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The hand preference of college students correlated significantly with the writing hand of their biological parents but not that of their stepparents. The results are consistent with a genetic theory of the origin of human handedness.
The amplitiude of evoked responses of occipital cortex in man depends on the visual field in which the stimulus appears. Greater responses occurred repeatedly for two of three subjects, both left-handed. when the stimululs appeared in the left field than in the right. Subsequent tests of 13 right- and 13 left-handed males indicted that the magnitude of the response of the right lobe, relative to that of the left, was greater for left-handed individuals. We conclude that the difference in amplitude between the two lobes is related to handedness.
Cognitive activity resulted in increased flow of blood to the cerebral hemispheres. The increase was greater to the left hemisphere for a verbal task and greater to the right hemisphere for a spatial task. The direction and degree of hemispheric flow asymmetry were influenced by sex and handedness, females having a higher rate of blood flow per unit weight of brain, and females and left-handers having a greater percentage of fast-clearing tissue, presumably gray matter.
Most newborn infants (65 percent) preferred to lie with their heads turned to the right, whereas 15 percent showed a distinct preference for the left. Orientation preference is maintained for at least 2 months and predicts preferential hand use in reaching tasks at both 16 and 22 weeks. Right head-orientation preference in early infancy may contribute to the early development of right-handedness.
The correlation of handedness with deformities, radiographic changes, and function of the hand was studied in a large group of patients with rheumatoid arthritis and a dominant right hand. There was no significant difference in the proportion of patients who had swan neck deformity, boutonnière deformity, uncorrectable ulnar deviation, and flexor tenosynovitis in the dominant and non-dominant hands. There were significantly greater radiological changes in the dominant hand, however, and the middle and index fingers were most severely affected. The severe involvement of these fingers may be related to their greater use in daily activities. There was also more severe functional impairment in the dominant hand.
The idea that visually guided action is independent of visual perception has been supported by neurological, neuropsychological, and behavioral studies. In healthy subjects, evidence for this distinction has come from psychophysical studies of the effects of visual illusions on perceptual judgments and object-directed grasping. This evidence is limited, however, by the fact that virtually all studies have involved right-handed subjects using their dominant hand, which is presumably controlled by the left hemisphere. There is tentative evidence from earlier neurological studies that the left hemisphere may in fact play a special role in the integration of visual and motor information during grasping. We designed two experiments to test this idea. The first experiment involved pictorial illusions, which are known to have robust effects on perceptual judgments but little influence on grasping. Right- and left-handed subjects reached out and grasped objects embedded in two different visual illusions with either their dominant or their nondominant hand. For both right- and left-handed subjects, precision grasping with the left hand, but not with the right, was affected by the illusions. In a follow-up experiment, we examined precision grasping in a more natural setting and showed that left-handed subjects use their nondominant (right) hand significantly more as compared with right-handed subjects. We conclude that visuomotor mechanisms encapsulated in the left hemisphere play a crucial role in the visual control of action and that this hemispheric specialization evolved independently of handedness.
One could hypothesize from previous studies that gorillas, as a group, might show a right-hand preference, making this species an exception among nonhuman primates. A study of 10 captive gorillas observed while reaching for food and tested on unimanual and bimanual tasks does not support this conclusion. Instead, the present study found (a) a symmetrical distribution of subjects with right-hand (n = 3), left-hand (n = 3), and no hand preference (n = 4) when simply reaching for food and (b) a left-hand preference by 7 of 8 gorillas tested on a spatial task requiring precise alignment of two openings. These results stress the importance of considering the kind of task employed in the assessment of lateral preferences. Furthermore, it is suggested that it might be useful to distinguish between the handedness of a gorilla when simply reaching and its manual specialization for novel and complex tasks.
Alcohol in high doses is neurotoxic to the developing brain but it is not yet settled whether small doses give rise to more subtle effects. The aim of the study was to establish whether a moderate intake of alcohol in pregnancy would increase the frequency of left-handedness in the offspring. Such an association could indicate a possible subtle prenatal neurotoxic effect. This was a follow-up study of a group of pregnant women who took part in a community trial in 1984 to 1987. Data on alcohol consumption were reported by consecutively sampled pregnant women in the 36th week of gestation. Hand preference for their offspring was reported by the mothers in a self-administered questionnaire when their children were 5 to 9 years old. Ninety-one percent participated in the follow-up study. The study showed that 9.1% of the children were left-handed, with a higher prevalence among boys (11.8%). Results showed a slightly higher frequency of being left-handed among children exposed to alcohol in fetal life, but the findings were not statistically significant at a 0.05 level.
This article pursues the corollaries of the anatomy of handedness recently discovered. Specifically, it addresses the issues concerning central vision as it relates to the command center and the circuitry of the saccades. It presents data that support the directionality of callosal traffic in motor and sensory realms even further. Evidence is presented that denotes a relationship between the anatomy sustaining movement control and that responsible for the part of the vision handled by the maculae. The evidence shows bypassing of the callosum by fibers serving the central vision. This aspect has ramifications for surgical approach to the third ventricle by callosotomy, relaxing the earlier prohibitions advocated in approaching the third ventricle via splenectomy.
Handedness was assessed in 87 per cent (n = 116) of all known schizophrenics from a discrete geographical area, Nithsdale in Dumfries and Galloway Region. Seventy-three per cent were right-handed, a proportion greater than that found in a normal population. It was especially Feighner positive schizophrenics and non-in-patients who produced the excess of right-handers. Within the Feighner positive group, 68 per cent of mixed or left-handers, but only 29 per cent of right-handers, had tardive dyskinesia.
The relationship between hand preference, age, and developmental functioning was examined in 70 autistic patients. Unilateral or mixed handedness appeared to be stabilized by the age of five years. Patients with established hand lateralization tended to function better in all developmental areas including intelligence, language, and visuospatial abilities. It is a tenable hypothesis that the presence or absence of hand lateralization by age five may be an important predictor of outcome in autism.
This study investigates whether there is any difference in the month of birth between people with schizophrenia and controls in Korea. When 1606 patients with schizophrenia were compared with 4582 age- and sex-matched controls, there was no statistically significant difference in the month of birth, the season of birth of schizophrenic patients was not related to sex, family history or handedness.
OBJECTIVE: To determine the proportion of individuals in a clinic-based setting that present with asymmetric Parkinson disease (PD) and identify predictive factors associated with asymmetric symptoms. METHODS: The authors examined right vs left difference scores on the Unified Parkinson Disease Rating Scale motor subscale in a consecutive clinical series of 1,277 individuals diagnosed with PD. Predictors of asymmetry included sex, symptomatic disease duration, age at onset, initial motor symptom laterality, handedness, and medical history variables (e.g., family history of PD). RESULTS: Nearly half the sample (46%) met criteria for asymmetric disease based on a right vs left difference score of > or =5 points, and 12% of the sample had a difference score of > or =10 (difference score: mean = 4, SD = 3.4). All three cardinal features of PD showed characteristics of asymmetric disease presentation. Multiple regression analyses showed that an increased discrepancy between right- and left-sided symptoms was significantly associated with a shorter disease duration, younger age at symptomatic onset, asymmetric initial symptom onset, hand dominance, and a positive self-reported family history of "other" neurodegenerative disorder. Hand dominance was related to the side of asymmetric disease such that left-handed individuals tended to have more severe disease on the left side of the body. CONCLUSION: Asymmetric presentation of Parkinson disease features was a common occurrence in the clinical cohort. Asymmetry was reliably predicted by several clinical characteristics, although the moderate level of explained variance (i.e., between 16 and 23%) highlighted the need for additional research examining predictive models of asymmetric disease. Recommendations for the classification and measurement of asymmetric disease are discussed.
An excess of left-handers among males has been attributed to early androgen exposure. This theory was supported by our observation that girls with congenital adrenal hyperplasia (CAH) are more left-biased than their normal sisters. Male CAH patients, with prenatal androgen exposure similar to that of unaffected brothers, had typical male-handedness patterns.
Healthy children and undergraduates were observed for hand preference and measured for hand skill in representative samples collected over some years. Writing and throwing were observed for 2844 participants drawn from primary, secondary and higher levels of education. The 12 actions of a standard questionnaire were observed for 2388 secondary school children and undergraduates. These findings provide normative data for comparison with selected samples that may be classified in a variety of ways, including subgroups previously defined and ordered for relative hand skill. Differences between the sexes were found only for certain subgroups of right-mixed-handers. Undergraduates were less variable for hand skill asymmetry than schoolchildren. Interpretations in the light of the RS theory show why statistical effects for comparisons with selected groups are likely to be small. Increased non-right-handedness may be caused by several influences on cerebral dominance, natural and pathological.
Self-reported injuries among left-handed and right-handed people were compared in a survey of 1,896 college students in British Columbia, Canada. Left-handers were more likely to report having an injury requiring medical attention during the last two years (OR = 1.89, 95% CI = 1.39, 2.58). Relative risk was highest for left-handed males when driving motor vehicles (OR = 2.35, CI = 1.25, 4.43). Regardless of handedness, males had slightly higher relative risks of injury than females.
This study tested the hypothesis that left-handed individuals are more aware than right-handed individuals of others' handedness. 18 left-handed and 18 right-handed college students were shown a drawing of 8 children at a party. Seven children held objects in the left hand, while one held an object in the right hand. After 2 1/2 min. the drawing was removed and subjects answered 15 questions about its contents. Included were 2 questions asking how many children were holding something in the right or left hand. Compared with right-handed subjects, left-handed subjects reported significantly more children holding something in the left hand and significantly fewer holding something in the right hand. The two groups did not differ on any other questions.
Handedness and mental rotation test scores were examined by sex and generation for 801 individuals in 200 families. An orderly relationship between bilateralization of function on the hand preference task and mental rotation test scores was found.