Mitra Ameli

University of Cologne, Köln, North Rhine-Westphalia, Germany

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Publications (23)54.69 Total impact

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    ABSTRACT: This study investigated whether a period of low frequency rTMS preconditioned by tDCS over the primary motor cortex modulates control of grip force in Parkinson's disease. The presented results are from the same patient cohort tested in an earlier study (Gruner et al. J Neural Transm 2010: 117: 207-216). 15 patients with Parkinson's disease (mean age: 69 ± 8 years; average disease duration: 5 ± 3 years) on dopaminergic drugs performed a grasp-lift task with either hand before (baseline) and after a period of 1Hz rTMS (90% of the resting motor threshold; 900 pulses) preconditioned by sham, anodal or cathodal tDCS (1mA, 10 min) over the primary motor cortex. We found that compared with baseline, none of the grip force parameters was significantly influenced by either stimulation session and concluded that grasping is a higher order motor skill, which cannot be modulated by tDCS preconditioned 1Hz rTMS in PD.
    Motor control 04/2012; 16(2):284-92. · 1.39 Impact Factor
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    ABSTRACT: The ability to rapidly establish a memory link between arbitrary sensory cues and goal-directed movements is part of our daily motor repertoire. It is unknown if this ability is affected by middle cerebral artery stroke. Eighteen right-handed subjects with a first unilateral middle cerebral artery stroke were studied while performing a precision grip to lift objects of different weights. In a "no cue" condition, a noninformative neutral visual stimulus was presented before each lift, thereby not allowing any judgment about the object weight. In a "cue" condition arbitrary color cues provided advance information about the weight to be lifted in the subsequent trial. Subjects performed both conditions with either hand. During "no cue" trials subjects scaled their grip force according to the weight of the preceding lift, irrespective of the hand performing the lift or the hemisphere affected. The presentation of color cues allowed patients with right hemispheric stroke, but not those with left hemispheric stroke, to scale their grip force according to the weight in the upcoming lift when lifting the weight with the unaffected hand. Color cues did not allow for a predictive scaling of grip force according to the weight of the object to be lifted when lifting with the affected hand, irrespective of the affected hemisphere. These data imply that the ability of visuomotor mapping in the grip-lift task is selectively impaired in the affected hand after right middle cerebral artery stroke, but in both hands after left middle cerebral artery stroke.
    Neuroscience 03/2012; 210:128-36. · 3.12 Impact Factor
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    ABSTRACT: Animal models of stroke demonstrated that white matter ischemia may cause both axonal damage and myelin degradation distant from the core lesion, thereby impacting on behavior and functional outcome after stroke. We here used parameters derived from diffusion magnetic resonance imaging (MRI) to investigate the effect of focal white matter ischemia on functional reorganization within the motor system. Patients (n = 18) suffering from hand motor deficits in the subacute or chronic stage after subcortical stroke and healthy controls (n = 12) were scanned with both diffusion MRI and functional MRI while performing a motor task with the left or right hand. A laterality index was employed on activated voxels to assess functional reorganization across hemispheres. Regression analyses revealed that diffusion MRI parameters of both the ipsilesional corticospinal tract (CST) and corpus callosum (CC) predicted increased activation of the unaffected hemisphere during movements of the stroke-affected hand. Changes in diffusion MRI parameters possibly reflecting axonal damage and/or destruction of myelin sheath correlated with a stronger bilateral recruitment of motor areas and poorer motor performance. Probabilistic fiber tracking analyses revealed that the region in the CC correlating with the fMRI laterality index and motor deficits connected to sensorimotor cortex, supplementary motor area, ventral premotor cortex, superior parietal lobule, and temporoparietal junction. The results suggest that degeneration of transcallosal fibers connecting higher order sensorimotor regions constitute a relevant factor influencing cortical reorganization and motor outcome after subcortical stroke. Hum Brain Mapp, 2011. © 2011 Wiley-Liss, Inc.
    Human Brain Mapping 10/2011; · 6.88 Impact Factor
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    ABSTRACT: The purpose of this study was to investigate the potential of 3'-deoxy-3'-[¹⁸F]fluorothymidine ([¹⁸F]FLT) positron emission tomography (PET) to detect early treatment responses in gliomas. Human glioma cells were stably transduced with genes yielding therapeutic activity, sorted for different levels of exogenous gene expression, and implanted subcutaneously into nude mice. Multimodality imaging during prodrug therapy included (a) magnetic resonance imaging, (b) PET with 9-(4-[¹⁸F]fluoro-3-hydroxymethylbutyl)guanine assessing exogenous gene expression, and (c) repeat [¹⁸F]FLT PET assessing antiproliferative therapeutic response. All stably transduced gliomas responded to therapy with significant reduction in tumor volume and [¹⁸F]FLT accumulation within 3 days after initiation of therapy. The change in [¹⁸F]FLT uptake before and after treatment correlated to volumetrically calculated growth rates. Therapeutic efficacy as monitored by [¹⁸F]FLT PET correlated to levels of therapeutic gene expression measured in vivo. Thus, [¹⁸F]FLT PET assesses early antiproliferative effects, making it a promising radiotracer for the development of novel treatments for glioma.
    Molecular imaging and biology: MIB: the official publication of the Academy of Molecular Imaging 06/2011; 13(3):547-57. · 2.47 Impact Factor
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    ABSTRACT: Psychogenic tremor is the most common psychogenic movement disorder. Its prognosis is widely held to be poor and strongly depends on the patient's insight into the psychogenicity of the syndrome. The clinical value of transcranial magnetic stimulation (TMS) for (i) establishing the diagnosis with a high level of certainty, (ii) modulating symptom severity and (iii) facilitating patients' insight into psychogenicity was tested in 11 patients with psychogenic tremor of the upper limb. After explaining the psychogenic origin of the syndrome and providing a neurobiological model, 30 TMS pulses were applied over the hand area of the primary motor cortex contralateral to the affected hand(s) at a rate of 0.2 Hz. 15 pulses were administered at intensities of 120 % and 140 % of the resting motor threshold, respectively. Kinematic motion analysis was used to document the effectiveness of the TMS procedure. All patients met the diagnostic criteria of conversion disorder. Time elapsed since symptom onset was on average 48 to 57 months. Tremor affected both hands in 8 patients, one patient had additional head tremor. The TMS procedure caused a significant reduction of tremor frequency and thus established the diagnosis of documented psychogenic tremor according to the criteria proposed by Fahn and Williams (1988) in each patient. The duration of symptom relief was transient in 7 patients, 4 patients had lasting symptom relief. The present pilot study demonstrates that TMS is a helpful tool to (i) establish the diagnosis of psychogenic hand tremor with a high level of certainty, (ii) reduce tremor intensity and (iii) facilitate the patient's insight into the psychogenic origin of the syndrome as a prerequisite to obtain adherence to psychotherapy.
    Fortschritte der Neurologie · Psychiatrie 04/2011; 79(4):226-33. · 0.85 Impact Factor
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    ABSTRACT: Empirical evidence for an essential role of the hippocampal system in arbitrary visuo-motor mapping suggests that acquisition and retrieval of arbitrary visuo-motor mapping might be impaired in mild cognitive impairment (MCI) and Alzheimer's disease (AD). The present pilot study investigated whether MCI of amnestic type or AD impact upon the capacity to scale grip force in a predictive manner to the mass of an object to be lifted based on learned associations between arbitrary colour cues and mass. Patients with MCI (n=8) and AD (n=8) grasped and lifted two different masses (400g and 600g) in random order using a precision grip between index finger and thumb. In a "no cue" experiment, a non-informative neutral visual stimulus was presented prior to each lift, thereby disallowing any prediction about which of the two masses was going to be lifted in the next trial. In a "cue" experiment an arbitrary colour cue provided advance information about which of the two masses to be lifted. In the "no cue" condition patients scaled their grip force according to the mass of the preceding lift. In the "cue" experiment neither patients with amnestic MCI nor those with AD were able to adjust their grip force based on visuo-motor mappings with arbitrary colour cues. These preliminary data suggest that the hippocampal system plays an essential role for arbitrary visuo-motor mapping in the grip-lift task.
    Clinical neurology and neurosurgery 02/2011; 113(6):453-8. · 1.30 Impact Factor
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    ABSTRACT: To investigate whether a period of 1 Hz repetitive transcranial magnetic stimulation (rTMS) over M1 preconditioned by tDCS improves bradykinesia of the upper limb in Parkinson's disease (PD). Fifteen patients with PD performed index finger, hand tapping and horizontal pointing movements as well as reach-to-grasp movements with either hand before (baseline conditions) and after a period of 1 Hz rTMS preconditioned by (1) sham, (2) anodal or (3) cathodal tDCS over the primary motor cortex contralateral to the more affected body side. Movement kinematics was analysed using an ultrasound-based motion analyser at baseline, immediately after and 30 min after each stimulation session. Dopaminergic medication was continued. Compared to baseline, 1 Hz rTMS significantly increased the frequency of index finger and hand tapping as well as horizontal pointing movements performed with the contralateral hand. Movement frequency increased up to 40% over 30 min after cessation of the stimulation. Preconditioning with cathodal tDCS, but not with anodal tDCS, reduced the effectiveness of 1 Hz rTMS to improve tapping and pointing movements. There was no significant increase of movement frequencies of the ipsilateral hand induced by 1 Hz rTMS preconditioned by either tDCS session. Movement kinematics of reach-to-grasp movements were not significantly influenced by either stimulation session. In PD the beneficial effects of 1 Hz rTMS over the primary motor cortex on bradykinesia of simple finger, hand and pointing movements is reduced by preconditioning with cathodal tDCS, but not with anodal tDCS. Preconditioning with tDCS is a powerful tool to modulate the behavioural effect of 1 Hz rTMS over the primary motor cortex in PD.
    Journal of Neural Transmission 02/2010; 117(2):207-16. · 3.05 Impact Factor
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    ABSTRACT: The objective of this study is to investigate whether subjects with Parkinson's disease are able to use arbitrary color cues linked to the mass of an object to be lifted allowing for the predictive selection of appropriate grip forces. Fourteen patients with Parkinson's disease used a precision grip to lift two objects of different masses (400 and 600 g) in random order. In a "no cue" condition, a noninformative neutral visual stimulus was presented before each lift, thereby not allowing any judgement about which mass to be lifted. In a "cue" condition an arbitrary color cue provided advance information about which of the two masses patients would have to lift in the subsequent trial. Patients performed the conditions with either hand and by both on and off drugs. In the "no cue" trials patients scaled the predictive grip force output according to the perceived mass of the preceding lift. In the "cue" experiment patients scaled grip force in a predictive manner to mass based on the provided color cues. The ability of arbitrary visuomotor mapping was evident at either hand and not influenced by medication on/off. The precision of arbitrary visuomotor mapping correlated negatively with age, but not with disease duration, severity of motor disability on and off drug, severity of cognitive impairment on and off drug, or the amount of levodopa equivalent daily dosage of dopaminergic drugs. These data imply that Parkinson's disease does not preclude the ability of visuomotor mapping in the grip-lift task.
    Movement Disorders 08/2009; 24(13):1925-33. · 5.63 Impact Factor
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    ABSTRACT: Within the concept of interhemispheric competition, technical modulation of the excitability of motor areas in the contralesional and ipsilesional hemisphere has been applied in an attempt to enhance recovery of hand function following stroke. This review critically summarizes the data supporting the use of novel electrophysiological concepts in the rehabilitation of hand function after stroke. Repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) are powerful tools to inhibit or facilitate cortical excitability. Modulation of cortical excitability may instantaneously induce plastic changes within the cortical network of sensorimotor areas, thereby improving motor function of the affected hand after stroke. No significant adverse effects have been noted when applying brain stimulation in stroke patients. To date, however, the clinical effects are small to moderate and short lived. Future work should elucidate whether repetitive administration of rTMS or tDCS over several days and the combination of these techniques with behavioral training (ie, physiotherapy) could result in an enhanced effectiveness. Brain stimulation is a safe and promising tool to induce plastic changes in the cortical sensorimotor network to improve motor behavior after stroke. However, several methodological issues remain to be answered to further improve the effectiveness of these new approaches.
    Neurorehabilitation and neural repair 07/2009; 23(7):641-56. · 4.28 Impact Factor
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    ABSTRACT: Facilitation of cortical excitability of the ipsilesional primary motor cortex (M1) may improve dexterity of the affected hand after stroke. The effects of 10 Hz repetitive transcranial magnetic stimulation (rTMS) over ipsilesional M1 on movement kinematics and neural activity were examined in patients with subcortical or cortical stroke. Twenty-nine patients with impaired dexterity after stroke (16 subcortical middle cerebral artery [MCA] strokes, 13 MCA strokes involving subcortical tissue and primary or secondary cortical sensorimotor areas) received 1 session of 10 Hz rTMS (5-second stimulation, 25-second break, 1,000 pulses, 80% of the resting motor threshold) applied over: 1) ipsilesional M1 and 2) vertex (control stimulation). For behavioral testing, 29 patients performed index finger and hand tapping movements with the affected and unaffected hand prior to and following each rTMS application. For functional magnetic resonance imaging, 18 patients performed index finger tapping movements with the affected and unaffected hand before and after each rTMS application. Ten-Hz rTMS over ipsilesional M1, but not over vertex, improved movement kinematics in 14 of 16 patients with subcortical stroke, but not in patients with additional cortical stroke. Ten-Hz rTMS slightly deteriorated dexterity of the affected hand in 7 of 13 cortical stroke patients. At a neural level, rTMS over ipsilesional M1 reduced neural activity of the contralesional M1 in 11 patients with subcortical stroke, but caused a widespread bilateral recruitment of primary and secondary motor areas in 7 patients with cortical stroke. Activity in ipsilesional M1 at baseline correlated with improvement of index finger tapping frequency induced by rTMS. The beneficial effects of 10 Hz rTMS over ipsilesional M1 on motor function of the affected hand depend on the extension of MCA stroke. Neural activity in ipsilesional M1 may serve as a surrogate marker for the effectiveness of facilitatory rTMS.
    Annals of Neurology 04/2009; 66(3):298-309. · 11.19 Impact Factor
  • M Ameli, F Kemper, G Fink, DA Nowak
    Klinische Neurophysiologie - KLIN NEUROPHYSIOL. 01/2009; 40(01).
  • Klinische Neurophysiologie - KLIN NEUROPHYSIOL. 01/2009; 40(01).
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    ABSTRACT: When an object is repeatedly grasped and lifted, the balance between grip force (normal to the object's surface) and lift force (tangential to the object's surface) is programmed according to the mechanical object features within a few lifts. Information related to the mechanical object properties is easily transferred in between both hands, and the cerebellum may play an essential role for the integration and generalization of this information. Recently, we have shown that the transfer of weight-related information in between both hands is impaired in cerebellar degeneration (Nowak et al., Neuropsychologia, 43:20-27, 2005). Here, we investigated the role of the cerebellum for the inter-manual transfer of friction-related information. Healthy subjects and patients with either focal or generalized cerebellar disorders first repeatedly lifted an object with one hand followed by a series of lifts of the same object with the opposite hand. The experiments were performed with the object's grip surfaces covered with either silk or sandpaper. Patients and healthy subjects scaled grip force differentially to surface friction within a few lifts. However, the ability to transfer friction-related information from one hand to the other was disturbed in cerebellar patients. We interpret these data within the recent concept that the cerebellum is essential for the rapid integration and generalization of mechanical object features in between both hemispheres when handling objects in the environment.
    The Cerebellum 01/2009; 8(2):108-15. · 2.60 Impact Factor
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    ABSTRACT: The effect of electrical somatosensory stimulation on motor performance of the affected hand was investigated in 12 chronic subcortical stroke subjects. Subjects performed index finger and hand tapping movements as well as reach-to-grasp movements with both the affected and unaffected hand prior to (baseline conditions) and following (1) 2 h of electrical somatosensory stimulation (trains of five pulses at 10 Hz with 1 ms duration delivered at 1 Hz with an intensity on average 60% above the individual somatosensory threshold) of the median nerve of the affected hand or (2) 2 h of idle time on separate occasions at least 1 week apart. The order of sessions was counterbalanced across subjects. Somatosensory stimulation of the median nerve of the affected hand, but not a period of idle time, enhanced the frequency of index finger and hand tapping movements and improved the kinematics of reach-to-grasp movements performed with the affected hand, compared with baseline. Somatosensory stimulation did not impact on motor performance of the unaffected hand. The data suggest that electrical somatosensory stimulation may improve motor function of the affected hand after stroke; however, further studies are needed to test if the implementation of somatosensory stimulation in rehabilitation of hand function also impacts on manual activities of daily life after stroke.
    Journal of neurology, neurosurgery, and psychiatry 12/2008; 80(6):614-9. · 4.87 Impact Factor
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    ABSTRACT: In healthy people, electrical somatosensory stimulation modulates excitability in contralateral cortical motor areas. The question whether this is associated with a change in motor performance is still under debate. The effect of electrical somatosensory stimulation on motor performance of the hand was investigated in 14 healthy right-handed subjects. Subjects performed index finger and hand tapping movements as well as reach-to-grasp movements towards small and large cubes with each hand prior to (baseline condition) and following 2-hour electrical somatosensory stimulation (trains of 5 pulses at 10 Hz with 1 ms duration delivered at 1 Hz with an intensity on average 60 % above the individual somatosensory threshold) of the (i) right median nerve, (ii) left median nerve, (iii) right tibial nerve (control stimulation) and (iv) left tibial nerve (control stimulation) on separate occasions at least one week apart. The order of sessions was counterbalanced across subjects. Somatosensory stimulation of the median nerves, but not of the tibial nerves, reduced the frequency and velocity of index finger and hand tapping movements performed with the stimulated hand, compared to baseline. In contrast, the kinematics of reach-to-grasp movements remained unaffected by somatosensory stimulation. The data suggest that somatosensory stimulation interferes with the processing of highly automated open-loop motor output at the stimulated limb, as reflected by tapping movements, but not with the processing of closed-loop motor performance, as reflected by reach-to-grasp movements.
    Journal of Neurology 10/2008; 255(10):1567-73. · 3.58 Impact Factor
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    ABSTRACT: We tested the ability of healthy participants to learn an association between arbitrary sensory cues and the weight of an object to be lifted using a precision grip between the index finger and thumb. Right-handed participants performed a series of grip-lift tasks with each hand. In a first experiment, participants lifted two objects of equal visual appearance which unexpectedly and randomly changed their weight. In two subsequent experiments, the change in object weight was indicated by cues, which were presented (i) visually or (ii) auditorily. When no cue about the weight of the object to be lifted was presented, participants programmed grip force according to the most recent lift, regardless of the hand used. In contrast, participants were able to rapidly establish an association between a particular sensory cue with a given weight and scaled grip force precisely to the actual weight thereafter, regardless of the hand used or the sensory modality of the cue. We discuss our data within the theoretical concept of internal models.
    Neuropsychologia 02/2008; 46(9):2383-8. · 3.48 Impact Factor
  • Aktuelle Neurologie - AKTUEL NEUROL. 01/2008; 35.
  • Aktuelle Neurologie - AKTUEL NEUROL. 01/2008; 35.
  • Parkinsonism & Related Disorders - PARKINSONISM RELAT DISORD. 01/2008; 14.
  • Aktuelle Neurologie - AKTUEL NEUROL. 01/2008; 35.

Publication Stats

213 Citations
54.69 Total Impact Points

Institutions

  • 2008–2012
    • University of Cologne
      • Department of Neurology
      Köln, North Rhine-Westphalia, Germany
  • 2011
    • RWTH Aachen University
      • Department of Neurology
      Aachen, North Rhine-Westphalia, Germany