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PubMed1994

Physiological motor asymmetry in human handedness: evidence from transcranial magnetic stimulation.

We hypothesized that human handedness might be associated with measurable differences in the excitability of the motor system. We compared the thresholds for electromyographic activation of the left and right abductor pollicis brevis (APB) and biceps muscles in 30 left-handers and 30 right-handers, by varying the direction of a brief monophasic pulse in a circular electromagnetic coil centered over the vertex of the scalp. In right-handers, we found that the threshold for activation of muscles in the right arm was lower than the threshold for activation of corresponding muscles in the left arm. In left-handers, the reverse was true. Threshold asymmetry was influenced significantly by the consistency with which each subject used the writing hand to perform other motor tasks, and was not significant between non-consistent left-handers and right-handers. Our results indicate that human handedness, and in particular, consistency of hand preference, are associated with lateralized differences in the excitability of motor system projections activated by transcranial magnetic stimulation. Our findings might reflect physiological differences in corticospinal tract function or cortical motor representation.

Adult↗
PubMed1993

The influence of stimulus intensity, contralateral masking and handedness on the temporal N1 and the T complex components of the auditory N1 wave.

Components of the auditory N1 wave were recorded to confirm previous findings of contralateral dominance of the negative component (Tb) of the T complex and to examine the differential sensitivity of N1 components to stimulus intensity, contralateral masking and handedness. EEG was recorded from Cz, T3, T4, T5, T6, and at points midway between C3 and T3 and C4 and T4 using a non-cephalic (S-V) reference. Stimuli of 70 and 90 dB SL were presented monaurally with and without contralateral white noise masking. The N100 component generally occurred at all sites and at temporal sites tended to be larger ipsilateral to stimulation and occurred earlier at ipsilateral compared to contralateral sites. Tb was seen at temporal sites and proved to be larger and earlier contralaterally. The positive component (Ta) of the T complex tended to be larger ipsilaterally although its latencies, like Tb, were earlier contralaterally. Although ERP differences associated with handedness were observed they were unrelated to ipsilateral/contralateral auditory pathway patterns. Results are discussed in terms of the functional independence of negativities recorded at temporal sites and the differential utility of these negativities in the examination of auditory pathway function.

Acoustic Stimulation↗
PubMed1996

The effects of handedness and type of movement on the contralateral preponderance of mu-rhythm desynchronisation.

Event-related desynchronisation (ERD) of mu-rhythm was studied in 12 right-handed and 11 left-handed subjects during brisk and slow self-paced index finger movements of dominant and nondominant hand. Electroencephalogram (EEG) was recorded from the sensorimotor hand area of both hemispheres. The contralateral preponderance of mu-rhythm ERD in the pre-movement period showed the following changes: (i) the contrasts between left- and right-finger movements were larger and earlier in the dominant than nondominant hemisphere in both handedness groups; (ii) right-handed subjects showed larger lateralisation of mu-rhythm ERD prior to right-finger as compared to left-finger movements, whereas about equal contralateral preponderance for both sides was found in the left-handed; (iii) the lateralisation of mu-rhythm ERD was lower prior to brisk as compared to slow movements, especially in the left-handed subjects. The results demonstrate that hand dominance, handedness and type of movement influence the proportion of pre-movement mu-rhythm desynchronisation in the left and right peri-rolandic area.

Adult↗
PubMed1983

The development of handedness and dichotic ear listening asymmetries in relation to school achievement: a longitudinal study.

To assess the development of dichotic ear asymmetries and handedness, 208 male school children were evaluated in kindergarten and at Grades 2 and 5 (ages 66, 92, and 130 months of age, respectively) with a dichotic listening task and a hand preference test. The Wide Range Achievement Test (WRAT) also was administered at each of the three grade levels. There was significant variability in handedness scores over time only for those subjects whose scores at initial testing, that is, in kindergarten, identified them as non-right-handers. Both right and left handers had a significant increase in dichotic listening scores over time; however, only right handers had a significant right ear advantage at each evaluation. Regression analyses showed that combined hand preference scores and ear recall scores at each probe when combined accounted for almost 44% of the variance in WRAT achievement scores at Grade 5. Ear asymmetry scores, however, were not predictive of school achievement.

Achievement↗
PubMed1987

Left-handedness: its association with allergic disease.

It has been postulated that anomalous cerebral dominance is associated with disorders of the immune system and increased incidence of autoimmune diseases has been reported in left-handed individuals. In this study, 313 patients attending an allergy clinic were assessed for left- and right-handedness, using the Edinburgh Handedness Inventory. The results were compared to those in 350 age- and sex-matched control individuals. It was found that significantly more (P less than 0.02) left-handers than right-handers attended the clinic. Among atopic patients in general, patients with IgE-mediated symptoms, patients with urticaria and patients with eczema, there was a highly significant increase in left-handers (P less than 0.005). The results are discussed in terms of dominance.

Asthma↗
PubMed1989

Effects of cultural background and education on handedness.

A 5-item handedness questionnaire was given to 317 subjects in four different groups: (1) 51 Tucano (Amazonian jungle) adolescents (36 male, 15 female); (2) 66 Spanish-speaking adolescents (43 male, 23 female) with similar age and educational background to the Tucano group; (3) 100 urban subjects (50 male, 50 female) with a low educational level; and (4) 100 urban subjects (50 male, 50 female) with a high level of education. Hand preference scores were not affected by sex or educational level. The incidence of left-handedness was lower in the Tucano group than in the other groups, despite the fact that the Tucano culture is a highly permissive one. The two rural groups showed less extreme hand preferences than the urban groups, and the Tucano in particular were less likely to indicate extreme hand preferences on any of the items. These results indicate significant effects of culture and environment on declared hand preference, and may be pertinent to recent discussions of cerebral organization in illiterates.

Adolescent↗
PubMed1989

Ambiguous-handedness: incidence in a non-clinical sample.

Using a handedness demonstration preference test under simple and complex task conditions, incidence rates for right, left, and mixed hand preferences were identified in a non-clinical sample. A relatively low incidence rate of ambiguous-handedness was also demonstrated, supporting earlier hypotheses that this subtype is rare among normals.

Adult↗
PubMed1989

Sex, handedness and side of nose modulate human odor perception.

Multidimensional scaling was used to analyze odor similarity judgments obtained by monorhinic (single nostril) stimulation from normal subjects (N = 52), equally partitioned by sex and handedness. Neither sex nor handedness nor side of nose appeared to alter the position of stimuli on a two-dimensional map of odor similarity. However, women produced significantly more consistent maps than men. This result was not due to differential utilization of axes in the multidimensional perceptual space, nor to differences in verbal labeling. Left versus right nostril asymmetries were significantly greater in dextrals.

Adult↗
PubMed1991

Age and cohort effects in adult handedness.

A systematic increase with age of the strong right-handers/mixed right-handers ratio, in normal adults, was found in Algeria, Greece, Italy, France and Spain. This age effect on adult handedness is not easily explained by variations in the social pressure against left-hand use, differential mortality, or information bias. There was no systematic decrease in the frequency of left-handedness with age. Left-hand writing among left-handers was common in the youngest age group and rare after 40 years of age.

Adolescent↗
PubMed1992

Reading disability, immune disorders and non-right-handedness: twin and family studies of their relations.

Geschwind and colleagues discussed associations among learning disorders, immune disorders and non-right-handedness. In this study, we examined the associations between reading disability (RD) and both immune disorders (ID) and non-right-handedness (NRH) in family and twin samples (total N = 1731 cases) identified through an RD proband. We also conducted co-segregation analyses to ascertain the degree to which NRH, ID and RD were biologically related. There was little evidence for an overall association between RD and NRH. There was not convergent evidence across all four samples for an association between RD and ID, although we did find an association between RD and ID in two of four samples. Nor was there strong support for a subtype where RD and NRH, or RD and ID, co-segregate in families. These data suggest that the associations postulated by Geschwind and colleagues are not robust in RD samples, although we cannot completely rule out the possibility of an RD plus ID subtype.

Abortion, Spontaneous↗
PubMed1995

Cerebellar volume asymmetries are related to handedness: a quantitative MRI study.

Four cerebellar subregions were delineated (left, right; anterior, posterior), and their volumes measured on contiguous 3.1 mm coronal MR images in 15 dextral and 8 nondextral healthy control subjects. (1) Left and right cerebellar hemisphere volume asymmetries interacted with anterior-posterior level (anterior: right > left; posterior: left > right), following a pattern commonly found in the neocortex; (2) A significant handedness effect was found (P < or =0.01) on a composite index of cerebellar asymmetry, such that dextrals showed more asymmetry than nondextrals. These data suggest that the same pattern of asymmetries observed at the neocortical level is also present in the metencephalon. These asymmetries, possibly resulting from multiple developmental growth gradients acting on the metencephalon early in gestation, are associated with handedness differences in adulthood.

Adult↗
PubMed1985

Left-right differences in the Hoffmann reflex recovery curve associated with handedness in normal subjects.

The relation between handedness and the Hoffmann (H) reflex recovery curve was studied in normal subjects. In right handers, the H response recovery curve from the right leg was significantly lower than that from the left leg. The opposite finding was obtained from the left handers. In mixed handers (ambidexters), there was no significant difference between the recovery curves from the right and left legs. It was concluded that there is a close relationship between handedness and the height of the H response recovery curves from the right and left sides.

Female↗
PubMed1994

Dyslexia, handedness and syndromes of psychosis-proneness.

In an earlier study, adult dyslexia was found to be strongly associated with positive schizotypal traits, and particularly with unusual perceptual experiences. However, recent evidence suggests that the structure of psychosis-proneness in normals may involve three or four distinct yet related dimensions. Therefore a further study was conducted, using a wider range of measures, to explore associations between dyslexia and these different syndromes of psychosis-proneness. Relationships with handedness were also investigated. If three syndromes of psychosis-proneness were delineated, broadly corresponding to "Active", "Withdrawn" and "Schneiderian/Unreality" syndromes of schizophrenia, dyslexics showed elevations on both positive syndromes (Active and Unreality), but not on the negative, Withdrawn syndrome. With a four-factor model only one dimension, perceptual/cognitive anomalies, distinguished dyslexics from controls. These findings confirm an association between dyslexia and positive, but not negative, schizotypal traits. Mixed-handedness was strongly associated with dyslexia, and in controls with those measures of psychosis-proneness involving unusual perceptual experiences. This suggests that reduced lateralization may be a feature common to both dyslexia and the Unreality syndrome of schizotypy, which may help to account for the strong relationship between them.

Adolescent↗
PubMed1991

Left handedness is uncommon in breast cancer patients.

Left handedness was found to be significantly less common among patients with breast cancer in southern Sweden (1.5%) than among a female referent population (5%) (P less than 0.0025). The findings lend support to theories suggesting that hormonal factors in early life are of importance both for handedness and for the risk of breast cancer.

Adolescent↗
PubMed1992

How sensitive are handedness prevalence figures to differences in questionnaire classification procedures?

Questionnaire data from 572 subjects show that the proportion of right-handers to nonright-handers varies greatly (from 1:100 to 92:8) as a function of questionnaire length, graded or forced response to items, and cut-off criteria. For this reason, the right-handed/nonright-hander dichotomy is singularly unsuited as a basis for classification when handedness is to be related to some other neuropsychological factor as an independent variable. This is especially the case when very strict cut-off criteria are used to define right-handedness (e.g., only those individuals who prefer the right hand for all activities listed).

Adult↗
PubMed1984

Hemispheric asymmetry of EEG alpha activation: effects of gender and familial handedness.

Twenty-four male and twenty-four female undergraduates took part in an experiment to investigate the effects of gender and familial handedness on hemispheric activation during numeric and visuospatial thinking. Each gender group was divided into twelve subjects with close left handed relatives and twelve subjects without. All subjects were overtly right handed. EEG alpha activity was recorded from left and right occipital and parietal regions with respect to mastoid references while the subjects performed numeric tasks with eyes open and with eyes closed, a face-recognition and a tactile-discrimination (figural-unification) task. EEG alpha power was quantified during these conditions and during relaxed wakefulness with eyes open and eyes closed. Relative activation, (suppression of alpha activity from rest) of left and right parietal regions during numeric and spatial tasks was found to depend upon gender and familial handedness. Males, not females, tended to switch from left hemisphere activation during face recognition. Irrespective of gender and to some extent of task, a tendency towards greater activation of the right hemisphere was associated with the possession of left handers among close relatives.

Adolescent↗
PubMed1995

Spatial ability, handedness, and human sexual orientation.

We investigated the relations among mental rotations and spatial perception abilities, handedness, and sexual orientation in both men and women. The present study included a relatively large sample and attempted to control statistically for important covariates such as general intelligence. Significant sex differences were obtained for mental rotations and spatial perception, but not for handedness. None of these measures was significantly related to sexual orientation within either sex.

Adult↗