The distribution of hand preference in normal men and women

Testosterone and somatosensory evoked potentials from right and left posterior tibial nerves in right-handed young adults

The relationship between serum testosterone level and somatosensory evoked potentials (SEP) from right and left posterior tibial nerves (PTN) was studied in right-handed young adults. Hand preference was assessed by the Edinburgh Handedness Inventory. The amplitudes of P39 and N49 components of the SEPs from the left and right hemispheres of men and only from the left hemisphere of women were found to be negatively linearly and significantly correlated with serum testosterone. There was no significant correlation between P58 and N76 components and serum testosterone in these subjects. The correlations were found to be more prominent for the left hemisphere than the right hemisphere. The data were also analyzed considering eye and foot preferences. It was concluded that testosterone could be associated with the development of the somatosensory system during adolescence.

Testosterone and hand performance in right-handed young adults

The relationship between serum testosterone level and hand performance was studied in right-handed young adults without familial sinistrality. Hand performance was measured by a dot-filling task, which was found to be associated with serum testosterone depending upon sex. In women, the right- and left-hand performance was found to be negatively linearly related to testosterone; there was no significant correlation between the right- minus left-hand performance and testosterone. In men, right- and left-hand performance were found to be directly and inversely related to testosterone, respectively. This pattern exhibited some variations depending on eye and foot preferences. The difference in performance between hands was found to be positively linearly related to serum testosterone levels in men.

Relationship of testosterone and nonverbal intelligence to hand preference and hand skill in right-handed young adults

The relationship between serum testosterone level and nonverbal intelligence was studied in right-handed young adults with regard to handedness. Hand preference was assessed by the Edinburgh Handedness Inventory. Hand skill was measured by a peg moving task. Serum testosterone level was determined using tritium-marked-radioimmunoassay. Visual-spatial performance (nonverbal intelligence) was measured by Cattell's Culture Fair Intelligence Test. In men with consistent right-hand preference (GSs: 80 to 100), IQ was found to be positively linearly related to serum testosterone, which exhibited two regression lines belonging to low and high difference in skill between hands. In females with consistent right-handedness, there was a negative linear correlation between IQ and serum testosterone, which also exhibited two different regression lines according to difference in skill between hands. In males with moderate right-hand preference (GSs 50 to 75), IQ was found to be positively linearly related to serum testosterone, exhibiting two different (same slopes) regression lines according to difference in skill between hands. In females with moderate right-hand preference, IQ first increased and then decreased with serum testosterone, exhibiting a quadratic relationship. These results suggested that serum testosterone in young adults may be associated with visual-spatial performance depending upon sex, hand preference, and hand skill.

Testosterone and nonverbal intelligence in right-handed men and women

The relationship between serum testosterone level and nonverbal intelligence was studied in right-handed young adults. Hand preference was assessed by the Edinburgh Handedness Inventory. Serum testosterone level was determined using tritium-marked-radioimmunoassay. Only in men, nonverbal intelligence (Cattell's Culture Fair Intelligence Test) was found to be significantly and directly related to serum testosterone levels. It was concluded that the serum testosterone in young adults is associated with nonverbal intelligence exhibiting fundamental differences between men and women.

Relation of testosterone and hand preference in right-handed young adults to sex and familial sinistrality

The relationship between serum testosterone level and the degree of hand preference was studied in right-handed young adults. Hand preference was assessed by the Edinburgh Handedness Inventory. Serum testosterone level was determined using tritium-marked-radioimmunoassay. There was no significant correlation between these variables in males without FS. In males with FS and in females with and without FS, the serum testosterone levels were found to be negatively linearly correlated with the degree of the right-hand preference. Similar results were obtained with respect to foot and eye preferences. It was concluded that not only prenatal testosterone but adult testosterone also may exert a life long influence on cerebral lateralization; this effect seems to be much more pronounced in the female than male brain, which may exert a female-like pattern under genetic control.

Relation of spatial reasoning ability to hand performance in male and female left-handers to familial sinistrality and writing hand

The relation of mental ability for spatial reasoning to hand performance was studied in male and female left-handers considering familial sinistrality and writing hand. Hand performance was assessed by a dot-filling test; hand preference was assessed by the Edinburgh Handedness Inventory (Geschwind scores). Nonverbal intelligence (spatial reasoning) was measured by the Cattell's Culture Fair Intelligence Test. The relationship between IQ and hand performance was found to be more complicated than expected. This was associated with sex, familial sinistrality, and writing hand, which created different patterns in interactions between motor and cognitive systems. It was concluded that the brain benefits from different strategies by using both hemispheres in a competitive and complementary manner where necessary to achieve a high visual-spatial performance depending upon genetic preprograms.

The left brain determines the degree of left-handedness

The contribution of right- and left-hand skills to left-handedness was studied in 42 left-handed male subjects. Hand preference was assessed by the Edinburgh Handedness Inventory. Hand skill was assessed by a peg-moving task; 10 trials were given to each hand. Peg-moving times decreased linearly with each trial (visuomotor learning). Both hands exhibited equal learning capacities. The learning curves were the same for the left-hands of left-handers with and without familial sinistrality (FS). The right-hand of left-handers with FS was found to be slower than that without FS. The right- and left-hand skills and their learning curves were about the same in left-handers with right-hand writing, exhibiting no difference from the left-hand skill and learning curve of left-handers with left-hand writing. Right-hand skill decreased linearly as left-hand preference increased from -40 to -100; left-hand skill was not related to hand preference. Right-minus left (R-L) time for peg moving increased linearly with hand preference from -40 to -100. R-L time for peg moving linearly decreased as the right-hand skill increased; the left-hand skill was not associated with R-L time for peg moving. It was concluded that the right hand (left brain) determines left-handedness; the neural structures only on the left side exhibit pronounced plastic changes to genetic and environmental influences in left-handers.

Relation of hand skill to spatial reasoning in male and female left-handers with left- and right-hand writing

The relation of mental ability for spatial reasoning (Cattell's Culture Fair Intelligence Test) to hand skill assessed by peg-moving task was studied in normal left-handers. Nonlinear, quadratic relationships were established between these two parameters exhibiting different characteristics according to sex and writing hand. It was concluded that the contributions of the right and left cerebral hemispheres to the cognitive-motor output of the brain depend on sex and writing hand as well as the degree of left-handedness in left-handers.

Relation of hand performance and preference in male and female left-handers to familial sinistrality and writing hand

The relations of hand performance to the degree of left-hand preference, and left- minus right-hand performance were studied in left-handed male and female subjects considering familial sinistrality and writing hand. Hand performance was assessed by a dot-filling test; hand preference was assessed by the Edinburgh Handedness Inventory. It was established that there were fundamental differences in relationships between performance and preference measures to sex, familial sinistrality, and writing hand, which also created different patterns in the relationships between hand performance and the difference in performance between hands.

There is a close relationship between hand skill and the excitability of motor neurons innervating the postural soleus muscle in left-handed subjects

The claim that there is not a consistent inhibition of the H-reflex from the dominant leg was examined and rejected. It was re-established that there is an inverse relationship between hand skill and the excitability of motoneurons innervating the postural soleus muscle in left-handed subjects. In left-handers with significantly better left-hand skill, the height of the H-reflex recovery curve was significantly higher on the right leg (nondominant) than the left leg (dominant). There was a positive linear correlation between the asymmetries of hand skill greater than zero (better left-hand skill) and the H-reflex recovery curves from the right and left legs greater than zero (right dominance in reflex excitability). In left-handers with no significant difference between the right- and left-hand skills, there was no significant difference between the mean recovery curves from the right and left legs for the interstimulus intervals from 40 to 100 ms; the height of the left recovery curve was found to be significantly higher than the height of the right recovery curve for the interstimulus intervals from 150 to 1000 ms. It was concluded that there is close relationship between hand skill and motoneuronal excitability from right and left soleus muscle with regard to support and operative functions of legs in left-handers.

Paw preference in cats: distribution and sex differences

Paw preference assessed by a food-reaching test was studied in male and female cats. Of the total sample (N = 66), 34 (51.5%) were right-preferent, 24 (36.4%) left-preferent, and 8 (12.1%) ambilateral. In the total sample, there was evidence for an overall paw preference, general paw preference, right-, and left-paw preference. The distribution of the right- minus left-paw reaches was neither normal, nor U or J shaped. Of the males (N = 24), 10 (41.7%) were right-pawed, 12 (50.5%) left-pawed, and 2 (8.3%) ambilateral. In males, there was evidence for an overall, general, and right-, left-paw preference relative to no preference. The right- minus left-paw reaches fitted to guassian data with two prominent peaks due to the right- and left-preferents. In females (N = 42), 22 (52.4%) were right-preferent, 14 (33.3%) left-preferent, and 6 (14.3%) ambilateral. There was an overall, general, and right-preference but not a left-preference relative to no preference. The distribution of the right- minus left-paw reaches was neither normal nor U or J shaped. The female right-preferents showed a right-bias compared to males. The left-preferent males were more left-preferent than the right-preferent males are right preferent. The mean right- minus left- paw reaches for the female right-preferents were significantly higher than those for the male right-preferents. There was no significant difference between the right- minus left-paw reaches of the male and female left-preferents. The paw preferences exhibited consistency over time; no learning tendencies were established during testing periods for at least 10 days. Considering the mean right-paw reaches for each successive day (N = 10), the mean right-paw uses in the right-preferents was higher in females than males. The mean left-paw uses in left-preferents was about the same for males and females. In males, the mean left-paw uses for the left-pawed males were higher than the right-paw reaches for the male right-preferents. In females, there was no difference between the right paw reaches of the right-preferents and the left-paw reaches of the left-preferents. It was concluded that there is a right-bias in paw preference of cats, which is caused by the female right-preferents under the influence of a biological factor.(ABSTRACT TRUNCATED AT 400 WORDS)

Cerebral somatosensory potentials evoked by posterior tibial nerve stimulation: lateralization and relation to handedness in left-handed normal subjects

Somatosensory potentials evoked by stimulation of the right and left posterior tibial nerves were studied in left-handed normal subjects. Hand preference was assessed by the Edinburgh Handedness Inventory; a laterality score (Geschwind score) was calculated for each subject. Hand skill was assessed by the peg moving task. The mean amplitude of the N1 wave from the right cerebral cortex was found to be significantly larger than that from the left cerebral cortex. In the subjects without familial sinistrality, there was no statistically significant difference between the evoked potentials from the right and left sides. In the subjects with familial sinistrality, the mean amplitude of the N1 wave from the right cerebral cortex was found to be significantly larger than that from the left cerebral cortex. There was an inverse relationship between the lateralization quotient (LQ) for the N1 wave and left-hand preference. The amplitudes of the P1, N1, and P2 waves from the right cerebral cortex were positively linearly correlated with left-hand preference. There was an inverse relationship between LQ for the P1 and N1 waves and the right-hand skill. The left-hand skill was not correlated with LQ for the evoked potential. The LQs for the P1 and N1 waves were negatively linearly correlated with the difference between the right and left hand skills (right minus left peg moving times). The amplitudes of the P1 and N1 waves from the left cerebral cortex were found to be inversely related to the right hand skill. There was no relationship between the evoked potential amplitudes from the right cerebral cortex and left hand skill in the total sample. It was concluded that the stronger sensory feedback for the somatomotor foot area within the right cerebral cortex would contribute to left-footedness in left-handers; the asymmetric organization of the somatosensory potentials evoked by stimulation of the right and left PTNs correlates with hand preference and skill, but in an unexpected manner.

The H-reflex recovery curve from the wrist flexors: lateralization of motoneuronal excitability in relation to handedness in normal subjects

Spinal motor asymmetry was studied in relation to handedness. Hand preference was assessed by Oldfield's Questionnaire and Geschwind scores. hand skill was evaluated by a peg moving task. The motoneuronal excitability was assessed by the size and recovery curve of the H-reflex elicited by stimulation of the right and left median nerves. H-reflex was recorded by cup electrodes placed over the wrist flexors. The mean reflex latencies from the right and left sides were 23.4 and 23.2 ms, respectively. The mean amplitude of the maximum H reflex was significantly higher on the right side than the left side in right-handers without familial sinistrality (FS). There were no significant side differences in the amplitudes of H-reflexes of the right-handers with FS. A genetic factor was suggested to involve this left shift of spinal motor lateralization in right-handers with FS. The recovery curve studies showed that the motoneuronal excitability was higher on the right than the left in right-handers without FS. There was no excitability difference between the right and left sides of the right-handers with FS. In left-handers, the motoneuronal excitability was significantly higher on the left than the right side. Voluntary flexions of the wrist increased the H-reflex especially on the right side of the right-handers. There was no relationship between this corticospinal facilitation and baseline EMG activity. The H-reflex amplitude was found to be inversely correlated with hand skill in right-handers. It was concluded that motoneuronal excitability is associated with handedness and also depends on FS. It was suggested that small reflexes are especially suitable in fine motor control of rapid aimed-movements, as the well-established relation between the size of motor units and fine motor control.

The Hoffmann reflex from the flexor pollicis longus of the thumb in left-handed subjects: spinal motor asymmetry and supraspinal facilitation to Cattell's intelligence test

The spinal motor asymmetry was studied in left-handers. Hand preference was assessed by Geschwind scores (GS), and hand skill by peg moving task, the reflex responses were recorded from the long flexor muscle of the thumb. The H-reflex could be elicited by averaging during cortico-spinal facilitation (voluntary isometric force). The Cattell's Culture Fair Intelligence Test was used to assess the individual differences in mental abilities. H-reflexes were found to be significantly larger on the left than the right side. The amplitude of H-reflex increased linearly with force applied to transducer by the thumb. This facilitation was more pronounced for the left than the right reflexes. Removal of the visual visual input caused facilitation in H-reflex (supraspinal disinhibition). Post-activation potentiation was also observed in H-reflex. There was a positive linear correlation between the degree of left-hand preference (-GSs) and left-hand skill. The correlation for the right-hand skill was not significant. There was a linear correlation between the degree of left-hand preference and the right minus left hand skill. There was an inverse correlation between left-hand skill and H-reflex from left. The correlation for the right side did not reach the 5% significance level. The force-reflex relation did not show any significant change to IQ for the right H-reflex. The left H-reflexes were significantly larger in subjects with high IQ than those with low IQ. The regression line and its slope for the force-reflex relation on the left was found to be higher in subjects with high IQ than those with low IQs. There was a positive linear relationship between IQ and H reflex from left. The correlation for the right side was not as pronounced as that for the left side. The left minus right H reflex was also positive linearly correlated with IQ. These results provide further evidence for the psycho-motor hypothesis (Tan. 1988b) as well as the spinal motor asymmetry to handedness. It was suggested that lateralization of cognitive and motor functions would be essential to create subjects with high psychomotor capacity.

Right and left hand skill in left-handers: distribution, learning, and relation to nonverbal intelligence

The relation of hand skill to nonverbal intelligence (spatial reasoning) tested by Cattle's Culture Fair Intelligence Test was studied in left-handed subjects. Hand skill was assessed by the peg moving test, which revealed that some of the left-handers (Geschwind scores and self-reports) were ambidexters. The distribution for right hand skill fitted to Gaussian data better than that for left hand skill. The R-L difference between the hands in peg moving times could also be described by normal distributions in the total sample, ambidexters, and left-handers. The right and left hands of ambidexters were as fast as the left-handers. In left-handers, the right hand was significantly slower than the left hand. In males, right-hand skill fitted to Gaussian data better than left-hand skill. In males and females, right and left-hand skill fitted to Gaussian data. Left-hand skill fitted to Gaussian data better in females than males. The difference between right- and left-hand peg-moving times was found to be larger in females than males. There was no significant difference between the right- and left-hand peg moving times of the male and female left-handers. The mean peg moving times for the right and left hands linearly decreased at each successive trial (N = 10). This motor learning was found to be better in left-handers with high IQs than those with low IQs. The right hand of left-handers with high IQs was faster than that with low IQs. The motor learning of the left hand was not different in left-handers with high and low IQs. The regression line for ambidexters exhibited less learning than that for left-handers. It was suggested that right hand skill is associated with nonverbal intelligence in left-handers, indicating the importance of left hemispheric processing in this kind of cognitive performance.