Familial Sinistrality Research Articles

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.

Hormone and hemisphericity hypotheses regarding cognitive sex differences: Possible future explanatory power, but current empirical chaos

Two general hypotheses regarding the possible basis of cognitive sex differences posit sex steroid hormone differences and differences in hemispheric specialization characteristics as responsible. This article reviews (1) a limited segment of the literature regarding sex steroid influences, namely, that dealing with “activating” influences; and (2) some data suggesting that dextral women who are positive for familial sinistrality could be a group who contribute heavily to the mean sex difference in spatial ability. The general conclusion of these reviews is that despite the promise of some future integration of hormone and hemispheric specialization hypotheses and understanding of how they might relate to cognitive sex differences, present data are highly inconsistent.

Dyslexia and corpus callosum morphology.

There is evolving evidence that developmental dyslexia is associated with anomalous cerebral morphology in the bilateral frontal and left temporoparietal regions. This study examined the morphology of the corpus callosum, as possible deviations in other important structures are poorly understood in this behaviorally diagnosed syndrome. Magnetic resonance imaging scans were obtained from children with developmental dyslexia and from matched control children. Morphometric measurements were examined to determine if regional differences existed in the corpus callosum between these two groups of children. Magnetic resonance imaging studies were completed at Athens (Ga) Magnetic Imaging. Sixteen developmental dyslexic children (mean age, 9.7 years) and a matched sample of children who were diagnosed as being normal were examined by using a reliable comprehensive diagnostic process. Using a midsagittal magnetic resonance imaging scan, corpus callosum morphology was evaluated by segmenting the corpus callosum into five regions of interest. Analysis of the corpus callosum revealed that the anterior region of interest (the genu) was significantly smaller in the dyslexic children. Significant correlations existed between reading achievement and the region-of-interest measurements for the genu and splenium. Measured intelligence, chronologic age, and gender were not related to region-of-interest measurements of the corpus callosum. Consistent with previous studies, the dyslexic individuals were characterized by significant psychiatric comorbidity, particularly attention-deficit disorder with and without hyperactivity. Reported familial left-handedness also distinguished the dyslexic children. Subtle neurodevelopmental variation in the morphology of the corpus callosum may be associated with the difficulty that dyslexic children experience in reading and on tasks involving interhemispheric transfer.

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 s 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.

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.

Human growth hormone may differentially influence the grasp reflex in human neonates on the basis of genetically predetermined neural pattern of brain organization in utero.

The relations of the grasp-reflex strengths from right (R) and left (L) hands to human growth hormone (hGH) levels were studied in human neonates within the first day after birth. In right-handed (RH) males without familial sinistrality (-FS), grasp reflex from right and left hands directly correlated with hGH. In RH, -FS females, grasp reflex from right and left hands inversely correlated with hGH. In -FS, LH males, grasp reflex from right and left inversely correlated with hGH (no significant correlations in LH, -FS females). The R-L grasp reflex decreased linearly with hGH, only in RH, -FS males. These results indicated that hGH may affect cerebral development according to genetically predetermined neural patterns in utero.

Finger-Tapping Interference as Produced by Concurrent Verbal and Nonverbal Tasks: An Analysis of Individual Differences in Left-Handers

Verbal cerebral asymmetry was examined in 96 right- and left-handed college students using dual-task methods. The manual task was finger-tapping; verbal tasks were anagram-solution in silent and aloud conditions; nonverbal tasks were solution of Raven′s Progressive Matrices and forms memory. Both handedness groups were sensitive to the task manipulation, i.e., verbal tasks produced a significant change in tapping rate from a no-change rate of zero; nonverbal tasks produced no significant change in tapping rate. Right-handers experienced the expected asymmetric manual performance indicative of left-hemisphere language laterality. Left-handers as a group experienced no asymmetric pattern but rather a percentage decrease in both hands which suggested bilateralization of language functions. Only when examining manual performance patterns within specific left-handed subpopulations (composed of a complete crossing of handwriting posture, familial sinistrality, and sex) did laterality patterns emerge. Specifically, asymmetric manual performance was found only in familial sinistral inverted posture females. Results demonstrate the advantage of controlling for subject characteristics when assessing cerebral laterality in left-handers.

Special talents in Geschwind's and Galaburda's theory of cerebral lateralization: an examination in a female population.

Geschwind and Galaburda (1985) proposed that delayed growth of posterior left hemisphere sites in male dyslexics are associated with markers of anomalous dominance (AD) and special cognitive talents. We found that talent in a female population was related to the strength of nonright-handedness, and was elevated in right-handed individuals with histories of familial left-handedness. Subjects reporting a history of dyslexia tended to be musically talented. While immune disorders were not related to talent for the whole population, they did co-occur with talents in a group of 10 individuals reporting 7 or more AD markers.

Pathological left-handedness. Left-handedness correlatives in adult epileptics.

Factors associated with left-handedness were examined in a large sample of adults who suffered with epileptic seizures (n = 446) in an attempt to delineate the concept of pathological left-handedness. Three main pathological factors were found associated with left-handedness: (i) right-hemiparesis of early onset; (ii) cognitive deficit; (iii) evidence of left-hemisphere disease on clinical examination. Familial sinistrality was also associated with left-handedness, independently of the above-mentioned pathological factors. Results support a clear-cut distinction between normal and pathological left-handedness. This distinction seems presently important for the evaluation of the great number of anomalies proposed to be associated with left-handedness.

Left-handedness and old age: Do left-handers die earlier?

Data are presented on the prevalence of current left-handedness and prior left-handedness (switched) in 2787 subjects from 21 to 101 years of age. In addition, data on sex differences, familial sinistrality, hand posture when writing, and education were recorded. Two hypotheses were tested. The elimination hypothesis states that reduced frequency of left-handers in old age is due to reduced longevity. The modification hypothesis states that differences in the number of left-handers between older and younger persons are due to changing patterns of social norms. The results showed a decreasing prevalence of left-handedness across the age span, with 15.22% in the youngest group (21–30 years), but only 1.67% in subjects older than 80 years. There was however a corresponding increase in the number of subjects who had switched hand for writing, 2.69% in the youngest group to 6.75% in subjects 80 years and above. This supports the modification hypothesis and questions the elimination hypothesis. However, the mean percent score was still lower in subjects above compared to below age 40 after correction for hand switching. Thus, although changes in social norms towards left-handers seem to be the most likely explanation, we have not empirically disproved the elimination hypothesis.

The influence of familial sinistrality on the lateralization of unfamiliar music perception in nonmusicians.

The influence of familial sinistrality on the lateralization of unfamiliar music perception in nonmusicians.

Infant Resuscitation Is Associated with an Increased Risk of Left-handedness

The etiology of left lateral preference is not well understood, but some studies have suggested that it can be caused by complications at birth. The authors used data from the Child Health and Development Study, a large prospective study of pregnancy and child development conducted 1959-1966 in the San Francisco Bay Area of California, to examine the association between specific birth stressors and hand and foot preference. The study population consisted of 6,968 5-year-olds with no severe congenital abnormalities, and the authors controlled for potential demographic confounders and familial left-handedness. Infants who required resuscitation after delivery or who were twins or triplets were about twice as likely to demonstrate left hand preference at age 5 years (odds ratio (OR) = 1.8, 95% confidence interval (CI) 1.3-2.5, and OR = 2.2, 95% CI 1.2-4.0, respectively). Left-footedness was also significantly associated with the same stressors. No other individual stresses were significantly associated with left-lateral preference, and a composite measure indicated only a weak association. Although males, blacks, and those with left-handed siblings are more likely to show left lateral preference, these variables do not confound the association between birth stress and left lateral preference. These results indicate that specific types of birth stress are strongly associated with left hand and foot preference; however, much of the left laterality in non-clinical populations remains unexplained.

Pathological left-handedness revisited: Dichotic listening in children with left vs right congenital hemiplegia

Thirty-one children with right ( n = 18) and left ( n = 13) congenital hemiplegia were compared for incidence of hand- and foot-preference, eye-dominance, and familial sinistrality. In addition, they were tested with dichotic listening for correct reports of consonant-vowel syllables. The two groups of children were closely matched on IQ and sensory functioning. Children with mental retardation, or epileptic seizures were not included. The results showed that 89% of the left hemisphere impaired (LHI) children were left-handed, all of them preferred the left foot, and 72% were left eye-dominant. In the right hemisphere impaired (RHI) group, everyone (100%) preferred the right hand and foot, and 62% were right eye dominant. The dichotic listening results showed a significant right ear advantage (REA) in the RHI-group, and a significant left ear advantage (LEA) in the LHI-group. The results are discussed in the framework of pathological handedness and shifts in hemisphere control of language in children with early brain injury. It is argued that the homogenous samples, except for the site of lesion, provides an interesting possibility to compare cognitive effects of left and right hemisphere impairement in children.

Relation of nonverbal intelligence assessed by Cattell's Culture Fair Intelligence Test to latencies of the somatosensory evoked potentials elicited by stimulation of the posterior tibial nerves in right-handed male and female subjects.

The association of nonverbal intelligence (NVI) with latencies of the somatosensory evoked potentials from the right and left posterior tibial nerves (PTNs) was studied in right-handed male and female subjects without familial sinistrality (FS-). There was a significant negative linear correlation between N49-P39 interpeak latencies from the right and left PTNs in females and a significant positive linear correlation between these parameters in males. There was no significant correlation between P58-N49 interpeak latencies and NVI in females, but a significant negative linear correlation in males. The N76-P58 interpeak latencies were found to be positively linearly related to NVI only in females; there was no correlation between these parameters in males. There was no significant correlation between IQ and side differences in SEP latencies in females. The right minus left P39 latencies from the right and left PTN were found to be negatively linearly related to IQ in males. In females with nearly equal heights, latencies of N49 waves were found to be negatively linearly related to IQ. In males with nearly equal heights, only P39 and P58 waves from the right PTN were found to be negatively linearly related to IQ. These results did not support the hypothesis of speed of information processing by the brain in behavioral intelligence. An asymmetrical organization of the male brain seems to be disadvantageous for nonverbal intelligence; the female brain appeared to be independent of the degree of asymmetrical organization of the brain in this respect.

Right and left hand skill in relation to cerebral lateralization in right-handed male and female subjects: the prominent role of the right brain in right-handedness.

The associations between right and left hand skills to cerebral motor lateralization were studied in right-handed subjects with (FS+) and without (FS-) familial sinistrality. Hand preference was assessed by Oldfield questionnaire and hand skill by the peg moving task. The mean peg moving times (PMTs) and their standard deviations (SDs) were calculated for each hand. There was a significant positive linear correlation between the mean right and left hand PMTs. In males, the mean difference between the left and right PMTs (L-R) showed a significant negative linear correlation with the mean right hand PMTs. There was no significant correlation between these parameters in females. The mean L-R PMTs were found to be positively linearly correlated with the mean left hand PMT in FS- males, FS- and FS+ females (no correlation in FS+ males). The results indicated the contribution of the mean left hand PMTs to L-R hand skill is much higher than that of the mean right hand PMTs. In males, there was no significant correlation between SDs of the mean right and left hand PMTs. In females, SD of the mean right hand PMT was found to be positively linearly related to SD of the left hand PMT. In males, L-R SDs were found to be negatively linearly related to SDs of the mean right hand PMTs and positively linearly related to the SDs of the mean left hand PMTs. In females, only the mean left hand PMT positively linearly correlated with L-R SDs. Here again, the left hand prominently influenced the L-R SDs. In males, SD for the mean right hand PMT showed no relation to right hand PMT. There was, however, a negative linear correlation between SD of the mean right hand PMT and the left hand PMT (no correlations in female). It was concluded that the left hand (right brain) would be of higher significance than the right hand (left brain) in determining the degree of the right-bias in hand skill and its stability in right-handers.

Contributions of the right and left brains to manual asymmetry in hand skill in right-handed normal subjects.

The relation of intermanual difference in hand skill to cerebral lateralization was studied in right-handed male and female subjects. Hand preference was assessed by the Edinburgh Handedness Inventory. Hand skill was measured by the peg moving task. In subjects with familial sinistrality (FS+), the mean right hand peg moving times (PMTs) were found to be significantly and negatively linearly correlated with the mean left minus right (L - R) hand PMTs in females (no correlation in males). Contrarily, there was a direct relationship between the mean L - R hand PMTs and the mean left hand PMTs in FS+ males (no correlation in FS+ females). Similar results were obtained with the FS- subjects. The correlations were modified by eye and foot preferences. The overall results suggested that generally the right brain in males and the left brain in females are of importance in determining the intermanual difference in hand skill; an insufficient right brain (a slower left hand) in males and a sufficient left brain (a faster right hand) in females would create a more asymmetrical organization in skill between hands.

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

The associations among hand preference, hand skill (peg moving time, PMT) and hand performance (dot filling/20 s) were analyzed in left-handed subjects. In the total sample, the degree of left-hand preference linearly decreased from -100 to zero (Geschwind scores, GSs) as the number of dots placed by the right hand increased (direct correlation); the left hand did not show any significant relation to GSs. The right-hand PMT linearly decreased as the GSs decreased (negative linear correlation); the left hand skill did not exhibit any significant correlation with GSs. There was a negative linear correlation between right-hand PMT and dot-filling with right hand; the left-hand PMT was not related to dot-filling with left hand. In males, the right-hand PMT showed a negative linear correlation with GSs; no significant correlation between PMT and GSs was found for the left hand. There was a negative linear correlation between right minus left (R - L) PMT and GSs. Dot-filling with right hand was found to be positively linearly correlated with GSs (no correlation for the left hand). The L - R dot-filling showed a negative linear correlation with GSs. PMT for the right hand exhibited a significant negative linear relation to dot-filling only with right hand. Sex and familial sinistrality caused minor changes in these relationships. It was concluded that the left brain would constitute the main factor determining the degree of left-handedness.

Relationship of serum zinc levels to hand preference, skull length and serum gonadal hormone levels in right-handed young adults.

The association between serum zinc (Zn) level and the degree of hand preference was studied in right-handed young adults. Hand preference was scored by the Waterloo Handedness Questionnaire. Serum Zn level was determined by the flow injection analysis-atomic absorption technique. Zinc was found to be positively linearly and significantly correlated with the degree of right hand preference in the sample of males with familial sinistrality (FS+) and FS- females with right eye and right foot preference. There was a negative linear correlation between these variables in FS+ females. Skull length showed a significant negative linear correlation with zinc in FS+ males and females, but a positive linear correlation in FS- females. In FS- females, there was a significant positive linear correlation between serum gonadal hormone binding globulin (GBG) and serum Zn levels. In FS+ males, there was a significant negative linear correlation between serum GBG and Zn levels, and a significant positive linear correlation between serum free testosterone level and serum Zn level. It was suggested that zinc may influence the degree of the right hand preference by hormonal mechanisms according to genetically established brain organization.

Dependence of intermanual difference in hand skill on right or left cerebral motor control in right-handed male and female subjects.

The relations of the mean differences in right and left hand skills (L-R) to the mean right and left hand skills were studied in right-handed male and female subjects with and without familial sinistrality (FS+, FS-). Hand skill was measured by the peg moving task. In FS+ males, there was a significant negative linear correlation between L-R and right hand peg moving times (PMTs). In FS+ females, there was a significant positive linear correlation between L-R and left hand PMTs. There were no significant correlations between L-R and left hand PMTs in FS+ males, and right hand PMTs in FS+ females. FS- subjects could be described as follows. In males and females with right eye and right foot preference, L-R PMTs were found to be positively linearly correlated with left hand PMTs (no correlation between L-R and right hand PMTs). In subjects with left eye and right foot preference, the correlations were found to be similar to those for FS+ subjects. In subjects with mixed eye and right foot preference, there was a negative linear correlation between L-R and right hand PMTs in females; a positive linear correlation between L-R and left hand PMTs in males. There were no significant correlations between L-R and right hand PMTs in males, and left hand PMTs in females. These results indicated that left brain in FS+ males, and right brain in FS+ females would produce the L-R difference between hands in PMTs.(ABSTRACT TRUNCATED AT 250 WORDS)

Motor stability in visuomotor control of repetitive hand movements and its differential cerebral control in right-handed subjects.

The stability of asymmetric motor control was studied in right-handed subjects. Hand skill was assessed by a peg moving task in ten trials. The mean peg moving time (PMT) and its standard deviation (SD) were calculated for each hand. Standard deviation was taken as an index of the stability of visuomotor control. The mean rate of a repetitive movement (mean PMT) did not always show an association with its stability (SDs). This depended upon familial sinistrality, sex, and cerebral lateralization such as eye and foot preferences of the subjects. The left-right differences in movement stabilities also showed different contributions of the right and left brains of the subjects depending upon these factors. It was suggested that these factors should be taken into consideration in studies concerning the hemispheric control of especially corrective components of skilled movements of hands.