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The present study was designed to assess the validity of the Torque Test as a measure of functional lateral dominance in children. One hundred forty-nine children were administered the Torque Test and The Harris Test of Lateral Dominance. A low but statistically significant correlation was found between torque and total lateral dominance.
Eight hundred psychiatric patients and eight hundred controls completed a handedness preference questionnaire. There was no significant difference in handedness between the two samples, but, contrary to some previous reports, excess of sinistrality was not associated with male sex. The distribution of handedness was similar in neurotics and controls, but among psychotics in general there was a higher proportion of fully right-handed subjects. Among schizophrenics there was a significantly higher proportion of left-handed writers among males than females. There were relatively few left-handed writers of either sex among patients with affective psychosis. Female patients with personality disorders had a significantly higher proportion of mixed handedness than controls. The findings are considered in relation to suggestions that functional psychoses may be associated with asymmetrical cerebral dysfunction, and that poorly lateralized function may be related to anomalous psychological development.
This study is concerned with the problem of hemispheric specialization and/or cooperation in relation to development and manual laterality. The processing of alphabetic signs and its relationship to interhemispheric transfer and functional hemispheric asymmetries were studied by comparing left- and right-handed girls during acquisition of reading. The children perform matching tasks with letters having different orientations and with meaningless forms having the same orientations as the letters. Each subject performed the matching under three conditions: right/left intermanual transfer, left/right intermanual transfer, and dichaptic exploration. Results indicate: (1) A differentiated development between the two handednesses. (2) The functional lateralization change was different for left- and right-handed girls, a greater effect of the ability to identify the letter on matching tasks was observed for the right-handed children than for the left-handed children. These last results are discussed with regard to inter-hemispheric transfer and functional hemispheric asymmetry changes. We hypothesized a strategy difference between left- and right-handed girls and a difference in their ability to change their cognitive strategy (left-handers continue to favor a spatial coding with letters).
We revealed functional lateralization of the chick visual system by placing injections of monosodium glutamate (0.5 microl, 100 mM) into the left or right Wulst regions of the hemispheres, and examined the effects of light experience before hatching on this lateralization. Following exposure of the left or right eye to light for 24 h beginning on day 18 of incubation, the chick's ability to categorize grain as distinct from pebbles was impaired by glutamate treatment of the Wulst contralateral to the exposed eye. Attack and copulation scores were also elevated. Following incubation of the eggs in darkness or with both eyes exposed to light, treatment of neither the left or right Wulst affected performance on the pebble-grain task: showing that either the left and right Wulst can assume control of this function. Treatment of either the left or right Wulst of these chicks elevates attack and copulation. However, examination of the distribution of attack scores revealed a bimodality in the attack scores of the chicks treated with glutamate in the right Wulst and not those treated in the left Wulst. In summary, light stimulation of one eye during a critical period of embryonic development causes the visual Wulst contralateral to the light exposed eye to develop dominance over its equivalent region in the other hemisphere. Without this lateralized stimulation of light both the left and right Wulst regions are largely but not exactly equivalent.
Origin and ontogenesis of human brain laterality are unknown. Using in vivo magnetic resonance morphometry we measured cerebral hemispheric asymmetry of the planum temporale, a structural substrate of functional laterality, in pairs of monozygotic twins concordant or discordant for handedness. In both groups, intraclass (i.e., within twin pair) correlations were low. The right-handers showed leftward asymmetry whereas the left-handers lacked asymmetry. The discordance for lateralized brain anatomy can be accounted for by ontogenetic models assuming twinning of an asymmetrical germ or differential action of nongenetic factors within twin pairs in utero. The findings confirm a coupling of lateralized structure and function of the human brain. At least in monozygotic twins, early epigenetic factors must play a role in anatomofunctional laterality development.
Besides a well-established role in neuronal communication in the adult central nervous system, neurotransmitters have diverse tasks in the embryonic brain, ranging from early developmental functions in morphogenesis /13/, to later functions in target selection and synapse formation /87/. For example, growth cones of developing neurons are known to release transmitters /26,36,88,110,115/ and respond to transmitters released from other neurons /35,44,59, 61,70/. Moreover, depletion of transmitters during embryonic development results in developmental deficits of the brain /21,48,84,109/, suggesting that transmitters have crucial roles as morphogens and/or neurotrophic factors. Although recently the idea of neurotransmitters being important for neural development has been challenged /99/, there is a vast amount of literature that seems to support the hypothesis that neurotransmitter release in the developing central nervous system is crucial for proper brain development. In this review we focus on the roles that neurotransmitters play in neurite outgrowth, target selection and synapse formation, with particular emphasis on the effects of the transmitters serotonin and dopamine.
UNLABELLED: The aim was to assess motor function during infancy in order to predict later function, mainly cerebral palsy. The neuromotor development of a population-based cohort of 209 of 236 (89%) survivors with a birthweight less than 2000 g was assessed using the Infant Neurological International Battery (INFANIB) and detailed neurological assessment. The infants were classified as being normal, dystonic, hypotonic or having suspected cerebral palsy (CP) at 4, 7, 13 and 18 mo corrected age if birthweight was less than 1500 g (n = 119) and at 7 and 13 mo if birthweight was 1500-1999 g (n = 90). Those with dystonia or suspected CP were followed until diagnosed as normal or as having CP after at least 36 mo of age. Fourteen (7%) finally developed CP. Motor function at 4 mo was inaccurate in predicting function at 7 mo and later. All who were normal at 7 mo remained normal in the follow-up period. Eight of 65 who were dystonic at 7 mo developed suspected CP, and three judged as suspected CP were eventually normal. The 14 who developed CP were judged as suspected CP (n = 5) or dystonic (n = 8) and one as hypotonic at 7 mo of age. CONCLUSIONS: The specificity of motor evaluation at 7 mo corrected age regarding CP is unsatisfactory, since dystonia at this age is most often transient. A normal neuromotor assessment at 7 mo is highly predictive of subsequent normal motor function.
OBJECTIVE: To investigate the brain functional laterality in motor areas during motor execution systematically. METHODS: Functional magnetic resonance imaging (fMRI) was employed combined with right hand sequential finger movement task to investigate brain activation pattern and laterality in 8 right-handed subjects. 3dDeconvolve program of AFNI was used to estimate the hemodynamic response function and to generate activation maps. Then the laterality index (LI) was calculated and tested statistically. RESULT: All motor areas including the areas which were previously considered to be engage in movement preparation only were activated in movement execution. In the activation map, it appeared left lateralization in cerebra and right lateralization in cerebella. After further statistical test, it was found that in primary motor area (M1), supplementary motor area (SMA) and posterior parietal cortex (PPC), there were left lateralization. While in premotor cortex (PMC), cingulate gyrus and basal ganglia (BG), the lateralization tendency was not obvious. The activation in cerebella is characterized with right lateralization. CONCLUSION: Though there are tiny differences among subjects, most of the motor areas appear lateralized activation. Past studies only observed laterality in several motor areas. It may be due to the difficulty of the task or the experimental design.
While recent experimental work has defined asymmetries and lateralization in left and right cortical maps, the mechanisms underlying these phenomena are currently not established. In order to explore some possible mechanisms in theory, we studied a neural model consisting of paired cerebral hemispheric regions interacting via a simulated corpus callosum. Starting with random synaptic strengths, unsupervised (Hebbian) synaptic modifications led to the emergence of a topographic map in one or both hemispheric regions. Because of uncertainties concerning the nature of hemispheric interactions, both excitatory and inhibitory callosal influences were examined independently. A sharp transition in model behavior was observed depending on callosal strength. For excitatory or weakly inhibitory callosal interactions, complete and symmetric mirror-image maps generally appeared in both hemispheric regions. In contrast, with stronger inhibitory callosal interactions, partial to complete map lateralization tended to occur, and the maps in each hemispheric region often became complementary. Lateralization occurred readily toward the side having a larger cortical region or higher excitability. Asymmetric synaptic plasticity, however, had only a transitory effect on lateralization. These results support the hypotheses that interhemispheric competition occurs, that multiple underlying asymmetries may lead to function lateralization, and that the effects of asymmetric synaptic plasticity may vary depending on whether supervised or unsupervised learning is involved. To our knowledge, this is the first computational model to demonstrate the emergence of topographic map lateralization and asymmetries.
Two experiments are reported examining individual differences in the processing of centrally presented stimuli containing two dimensions of information lateralized to opposite cerebral hemispheres. Left-handers, arising from (a) their lesser degree of functional lateralization and (b) their greater degree of callosal connectivity, were hypothesized to exhibit greater interdimensional (and presumably interhemispheric) interaction. Experiment 1 utilized local-global stimuli, and left-handers were found to be impaired at keeping the two dimensions independent and superior at integrating the two dimensions. Experiment 2 used Stroop stimuli, and left-handers again were impaired at keeping the two dimensions independent (i.e., showed greater Stroop interference). Correlational analyses indicated that the mechanisms of interdimensional integration versus independence are at least partially independent from one another. Results suggest that aspects of interhemispheric interaction can be addressed via the use of nonlateralized input.
The medial prefrontal cortex (mPFC) is highly activated by stress and modulates neuroendocrine and autonomic function. Dopaminergic inputs to mPFC facilitate coping ability and demonstrate considerable hemispheric functional lateralization. The present study investigated the potentially lateralized regulation of stress responses at the level of mPFC output neurons, using ibotenic acid lesions. Neuroendocrine function was assessed by plasma corticosterone increases in response to acute or repeated 20 min restraint stress. The primary index of autonomic activation was gastric ulcer development during a separate cold restraint stress. Restraint-induced defecation was also monitored. Plasma corticosterone levels were markedly lower in response to repeated versus acute restraint stress. In acutely restrained animals, right or bilateral, but not left mPFC lesions, decreased prestress corticosterone levels, whereas in repeatedly restrained rats, the same lesions significantly reduced the peak stress-induced corticosterone response. Stress ulcer development (after a single cold restraint stress) was greatly reduced by either right or bilateral mPFC lesions but was unaffected by left lesions. Restraint-induced defecation was elevated in animals with left mPFC lesions. Finally, a left-biased asymmetry in adrenal gland weights was observed across animals, which was unaffected by mPFC lesions. The results suggest that mPFC output neurons demonstrate an intrinsic right brain specialization in both neuroendocrine and autonomic activation. Such findings may be particularly relevant to clinical depression which is associated with both disturbances in stress regulatory systems and hemispheric imbalances in prefrontal function.
After unilateral cerebral hemisphere stroke, resulting in contralateral arm symptoms but largely sparing higher cerebral function, ipsilateral arm function is generally considered to be unaffected. In this study, 8 subjects with acute unilateral cerebral infarction (confirmed by CT scan) and primarily motor deficits underwent 11 computerized and 6 clinical assessments between 11 days and 12 months poststroke, and were compared with 12 normal subjects. Computerized tests comprised 3 pursuit tracking tasks (preview-random, step and a combination of these), designed to measure different aspects of integrated sensory-motor (S-M) function, and 12 tasks aimed at breaking tracking into various sensory, perceptual and motor components (joint movement sense, visual resolution, object perception, static and dynamic visuospatial perception, range of movement, grip and arm strength, reaction time, speed, static and dynamic steadiness). The asymptomatic arm was impaired on all but one of the computerized tests throughout the 12-month period, although to a lesser degree than the symptomatic arm. Grip strength was marginally impaired initially. Incomplete neurological recovery was seen in the asymptomatic arm for all functions except strength, speed and steadiness, possibly indicating their resistance to improvement. Clinical assessment detected no asymptomatic arm impairment and only a mild transient deficit of higher mental function. Our data suggest that (1) all cerebral hemisphere areas involved in S-M functions can exert some degree of bilateral motor control; (2) ipsilateral influence is never greater than contralateral influence, and is usually considerably less; and (3) the proportion of ipsilateral to contralateral control is closely related to the degree of continuous sensory feedback required by the particular task. The mechanism and degree of ipsilateral dysfunction can be explained by a 3-tier cerebral model of S-M integration comprising a lower level of functions with high contralateral specificity (somatosensory and motor), a middle level of non-limb-specific partially lateralized functions (ideomotor praxis and visuospatial perception) and an upper level of global mental activities (intellect, alertness, etc.).
Dichotic listening (DL) is a neuropsychological technique for the study of functional laterality. Based on behavioral patient studies, the "structural theory" states that lateralization of the auditory input during DL is allowed by an inhibition of the ipsilateral pathways. We aimed here at extending this theory to provide a neurophysiological basis of verbal DL. We investigated the magnetic responses of the primary auditory cortices elicited by dichotic consonant-vowel syllables. Dichotic stimuli consisted of 2 syllables pairs, a "competing" one composed by syllables with high spectral overlap (/da/ and /ba/) and a "noncompeting" pair (/da/ and /ka/). One of the syllables in each pair was delivered at 2 intensities, whereas the other did not change. A reduced increase of source intensity in response to dichotic pairs at the 2 levels was assumed to indicate pathway inhibition effects. We obtained that the left ipsilateral pathway (i.e., the left ipsilateral signal) was strongly inhibited by the right contralateral one. Conversely, the right ipsilateral pathway did not show an inhibition larger than the left contralateral one. These results extend the notion of auditory functional asymmetries by showing that beyond hemispheric functional specialization there is an asymmetry within the ascending auditory system, which is based on a competition mechanism. The larger the competition between the left and right ear stimuli, the larger are the inhibition effects, which determine the pathway asymmetry. These findings represent as well a neurophysiological basis for the "structural theory" explaining the right ear preference usually found in verbal DL tasks.
OBJECTIVE: The aim of this study was to determine differing reactions of the left and right eyes with regard to pupillary light reflex (PLR) parameters. METHODS: All together 90 healthy subjects were included. In the first test series, 34 subjects were investigated on both eyes (left eye was tested first, three tests per day and one reliability test). In the second test series, 32 subjects were studied while changing the beginning side. In the last test series, 29 subjects were investigated 12 times each within 1h (beginning side changed, without spoken advice). Infrared pupillometry was used to study pupil diameter, latency time, relative amplitude, contraction/dilation velocity, and pupil redilation time. RESULTS: The study demonstrated significant differences of PLR parameters between both eyes. In contrast to the pupil diameter of the left eye the parasympathetically-dominated right eye was not influenced by vocal instructions or by changing the beginning side. CONCLUSIONS: PLR parameters might indicate functional lateralization of autonomic function in the central nervous system. High sensitivity of the procedure (arousal due to spoken advice, time of day) is advantageous for various psychophysiological investigations. SIGNIFICANCE: Differences between both eyes might point towards cortical lateralization of central autonomic function.
Asymmetry of the planum temporale, a language-related intrasylvian area on the superior temporal gyrus, is the most remarkable anatomical left-right asymmetry of the human brain. The in vivo application of magnetic resonance morphometry in 52 healthy volunteers (26 dextrals and 26 sinistrals) revealed that planum temporale asymmetry is correlated with hand dominance. Left-handers had a significantly lesser degree of leftward planum temporale asymmetry than right-handers. Thus, a structural-functional relation exists in cerebral asymmetry. The correlation is likely to reflect language representation. Because familial sinistrality influenced the anatomical pattern in left-handers and planum temporale asymmetry is already present in the newborn, prenatal factors must play an important role in the development of functional laterality.
Left or right unilateral removal of a cerebellar hemisphere resulted in a high mortality rate caused by anorexia, not previously seen in cerebellectomized animals. The reduced post-surgical gain in body weight may be explained by oropharyngeal dyspraxia or a loss in appetite. However, the growth rate of the surviving animals was similar to that of controls. After unilateral damage of the cerebellum, deficits were observed in motor coordination tasks, such as the rotorod, the hole-board, and the stationary beam, and the left hemisphere group fell from a suspended wire sooner than controls. The motor deficits were more pronounced after left as opposed to right cerebellar damage on the rotorod, implying a certain degree of functional lateralization for this test.
The purpose of this study was to examine whether or not early indications of lateralization could be found in the perinatal period. The position in the fetal period and spontaneous head-turning soon after birth of one hundred and twenty-two subjects were measured. These subjects' hand activities (preference and manipulation) in infancy were later investigated through a questionnaire given to their parents. Results showed that the position in the fetal period and head-turning soon after birth were related to the functional asymmetries of hand activity in infancy. In addition, the results on the hand activity in infancy suggested that the developmental process of manipulation was different from that of hand preference with respect to functional lateralization.
Despite considerable speculation in the research literature regarding the complementarity of functional lateralization of prosodic and linguistic processes in the normal intact brain, few studies have directly addressed this issue. In the present study, behavioral laterality indices of emotional prosodic and traditional linguistic speech functions were obtained for a sample of healthy young adults, using the dichotic listening method. After screening for adequate emotional prosody and linguistic recognition abilities, participants completed the Fused Rhymed Words Test (FRWT; Wexler & Halwes, 1983) and the Dichotic Emotion Recognition Test (DERT; McNeely & Netley, 1998). Examination of the difference in ear asymmetries for these measures within individuals revealed a complementary pattern in 78% of the sample. However, the correlation between laterality quotients for the FRWT and DERT was near zero, supporting Bryden's model of "statistical" complementarity (e.g., Bryden, 1990).