Cerebral organization of motor programming and verbal processing as a function of degree of hand preference and familial sinistrality

Characteristics of the bimanual deficit using grip strength

Grip strength was used to evaluate bimanual functioning and the bimanual deficit as a measure of the relationship between the hands and the hemispheres. Participants were 174 right-handed individuals. Experiment 1 measured maximal, unimanual, and bimanual grips. There were two bimanual, simultaneous grip conditions: (1) symmetrical (hands perform the same grip) and (2) asymmetrical (different grips for each hand). Decrements were equivalent for preferred and nonpreferred hands and were similar for males and females. Experiment 2 consisted of three variations of the bimanual, asymmetrical grip condition used in Experiment 1. Emphasis was imposed on a single hand via a performance criterion and feedback. Results indicated that emphasis imposed on either hand produced a strength increment compared to that hand's baseline, but did not affect the concurrently performing hand. Results suggest that the bimanual coordination is governed at a non-lateralised or inter-hemispheric level for both males and females.

Manual asymmetry in a complex coincidence-anticipation task: handedness and gender effects

This study investigated the effects of handedness and gender on manual asymmetry in the performance of a complex coincidence-anticipation task. Left-handed (N=63) and right-handed (N=93) undergraduate students (78 males, 78 females) were required to press six buttons sequentially in conjunction with visual stimulation provided by a coincidence-anticipation apparatus. Participants were further separated into subgroups based on the degree of hand preference. Timing accuracy (AE, CE, VE) and timing response (IT, MT, AT) were analysed. Results showed that, concerning accuracy, (i) strong left-handers were more accurate than the other groups; (ii) performance with the preferred hand was superior to that of the non-preferred hand; and (iii) males outperformed females. Concerning timing response, (i) the preferred hand was faster than the non-preferred hand for movement time and (ii) males were faster in initiating the movement than females. These findings indicate that coincidence-anticipation competence appears to be influenced by hand preference, performing hand, and gender. In addition, findings are discussed in the framework of the hemispheric functional lateralisation for the planning and organisation of movement execution.

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.

Intentional and attentional dynamics of speech-hand coordination

Interest is rapidly growing in the hypothesis that natural language emerged from a more primitive set of linguistic acts based primarily on manual activity and hand gestures. Increasingly, researchers are investigating how hemispheric asymmetries are related to attentional and manual asymmetries (i.e., handedness). Both speech perception and production have origins in the dynamical generative movements of the vocal tract known as articulatory gestures. Thus, the notion of a "gesture" can be extended to both hand movements and speech articulation. The generative actions of the hands and vocal tract can therefore provide a basis for the (direct) perception of linguistic acts. Such gestures are best described using the methods of dynamical systems analysis since both perception and production can be described using the same commensurate language. Experiments were conducted using a phase transition paradigm to examine the coordination of speech-hand gestures in both left- and right-handed individuals. Results address coordination (in-phase vs. anti-phase), hand (left vs. right), lateralization (left vs. right hemisphere), focus of attention (speech vs. tapping), and how dynamical constraints provide a foundation for human communicative acts. Predictions from the asymmetric HKB equation confirm the attentional basis of functional asymmetry. Of significance is a new understanding of the role of perceived synchrony (p-centres) during intentional cases of gestural coordination.

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.