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V Hömberg

Publications and source records attributed to V Hömberg.

At least 55 records · Page 3Linked to original sources
PubMed1992

Magnetoelectrical stimulation of motor cortex in children with motor disturbances.

Transcranial magnetoelectrical stimulation (TMS) is now widely used as a diagnostic tool in adults. In this study we report our experiences with this technique in children with central motor disturbances. We used a Cadwell MES10 magnetoelectrical stimulator with a maximal magnetic field of 2 tesla. The stimulation procedure followed a standardized protocol, with the patients being as relaxed as possible in order to avoid contamination of parameters with different preinnervational levels. Stimulation data were compared to a data base obtained in 58 normal children. The first group of patients consisted of 20 children aged from 7 months to 16 years with hemiparesis of different etiologies. Neuroimaging data were correlated with the results of magnetoelectrical stimulation. In 13 patients a pathological pattern of TMS could be detected, and in 7 of these a corresponding lesion of the cortico-spinal tract was found in CT or MRI scans. In 7 children TMS was normal, in spite of a clear-cut lesion of the cortico-spinal tract in CT or MRI scans in 4 of them. The second group of patients consisted of 16 children with extrapyramidal disease, mostly of hereditary origin, such as DOPA-responsive dystonia or benign hereditary chorea. TMS showed a normal response pattern in this group. We discuss problems and possible pitfalls in TMS in childhood in evaluating the diagnostic value of TMS. At the moment the diagnostic usefulness of TMS in children with motor disturbances appears limited and calls for careful interpretation.

Adolescent↗
PubMed1992

Maturation of set-modulation of lower extremity EMG responses to postural perturbations.

To analyse the influence of different "postural sets" on stance stabilizing EMG responses in children, EMG responses to toe-up tilt perturbations were recorded in 70 children between the age of 9 months and 10 years, as well as in a control group of 10 adults under different postural set conditions, using either bilateral destabilization with eyes opened, eyes closed, or introducing additional minute upper extremity support. Recordings were also made with the children seated in front of the platform with the ankle joint angle being identical to that in the standing condition. Also recordings were made after unilateral destabilization in bilateral lower leg muscles, to determine if there is a generalization of EMG response patterns to the mechanically not disturbed side. Across all age-groups the principal modulation of EMG response changes according to postural conditions was identical. Long latency (LL) EMG responses were down-regulated when additional upper extremity support was provided. LL-responses were abolished in the sitting condition. With unilateral destabilizations throughout all age-groups short latency responses were restricted to the perturbed side, whereas long latency responses could be obtained symmetrically. The proximal to distal gradient of recruitment of muscle groups, remained identical across all age-groups. The data indicate that the basic organizational principle of stance stabilizing EMG responses and their modification by postural sets remains invariant across development. This indicates that the involved organizational principles are present as soon as a child is able to stand upright and are not subject to further shaping by motor learning.

Child↗
PubMed1991

Maturation of lower extremity EMG responses to postural perturbations: relationship of response-latencies to development of fastest central and peripheral efferents.

EMG responses to toe-up tilt perturbations on a movable platform system were analysed in 86 children between the age of 12 months and 13 years. To assess the relative contribution of peripheral and central nerve conduction properties, a concomitant recording of the fastest efferent pathways in the central and peripheral motor system was made using non-invasive transcranial magnetic stimulation of motor cortex and peripheral nerve roots. This allowed the determination of the fastest downstream efferent connection times from motor cortex to lumbar motor neuron pools and to measure the fastest efferent conduction from these motor neuron pools to effector muscles in the lower leg. The sequence observed for stance stabilizing EMG responses was similar to that obtained in earlier studies with short latency (SL) and middle latency (ML) companents occurring in the stretched triceps surae muscle and long latency (LL) responses occurring in the non-stretched tibialis anterior muscle. Homologous responses were also obtained in upper leg muscles, being recruited consistently later than those in lower leg muscles across all age groups. In the short latency range two different SL1- and SL2-responses were obtained in children of all age groups as well as in adult controls. Both the SL1- and the SL2-responses showed a flat developmental profile, reaching adult values between 20 and 30 months of age which correlated with that of the fastest efferents from lumbar motor neuron pools to leg muscles, i.e. the final motor path. ML-responses showed a steeper developmental profile.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Impairment of visual perception and visual short term memory scanning by transcranial magnetic stimulation of occipital cortex.

Transcranial magnetic stimulation (TMS) of occipital cortex was performed using a magneto-electric stimulator with a maximum output of 2 Tesla in 24 normal volunteers. The identification of trigrams, presented for 14 ms in horizontal or vertical arrays was significantly impaired when the visual stimulus preceded the occipital magnetic shock by 40 to 120 ms. The extent of impairment was related to TMS intensity. The latency of perceptual impairment was shorter for more intense TMS. No perceptual impairment was obtained by "sham" stimulation when TMS shocks were applied to the upper cervical region rather than the occipital region to rule out unspecific startle reactions affecting attention possibly responsible for the observed reduction in performance. Occipital TMS did not evoke systematic eye movements except for blink responses at latencies beyond 40 ms which were too late to interfere with visual input. Depending on the required serial order of readout of the trigram perceptual impairment was more marked for the second and third part of the trigram. This demonstrates that TMS interferes with the internal serial processing of visual input. To elucidate this further, TMS was used in a Sternberg short term visual memory scanning task. TMS caused a marked decrease in memory scanning rates whereas visual stimulus encoding and storage remained unaffected when tested at various TMS delays. TMS appears to be a useful method to study processes of visual perception and short term memory handling in the occipital cortex. Advantages over classical visual masking techniques especially regarding topical localisation are discussed.

Adult↗
PubMed1991

Influence of stimulus repetition rate on cortical somatosensory potentials evoked by median nerve stimulation: implications for generation mechanisms.

Despite growing clinical and experimental interest in the cortical components of somatosensory evoked potentials (SEPs) little is known about their physiological dynamics, e.g. with changing stimulation parameters. This paper reports the influence of varying stimulus repetition rate from 0.5 to 5 Hz on cortical SEPs up to 60-msec latency after right median nerve stimulation, separately analyzed at frontal (F3), central (C3) and parietal (P3) electrodes. The amplitudes of early frontal P20 and N25, central P14 and N18, and parietal N20 did not change with stimulation rate. Later deflections were significantly modified when their amplitudes were determined with respect to the baseline: at F3 negative N30 and N60 diminished and positive P40 was enhanced with increasing rate of stimulation. At P3 the effects were the reverse, so that positive P27 and P45 were attenuated while negative N34 and N60 were enhanced. At C3 both positive P22 and P40 and negative N60 were reduced. However, the corresponding peak-to-peak amplitudes changed much less. We conclude that SEP waveforms following the earliest cortical deflections are very sensitive to small changes in stimulation frequency. The opposite changes at F3 compared with P3 probably represent the opposite scalp field poles from horizontally oriented generator(s) located within the primary sensorimotor cortex (SMI). We suggest that the rate effects are partly due to selective sensitivity of postexcitatory inhibitory postsynaptic potentials to stimulation frequency.

Adult↗
PubMed1991

Transcranial stimulation of motor cortex in upper motor neurone syndrome: its relation to the motor deficit.

The purpose of this investigation was to clarify the functional significance of the fastest cortico-motoneuronal connections in chronic upper motor neurone syndromes. Using magneto-electrical stimulation of motor cortex the intactness of cortico-motoneuronal connections was assessed in 51 patients presenting with variable degrees of impairment. There was a gross correlation between clinical impairment of the patient and the degree of pathology of cortico-motoneuronal efferents. Covariation of clinical data with transcranial stimulation was better than covariation with the size of lesion on CT scans. In some patients, however, definite clinical impairment, especially affecting distal fractionated movements, was associated with completely normal responses. There was no evidence of response abnormality in distal muscles ipsilateral to the hemispheric lesion. The data indicate that motor deficit can exist in the presence of normal cortico-motoneuronal conduction times, showing that intactness of these connections is not a sufficient condition for preservation of voluntary motor activities. This underlines the importance of other pathways for the pathogenesis of upper motor neurone syndromes.

Adult↗
PubMed1991

Modification of cortical somatosensory evoked potentials during tactile exploration and simple active and passive movements.

The present study compares the effects of different types of movement on median nerve somatosensory evoked potentials (SEPs) recorded from frontal, central and parietal electrodes. Test conditions included tactile exploratory movements, repetitive active and passive thumb movements and isometric contraction. All these conditions modified the SEPs in a similar manner. Parietal N20, P25, and N60, central P22 and N32, and frontal N25, N30 and P40 deflections were diminished, while later centro-parietal P40 and fronto-central N60 were unchanged. A small frontal P35 emerged during movement. The subcortical P14 was not changed in any of the conditions. The similar modulatory effects of simple active movements and of tactile exploration indicate that the modification of SEPs does not depend on the importance of proprioceptive feedback information for movement execution. As all modulatory effects were present also during passive movement, these observed effects are most likely to be caused by afferent occlusion in the ascending thalamo-cortical pathways or sensorimotor cortical cell populations.

Adult↗
PubMed1991

Magnetic stimulation of motor cortex and nerve roots in children. Maturation of cortico-motoneuronal projections.

Magnetoelectrical stimulation of motor cortex and peripheral nerve roots was used to establish the maturational profiles of central and peripheral nervous system conduction times in normal children in upper and lower extremity muscles. To obtain true central conduction times, not contaminated by variation due to different preinnervational levels, a protocol using stimulation under full muscular relaxation was used. With this protocol clear responses of the upper extremity could be obtained after the first year of life, whereas in the lower extremity they could not be obtained before the fourth year of life. The developmental profile of central conduction times to upper and lower extremity muscles showed an age-dependent acceleration with adult values not being reached before the age of about 10 years. In contrast, peripheral conduction times obtained after cervical or lumbar root stimulation to upper and lower extremities showed a much faster maturational profile, with adult values being reached at about the age of 3 years. The data are discussed in relation to the available literature on neuromorphological development and provide normative values for the understanding of normal development of motor control in children as well as for application of this technique in children with motor disturbances.

Adolescent↗
PubMed1990

Central motor conduction to hand and leg muscles in Huntington's disease.

Using electromagnetic stimulation of motor cortex and cervical or lumbar roots, central conduction times to the thenar and abductor hallucis muscles bilaterally were determined in a population of 32 patients with definite Huntington's disease (HD) and 14 subjects at risk. The HD patients showed a wide variety of different severity of choreatic movements, disease duration, and total disability. None of the stimulation parameters (latency after cortical stimulation, amplitude, threshold, or central conduction time) revealed statistically significant abnormalities compared with a normal control group as well as between patient subgroups. The data indicate that central motor conduction to upper and lower extremity muscles remains normal in Huntington's disease irrespective of the severity of the disorder.

Adolescent↗
PubMed1990

Hemispheric specialization in visual, tactile and crossmodal assembling tasks.

There is ample evidence that the right or non-language related hemisphere of the brain is superior in processing of spatial information. This issue appears less clear when a task involves elaborate mental operations that require the integration of spatial information at a stage beyond mere perceptual discrimination. Examples are block design tasks, which are frequently used as estimates of general intelligence. Results of these tests have been contradictory as to whether there is a right hemispheric advantage for their execution. This study was aimed to look at a possible hemispheric preponderance in block design tasks comparing visual, tactile and crossmodal spatial performance. A two-dimensional template had to be reproduced by arranging cubes with surfaces different in both colour and texture. In the visual condition the template was given in the visual modality and the cube arrangement was under visual control. In the tactile condition the template was presented tactually and the cube assembly had to be done under entirely tactual control. In the crossmodal condition the template was presented visually and the assembly was restricted to tactual control. Task completion time (TCT) and number of correct responses (NCR) were compared between right hand and left hand responses. Only in the crossmodal condition a constant left hand superiority of performance was found. Non-crossmodal tasks did not show a constant hemispheric preponderance. In the tactile condition allowing for easy differentiation of input to one or the other hemisphere TCTs varied only according to the compatibility of side of afferent input and side of assembling action irrespective of the hemisphere engaged. It is concluded that mental operations requiring spatial assembling not necessarily engage the non-dominant hemisphere to a larger extent than the language dominant hemisphere. For crossmodal information processing, however, the non-dominant hemisphere appears to be superior.

Adult↗
PubMed1990

EMG responses in leg muscles to postural perturbations in Huntington's disease.

This paper compares leg muscle electromyogram (EMG) responses to sudden toe-up tilts of a moveable platform in patients with Huntington's disease (HD), clinically normal offspring at risk of developing HD (HD risks) and healthy controls. The EMG pattern in standing subjects and patients consisted of short- and middle-latency responses (SL and ML) in the stretched triceps surae muscles and long-latency responses (LL) in the shortened tibialis anterior muscles. The SL response could be further divided into two distinct subcomponents termed SL1 and SL2. An ML response was identified in only 50% of normal subjects and patients. HD patients differed from normal subjects by showing delayed onset latencies and prolonged durations for the LL response, and smaller amplitudes for the ML response. The subjects at risk also showed diminished ML amplitudes and prolonged LL durations, but normal LL onset latencies. In the sitting condition, the EMG responses of the HD patients and of the HD risks did not differ from those of controls: in all groups SL1 was reduced and delayed, SL2 slightly enhanced, while ML and LL were absent. Because both afferent and efferent conduction times are normal in HD, the delayed LL onset reflects abnormal supraspinal organisation of postural control in HD, and indicates that basal ganglia may have a modulatory effect on the LL responses. The normal EMG responses in the sitting patients suggest appropriate regulation of these responses according to postural set in HD.

Adult↗
PubMed1989

Motor control in childhood onset dopa-responsive dystonia (Segawa syndrome).

To elucidate the pathophysiological features of childhood onset dopa-responsive dystonia (DRD) we used a variety of quantitative analysis techniques to evaluate aspects of reflex- and voluntary motor control in two brothers with this disorder. The observed patterns were compared with those obtained in patients with adult onset Parkinson's disease (PD) and Huntington's disease (HD). In both brothers onset of the disease was in the first decade. Both responded either to treatment with L-Dopa or a combination of L-Dopa with trihexiphenidyl. Neurophysiological studies revealed slowing of different upper extremity voluntary motor activities and a low frequency postural tremor similar to results in other basal ganglia disorders including PD. In contrast to adult onset PD, fastest isometric voluntary index finger contractions did not show the typical kinetic tremor oscillations superimposed on the force trajectories. Also, different to adult PD, no impairment of stance regulating reflexes or saccadic and smooth pursuit eye movements was found in DRD. Magnetoelectrical stimulation of motor cortex showed normal efferent cortical spinal activity. Data indicate that like in other basal ganglia diseases slowing of voluntary motor activity is also a constant feature in DRD. DRD patients show, however, a clear difference to the pattern of motor abnormalities obtainable in PD. Both the pattern of motor control abnormalities is different, and the longlasting effect. In contrast to PD the pathophysiological mechanism in DRD possibly involves a lack of maturation of dopaminergic substantia nigra neurons rather than a degenerative process.

Adolescent↗
PubMed1987

Neuromuscular, autonomic and central cholinergic hyperactivity associated with thymoma and acetylcholine receptor-binding antibody.

Two cases of a neuromuscular hyperactivity syndrome associated with a proliferative thymoma and high serum titres of acetylcholine receptor (AChR) antibody with no signs of myasthenia are reported. The clinical and electrodiagnostic findings indicated generalized cholinergic hyperactivity at the neuromuscular junction and in the autonomic and central nervous system, resulting in generalized myokymia, excessive sweating and intermittent psychotic behaviour. The association with thymoma and raised AChR antibody suggests that this syndrome represents a unique type of autoimmune disease, in which antibodies against the AChR facilitate rather than inhibit cholinergic action. This conclusion is supported by the remission of symptoms after thymectomy and with immunosuppressive therapy in one case.

Adult↗
PubMed1987

Stability of frequency during long-term recordings of hand tremor.

During recording of physiological postural hand tremor over a period of 60 min tremor peak frequency (PF) did not change in 14 normal subjects as long as the mechanical conditions were not changed. In contrast, tremor amplitude and synchronization of the corresponding EMG varied considerably. Any alteration in hand mechanics such as changing hand position or adding masses led to changes of PF according to the alteration in mechanical resonant properties. The results show that PF of physiological postural hand tremor is mainly determined by mechanical factors. There is no evidence for a systematic decrease of PF (Stiles et al. 1976) or for the emergence of a formerly described (Lippold 1981) 4-6 Hz tremor component with prolonged maintenance of posture. In the pathological tremor forms of Parkinson's disease or essential tremor PF also remained unchanged during prolonged maintenance of posture.

Adolescent↗
PubMed1987

Impairment of rapid movement in Huntington's disease.

Patients with Huntington's disease (HD) and relatives at risk were examined with respect to their capacity to produce rapid voluntary motor activity. For this purpose, the fastest possible self-paced single isometric forefinger extensions and the fastest alternating forefinger movements were tested. In addition to these fastest voluntary performances, the time course of spontaneous hyperkinetic finger movements and the peak frequency of finger and hand tremor were analysed as a measure of the temporal characteristics of involuntary movements. Comparison of these parameters in HD patients and individuals at risk with age and sex-matched normal controls revealed a significant slowing of all types of contractions or movements in the majority (up to 95%) of the patients and in up to 40% of the relatives at risk. Reaction times were only slightly prolonged, and the abnormalities of the movement parameters showed no correlation with detailed psychometric data. Hence it is unlikely that the disturbance in the execution of rapid motor acts is due to dementia. Tremor was also slower than normal and the hyperkinesias were still slower than the fastest voluntary contractions. It appears from this study that slowness of motor performance is not only evident in Parkinson's disease but may represent a more general dysfunction in basal ganglia disease.

Adult↗