Biomedical subjects

U Tan

Publications and source records attributed to U Tan.

At least 37 records · Page 2Linked to original sources

PubMed1995

Growth hormone limits the brain/body development before birth in relation to sex, grasp-reflex asymmetry and familial sinistrality of human neonates.

Since there is no theological explanation for high growth hormone (GH) concentrations in perinatal blood, GH concentrations from umbilical cord blood were studied in relation to body weight and head circumference (brain weight) in the human neonates. GH exhibited inverse correlations with body weight and head circumference in these subjects, which depended upon sex, familial sinistrality (FS), and grasp-reflex dominance. This implies that GH may adversely influence the brain/body development during perinatal development on the basis of a genetically predetermined brain organization. It was suggested that the lipolytic and anti-insulin GH effects may be responsible for its body-weight reducing effects; the anti-insulin GH actions may be responsible for its brain-weight reducing effects. As a result of these actions, GH may limit the brain/body development, to induce a balanced growth during perinatal period.

Birth Weight↗

PubMed1994

The grasp reflex from the right and left hand in human neonates indicates that the development of both cerebral hemispheres in males, but only the right hemisphere in females, is favoured by testosterone.

The grasp reflex was studied in relation to serum free testosterone levels in human neonates. In the total and -FS (no familial sinistrality) males, the grasp reflex (especially that from the right hand) significantly increased as testosterone increased. In the total and -FS females, there was a significant positive linear correlation between testosterone and the grasp-reflex strength from the left hand, but not from the right hand. In +FS males, there was a significant negative correlation between the grasp-reflex strength from the left hand and testosterone, but not from the right hand; there were no significant correlations in the +FS females. The right minus left (R - L) grasp-reflex strength linearly increased with testosterone in females with normal testosterone levels, but linearly decreased in females with high testosterone levels. The log R - L grasp reflex increased with testosterone in males. It was concluded that testosterone may be beneficial for the development of the left brain in -FS males and the left brain in -FS females, but may have detrimental effects on the right brain in +FS males. The growth-promoting asymmetric effects of testosterone on the brain may depend upon genetic organization of the brain.

Brain↗

PubMed1994

Role of prenatal position in grasp-reflex asymmetry in human neonates.

Grasp-reflex strengths were quantitatively measured from the right and left hands of 70 full-term human neonates. The right-left grasp-reflex linearly correlated with grasp-reflex only of the right hand in neonates with a right-ear-facing-out prenatal position. In neonates with left-ear-facing-out prenatal position, this grasp-reflex linearly increased with the grasp-reflex of the right hand and linearly decreased with the grasp reflex of the left hand. It was suggested that grasp-reflex asymmetry in neonates may, at least partly, depend upon prenatal position, which may also influence the later developing hand preference in humans.

Female↗

PubMed1994

Amount of asymmetry in grasp reflex depends on the grasp reflex of the left hand in human neonates.

Grasp-reflex strengths from right and left hands were measured in 33 human neonates. There was no significant correlation between right minus left grasp-reflex strength and grasp-reflex strength from the right hand. The grasp-reflex strength of the left hand was negatively linearly correlated with the right minus left grasp-reflex strength. It was suggested that the right brain may be the main determinant for the motor asymmetry in hands.

Brain↗

PubMed1994

Relation of serum free-testosterone level to grasp-reflex strength in human neonates with right-ear and left-ear facing out in-utero positions.

The relation of the grasp-reflex strength to serum free-testosterone level was studied in human neonates with right and left ear facing out in utero positions. The grasp-reflex strengths from the right and left hands were found to be inversely correlated with testosterone in neonates with right-ear-out position. In neonates with left-ear-out in utero position, the grasp-reflex strength only from the left hand inversely correlated with testosterone. Left-dominance decreased and right dominance in grasp reflex increased linearly with testosterone only in females with left-ear-out in utero position. These results supported the theory of prenatal origins of cerebral lateralization (Previc, 1991). It was concluded that testosterone may favour the maturation of both hemispheres in neonates with right-ear-out in utero position, and only the right-hemispheric development in subjects with left-ear-out in utero position; testosterone may be a male hormone influencing the cerebral lateralization on the ground of genetically and even environmentally predetermined cerebral organization.

Ear↗

PubMed1994

Correlations between grasp-reflex strengths and serum thyroid-hormone levels depending upon sex and familial sinistrality in human neonates: importance of genetically predetermined cerebral organization.

Relations of grasp-reflex strengths to serum free-thyroid hormone levels were studied in human neonates. In right-dominant (RH) males and females without familial sinistrality (-FS), grasp-reflex strengths from right (R) and left (L) inversely correlated with serum triiodothyronine (T3). In RH, +FS males, grasp-reflex strengths from R and L hands directly correlated with T3 (no correlations in RH, +FS females). There was no significant correlation between grasp reflex and T3 in non-right-handed (NRH), -FS neonates. In NRH +FS neonates, there was a significant negative linear correlation between grasp reflex from left and T3 only in NRH, +FS males. The following correlations were found between grasp reflex and thyroxine (T4): direct relation in RH, +FS males and females; inverse relation in NRH, -FS females only for the right hand; inverse correlations in NRH, +FS females. The R-L grasp reflex directly correlated with T3 in RH, -FS males, and inversely correlated with T3 in RH, -FS females (no significant correlations in others). These results indicated that thyroid hormones may influence cerebral maturation and lateralization differentially according to genetically predetermined cerebral organization. The generalizations of the hormonal effects on, at least, cerebral functioning would be wrong, if the genetically predetermined main features of the brain are neglected.

Brain↗

PubMed1993

Sexual dimorphism in linear measures of the corpus callosum in cats.

The sexual dimorphism in the linear measures of the corpus callosum was studied in adult cats. In absolute measures, males had significantly larger genu, isthmus, and splenium than females; the mean absolute lengths were not significantly different in males and females. There were significant positive linear correlations between callosal measures and brain weight in the male and female cats, (no significant correlation between isthmus width and brain weight in females). The mean callosal measures predicted from brain weights in regression equations were found to be significantly greater in males than in females. This sexual dimorphism in callosal measures of cats showed similarities with rats, but not with humans. It was suggested that this may be due to cognitive differences between animal and human brains as well as brain development under relatively simple environmental factors such as gonadal hormones (testosterone) in animals compared to human brains.

Animals↗

PubMed1993

Sex-dependent relations of grasp-reflex strengths from right and left hands to serum gonadotropin (FSH and LH) levels in human neonates with regard to cerebral lateralization.

The relation of grasp-reflex strength to serum FSH and LH levels were studied in human neonates. The grasp-reflex strengths from the right and left hands were found to be negatively linearly correlated with serum FSH level in males without familial sinistrality (-FS), but there was no significant correlations between these parameters in females. Serum LH levels were not correlated with grasp reflex in -FS neonates. The grasp-reflex strength from the right hand showed a significant negative linear correlation with LH only in +FS males. The right minus left (R-L) grasp-reflex strength decreased linearly with serum LH levels only in +FS males. These results did not support the testosterone hypothesis of cerebral lateralization. It was suggested that FSH and LH may indirectly influence the brain development according to sex and genetically pre-determined cerebral organization.

Female↗

PubMed1993

Sexual dimorphism in body and brain weight and its association with paw preference in cats.

Sexual dimorphism in body and brain weight was studied in cats. Paw preference was assessed by food reaching test. Sexual dimorphism in body weight related to paw preference. Males weighted more than females in total sample and non-right-handed (NRH) cats (no significant difference in right-handed group). NRH males weighted more than right-handed (RH) males (no difference in females). Absolute total-brain weight did not show sexual dimorphism. Relative total-brain weight was sexually dimorphic only in NRH cats (females more than males). RH males weighted more than NRH males (no significant difference in females). Only absolute right-brain weighted more in males than females (total sample). Otherwise, no significant difference was found between absolute right- and left-brain weights of male and female cats. The relative right- and left-brain weighted more in females than males only in NRH cats (no sexual dimorphism in RH cats); more in RH males than NRH males; no difference in RH and NRH females. The overall results indicated that sexual dimorphism in body and brain weight is associated with cerebral lateralization in cats.

Animals↗

PubMed1993

Sensory nerve conduction velocities are higher on the left than the right hand and motor conduction is faster on the right hand than left in right-handed normal subjects.

Lateralization in the sensory and motor nerve conduction velocities was studied in right-handed normal subjects. The nerve conduction velocities (NCVs) were measured in hands. Sensory NCVs were found to be higher on the left hand than the right hand. The motor NCVs did not show a statistically significant difference between the right and left hands. However, the motor conduction velocity measured from median nerve to the action potential from abductor pollicis brevis muscle was found to be significantly higher in the right hand than the left hand. It was concluded that fast conducting neuromuscular junctions on the right hand muscles would contribute to relatively fast right hand in right-handers. Relatively fast conducting sensory nerves in the left hand may contribute to a relatively better perception by the right cerebral hemisphere in right-handers.

Brain↗

PubMed1993

Inverse relationship between the size of pattern reversal visual evoked potentials from the left brain and the degree of left-hand preference in left-handed normal subjects: importance of the left brain.

The relation of the degree of left-hand preference to pattern reversal visual evoked potentials (VEPs) from right and left brain was studied in male left-handers. The degree of the left-hand preference was assessed by the Waterloo Handedness Questionnaire. Visual stimuli consisted of black and white checkerboard patterns generated on a TV screen. VEPs were simultaneously recorded from occipital leads of the right and left hemispheres. The degree of left-hand preference was found to be inversely and significantly related to size of VEPs only from left brain, not from right brain. That is, the conduction time, amplitude, duration, and area of N1-P1 waves linearly decreased as the degree of left-hand preference increased. These results were in accord with the testosterone hypothesis of cerebral lateralization, but not compatible with the right shift theory of handedness. It was concluded that visuomotor control by the left brain would be the main biological correlate of left-hand preference with regard to sensorimotor and cognitive functions.

Adolescent↗

PubMed1993

The end point of the sylvian fissure is higher on the right than the left in cat brain as in human brain.

The height of the end point of the sylvian fissure (SF) was analyzed in the right and left brains of male and female adult cats. A corrected SF asymmetry coefficient (AC) was computed for each brain. An AC larger than zero (AC+) showed a rightward asymmetry, and an AC smaller than zero (AC-) a leftward asymmetry. In the total sample, ACs fit a normal distribution with a mean significantly larger than zero. Of these brains, 75% had ACs larger than zero median; 23.4% had ACs smaller than zero median. Of 11 right-pawed cats, 90.9% had ACs larger than zero. Of 13 left-pawed male cats, there was no significant difference between AC+ and AC- brains. In right-pawed female cats, the right SF was also higher in most animals, but the difference did not reach the 5% significance level. In left-pawed female cats, the number of AC+ brains significantly exceeded that of AC-brains. Thus, the brains of the left-pawed male cats resembled those of the right-pawed female cats; right-pawed male cats resembled left-pawed female cats with regard to asymmetries in SF height. It was concluded that the human brain is not unique in SF asymmetries, which may be linked to manual asymmetry and sex hormones.

Animals↗

PubMed1993

Normal distribution of hand preference and its bimodality.

The distribution of hand preference was studied in human subjects by means of The Waterloo Handedness Questionnaire and Edinburgh Handedness Inventory. The Waterloo Handedness scores (WS) and Geschwind Scores (GS) were estimated. Left-handers (WS < 0; GS < 0) and right-handers (WS > 0; GS > 0) constituted separate groups (dichotomy). The WSs, and to a lesser extent GSs, were distributed normally when only the right-handers were considered. There was a significant positive-linear correlation between WSs and GSs. These results suggested that a detailed questionnaire such as the Waterloo Handedness Questionnaire would be more appropriate than concise questionnaires in assessing hand preference. A normally distributed right-hand preference and a widely dispersed left-hand preference also supports the concept of anomalous dominance for left-handedness.

Adolescent↗

PubMed1993

Association of serum-free-testosterone level with hand preference in right-handed young females.

The relationship between the degree of right-hand preference and serum free-testosterone level was studied in right-handed female subjects, who were 17-19 years old. It was assumed that free testosterone levels in serum of young female subjects would reflect the perinatal testosterone levels. Hand preference was assessed by the Edinburgh Handedness Inventory (Geschwind score, GS) and Waterloo Handedness Questionnaire (Waterloo score, WS). The degree of the right-hand preference linearly and significantly increased as the serum free-testosterone level increased in the moderately right-handed (GS = < 70) subjects. There was only a marginally significant negative linear correlation between these parameters in the strongly right-handed subjects (GS > 70). These results only partly supported the testosterone hypothesis of cerebral lateralization that testosterone would slow the growth of the left cerebral hemisphere, reducing the degree of right hand preference. The results also suggested a trophic effect of testosterone especially on the left cerebral cortex in females. Activational effects of testosterone may also contribute to an increase in the degree of right-hand preference in right-handed young females.

Adolescent↗

PubMed1993

The role of right- and left-brain weights in cerebral lateralization of right- and left-pawed male and female cats.

The contributions of right- and left-brain weights to the ratio of the left- to the right-brain weight (L/R) were studied in cats. Brain weight was expressed as the ratio of brain weight to body weight. The relative right- and left-brains in the right-pawed male cats were found to be heavier and more asymmetric (L/R < 0) than those in the left-pawed male cats. Only in right-pawed males was the mean L/R ratio found to be significantly smaller than zero. The left-pawed males had smaller and more symmetric brains than the right-pawed males. There was no significant difference between L/R ratios in the right-pawed and left-pawed females. The mean L-R brain weight was found to be significantly smaller than zero in the right-pawed male and left-pawed female cats (no significant difference in other samples). The L/R ratio linearly increased as the relative right-brain weight decreased in the right-pawed and left-pawed males; the L/R ratio linearly increased as the right-brain weight and especially the left-brain weight increased in the right-pawed and left-pawed females. These results partly supported the testosterone hypothesis of cerebral lateralization. The results have also suggested that the right brain in males and the left brain in females would be the main factor determining cerebral lateralization in cats.

Animals↗

PubMed1993

Brain weight is not always directly related to body weight in cats: the roles of right and left cerebral hemispheres, paw preference and sex-related differences.

The relationship between weights of the cerebral hemispheres and body weight was studied in cats. The total weight of the right (R) and left (L) cerebral hemispheres was not significantly correlated with body weight in right-pawed (RH) male cats and left-pawed (LH) female cats. There was a significant positive linear correlation between R + L brain weight and body weight in RH female and LH male cats. The right-brain weight was directly correlated with body weight in RH female and LH male cats (no significant correlation between right-brain and body weight in RH males and LH (females). The left-brain weight was found to be directly related to body weight in RH males, RH females, and LH males, but inversely related to body weight in LH females. It was suggested that some hormonal factors influencing body growth may affect the development of the brain growth asymmetrically and differentially.

Animals↗

PubMed1993

Distribution of paw preference in mongrel and tortoise-shell cats and the relation of hemispheric weight to paw preference: sexual dimorphism in paw use and its relation to hemispheric weight.

The distribution of the right minus left (R - L) paw use and its relation to hemispheric weight was studied in tortoise-shell cats. Paw preference was assessed by a food reaching test. All males (N = 9) were left-preferent; females (N = 13) were predominantly right-preferent. There was an inverse relationship between the degree of left-paw preference and the right-brain weight in males (no correlation with left-brain weight). In females, the R - L paw use showed a negative linear correlation with the right- and left-brain weights: the right-pawedness decreased and the left-pawedness increased as the right- and left-brain weights increased. The distributions of the R - L paw use as well as the relationships between brain-weight and pawedness exhibited sexual dimorphism. The results suggest that mainly the genetic and hormonal factors may play an important role in emergence of motor asymmetry in cats. Annett's right shift theory of handedness was also discussed in light of these results.

Animals↗

PubMed1993

Grasp reflex strength from right and left hands is associated with pH stressor from the umbilical arterial blood in human newborns: handedness and sex-related differences.

Grasp reflex and its asymmetry was studied in relation to pH of the umbilical blood in human newborns, to examine whether the degree of acidity in fetal blood (birth stress) is associated with cerebral laterality. Low pH values were considered as an index for birth stress. Grasp-reflex strength was found to be directly related to pH in total sample. There were sex-related differences. Namely, this correlation was true only for female newborns, not for males. Right minus left grasp-reflex strength linearly increased with pH, i.e., low pH values were associated with left-hand dominance, but only in males. The grasp-reflex asymmetry was not related to pH in females. It was concluded that blood pH may be associated with motor asymmetry and motor development in human newborns, but show sex-related differences; female brain seemed to be more sensitive to pH changes than male brain. The results partly supported the Bakan's hypothesis that birth stress may be associated with left-handedness.

Dominance, Cerebral↗