condition that only left-handed males were considered, or that the left-handers were also left-eyed, or that spontaneous otoacoustic emissions were present in the left ear of the left-handers, or when only left-handers without mixed-handers were considered.     

Motor control of the hands: the effect of familial sinistrality.

Left- and right-handed subjects, selected on the basis of degree of hand preference and for the presence or absence of familial sinistrality, responded to monaurally presented tonal stimuli (440 Hz note played on four different instruments) using their right and left hands on separate occasions. It was found that in both the strong left-handers and the inconsistent strong right-handers, motor control of the hands was related to familial sinistrality (FS). Specifically, strong left-handers and inconsistent strong right-handers with FS have a difference in the motor control of the hands in the left hemisphere, with a left hemisphere-left hand advantage. Strong left-handers and inconsistent strong right-handers with no FS have a difference in the motor control of the hands in the right hemisphere, with a right hemisphere-left hand advantage.     

Tachistoscopic recognition of Kana and Hangul words,handedness and shift of laterality difference

Nonsense Kana words as verbal stimuli and Hangul words (Korean orthographic characters) as non-verbal were presented tachistoscopically in the left or right visual field to normal right-handed, non-familial left-handed and familial left-handed Japanese subjects, who have not seen Hangul characters. Right-handers showed a significant right (or left) field superiority for the recognition of verbal (or non-verbal) stimuli. This pattern of differences found in right-handers is, though to a slightly lesser degree, also present in non-familial left-handers, while it is absent in familial left-handers. Initial left field superiority for Hangul word recognition shifted to no laterality difference in left-handers as well as in right-handers during the learning period for Hangul words.     

Asymmetry in corticomotor facilitation revealed in right-handers in the context of haptic discrimination

In this study we asked whether asymmetries related to handedness in right-handers (n=10) and left-handers (n=10) could influence hemispheric motor facilitation when the preferred or less-preferred hand is engaged in haptic sensing. Transcranial magnetic stimulation (TMS) was used to assess corticomotor excitability when young participants performed a precision grip under two conditions, i.e., with or without a haptic sensing component. In the grip condition participants were required to grasp a 5-mm thick plate between thumb and index fingers, whereas in the haptic condition they performed the same action but were also required to make judgements about the plate's thickness, i.e., either thin (5 mm) or thick (10 mm). Analysis of task-related variations in motor evoked potentials (MEP) amplitude recorded in hand muscles revealed a significant task×hand/hemisphere interaction only in the group of right-handers when the left hand/right hemisphere was engaged in haptic sensing as opposed to simply gripping. Collectively, these results are congruent with other TMS reports describing a greater degree of hemispheric asymmetry in right-handers, who are typically more strongly lateralised than left-handers. Our results with regard to a rightward hemispheric asymmetry for MEP facilitation with haptic sensing are also congruent with the predominant role ascribed to the right sensorimotor cortex in the processing of proprioceptive information.     

Handedness, laterality and the size-weight illusion

The goal of this study was to determine how handedness and lifting hand influence the way in which we lift objects and perceive their weights. To this end, we examined the fingertip forces and perceptual judgements of 30 left-handers and 30 right-handers during lifts of specially constructed ‘size-weight illusion’ (SWI) cubes with their left and right hands. All participants completed a series of lifts first with one hand and then the other, so we could additionally examine asymmetries in the retention and transfer of force information between the limbs. Right-handers experienced a larger illusion with their left hand than they did with their right hand, whereas left-handers showed no such asymmetry in their illusions. The perceptual illusion’s independence from the application of fingertip force was highlighted by an unexpected lack of asymmetry in terms of fingertip force scaling. Left- and right-handers showed no dominant hand advantage in this task – they were no more skilled at correcting their fingertip force errors with their preferred hand than they were with their non-preferred hand. In addition, although no asymmetries were observed with regard to the most efficient direction of intermanual transfer, the right-handed individuals transferred force information between the hands more effectively than the left-handers. Overall, these findings indicate that hand dominance does not affect the control of the fingertip forces, suggesting that existing models of cerebral laterality must be re-visited to consider kinetic (i.e., related to forces), as well as kinematic (i.e., related to movement) variables.     

Interhemispheric cooperation of left- and right-handers in mental calculation tasks

Relations between handedness and interhemispheric processing in cognitive tasks were examined. Thirty six right-handers and thirty left-handers (familial and nonfamilial left-handers) were asked to add two numbers which were presented tachistoscopically. Two numbers were displayed either to one visual field, or one to the left and one to the right visual field simultaneously. In Experiment 1, the numbers were displayed in Arabic numerals, and in Experiment 2 one of the numbers was displayed in Kanji and one in Arabic numerals. The results of Experiment 1 showed a bilateral advantage, however no subject group difference was shown in the performance of the three (left unilateral, right unilateral, and bilateral) presentation conditions. Though familial left-handers showed a weaker tendency to different patterns than right and non-familial left-handers, the results of Experiment 2 were largely similar to those of Experiment 1. These findings suggest that interhemispheric processing may not differ between left- and right-handers.     

Asymmetric spatiotemporal patterns of event-related desynchronization preceding voluntary sequential finger movements: a high-resolution EEG study.

OBJECTIVE: To study spatiotemporal patterns of event-related desynchronization (ERD) preceding voluntary sequential finger movements performed with dominant right hand and nondominant left hand. METHODS: Nine subjects performed self-paced movements consisting of three key strokes with either hand. Subjects randomized the laterality and timing of movements. Electroencephalogram (EEG) was recorded from 122 channels. Reference-free EEG power measurements in the beta band were calculated off-line. RESULTS: During motor preparation (-2 to -0.5s with respect to movement onset), contralateral preponderance of event-related desynchronization (ERD) (lateralized power) was only observed during right hand finger movements, whereas ERD during left hand finger movements was bilateral. CONCLUSIONS: For right-handers, activation on the left hemisphere during left hand movements is greater than that on the right hemisphere during right hand movements. SIGNIFICANCE: We provide further evidence for motor dominance of the left hemisphere in early period of motor preparation for complex sequential finger movements.     

Cerebral lateralization of praxis in right- and left-handedness: same pattern, different strength

We aimed to investigate the effect of hand effector and handedness on the cerebral lateralization of pantomiming learned movements. Fourteen right-handed and 14 left-handed volunteers performed unimanual and bimanual tool-use pantomimes with their dominant or nondominant hand during fMRI. A left hemispheric lateralization was observed in the right- and left-handed group regardless of which hand(s) performed the task. Asymmetry was most marked in the dorsolateral prefrontal cortex (DLPFC), premotor cortex (PMC), and superior and inferior parietal lobules (SPL and IPL). Unimanual pantomimes did not reveal any significant differences in asymmetric cerebral activation patterns between left- and right-handers. Bimanual pantomimes showed increased left premotor and posterior parietal activation in left- and right-handers. Lateralization indices (LI) of the 10% most active voxels in DLPFC, PMC, SPL, and IPL were calculated for each individual in a contrast that compared all tool versus all control conditions. Left-handers showed a significantly reduced overall LI compared with right-handers. This was mainly due to diminished asymmetry in the IPL and SPL. We conclude that the recollection and pantomiming of learned gestures recruits a similar left lateralized activation pattern in right and left-handed individuals. Handedness only influences the strength (not the side) of the lateralization, with left-handers showing a reduced degree of asymmetry that is most readily observed over the posterior parietal region. Together with similar findings in language and visual processing, these results point to a lesser hemispheric specialization in left-handers that may be considered in the cost/benefit assessment to explain the disproportionate handedness polymorphism in humans.     

DEVELOPMENT OF MOTOR CO-ORDINATION BY NORMAL LEFT-HANDED CHILDREN

Ninety-six normal left-handed children were tested for motor co-ordination on a series of timed repetitive tasks, alternating left and right hands, feet and fingers. Preferred hand advantage could be demonstrated to the same degree for the left hand of these children as it had been for the preferred right hand in previously studied groups of the same age (Denckla 1973, 1974). The only test (finger to thumb successive opposition) that failed to show a preferred hand advantage in left-handers also had failed to show such an advantage among right-handers. This same test was performed more rapidly by left-handed girls than boys, as it had been by right-handed girls. However, left-foot superiority appeared to be less well established among left-handers than superiority of the right foot among right-handers, and at a later age. Left-handed children were less likely than their right-handed counterparts to choose their preferred hand when trying out a new task. Writing posture, i.e. whether inverted or straight, could not be established unambiguously for the left-handed children up to the age of 10, and often differed for writing and printing.