Do environmental and hereditary factors affect the psychophysiology and left-right shift in left-handers?

The principal objective of this study was to investigate the reality of sinistrality in left-handed subjects. The subjects were assessed by a 20-item questionnaire with two groups taken from Oldfield's and Yetkin questionnaires. The relation of different effects on left-hand preference was studied in men and women considering familial information and writing hand. The degree of hand preference was determined by Geshwind scores (GSs). The GS degrees of hand preferences were divided into weak and strong left-hand ranging from -20% to -100%. After assessing the GSs we asked the subjects to answer 22 questions with different aims, which were especially written for only left-handers. Some of them were based on familial sinistrality and hereditary relation to left-handers. The others concerned hand, foot, eye, shoulder, and ear preferences; the psychology of left-handedness; the knowledge concerned with left-handedness; the success, ability, and interest education and skill, and morphological differences in hand and foot sizes. In the present study, it was found that the subjects have had at least one left-handed person in their family or among their relatives. Some subjects had shifted their left hand preference in favor of their right hands. Nevertheless, the left-handers have been found as a presence with their own peculiarities.

Dynamic cortical activity in the human brain reveals motor equivalence

That animals and humans can accomplish the same goal using different effectors and different goals using the same effectors attests to the remarkable flexibility of the central nervous system. This phenomenon has been termed 'motor equivalence', an example being the writing of a name with a pencil held between the toes or teeth. The idea of motor equivalence has reappeared because single-cell studies in monkeys have shown that parameters of voluntary movement (such as direction) may be specified in the brain, relegating muscle activation to spinal interneuronal systems. Using a novel experimental paradigms and a full-head SQUID (for superconducting quantum interference device) array to record magnetic fields corresponding to ongoing brain activity, we demonstrate: (1), a robust relationship between time-dependent activity in sensorimotor cortex and movement velocity, independent of explicit task requirements; and (2) neural activations that are specific to task demands alone. It appears, therefore, that signatures of motor equivalence in humans may be found in dynamic patterns of cortical activity.