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Biomedical subjects

H Forssberg

Publications and source records attributed to H Forssberg.

At least 37 records · Page 2Linked to original sources
PubMed1999

Shared memory representations for programming of lifting movements and associated whole body postural adjustments in humans.

This study examined whether the same memory representation is used for the parametric control of precision lifting and associated postural adjustments (APAs). Fifteen adults lifted object of different weights between the thumb and index finger. The employed grip, load (vertical lifting) forces, and ground reaction forces were recorded and the centre of pressure (COP) displacement as well as the corresponding first time derivatives were calculated. A highly significant correlation was found between the maximum rates of the load force, grip force and COP displacement rate. Different loads also influenced the onset of the COP displacement. The results corroborate the idea that the same memory representations which are used to control the manipulative lifting movement also control the APAs.

Adult↗
PubMed1999

An image registration strategy for multi-echo fMRI.

Functional magnetic resonance imaging (fMRI) based on multiple-echo T(2)* mapping has attracted much attention recently. The contrasts in the parametric T(2)* maps are usually too low to allow direct image registration. In this study, an image registration strategy has been proposed for single-shot multi-echo data sets acquired for dynamic T(2)* mapping. We performed image registration of the T(2)*-weighted images before the calculation of the T(2)* parameter maps using two different strategies. One is to perform separate image registration on each echo and the other is to use the same motion correction parameters extracted from the second echo for all the data. Both strategies increase the number of activated voxels and reduce the effective noise level. The results also indicate that, for a single-shot dual-echo image data set, it is slightly preferable to use the second echo for direct image registration and then apply the same motion correction parameters to the first echo images. J. Magn. Reson Imaging 1999;10:154-158.

Brain↗
PubMed1999

Neural control of human motor development.

It has been possible to expand considerably our understanding of human motor development by making a detailed analysis of various types of movement and muscular activation patterns during different stages of development. Alterations in development subsequent to the appearance of brain lesions have enabled valuable information to be collected about the underlying neural mechanisms, in addition to new information concerning the pathophysiology of cerebral palsy. Studies on the development of the corticospinal system indicate that plastic changes can take place after perinatal brain damage.

Aging↗
PubMed1999

Speech discrimination and phonological working memory in children with ADHD.

This study examined phonological working memory and speech discrimination among children with attention-deficit-hyperactivity disorder (ADHD) with and without motor problems. Forty-one children were assigned to three groups; children with ADHD (N=9), children with ADHD plus developmental coordination disorder (ADHD+, N=13), and age-matched control children (N=19). The subjects' ability to classify stimulus pairs was examined in two experiments. The first experiment required subjects to discriminate pairs of monosyllabic stimuli with contrasting consonants to test speech discrimination without using a working-memory load. In the second protocol, subjects were exposed to two- to five-syllabic non-word pairs with contrasting vowels in order to test speech discrimination with a working-memory load. The subjects classified the pairs as being either the same or different in both experiments. No significant differences were found between the subject groups in the discrimination task with monosyllables. When exposed to the two- to five-syllabic stimuli, the ADHD+ group scored significantly lower than both other groups. This was attributed to a higher sensitivity to working-memory load. Some possible explanations of this effect are discussed.

Adolescent↗
PubMed1999

Periventricular leucomalacia and preterm birth have different detrimental effects on postural adjustments.

Postural adjustments during sitting on a moveable platform were assessed by means of multiple surface EMGs of neck, trunk and leg muscles and kinematics in three groups of children, aged 1 1/2-4 1/2 years. The first group consisted of 13 preterm children (born at a gestational age of 25-34 weeks), whose neonatal ultrasounds had shown distinct lesions of the periventicular white matter (PWM). The second group was the preterm control group, consisting of 13 preterm children with normal neonatal brain scans, matched to the PWM group with respect to gestational age at birth, birth weight, sex and age of postural assessment. The third group was formed by 13 healthy children born at term and matched to the PWM group with respect to sex and age at examination. In addition to the postural assessment an age-specific neurological examination was carried out. Three of the children of the PWM group developed a cerebral palsy syndrome, nine showed minor neurological dysfunction and one child was neurologically normal. In the preterm control group one child showed minor neurological dysfunction, while the remaining 12 children of this group and all children of the full-term group were neurologically normal. The postural assessment revealed that preterm birth was associated with two types of postural dysfunction. One dysfunction was related to the presence of a PWM lesion and consisted of a limited repertoire of response variation. The other dysfunction was not related to the presence of a PWM lesion, but to preterm birth itself. It consisted of a change in the ability to modulate the postural responses. Preterm children showed a higher sensitivity to platform velocity than full-term children, and they lacked the capacity to modulate EMG amplitude with respect to initial sitting position.

Biomechanical Phenomena↗
PubMed1999

Impaired grip-lift synergy in children with unilateral brain lesions.

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.

Brain↗
PubMed1998

Development of postural control--differences between ventral and dorsal muscles?

Postural control is organized in basic, direction specific synergies which can be adapted to task-related conditions. Studies on the development of postural adjustments in young sitting children revealed that largely variable, direction specific muscle activation patterns are already present in 5-6 month old children not able to sit without support. With increasing age, the variation in muscle activation patterns decreases, resulting in a selection of the most complete patterns of synergist activation at 9-10 months of age. The synergy of the dorsal extensor muscles (during a forward sway of the body) develops faster than the synergy of the ventral flexors (during backward body-sway). A 'fixed' extensor synergy is prominently present between 9 months and 3 years, i.e. during the period when standing and walking abilities develop. With increasing age the 'fixed' extensor synergy gradually dissolves. The flexor synergy shows a larger flexibility than the extensor synergy, a difference which can be attributed to differences in stability limits and differences in the degree of supraspinal modulation.

Humans↗
PubMed1998

Postural control in sitting children with cerebral palsy.

Children with cerebral palsy (CP) display postural problems, largely interfering with daily life activities. Clarification of neural mechanisms controlling posture in these children could serve as a base for more successful intervention. Studies on postural adjustments following horizontal forward and backward displacements of a movable platform in ten school-age children with spastic diplegia and non-disabled controls revealed that sitting CP children, like standing CP children, show direction specific postural adjustments, indicating that the basic pattern of muscle coordination in these conditions is conserved. Dysfunctions are especially present in the modulation of the response pattern of ventral muscles during forward translations. They consist of: (1) a stereotyped and non-variable activation of all ventral muscles; (2) an abnormal top-down muscle recruitment; and (3) an excessive degree of antagonistic co-activation. The altered patterns of muscle coordination could be the result of two interacting mechanisms, the primary deficit due to the early brain damage and a compensation due to the postural instability. Especially the latter dysfunction furnishes opportunities for therapeutic help.

Cerebral Palsy↗
PubMed1998

Obstetric brachial plexus injuries: assessment protocol and functional outcome at age 5 years.

One hundred and five children with the whole spectrum of obstetric brachial plexus (OBP) injuries, from severe to full recovery, were examined at the age of 5 years with regard to motor and sensory functions as well as to use of the affected limb. Since root involvement level does not fully reflect the degree of disability, a classification based on range of motion and grip-strength was formulated and found to correspond well with functional abilities. The results from this study indicate that the eventual outcome in upper-plexus lesions is more complex than is commonly believed. Hand function is affected due to the effect of limited shoulder movements on hand positioning. Grip strength was also reduced in many of these children. All the children with total-plexus lesions had diminished grip strength and half of them had impaired tactile sensibility. In most children with total-plexus lesions, performance of activities in daily life was affected as were bimanual activities requiring use of the involved limb. Hand preference was affected in children with a right-sided injury. From a clinical perspective, as well as for research, it is important to describe OBP injuries not only in terms of impairment but also of disability.

Activities of Daily Living↗
PubMed1998

Postural adjustments during sitting at preschool age: presence of a transient toddling phase.

The present study investigated developmental changes in postural adjustments during preschool age. Postural responses during sitting on a moveable platform were assessed in 21 healthy children aged 1 1/2 to 4 1/2 years. Multiple surface EMGs of neck, trunk, and leg muscles were recorded during forward and backward translations. Comparable data were available for 11 infants seen three times between the ages of 5 and 10 months. The data revealed the existence of a transient period between the ages of 9 to 10 months and 2 1/2 to 3 years, during which perturbations in a sitting position are accompanied by high activity in the direction-specific agonist muscles and in the antagonist muscles. After this period, agonist activity became more variable, particularly so during backward translations, and antagonist activity disappeared. These changes could be attributed to biomechanical factors and to maturation of the nervous system.

Child Development↗
PubMed1997

Anticipatory control of manipulative forces in Parkinson's disease.

In a previous study we found that subjects with Parkinson's disease (PD) had an impaired capability to initiate and sequence successive movement phases during lifts of small objects using the precision grip, and that they had regular oscillations in the force rates. The present study examined whether these subjects could use anticipatory control, in which the force output is scaled prior to liftoff, based on the object's physical properties. Subjects lifted an instrumented test object between the tips of the thumb and index finger while the employed grip force, load force (vertical lifting force), and corresponding time derivatives were recorded. In the first experiment, the object's weight was varied to assess its influence on the isometric force output. Subjects with PD scaled the isometric force increase according to the object's weight. In another experiment, the weight changed in proportion to the volume to determine whether subjects could make associative transformations between visual size information and the weight of the object. Subjects with PD still scaled the forces toward the expected weight, proportional to the volume of the object. Finally, programmed adjustments in force to sudden self-induced load changes were examined while subjects dropped a disk with one hand into a plate attached to the bottom of the grip instrument, held with the other hand. Subjects with PD had preparatory increases in the grip force prior to the disk contact, which matched the change in load, though may have been more dependent on visual feedback. We conclude that subjects with PD are capable of using anticipatory control to parameterize the isometric force output during a familiar lifting task.

Conditioning, Psychological↗
PubMed1997

Coordination of manipulative forces in Parkinson's disease.

The coordination of manipulative forces was examined in 10 subjects with Parkinson's disease (PD) both OFF and ON medication while they grasped and lifted a small object using the precision grip. The development of grip (squeeze) force and load (vertical lifting) force was recorded and compared to a group of age-matched control subjects. Subjects with PD often exhibited a prolonged delay between the first digit contact with the object and initiation of the lifting drive. These subjects also exhibited stepwise increases in force, with regular oscillations in the force rates. However, once the vertical drive began, the main increase in grip and load force generally was in parallel and most other temporal aspects of the force coordination were similar to those of the control subjects. The extent to which the movement initiation was delayed was related to the stage of the disease, and most subjects improved ON medication. When the object was held in the air, subjects with PD used a grip force level which was similar to that of the control subjects, and all subjects adjusted their grip force according to the surface texture. Furthermore, they exhibited proper reflexive corrections to sudden changes in load (object perturbations), suggesting intact sensorimotor integration. We conclude that the most obvious impairments in the coordination of this task were delayed initiation of the grip-lift sequence and tremor-like oscillations superimposed on otherwise normal force.

Adaptation, Physiological↗
PubMed1997

The Stockholm Neonatal Project: neonatal mortality and morbidity at the Children's Centre, Karolinska Hospital.

Two hundred and ninety-one very-low-birth-weight (VLBW) infants were studied prospectively during the period of 1988-1993. All inborn VLBW infants and most of the VLBW infants born in Greater Stockholm and requiring neonatal intensive care were included in this study. The overall mortality was 17.5% and the mortality in the group with the lowest gestational age at birth, i.e. 23-24 weeks, was 25%. The mortality for boys was higher than for the girls. The mode of delivery, i.e. vaginal versus caesarean section and multiple birth, did not seem to affect the mortality rate. Respiratory insufficiency and/or cerebral complications were the most common cause of neonatal death. Patent ductus arteriosus was found in 35% of the infants, of whom 43% needed surgical ligation. One-third of infants with retinopathy of prematurity (30/92) required cryotherapy.

Cause of Death↗
PubMed1997

Diagnosis of intracranial lesions in very-low-birthweight infants by ultrasound: incidence and association with potential risk factors.

This study was designed to determine the frequencies of germinal matrix and ventricular haemorrhages as well as lesions in the white matter diagnosed by ultrasonography. In subsequent studies the effects of perinatal brain lesions on the cognitive and motor development of preterm children will be presented. Lesions of the white matter are probably more damaging than intraventricular and subependymal bleeds. Therefore, a modified classification of the lesions was used, clearly separating bleeds from white matter pathology. The study includes 291 infants with a body weight of < or = 1500 g consecutively admitted to the neonatal intensive-case unit at Karolinska Hospital from 1988 to 1993. Fifty-four (18.9%) died before 6 months. Two hundred and sixty-three infants were examined using ultrasound. Pathology due to bleeding was classified into three grades (B1-3) similar to Papile's first three grades. Pathology in periventricular white matter was classified into four groups (W1-4): W1 = subtle and We = distinctive white matter echodensities; W3 = cyst formation; W4 = large, intense echodensity. Forty-nine patients had abnormalities in the periventricular white matter (15 W1, 12 W2, 11 W3 and 11 W4) and 58 had subependymal (B1 = 29) or ventricular bleeding without (B2 = 13) or with dilatation (B3 = 16). Ventilator treatment was significantly associated with both B and W lesions. Low gestational age, low birthweight, small for gestational age, pre-eclampsia and caesarean section were significantly associated with B lesions whereas asphyxia, surfactant treatment, male patient sex and outborn were associate with W lesions; b 1-3 and W 1-4 lesions were thus partly associated with different potential risk factors. The pre- and perinatal potential risk factors could only partly explain the variance in the frequency of B and W lesions, indicating that there are yet unidentified risk factors for intracranial ultrasonographic pathology.

Cerebral Hemorrhage↗
PubMed1997

Perinatal risk factors and neuromotor behaviour during the neonatal period.

Preterm birth is associated with an increased risk for neurological handicaps. The purpose of the present study has been: to investigate the influence of perinatal risk factors on early neuromotor development during the neonatal period; to specify the neuromotor parameters particularly sensitive to perinatal complications; and to analyse whether the infant's age at test influences the results. Beside examination of passive/active muscle tone and automatic movements (22 parameters) was performed at 36 (101 infants) and 40 (153 infants) gestational weeks. Low birthweight and long treatment on a ventilator had a negative influence on the neuromotor behaviour at 36 weeks' gestation and white matter disturbances strongly affected the neuromotor parameters at 40 weeks. The development of rooting, sucking, swallowing and arm recoil after long-lasting ventilator treatment was affected by several neonatal risk factors. The development of passive muscle tone and several parameters measuring active muscle tone demonstrated individual consistency between tests, i.e. an infant's rank at 36 weeks' gestation was unchanged 4 weeks later, and some other parameters were not as consistent. The present study shows that several perinatal risk factors influence neuromotor behaviour already during the neonatal period. In addition, the present study provides data on the neuromotor behaviour during the neonatal period that will be related to later neurodevelopmental examinations in order to evaluate the prognostic value of testing neuromotor development.

Developmental Disabilities↗