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Hans Forssberg

Publications and source records attributed to Hans Forssberg.

36 records · Page 2Linked to original sources
PubMed2004

Dissociating brain regions controlling the temporal and ordinal structure of learned movement sequences.

We used functional magnetic resonance imaging to investigate if different brain regions are controlling the temporal and ordinal structure of movement sequences during performance. Human subjects performed overlearned spatiotemporal sequences of key-presses using the right index finger. Under different conditions, the temporal and the ordinal structure of the sequences were varied systematically in relation to each other, using a factorial design: COMBINED had a rhythm of eight temporal intervals and a serial order of eight keys; TEMPORAL had an eight-interval rhythm produced on one key; ORDINAL had an isochronous rhythm and an eight-key serial order; two control conditions had an isochronous pulse performed on one or two keys, respectively. Brain regions involved in rhythmic and ordinal control of the sequences were revealed by analysing main effect contrasts for the corresponding factors. TEMPORAL and ORDINAL were also compared directly to test for significant differences. A dissociation was found between largely the presupplementary motor area, the right inferior frontal gyrus and precentral sulcus, and the bilateral superior temporal gyri, involved in temporal control, and lateral fronto-parietal areas, the basal ganglia and the cerebellum, which were implicated in ordinal control. The vermis and the superior colliculus were the only regions with an activity increase specifically related to combining long temporal and ordinal sequences. We conclude that humans use different brain networks for temporal and ordinal sequence control, and that the performance of combined sequences activates both networks, the medial cerebellum, and the superior colliculus.

Adolescent↗
PubMed2004

Effects of passive-active movement training on upper limb motor function and cortical activation in chronic patients with stroke: a pilot study.

OBJECTIVE: To explore how repetitive passive-active movement training effects upper limb motor function and cortical activation in patients with stroke. DESIGN: Single-group treatment trial with baseline comparisons. PATIENTS: Ten chronic patients with stroke with paresis of the upper limb. METHODS: Assessments were performed during a 4-week baseline period before and once after 4 weeks of training using the Motor Assessment Scale of the upper limb, Nine Hole Peg Test, goniometer for range of movement and the modified Ashworth scale for muscle tone. Two patients underwent functional magnetic resonance imaging pre- and post-training. The treatment consisted of daily sessions of repeated functional reaching and grasping movements guided passively and attempted actively during 4 weeks. RESULTS: The group improved in range of motion and Motor Assessment Scale scores. Subjects reported improvements in a variety of daily tasks requiring the use of the affected upper limb. Increases in cortical activation in prefrontal and sensorimotor areas were observed in parallel with improvements of upper limb motor function in the 2 patients scanned. CONCLUSION: The 4-week training programme improved hand motor function and ability. Cortical activation on functional magnetic resonance imaging changed in parallel suggesting reorganization of areas related to movements of the paretic limb.

Cerebral Cortex↗
PubMed2003

[Rehabilitation after stroke. Imaging techniques show how the cortical reorganization is affected by training].

It is widely accepted that reorganisation of the brain occurs after a focal brain lesion such as stroke. Neuroimaging methods are used to study such reorganisation in vivo. Improvements in arm and hand motor function during recovery post-stroke have been related to reorganisation in primary and secondary sensorimotor areas by indirect measure of synaptic activity with functional MRI. Reorganisation occurs in both the affected and the unaffected hemispheres. Preliminary training studies post-stroke have shown correlations between improvements in motor function and brain activity changes. Recent research findings are reviewed herein. Further understanding of the neurobiological mechanisms of post-stroke recovery will lead to development of optimal treatment strategies during rehabilitation of stroke survivors.

Brain↗
PubMed2003

Preterm children have disturbances of white matter at 11 years of age as shown by diffusion tensor imaging.

Preterm birth frequently involves white matter injury and affects long-term neurologic and cognitive outcomes. Diffusion tensor imaging has been used to show that the white matter microstructure of newborn, preterm children is compromised in a regionally specific manner. However, until now it was not clear whether these lesions would persist and be detectible on long-term follow-up. Hence, we collected diffusion tensor imaging data on a 1.5-T scanner, and computed fractional anisotropy and coherence measures to compare the white matter integrity of children born preterm to that of control subjects. The subjects for the preterm group (10.9 +/- 0.29 y; n = 9; birth weight or= 2500; gestational age, >or= 37 wk). We found that the preterm group had lower fractional anisotropy values in the posterior corpus callosum and bilaterally in the internal capsules. In the posterior corpus callosum this difference in fractional anisotropy values may partially be related to a difference in white matter volume between the groups. An analysis of the coherence measure failed to indicate a group difference in the axonal organization. These results are in agreement with previous diffusion tensor imaging findings in newborn preterm children, and indicate that ex-preterm children with attention deficits have white matter disturbances that are not compensated for or repaired before 11 y of age.

Anisotropy↗
PubMed2003

Deficient coordination of associated postural adjustments during a lifting task in children with neurodevelopmental disorders.

Precision grip and concomitant anticipatory postural adjustments were investigated in 11 children (three females, eight males; mean age 9 years 1 month, SD 11 months) with attention-deficit-hyperactivity disorder (ADHD); 12 children (three females, nine males; mean age 9 years, SD 7 months) with developmental coordination disorder (DCD), and 13 children (two females, 11 males; mean age 9 years 9 months, SD 11 months) with a combination of ADHD and DCD (ADHD+). There were two comparison groups: an age-matched group (four females, 11 males; mean age 9 years 1 month, SD 14 months) and a younger age group (five females, six males; mean age 6 years 5 months, SD 8 months). Adaptation to different weights was evaluated by lifting a specialized grip instrument monitoring grip force, load force, and centre of foot pressure displacements. Children with ADHD+ showed: (1) excessive grip forces, (2) decreased amplitude and prolonged onset of postural adjustments, and (3) reduced ability to adapt the motor output. Children with ADHD and DCD did not scale manual and postural forces in amplitude and time domains. Children with DCD also differed in delayed timing of postural adjustments. Results indicate that children with ADHD and DCD show a spectrum of neural dysfunctions underlying poor motor coordination, which are not specific to the clinical disorder.

Attention Deficit Disorder with Hyperactivity↗
PubMed2003

Can a therapeutic dose of amphetamine during pre-adolescence modify the pattern of synaptic organization in the brain?

Stimulant drugs such as amphetamine have, for many decades, been the drugs of choice in the treatment of children with attention-deficit/hyperactivity disorder. However, little is known about their therapeutic mechanisms or about the consequences of their long-term exposure. In the present study we investigated whether repeated exposure of a low dose of amphetamine (0.5 mg/kg) to juvenile rats could induce long-term morphological alterations in the prefrontal cortex. In addition, to assess possible behavioural consequences of prolonged exposure to this drug, we examined whether changes in the motor response to various dopamine agonists occurred after this treatment. We found that this dose of amphetamine promotes plasma concentrations of amphetamine sulphate in juvenile rats to levels corresponding to the clinical range used for children with attention-deficit/hyperactivity disorder. Amphetamine (0.5 mg/kg; s.c.) was administered twice daily during postnatal days 22-34, and then the brains of the animals were evaluated 2 weeks later. This treatment produced an increase in dendritic length and branches of pyramidal neurons of the medial prefrontal cortex, but not in the nucleus accumbens. These changes were associated with an increase in the expression of calcium/calmodulin-dependent protein kinase II, a highly abundant signalling protein in the postsynaptic densities of excitatory synapses. Interestingly, amphetamine pre-treatment did not alter the motor response to various dopamine agonists, including amphetamine. These data suggest that clinical doses of stimulant drugs may be acting as a trophic support at the glutamatergic synapses, thereby enhancing dopamine-glutamate interactions in the prefrontal cortex.

Amphetamine↗
PubMed2003

Neural networks for the coordination of the hands in time.

Without practice, bimanual movements can typically be performed either in phase or in antiphase. Complex temporal coordination, e.g., during movements at different frequencies with a noninteger ratio (polyrhythms), requires training. Here, we investigate the organization of the neural control systems for in-phase, antiphase, and polyrhythmic coordination using functional magnetic resonance imaging (fMRI). Brisk rhythmic tapping with the index fingers was used as a model behavior. We demonstrate different patterns of brain activity during in-phase and antiphase coordination. In-phase coordination was characterized by activation of the right anterior cerebellum and cingulate motor area (CMA). Antiphase coordination was accompanied by extensive fronto-parieto-temporal activations, including the supplementary motor area (SMA), the preSMA, and the bilateral inferior parietal gyri, premotor cortex, and superior temporal gyri. When contrasting polyrhythmic tapping with in-phase tapping, activity was seen in the same set of brain regions, and in the posterior cerebellum and the CMA. Antiphase and polyrhythmic coordination may thus to a large extent use common neural control circuitry. In a separate experiment, we analyzed the neural control of the rhythmic structure and the serial order of finger movements during polyrhythmic tapping. Polyrhythmic tapping was compared with an isochronous coordination pattern that retained the same serial order of finger movements as the polyrhythm. This experiment showed that the preSMA and the bilateral superior temporal gyri may be crucial for the rhythmic control of polyrhythmic tapping, while the cerebellum, the CMA, and the premotor cortices presumably are more involved in the ordinal control of the sequence of finger movements.

Adult↗
PubMed2003

Control strategies correcting inaccurately programmed fingertip forces: model predictions derived from human behavior.

When picking up a familiar object between the index finger and the thumb, the motor commands are predetermined by the CNS to correspond to the frictional demand of the finger-object contact area. If the friction is less than expected, the object will start to slip out of the hand, giving rise to unexpected sensory information. Here we study the correction strategies of the motor system in response to an unexpected frictional demand. The motor commands to the mononeuron pool are estimated by a novel technique combining behavioral recordings and neuromuscular modelling. We first propose a mathematical model incorporating muscles, hand mechanics, and the action of lifting an object. A simple control system sends motor commands to and receives sensory signals from the model. We identify three factors influencing the efficiency of the correction: the time development of the motor command, the delay between the onset of the grip and load forces (GF-LF-delay), and how fast the lift is performed. A sensitivity analysis describes how these factors affect the ability to prevent or stop slipping and suggests an efficient control strategy that prepares and corrects for an altered frictional condition. We then analyzed fingertip grip and load forces (GF and LF) and position data from 200 lifts made by five healthy subjects. The friction was occasionally reduced, forcing an increase of the GF to prevent the object being dropped. The data were then analyzed by feeding it through the inverted model. This provided an estimate of the motor commands to the motoneuron pool. As suggested by the sensitivity analysis the GF-LF-delay was indeed used by the subjects to prevent slip. In agreement with recordings from neurons in the primary motor cortex of the monkey, a sharp burst in the estimated GF motor command (NGF) efficiently arrested any slip. The estimated motor commands indicate a control system that uses a small set of corrective commands, which together with the GF-LF-delay form efficient correction strategies. The selection of a strategy depends on the amount of tactile information reporting unexpected friction and how long it takes to arrive. We believe that this technique of estimating the motor commands behind the fingertip forces during a precision grip lift can provide a powerful tool for the investigation of the central control of the motor system.

Adult↗
PubMed2003

Evidence for the involvement of the posterior parietal cortex in coordination of fingertip forces for grasp stability in manipulation.

Grasp stability during object manipulation is achieved by the grip forces applied normal to the grasped surfaces increasing and decreasing in phase with increases and decreases of destabilizing load forces applied tangential to the grasped surfaces. This force coordination requires that the CNS anticipates the grip forces that match the requirements imposed by the self-generated load forces. Here, we use functional MRI (fMRI) to study neural correlates of the grip-load force coordination in a grip-load force task in which six healthy humans attempted to lift an immovable test object held between the tips of the right index finger and thumb. The recorded brain activity was compared with the brain activity obtained in two control tasks in which the same pair of digits generated forces with similar time courses and magnitudes; i.e., a grip force task where the subjects only pinched the object and did not apply load forces, and a load force task, in which the subjects applied vertical forces to the object without generating grip forces. Thus neither the load force task nor the grip force task involved coordinated grip-load forces, but together they involved the same grip force and load force output. We found that the grip-load force task was specifically associated with activation of a section of the right intraparietal cortex, which is the first evidence for involvement of the posterior parietal cortex in the sensorimotor control of coordinated grip and load forces in manipulation. We suggest that this area might represents a node in the network of cortical and subcortical regions that implement anticipatory control of fingertip forces for grasp stability.

Adult↗
PubMed2002

Brain regions controlling nonsynergistic versus synergistic movement of the digits: a functional magnetic resonance imaging study.

Human hand dexterity depends on the ability to move digits independently and to combine these movements in various coordinative patterns. It is well established that the primary motor cortex (M1) is important for skillful digit actions but less is known about the role played by the nonprimary motor centers. Here we use functional magnetic resonance imaging to examine the hypothesis that nonprimary motor areas and the posterior parietal cortex are strongly activated when healthy humans move the right digits in a skillful coordination pattern involving relatively independent digit movements. A task in which flexion of the thumb is accompanied by extension of the fingers and vice versa, i.e., a learned "nonsynergistic" coordination pattern, is contrasted with a task in which all digits flex and extend simultaneously in an innate synergistic coordination pattern (opening and closing the fist). The motor output is the same in the two conditions. Thus, the difference when contrasting the nonsynergistic and synergistic tasks represents the requirement to fractionate the movements of the thumb and fingers and to combine these movements in a learned coordinative pattern. The supplementary (and cingulate) motor area, the bilateral dorsal premotor area, the bilateral lateral cerebellum, the bilateral cortices of the postcentral sulcus, and the left intraparietal cortex showed stronger activity when the subjects made the nonsynergistic flexion-extension movements of the digits than when the synergistic movements were made. These results suggest that the human neural substrate for skillful digit movement includes a sensorimotor network of nonprimary frontoparietal areas and the cerebellum that, in conjunction with M1, control the movements of the digits.

Adult↗
PubMed2002

Sex differences in the motor inhibitory and stimulatory role of dopamine D1 receptors in rats.

We investigated sex differences in the motor responses to the full and selective dopamine D1-like receptor agonist, (+/-)-6-chloro-7,8-dihydroxyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide (SKF-81297; 0.3, 3, and 10 mg/kg, s.c.), in non-habituated adult rats. In general, SKF-81297 produced a biphasic effect on motor activity (including locomotion, rearing and exploratory activity) which consisted of an initial short inhibition followed by a long-lasting stimulation. These effects were dose- and sex-dependent. The inhibitory phase was more pronounced in males than females while the opposite was true for the stimulatory phase. Importantly, the motor inhibitory effects of SKF-81297 were not due to an increase in stereotypy (e.g., grooming activity). These biphasic effects on several motor parameters suggest the presence of two distinct dopamine D1 receptor populations which have opposite effects on motor activity and which are, in part, sexually dimorphic.

Animals↗
PubMed2002

Selective up-regulation of dopamine D1 receptors in dendritic spines by NMDA receptor activation.

Glutamate, by activating N-methyl-d-aspartate (NMDA) receptors, alters the balance between dopamine D1 and D2 receptor signaling, but the mechanism responsible for this effect has not been known. We report here, using immunocytochemistry of primary cultures of rat neostriatal neurons, that activation of NMDA receptors recruits D1 receptors from the interior of the cell to the plasma membrane while having no effect on the distribution of D2 receptors. The D1 receptors were concentrated in spines as shown by colocalization with phalloidin-labeled actin filaments. The effect of NMDA on D1 receptors was abolished by incubation of cells in calcium-free medium and was mimicked by the calcium ionophore ionomycin. Recruitment of D1 receptors from the interior of the cell to the membrane was confirmed by subcellular fractionation. The recruited D1 receptors were functional as demonstrated by an increase in dopamine-sensitive adenylyl cyclase activity in membranes derived from cells that had been pretreated with NMDA. These results provide evidence for regulated recruitment of a G protein-coupled receptor in neurons, provide a cell biological basis for the effect of NMDA on dopamine signaling, and reconcile the conflicting hyperdopaminergic and hypoglutamatergic hypotheses of schizophrenia.

Animals↗
PubMed2002

Increased brain activity in frontal and parietal cortex underlies the development of visuospatial working memory capacity during childhood.

The aim of this study was to identify changes in brain activity associated with the increase in working memory (WM) capacity that occurs during childhood and early adulthood. Functional MRI (fMRI) was used to measure brain activity in subjects between 9 and 18 years of age while they performed a visuospatial WM task and a baseline task. During performance of the WM task, the older children showed higher activation of cortex in the superior frontal and intraparietal cortex than the younger children did. A second analysis found that WM capacity was significantly correlated with brain activity in the same regions. These frontal and parietal areas are known to be involved in the control of attention and spatial WM. The development of the functionality in these areas may play an important role in cognitive development during childhood.

Adolescent↗
PubMed2002

Developmental risks and protective factors for influencing cognitive outcome at 5 1/2 years of age in very-low-birthweight children.

In a population-based follow-up study (the Stockholm Neonatal Project), 182 children with a birthweight of 1500 g or less (very-low birthweight: VLBW) and a control group of 125 children born healthy at term were examined with the Wechsler Preschool and Primary Scale of Intelligence-Revised (WPPSI-R) and a neuropsychological test battery (Nepsy) at 5 1/2 years of age. The WPPSI-R results of the VLBW children fell well within the normal range: WPPSI-R full-scale IQ 95.7, verbal subscale IQ 99.9, and performance subscale IQ 91.6. Nevertheless, the control group had significantly better results than the VLBW group which could be attributed to the greater variability of the VLBW group, with a larger proportion falling in the lower area of the IQ distribution, especially on the performance subscale. Likewise, the control group displayed better executive function (Nepsy). Paternal education was equal in the two groups and was the single most important predictor of IQ, possibly acting as a protective factor. The need for glasses or lenses was inversely associated with all IQ measures and severe retinopathy of prematurity (ROP) had the most negative impact on full-scale and performance IQ. These two IQ measures were also negatively associated with intrauterine growth retardation late in pregnancy. We conclude that VLBW children, in the absence of these identified risk factors, have normal cognitive development.

Child, Preschool↗
PubMed2002

Training of working memory in children with ADHD.

Working memory (WM) capacity is the ability to retain and manipulate information during a short period of time. This ability underlies complex reasoning and has generally been regarded as a fixed trait of the individual. Children with attention deficit hyperactivity disorder (ADHD) represent one group of subjects with a WM deficit, attributed to an impairment of the frontal lobe. In the present study, we used a new training paradigm with intensive and adaptive training of WM tasks and evaluated the effect of training with a double blind, placebo controlled design. Training significantly enhanced performance on the trained WM tasks. More importantly, the training significantly improved performance on a nontrained visuo-spatial WM task and on Raven's Progressive Matrices, which is a nonverbal complex reasoning task. In addition, motor activity--as measured by the number of head movements during a computerized test--was significantly reduced in the treatment group. A second experiment showed that similar training-induced improvements on cognitive tasks are also possible in young adults without ADHD. These results demonstrate that performance on WM tasks can be significantly improved by training, and that the training effect also generalizes to nontrained tasks requiring WM. Training improved performance on tasks related to prefrontal functioning and had also a significant effect on motor activity in children with ADHD. The results thus suggest that WM training potentially could be of clinical use for ameliorating the symptoms in ADHD.

Adolescent↗
PubMedDate not supplied

Temporal resolution of auditory perception and verbal working memory in 15 children with language impairment.

We investigated temporal resolution of auditory perception (TRAP), verbal working memory, and speech perception in 15 children with language impairment (LI) in comparison with a control group of 99 typical children. A computerized two-choice test was used to assess these three abilities. No deficits in TRAP were found in the LI group, and the thresholds were similar for both study groups. It was interesting that the variability was high for both groups and that the control group's performance was poorer than reported in some previously published studies. There were significant differences in the two groups' performance on speech perception and verbal working memory. Working memory was the most sensitive of these two measures.

Auditory Perception↗