Biomedical subjects

M Gerwig

Publications and source records attributed to M Gerwig.

12 recordsLinked to original sources

PubMed2006

Comparison of the electrically evoked leg withdrawal reflex in cerebellar patients and healthy controls.

The aim of this study was to analyze the contribution of the cerebellum in the performance of the lower limb withdrawal reflexes. This has been accomplished by comparing the electrically evoked responses in cerebellar patients (CBL) with those in sex- and age-matched healthy control subjects (CTRL). The stimulus was applied to the subjects' medial plantar nerve in four blocks of ten trials each with switching the stimulus from one leg to the other after each block. Responses of the main muscle groups (tibial muscle: TA; gastrocnemius muscle: GA; rectus femoris muscle: RF; biceps femoris muscle: BI) of both legs were recorded during each stimulus. The group of CBL patients consisted of both focally lesioned patients (CBLf) and patients presenting a diffuse degenerative pathology (CBLd). (1) For the withdrawal reflex in CTRL subjects, responses were observed in distal and proximal muscles of the ipsilateral side and corresponding concomitant responses on the side contralateral to the stimulation, whereas in CBL patients responses were restricted primarily to distal muscles, particularly the TA of the ipsilateral, i.e. the stimulated, side. (2) The sequence of activation of the different distal and proximal muscles ipsilateral to the stimulation, derived from latencies and times-to-peak, was for the CTRL group: TA-GA-BI-RF. This sequence was found also in the CBLf patients on their unaffected side. However, on their affected side CBLf patients showed very early GA activation, almost simultaneously with TA and RF activations and before BI activation. RF activation before BI activation was also found in CBLd. In the latter group, GA was activated after RF but before BI with all responses typically delayed. (3) The general pattern of the electrically evoked lower limb reflex consisted of an early, excitatory F1 component and a later, excitatory F2 component of larger amplitude observed in the CTRL subjects and the CBLd patients. In contrast to this pattern CBLf patients exhibited large F1 components followed by small F2 components. (4) The characteristic differences in the withdrawal reflex responses of cerebellar patients depended on the type of the lesion, providing evidence for an important involvement of the cerebellum in the control of the performance of withdrawal reflexes.

Action Potentials↗

PubMed2006

Activation of cerebellar nuclei comparing finger, foot and tongue movements as revealed by fMRI.

The aim of the present study was to compare possible activation of the interposed and dentate cerebellar nuclei during finger, foot and tongue movements using functional magnetic resonance imaging (fMRI). Nineteen healthy control subjects performed sequential finger and repetitive tongue and foot movement tasks. Thin slices (2.5mm) were acquired of the cerebellar region containing the cerebellar nuclei with high spatial resolution (matrix size 128 x 128 x 10) using a Siemens 1.5T Sonata system. Use of an eight channel head coil provided better signal-to-noise-ratio compared to standard head coils. Only data of those 12 subjects were included in final statistical analysis, who showed significant activation of the cerebellar nuclei at least in one task. Cortical activations of the superior cerebellum were found in accordance to the known somatotopy of the human cerebellar cortex. Nuclear activations were most significant in the sequential finger movement task. Both interposed nuclei and ipsilateral dentate nucleus were activated. Dentate activation was present in the more caudal parts of both the dorsal and ventral nucleus. Activation overlapped with motor and non-motor domains of the dentate nucleus described by Dum and Strick [R.P. Dum, P.L. Strick, An unfolded map of the cerebellar dentate nucleus and its projections to the cerebral cortex, J. Neurophysiol. 89 (2003) 634-639] based on anatomical data in monkey. Tongue movement related activations were less extensive and overlapped with activations of caudal parts of the dentate nucleus in the finger movement task. No nuclear activation was seen following foot movements. The present findings show that both interposed and dentate nuclei are involved in sequential finger movements in humans. Interposed nucleus likely contributes to movement performance. Although no direct conclusions could be drawn based on the present data, different parts of the dentate nucleus may contribute to movement performance, planning and possible non-motor parts of the task.

Adult↗

PubMed2006

Muscle force and fatigue in patients with sepsis and multiorgan failure.

INTRODUCTION: Neuromuscular abnormalities are found frequently in sepsis and multiorgan failure (MOF). Surprisingly, however, there are no data on maximum skeletal muscle force and fatigue in these patients. OBJECTIVES: To test the research hypotheses that adductor pollicis (AP) force would be lower in patients with sepsis, whereas fatigue would not differ between patients and immobilized but not infected volunteers. DESIGN AND SETTING: Prospective study; university intensive care unit and laboratory. PATIENTS: Patients with sepsis and MOF (sequential organ failure assessment (SOFA) score >10) and healthy volunteers. INTERVENTIONS: Fatigue was evoked during 20[Symbol: see text]min of intermittent tetanic ulnar nerve stimulation achieving 50% of maximum AP muscle force. MEASUREMENTS AND RESULTS: We measured evoked AP muscle force and fatigue, and compound muscle action potential (CMAP), and performed standard electrophysiological tests in 13 patients, and in 7 volunteers before and after immobilization. Maximum force (20+/-16 vs 65+/-19N; p<0.01) and CMAP (3.6+/-2.5 vs 10+/-2.5 mV; p<0.05) were markedly decreased in patients; however, fatigue and ulnar nerve conduction velocity did not differ from volunteers, and a decrement of CMAP was not observed with nerve stimulation frequencies up to 40 Hz. All patients with critical illness polyneuropathy, and an additional 50% of those without, had significant muscle weakness. CONCLUSION: Peripheral muscle force is markedly decreased in sepsis, without evidence for an increased fatigability. Muscle weakness was most likely due to a sepsis-induced myopathy and/or axonal neuropathy, and was not the result of an immobilization atrophy.

Action Potentials↗

PubMed2005

Trace eyeblink conditioning in human subjects with cerebellar lesions.

Trace eyeblink conditioning was investigated in 31 patients with focal cerebellar lesions and 19 age-matched controls. Twelve patients presented with lesions including the territory of the superior cerebellar artery (SCA). In 19 patients lesions were restricted to the territory of the posterior inferior cerebellar artery (PICA). A 3D magnetic resonance imaging was used to determine the extent of the cortical lesion and possible involvement of cerebellar nuclei. Eyeblink conditioning was performed using a 40 ms tone as conditioned stimulus (CS) followed by a stimulus free trace-interval of 400 ms and a 100 ms air-puff as unconditioned stimulus (US). In SCA patients with lesions including parts of the cerebellar interposed nucleus trace eyeblink conditioning was significantly impaired. Pure cortical lesions of the superior cerebellum were not sufficient to reduce acquisition of trace conditioned eyeblink responses. PICA patients were not impaired in trace eyeblink conditioning. Consistent with animal studies the findings of the present human lesion study suggest that, in addition to forebrain areas, the interposed nucleus is of importance in trace eyeblink conditioning. Although cortical cerebellar areas appear less important in trace compared with delay eyeblink conditioning, the present data strengthen the view that cerebellar structures contribute to different forms of eyeblink conditioning paradigms.

Adult↗

PubMed2005

Probabilistic 3D MRI atlas of the human cerebellar dentate/interposed nuclei.

In a previous study, a three-dimensional (3D) MRI atlas of the human cerebellar nuclei was introduced based on findings in one healthy human subject [Dimitrova, A., Weber, J., Redies, C., Kindsvater, K., Maschke, M., Kolb, F.P., Forsting, M., Diener, H.C., Timmann, D., 2002. MRI atlas of the human cerebellar nuclei. NeuroImage 17, 240-255]. The present MRI investigation was designed to study variability of the anatomy of the dentate/interposed nuclei in a larger group of healthy subjects. Similar to our previous study, iron-induced susceptibility artifacts were used to visualize the cerebellar nuclei as hypointensities on MR images. Data of 63 healthy subjects (27 female, 36 male; mean age 45.3+/-13.4 years, age range 22--71 years) were included. A 3D axial volume of the cerebellum was acquired using a T2*-weighted FLASH sequence on a Siemens Sonata 1.5 T MR scanner. Each volume was registered, re-sampled to 1.00 x 1.00 x 1.00 mm(3) voxel size and spatially normalized into a standard proportional stereotaxic space using SPM99. Dentate/interposed nuclei were traced on axial images and saved as regions of interest using MRIcro-software by two independent examiners. A probabilistic 3D MRI atlas of the cerebellar dentate/interposed nuclei is presented based on findings in all subjects.

Adolescent↗

PubMed2004

Eyeblink conditioning in patients with hereditary ataxia: a one-year follow-up study.

Delay eyeblink conditioning was examined in patients with genetically-defined heredoataxias and age-matched control subjects. 24 patients with spinocerebellar ataxia type 6 (SCA6), type 3 (SCA3), and Friedreich's ataxia (FRDA) participated. SCA6 affects primarily the cerebellum, whereas extracerebellar involvement is common in SCA3 and FRDA. Testing was performed in three sessions six months apart. Severity of ataxia was defined based on the International Ataxia Cooperative Rating Scale (ICARS). As expected, cerebellar patients were significantly impaired in eyeblink conditioning compared to controls. Signs of retention and further learning across sessions were present in controls, but not in the cerebellar patients. In addition, findings of disturbed timing of conditioned responses were observed. Both onsets and peaks of the conditioned responses (CRs) occurred significantly earlier in cerebellar patients. Shortened CR responses were most prominent in patients with primarily cerebellar cortical disease (SCA6). In the group of all cerebellar patients, the SCA3 and the FRDA group correlations between learning deficits and clinical findings were weak. Moderate-to-strong correlations were found in the SCA6 patients. There was no significant change, however, in clinical ataxia scores and CR incidence across the three sessions. In summary, impaired learning of conditioned eyeblink responses is a stable finding across multiple sessions in patients with degenerative cerebellar disorders. Eyeblink conditioning may be a useful measure of cerebellar impairment in patients with hereditary ataxias that primarily affect the cerebellum (such as SCA6). In other heredoataxias (such as SCA3 and FRDA), extracerebellar involvement not assessed by ICARS likely contributes to eyeblink conditioning abnormalities.

Adult↗

PubMed2004

Amplitude changes of unconditioned eyeblink responses in patients with cerebellar lesions.

Timing and amplitude parameters of unconditioned eyeblink responses were investigated in 24 patients with unilateral cerebellar lesions following infarcts within the territory of the superior cerebellar artery (SCA, n=12) and of the posterior inferior cerebellar artery (PICA, n=12). The extent of cortical cerebellar lesions, i.e., which lobules were affected and possible involvement of cerebellar nuclei, was determined by three-dimensional magnetic resonance imaging (3D MRI). Amplitude parameters of eyeblink responses were normalized and expressed as percentage of the unaffected side in patients and the second tested side in age-matched controls. Normalized peak amplitudes, burst area and burst duration were significantly increased in SCA patients with lesions restricted to cortical areas. Burst onset and time to peak were not significantly different compared with controls. Temporal and amplitude parameters of eyeblink responses were unchanged in SCA patients with additional involvement of cerebellar nuclei and in patients with lesions of the PICA territory. Consistent with animal lesion and recording studies and a recent human functional magnetic resonance imaging (fMRI) study, the present data suggest that cortical areas of the superior cerebellum are of importance in eyeblink control in humans. These areas partly overlap with areas known to be critical in eyeblink conditioning.

Adult↗

PubMed2004

Adult post-infectious thalamic encephalitis: acute onset and benign course.

We report on two young patients with an encephalitic syndrome and bilateral thalamic lesions following a presumably viral or mycoplasma respiratory tract infection with the main clinical symptoms of organic psychosis in the first and a prolonged amnestic syndrome and ataxia in the second case. Four months later the patients had recovered clinically and the thalamic lesions had resolved on magnetic resonance imaging in one case and almost completely in the other. We interpret the patients' illness as rare cases of a post-infectious acute thalamic encephalitis in adults. The cases and their relationship to possible post-infectious autoimmune inflammatory or toxic pathophysiological mechanisms are discussed and a review of the literature is provided.

Acute Disease↗

PubMed2003

Evaluation of cortical excitability by motor and phosphene thresholds in transcranial magnetic stimulation.

Motor threshold (MT), as determined by transcranial magnetic stimulation (TMS), is used as a parameter of cortex excitability. In TMS with single or repetitive pulses, stimulus intensities in general are referred to the individual MT, although it is unclear whether MT also reflects the excitability of nonmotor cortical areas such as the visual cortex. Visual cortex excitability can be assessed by thresholds for eliciting phosphenes (phosphene threshold, PT) following TMS over the occipital cortex. The question of a different efficacy of TMS pulses in distinct cortical areas was approached by comparing motor and phosphene thresholds using single-pulse TMS applied to the primary motor and visual cortex. The aim of the study was to clarify, whether MT and PT correlate with each other and whether MT possibly serves as a reasonable measure for the excitability of the visual cortex. In 32 healthy volunteers, TMS with biphasic single pulses was applied over the motor and visual cortex with a figure of eight-shaped coil connected to a Dantec MagPro stimulator. MT and PT were individually measured (percent of maximal stimulator output). Mean PT (61.4+/-11.7%) was significantly higher than mean MT (39.4+/-5.9%) (p=0.01). MT and PT did not correlate significantly (r=0.29, p>0.1). These findings suggest that the MT does not reflect the excitability of the visual cortex. Regarding excitatory effects, the efficacy of TMS may be different over the motor and visual cortex, likely related to a different excitability of these cortical areas. This should be considered in planning and execution of TMS studies of nonmotor cortical areas.

Adult↗

PubMed2003

Comparison of eyeblink conditioning in patients with superior and posterior inferior cerebellar lesions.

The aim of the present study was to compare eyeblink conditioning in cerebellar patients with lesions including the territory of the superior cerebellar artery (SCA) and in patients with lesions restricted to the territory of the posterior inferior cerebellar artery (PICA). The cerebellar areas known to be most critical in eyeblink conditioning based on animal data (i.e. Larsell lobule H VI and interposed nucleus) are commonly supplied by the SCA. Eyeblink conditioning was expected to be impaired in SCA, but not in PICA patients. A total of 27 cerebellar patients and 25 age-matched controls were tested. Cerebellar lesions were primarily unilateral (n = 20). Most patients suffered from ischaemic infarctions of the SCA (n = 11) or the PICA (n = 13). The other patients presented with cerebellar tumours (n = 2) and cerebellar agenesis (n = 1). The extent of the cortical lesion (i.e. which lobuli were affected) and possible involvement of the cerebellar nuclei was determined by 3D-MRI. As expected, the ability to acquire classically conditioned eyeblink responses was significantly reduced in the group of all cerebellar patients compared with the controls. In the patients with unilateral cerebellar lesions, conditioning deficits were present ipsilaterally. In SCA patients with lesions including hemispheral lobules VI and Crus I, eyeblink conditioning was significantly reduced on the affected side compared with the unaffected side. No significant difference between the affected and unaffected sides was present in patients with lesions restricted to the common PICA territory (i.e. Crus II and below). Conditioning deficits were neither significantly different in SCA patients with pure cortical lesions compared with SCA patients with additional nuclear impairment nor in SCA patients with unilateral lesions compared with SCA patients with bilateral lesions. To summarize, unilateral cortical lesions of the superior cerebellum appear to be sufficient to reduce eyeblink conditioning in humans significantly.

Adult↗

PubMed1994

[Recurrent pneumococcal meningitis after splenectomy].

We report the case of a female patient with thrombocytopenic purpura Werlhof. Splenectomy was followed by relapsing pneumococcal meningitis. Particularly, repetitive infections were caused by pneumococcus capsula type 13. This type is not included in the common 23-polyvalent vaccine matter. The necessity of splenectomy in autoimmunological diseases should be considered carefully in the individual case. Patients should be well informed of the high risk of infection after splenectomy and should undergo medical treatment immediately.

Adult↗

PubMed1993

Tremor due to stroke.

We report on four patients with unilateral tremor stemming from cerebrovascular accidents. In two patients with proven lesions of the thalamus, the tremor was irregular and, in addition, there was dystonic posturing of the affected arm. Tremor and dystonic posturing had appeared after the stroke. In the other two patients tremor had occurred immediately at the onset of the stroke and lasted only a few days. The tremors were of small amplitude and high frequency, and lesions could not be found on CT or MRI in these two patients. None of our patients showed signs of the so-called rubral tremor.

Aged↗