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B Pleger

Publications and source records attributed to B Pleger.

10 recordsLinked to original sources
PubMed2004

[Visual cortex in the Tolosa-Hunt syndrome. Functional imaging for the detection of a psychogenic disorder--a case report].

Besides painful ophthalmoplegia, patients suffering from Tolosa-Hunt syndrome often present increasing loss of visual perception. The impairment of the optic nerve leads to a delay of the VEP (visual evoked potentials) responses. Using the method of magnetic resonance imaging (MRI), some patients present unspecific alterations in the vicinity of the optic nerve. However, both methods (VEP and MRI) are unsuitable to assess the effect of an impaired optic nerve function on neuronal processing in the visual cortex. We report one patient suffering from Tolosa-Hunt syndrome affecting the optic nerve. We used fMRI (functional magnetic resonance imaging) to show how this impairment of the optic nerve alters cortical processing of visual information. The activity of the unaffected visual cortex was bilaterally reduced when compared to healthy volunteers but greater that obtained from patients suffering from bilateral occipital infarction. Our results offer new opportunities to assess the efficiency of therapy in patients with increasing loss of visual perception due to the Tolosa-Hunt syndrome. Further studies are necessary to investigate, whether fMRI also provides the possibility to assess the efficiency of drug therapy on optic nerve function.

Humans↗
PubMed2004

How does the brain accommodate to increased task difficulty in word finding? A functional MRI study.

In functional imaging of the brain, the difficulty of a task may be critical for the pattern of activation. Increased task difficulty could lead to increased activation in task-specific regions or to activation of additional, "compensatory" regions. A previous study with functional transcranial Doppler sonography (fTCD) showed no evidence that increased difficulty in word retrieval leads to a recruitment of areas homologous to language-related regions. The question remains how the brain accommodates increasing task difficulty. Because of limitations of fTCD method, we used functional magnetic resonance imaging (fMRI) in this study. We manipulated word retrieval difficulty in healthy subjects (n = 14) to determine whether the classical language-related brain regions are activated with increasing difficulty in word retrieval. fMRI demonstrated that with increased task difficulty (I) the lateralization of language-associated brain activation remained constant, (II) no additional activation of language-related regions of the dominant hemisphere, nor of homologous regions of the subdominant hemisphere, was evident, (III) additional activation was found in right posterior parietal cortex--typically associated with sustained attention and executive control. Thus, increased difficulty in word retrieval leads to coactivation of distinct brain areas, working together in a large cognitive network, rather than to increased activation of typically language-related areas.

Adult↗
PubMed2004

Amphetamine enhances training-induced motor cortex plasticity.

OBJECTIVES: Repetitive synchronized movements lead to short-term plastic changes in the primary motor cortex, which can be assessed by transcranial magnetic stimulation (TMS). Drugs which enhance such plastic changes could be of therapeutical interest, e.g. in patients with cerebral lesions. MATERIAL AND METHODS: We studied the effect of amphetamine on motor performance and plastic changes in the motor cortex as revealed by TMS mapping in healthy humans, who had to train a repetitive synchronized movement over 1 h. RESULTS: Cortical plastic changes observed after 1 h of training were more pronounced with amphetamine, whereas motor performance did not differ between training sessions with and without amphetamine. CONCLUSION: We conclude that amphetamine is able to enhance training-induced motor cortex plasticity. This effect could be due to its known influence on the GABAergic and glutamatergic system, but might also result from its role as an indirect catecholaminergic agonist.

Adult↗
PubMed2003

Bilateral motor cortex disinhibition in complex regional pain syndrome (CRPS) type I of the hand.

BACKGROUND: Complex regional pain syndrome type I (CRPS I) develops as a consequence of trauma affecting the limbs, without obvious nerve lesion. Its features include pain, edema, autonomic dysfunction, movement disorder, and trophic changes. CNS involvement is suggested by the symptoms, but the pathophysiology of CRPS I is unknown. OBJECTIVE: To assess excitability changes in the motor cortex in patients with CRPS I. METHODS: The authors studied 25 patients with unilateral CRPS I involving the hand by means of transcranial magnetic stimulation using a paired-pulse paradigm. Motor threshold (MT) and intracortical inhibition and facilitation were determined on the affected and the clinically unaffected side. A control group of 20 healthy subjects was studied. RESULTS: The authors found a significant reduction of intracortical inhibition on both sides of patients with CRPS compared with control subjects, whereas intracortical facilitation and MT did not differ significantly. However, in the patients' group, the presence of allodynia significantly decreased MT. CONCLUSIONS: The authors showed a bilateral disinhibition of the motor cortex in patients with complex regional pain syndrome.

Adult↗
PubMed2003

NMDA-mediated mechanisms in cortical excitability changes after limb amputation.

OBJECTIVES: The aim of our study was to determine the role of N-methyl-d-aspartate (NMDA)-mediated mechanisms in cortical excitability changes after limb amputation, and their possible relationship to phantom pain. MATERIALS AND METHODS: Sixteen upper limb amputees who were suffering from chronic phantom pain received the NMDA-antagonist memantine or placebo for 3 weeks. Intracortical inhibition (ICI) and intracortical facilitation (ICF) were determined at baseline and on day 21 using transcranial magnetic stimulation. Simultaneously, phantom pain intensity was assessed. RESULTS: Memantine reduced ICF and enhanced ICI to roughly the same extent as seen in healthy subjects in a previous study. These changes were not correlated to the reduction of phantom pain. CONCLUSION: We therefore conclude that NMDA-mediated mechanisms influence changes of ICI and ICF occurring after limb amputation. However, our results suggest that these cortical excitability changes and phantom pain are independent of each other.

Adult↗
PubMed2001

Repetitive training of a synchronised movement induces short-term plastic changes in the human primary somatosensory cortex.

The aim of our study was to assess possible short-term plastic changes in the human primary somatosensory cortex (S1) induced by a repetitive synchronised movement of the right thumb and shoulder. We therefore performed a source localisation of somatosensory evoked potentials after median nerve stimulation in twelve healthy subjects before and after 1 h of motor training. We found a significant medial shift of the N20 dipole on the left hemisphere after training, whereas the dipole location on the right hemisphere remained unchanged. However, no significant correlation was seen between the dipole shift and the improvement in motor performance. We conclude that repetitive synchronised movements are able to induce plastic changes in the contralateral S1, which might be mainly due to the synchronised proprioceptive input.

Adult↗
PubMed2001

Shifts in cortical representations predict human discrimination improvement.

We report experiments combining assessment of spatial tactile discrimination behavior and measurements of somatosensory-evoked potentials in human subjects before and after short-term plastic changes to demonstrate a causal link between the degree of altered performance and reorganization. Plastic changes were induced by a Hebbian coactivation protocol of simultaneous pairing of tactile stimuli. As a result of coactivation, spatial discrimination thresholds were lowered; however, the amount of discrimination improvement was variable across subjects. Analysis of somatosensory-evoked potentials revealed a significant, but also variable shift in the localization of the N20-dipole of the index finger that was coactivated. The Euclidean distance between the dipole pre- and post-coactivation was significantly larger on the coactivated side (mean 9.13 +/- 3.4 mm) than on the control side (mean 4.90 +/- 2.7 mm, P = 0.008). Changes of polar angles indicated a lateral and inferior shift on the postcentral gyrus of the left hemisphere representing the coactivated index finger. To explore how far the variability of improvement was reflected in the degree of reorganization, we correlated the perceptual changes with the N20-dipole shifts. We found that the changes in discrimination abilities could be predicted from the changes in dipole localization. Little gain in spatial discrimination was associated with small changes in dipole shifts. In contrast, subjects who showed a large cortical reorganization also had lowest thresholds. All changes were highly selective as no transfer to the index finger of the opposite, non-coactivated hand was found. Our results indicate that human spatial discrimination performance is subject to improvement on a short time scale by a Hebbian stimulation protocol without invoking training, attention, or reinforcement. Plastic processes related to the improvement were localized in primary somatosensory cortex and were scaled with the degree of the individual perceptual improvement.

Adult↗
PubMed2001

Assessment of reorganization in the sensorimotor cortex after upper limb amputation.

OBJECTIVE: We wanted to investigate plastic changes occurring in the motor and somatosensory cortex after upper limb amputation, and their possible relationship to phantom pain. METHOD: To assess these plastic changes, we used transcranial magnetic stimulation (TMS) and source localization of somatosensory evoked potentials (SEP). Eleven patients with upper limb amputation were investigated. The phantom pain intensity was assessed by visual analogue scaling (VAS). RESULTS: Using TMS mapping, we found a significant lateralization of the amplitude-weighted centre of gravity (P<0.01) and an enlargement of the excitable area (P<0.05) on the hemisphere contralateral to the amputation. SEP mapping showed a significant medialization of the N20 dipole (P<0.05) on this side. None of these changes correlated with the phantom pain intensity. CONCLUSIONS: We conclude that after limb amputation, the relationship between plastic changes occurring in the sensorimotor cortex and phantom pain seems to be more complex than previously believed.

Adult↗