Structural maturation of neural pathways in children and adolescents: in vivo study.
(1/2062)
Structural maturation of fiber tracts in the human brain, including an increase in the diameter and myelination of axons, may play a role in cognitive development during childhood and adolescence. A computational analysis of structural magnetic resonance images obtained in 111 children and adolescents revealed age-related increases in white matter density in fiber tracts constituting putative corticospinal and frontotemporal pathways. The maturation of the corticospinal tract was bilateral, whereas that of the frontotemporal pathway was found predominantly in the left (speech-dominant) hemisphere. These findings provide evidence for a gradual maturation, during late childhood and adolescence, of fiber pathways presumably supporting motor and speech functions. (+info)
Neuropsychological laterality indices of schizophrenia: interactions with gender.
(2/2062)
Neurobehavioral laterality indices were examined across motor, sensory, language versus spatial, and verbal memory versus spatial memory domains for 75 patients with schizophrenia (45 men, 30 women) and 75 demographically matched healthy controls. Patients were impaired across tasks, and laterality results varied by domain. There was no evidence for diagnosis by hemisphere interactions in motor, sensory, or memory tasks. However, patients were more impaired in language than in spatial domains, which suggests relatively greater left hemisphere dysfunction. This finding was mediated by the sex of the participant. While patients as a group showed greater language than spatial impairment, male patients showed expected superiority in spatial relative to language performance, whereas female patients performed the same on both functions. These results underscore the importance of examining sex differences in laterality effects. The findings also demonstrate that, although the left hemisphere model of schizophrenia may be partially supported by data on higher cognitive functions, this support does not extend to more basic motor and sensory domains. (+info)
Specific alteration of spontaneous GABAergic inhibition in cerebellar purkinje cells in mice lacking the potassium channel Kv1. 1.
(3/2062)
In the cerebellum, the basket cell innervation on Purkinje cells provides a major GABAergic inhibitory control of the single efferent output from the cerebellum. The Shaker-type K channel Kv1.1 is localized at the axon arborization preceding the terminal of the basket cells and is therefore a potential candidate for regulating the GABAergic inhibition. In this study, we directly assess this role of Kv1.1 by electrophysiological analysis of Kv1.1 null mutant mice. Whole-cell patch-clamp recordings of spontaneous IPSCs (sIPSCs) were made from Purkinje cells in thin cerebellar slices from postnatal day (P)10-15 Kv1.1-null mutants using wild-type littermates as controls. The null mutation confers a very specific change in the sIPSC: the frequency increases about twofold, without accompanying changes in the mean and variance of its amplitude distribution. The frequency and amplitude of the miniature IPSCs (mIPSCs) are unaffected. Spontaneous firing rate of the basket cells is unaltered. Evoked IPSC does not show multiple activity in the mutants. Motor skills tests show that Kv1.1 null mice display a compromised ability to maintain balance on a thin stationary rod. We conclude that the Kv1.1 null mutation results in a persistent elevation of the tonic inhibitory tone on the cerebellum Purkinje cell efferent and that this is not fully compensated for by residual Shaker-type channels. We further suggest that the increase in inhibitory tone in the mutants might underlie the behavioral deficits. At the cellular level, we propose that Kv1.1 deletion enhances excitability of the basket cells by selectively enhancing the likelihood of action potential propagation past axonal branch points. (+info)
Long-term neurological dysfunction and neonatal hypoglycaemia after diabetic pregnancy.
(4/2062)
AIM: To determine if children born to mothers with diabetes mellitus during pregnancy, who subsequently developed neonatal hypoglycaemia, experienced long-term neurological dysfunction. METHODS: Thirteen children with, and 15 without, neonatal hypoglycaemia (blood glucose < 1.5 mmol/l) were randomly selected from a larger cohort and investigated at the age of 8 years. They were also compared with 28 age matched healthy controls. RESULTS: Children with neonatal hypoglycaemia had significantly more difficulties in a validated screening test for minimal brain dysfunction than controls and were also more often reported to be hyperactive, impulsive, and easily distracted. On psychological assessment, they had a lower total development score than normoglycaemic children born to diabetic mothers, and control children. CONCLUSIONS: Neonatal hypoglycaemia in diabetic pregnancy was associated with long-term neurological dysfunction related to minimal brain dysfunction/deficits in attention, motor control, and perception. (+info)
Biochemical hypothyroidism secondary to iodine deficiency is associated with poor school achievement and cognition in Bangladeshi children.
(5/2062)
Iodine deficiency in pregnancy leads to poor cognitive function in the offspring; however, the effect of concurrent iodine deficiency on school-aged children is not clear. Several studies have shown that school children in iodine-deficient villages have poorer cognitive function than children in iodine-sufficient villages. However, villages differ in many factors that may also detrimentally affect children's development. In addition, the children's nutritional and health status has not usually been taken into account. In this study, we compared the cognitive function and school achievement levels of 170 children who had recently had low thyroxine (T4) levels [T4 /=70 nmol/L (euthyroid)]. The children were matched for school and grade level and came from the same iodine-deficient regions in rural Bangladesh. They were given a battery of cognitive, motor and school achievement tests. We also measured their nutritional status, examined their stools for geohelminths and assessed their home environments. A factor analysis of cognitive and motor function tests yielded two factors, a general cognitive factor and a fine motor factor. The children's height and arm circumference, experience of hunger, parental characteristics and stimulation in the home made independent contributions to their test scores. Controlling for these variables, the hypothyroid children performed worse than the euthyroid children on reading and spelling and the general cognitive factor. These findings indicate that a large number of disadvantages including hypothyroidism are related to the poor development of these children. (+info)
Functional coupling of human cortical sensorimotor areas during bimanual skill acquisition.
(6/2062)
Bimanual co-ordination of skilled finger movements is a high-level capability of the human motor system and virtually always requires training. Little is known about the physiological processes underlying successful bimanual performance and skill acquisition. In the present study, we used task-related coherence (TRCoh) and task-related power (TRPow) analysis of multichannel surface EEG to investigate the functional coupling and regional activation of human sensorimotor regions during bimanual skill acquisition. We focused on changes in interhemispheric coupling associated with bimanual learning. TRCoh and TRPow were estimated during the fusion of two overlearned unimanual finger-tapping sequences into one novel bimanual sequence, before and after a 30-min training period in 18 normal volunteers. Control experiments included learning and repetition of complex and simple unimanual finger sequences. The main finding was a significant increase in interhemispheric TRCoh selectively in the early learning stage (P < 0.0001). Interhemispheric TRCoh was also present during the unimanual control tasks, but with lower magnitude, even if learning was involved. Training improved bimanual sequence performance (from 58.3+/-24.1 to 83.7+/-15.3% correct sequences). After training, interhemispheric (bimanual) TRCoh decreased again, thereby approaching levels similar to those in the unimanual controls. We propose that the initial increase in TRCoh reflects changes in interhemispheric communication that are specifically related to bimanual learning and may be relayed through the corpus callosum. The present data might also offer a neurophysiological explanation for the clinical observation that patients with lesions of the corpus callosum may show deficits in the acquisition of novel bimanual tasks but not necessarily in the execution of previously learned bimanual activities. (+info)
Representational plasticity in cortical area 3b paralleling tactual-motor skill acquisition in adult monkeys.
(7/2062)
The representations of the surfaces of the hand in the primary somatosensory cortical field, area 3b, were reconstructed in detail in seven owl monkeys and two squirrel monkeys trained to pick up food pellets from five wells of different sizes. From an early clumsy performance in which several to many retrieval attempts were required for each successful pellet retrieval, the monkeys exhibited a gradual improvement in digital dexterity as shown by significant decreases in mean numbers of grasp attempts/successful retrieval and corresponding standard deviations (e.g. 5.8 +/- 4.5 and 4.8 +/- 3.1 respectively, for the smallest well) between the first and last training sessions. All monkeys commonly used alternative, specific retrieval strategies involving various combinations of digits for significant time epochs before developing a highly successful strategy, which, once achieved, was rapidly stereotyped. For example, the numbers of digit combinations used during the first five versus the last five training sessions decreased from 3.3 +/- 0.7 to 1.8 +/- 0.6 for the smallest well. In both owl and squirrel monkeys, as the behavior came to be stereotyped, monkeys reliably engaged limited surfaces of the glabrous tips of two digits (in eight monkeys), or of three digits (in one monkey) in the palpation and manipulation of these small pellets for their location, capture, and transportation to the mouth. In cortical area 3b, the magnification of representation of these differentially engaged glabrous fingertip surfaces was nearly 2x larger than for the corresponding surfaces of other hand digits, or for the contralateral cortical representations of the same digit surfaces on the opposite hand. In parallel, cutaneous receptive field for area 3b neurons representing crucial digital tip surfaces were less than half as large as were those representing the corresponding surfaces of control digits. Receptive field overlaps were smaller on the trained fingertips than on control fingers. Moreover, the proportion of small overlaps was greater for the trained digits (76 +/- 7%) than for the other digits of the same hand (49 +/- 5.4%). There was still a simple, single--but apparently topologically expanded--representation of these differentially engaged skin surfaces in these monkeys. Thus, with very limited manual exercise over a total period of a few hours of practice at a skill played out in brief daily sessions over a several week long training period, the representations of skin surfaces providing information crucial for successfully performing a small-object retrieval behavior appeared to be substantially remodeled in the most 'primary' of the SI somatosensory cortical fields, cortical area 3b. By that remodeling, behaviorally important skin surfaces were represented in a much finer representational grain than normal. Some implications of these findings for motor skill acquisition are discussed. (+info)
Impaired grip-lift synergy in children with unilateral brain lesions.
(8/2062)
Children with spastic hemiplegia have impaired dexterity in the affected extremity. The purpose of the present study was to investigate whether the force co-ordination pattern during precision grip in 13 children between 4 and 10 years of age with predominant unilateral brain lesions is related to manual dexterity and to the location and size of the brain lesion. The force co-ordination pattern was investigated by means of a specially designed object that monitored the isometric fingertip forces applied to the contact surfaces during precision grip. Hand function was measured by means of neurological examination, functional hand-grips and dexterity. Brain lesions were identified by series of ultrasound and MRI scans. Normally, the fingertip forces are applied to the object in the initial phase of the lift in an invariant force co-ordination pattern (i.e. grip-lift synergy), in which the grip and load forces are initiated simultaneously and increase in parallel with unimodal force rate trajectories. A majority of children with unilateral brain lesions had not developed the force co-ordination pattern typical for their age, but produced an immature or a pathological pattern. The developmental level of the grip-lift synergy was determined and quantified according to criteria derived from earlier studies on normally developed children. There was a clear relationship between the developmental level of the grip-lift synergy and impaired dexterity, indicating that proper development of the force co-ordination pattern is important for skilled hand function. The grip-lift synergy correlated with the total extent of lesions in the contralateral cortex and white matter and with lesions in the thalamus/basal ganglia, while no correlation was found for isolated cortical lesions. The results suggest that the neural circuits involved in the control of the precision grip are organized in a parallel and distributed system in the hemispheres, and that the basal ganglia are important during the formation of these circuits. Perinatal lesions in specific cortical motor areas may be compensated for by circuits elsewhere in the grip-lift motor system, while large lesions exclude this possibility. (+info)