The relation of hand preference to hand performance in left-handers: importance of the left brain

Evaluating the Symmetry in Plantar Pressure Distribution under the Toes during Standing in a Postural Pedobarographic Examination

Pedobarography is a safe, non-invasive diagnostic method that enables estimation of plantar pressure distribution. This article aims to describe the symmetry between right and left toes in the Polish adult population using data obtained during postural pedobarographic examinations. Eighty-two patients, both sexes, with a mean age of 42.12 (range 19–70), without significant pathologies, participated in the study. Plantar pressure was evaluated using a PEL38 pressure plate. The study applies the elements of Cavanagh’s classification to identify the foot sole regions: Hallux, Second Toe and Lateral Toe areas and the entire foot surface. The parameters measured included maximal and average pressures, total support area for each foot, and contact area of the foot with the ground at individual moments of standing. The results showed significantly greater loading under the right Hallux in women. As regards men, higher values in the whole foot pressure distribution were noted on the left side. Plantar pressure distribution does not increase along with the global factors such as age and body mass. The findings suggest that the asymmetry in the morphological structure of the foot does not determine the asymmetry in the plantar pressure distribution. None of the feet studied had full symmetry on the entire surface.

Unimanual and Bimanual Simultaneous Fingertapping in Schoolchildren: Developmental Aspects and Hand Preference-related Asymmetries

Computerised analysis of finger tapping was performed in 233 normal 5- to 12-year-old children whose hand preference was assessed with six demonstration actions. Performance with both hands became more rapid with age when tapping unimanually or simultaneously in phase with two hands as quickly as possible. There were no differences between the sexes. Performance with both hands also acquired more tapping regularity with age during unimanual tapping, whereas only the left hand did so during bimanual tapping. There was no age effect on the dexterity (speed) difference between unimanually tapping hands, nor on the relative time lag and the degree of synchrony between the hands in bimanual tapping. The degree of synchrony, however, becomes more stable in older children. The more righthanded children are, the faster the right hand is in unimanual tapping, and the more the right hand is ahead of the left hand during bimanual tapping. However, there is a right shift for both of these variables which makes them poor predictors of hand preference. These results suggest that there is a strong bias towards the right hand in complete righthanders as well as--to a lesser extent--in all others, which might be connected to the leading role of the left hemisphere for the performance aspects of hand motor function under study.

Somatosensory lateralization in the newborn brain

Since the onset and early postnatal development of hemispheric lateralization in the human brain are unknown, we studied cortical activation induced by passive extension and flexion of the hand in neonates using functional magnetic resonance imaging (fMRI). In contrast to that seen in older age groups, somatosensory areas in the pre- and postcentral gyri of the neonate showed no significant hemispheric lateralization at term. Instead, our findings from independent left- and right-hand experiments suggest the presence of an emerging trend of contralateral lateralization of the somatosensory system at around term.