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Marianne Dieterich

Publications and source records attributed to Marianne Dieterich.

At least 19 recordsLinked to original sources
PubMed2007

Functional brain imaging: a window into the visuo-vestibular systems.

PURPOSE OF REVIEW: Advances have been made in identifying how areas involved in processing vestibular, ocular motor, and visual information are represented in the human cortex as well as the cortical interaction between these systems in healthy subjects. RECENT FINDINGS: While we know how some vestibular and ocular motor disorders modify visuo-vestibular interaction by changing the 'normal' cortical activation-deactivation patterns, it is still early days in functional magnetic resonance imaging studies of patients with specific disorders. Findings from current brain imaging studies of several vestibular, ocular motor, and cerebellar disorders are presented. SUMMARY: The promise of more insights into the complex neuronal networks of the human cortex is great.

Brain Mapping↗
PubMed2006

Cerebral embolic ischemia in rats: correlation of stroke severity and functional deficit as important outcome parameter.

The embolic MCA occlusion model in rats is used for recanalisation studies in acute stroke. In addition to the determination of lesion size, the assessment of functional outcome may improve the value of this model. Male Wistar rats were submitted to MCA clot embolism or sham surgery. In order to achieve a larger variety of lesion volume, 2 subgroups (each 7 animals) were subjected to differently sized emboli (30 and 40 mm). Follow-up period was 6 days. Outcome assessment consisted of a test battery including parallel bar crossing, observation of behaviour in an open field and an 8-arm maze and a neurological score with ten different sensorimotor and coordinative items. Animals were perfusion-fixed on day 7 (blinded examination). For both subgroups, there were significant impairments with regard to performance on the Neuro score, parallel bar crossing and maze exploration. Improvement was only partial during the follow-up period. On follow-up day 6, there was still a significant correlation between total infarct volume and functional outcome on the Neuro score (R=0.80, p=0.0006) and the exploration behaviour in the maze (R=0.66, p=0.01). Application of emboli with a length of 40 mm caused more functional impairment and a more extended lesion volume compared with 30 mm. We present outcome tests that provide quantitative and objective tools to test functional impairment in rats following embolic stroke.

Analysis of Variance↗
PubMed2006

Brainstem and cerebellar fMRI-activation during horizontal and vertical optokinetic stimulation.

Animal studies have shown that not only cortical, but also brainstem and cerebellar areas are involved in the initiation and generation of optokinetic nystagmus (OKN), e.g., cortico-(pretecto)pontine-olivo-cerebellar pathways. The aim of this fMRI study was to identify and differentiate brainstem and cerebellar areas involved in horizontal and vertical OKN (h/vOKN) in humans. In a group of nine healthy volunteers, hOKN and vOKN were statistically compared with a stationary control condition. There were common activated regions for hOKN and vOKN directions located in the transition zone between the posterior thalamus and the mesencephalon bilaterally covering the pretectal nucleus complex, which is known to be a major structure within the afferent branch of the optokinetic system. Furthermore, during hOKN, activation occurred bilaterally in the mediodorsal and dorsolateral ponto-medullary brainstem, which could be best attributed to the reticular formation, especially the paramedian pontine reticular formation (PPRF). For vOKN, additional activated areas in the dorsal mesencephalic brainstem could be best localized to the ocular motor nuclei and the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF). For both OKN directions, the cerebellar activation was localized in the oculomotor vermis (declive VI, folium and tuber VIIA/B, in part pyramis VIIIA), and the flocculus bilaterally as well as widespread in the cerebellar hemispheres. In conclusion, fMRI allowed first attributions of neuronal substrates in the cerebellum and brainstem to hOKN and vOKN in humans. Consistent with the animal data, the dorsal ponto-medullary routes were involved bilaterally for hOKN, whereas the rostral mesencephalic routes were involved for vOKN.

Adult↗
PubMed2006

18F-fluorodeoxyglucose hypometabolism in cerebellar tonsil and flocculus in downbeat nystagmus.

A patient with downbeat nystagmus was examined by F-fluorodeoxyglucose-positron emission tomography once while off and twice while on successful treatment with 4-aminopyridine. All positron emission tomography scans of the patient showed a reduced cerebral glucose metabolism bilaterally in the region of the cerebellar tonsil and flocculus/paraflocculus when compared with a normal database of the whole brain. An additional region-of-interest analysis revealed that 4-aminopyridine treatment lessened the hypometabolism. This finding supports the hypothesis that the cerebellar tonsil and (para-) flocculus play a crucial role in downbeat nystagmus. The hypometabolism might reflect reduced inhibition or even disinhibition of the circuits to the vestibular nuclei, thus causing downbeat nystagmus. The reduced hypometabolism during treatment probably indicates an improvement of the cerebellar inhibition.

4-Aminopyridine↗
PubMed2006

Brain edema and intracerebral necrosis caused by transcranial low-frequency 20-kHz ultrasound: a safety study in rats.

BACKGROUND AND PURPOSE: Ultrasound-accelerated thrombolysis is a promising approach toward acute stroke treatment. In previous in vitro studies, we demonstrated enhanced thrombus destruction induced by 20-kHz ultrasound. However, little is known about biological interactions of low-frequency ultrasound with brain tissue. The aim of this in vivo MRI study was to assess safety aspects of transcranial low-frequency ultrasound in rats. METHODS: The cranium of 33 male Wistar rats was sonificated for 20 minutes (20-kHz continuous wave). Power output was varied between 0 and 2.6 W/cm2. Tympanal and rectal temperature was monitored. Diffusion-weighted imaging and T2-weighted imaging was performed before and 4 hours, 24 hours, and 5 days after sonification. Apparent diffusion coefficients (ADCs) and T2 relaxation time (T2-RT) were measured in regions of interest in the cortex and the basal ganglia. The animals were euthanized for histological evaluation thereafter. RESULTS: Tympanal temperature increased significantly during insonation with 1.1 and 2.6 W/cm2. ADCs decreased significantly at 0.5 and 1.1 W/cm2, indicating cytotoxic edema. T2-RT increased significantly in the 0.5 and 1.1 W/cm2 group, consistent with vasogenic edema. No changes were detectable in the low-power output group (0.2 W/cm2). After sonification with 2.6 W/cm2, a significant loss of neurons could be detected on histopathology. Furthermore, 3 animals developed circumscript cortical lesions that could be identified as parenchymal necrosis. CONCLUSIONS: Low-frequency ultrasound caused vasogenic and cytotoxic brain edema and intracerebral necrosis in a dose-dependent fashion. This study indicates therapeutic low-frequency ultrasound as being potentially harmful and underlines the necessity of careful evaluation in further animal models.

Animals↗
PubMed2006

Direction-dependent visual cortex activation during horizontal optokinetic stimulation (fMRI study).

Looking at a moving pattern induces optokinetic nystagmus (OKN) and activates an assembly of cortical areas in the visual cortex, including lateral occipitotemporal (motion-sensitive area MT/V5) and adjacent occipitoparietal areas as well as ocular motor areas such as the prefrontal cortex, frontal, supplementary, and parietal eye fields. The aim of this functional MRI (fMRI) study was to investigate (1) whether stimulus direction-dependent effects can be found, especially in the cortical eye fields, and (2) whether there is a hemispheric dominance of ocular motor areas. In a group of 15 healthy subjects, OKN in rightward and leftward directions was visually elicited and statistically compared with the control condition (stationary target) and with each other. Direction-dependent differences were not found in the cortical eye fields, but an asymmetry of activation occurred in paramedian visual cortex areas, and there were stronger activations in the hemisphere contralateral to the slow OKN phase (pursuit). This can be explained by a shift of the mean eye position of gaze (beating field) in the direction of the fast nystagmus phases of approximately 2.6 degrees, causing asymmetrical visual cortex stimulation. The absence of a significant difference in the activation pattern of the cortical eye fields supports the view that the processing of eye movements in both horizontal directions is mediated in the same cortical ocular motor areas. Furthermore, no hemispheric dominance for OKN processing was found in right-handed volunteers.

Adult↗
PubMed2005

Spatial neglect--a vestibular disorder?

The phenomenon of spatial neglect after right brain damage greatly helps our understanding of the normal mechanisms of directing and maintaining spatial attention, of spatial orientation, and the characteristics of neural representation of space. The intriguing symptom is a spontaneous orientation bias towards the right leading to neglect of objects or persons on the left. Interestingly, we observe similar symptoms namely a spontaneous bias of eyes and head along the horizontal dimension of space in patients with unilateral vestibular dysfunction. Further similarities concern anatomical findings. Both spatial neglect and vestibular processing at cortical level show dominance in the right hemisphere and involve common brain areas. Lesion studies in human and monkey, electrical and transcranial magnetic stimulation, as well as functional imaging results have revealed the superior temporal cortex, insula and the temporo-parietal junction to be substantial parts of the multisensory (vestibular) system as well as to be affected in spatial neglect. We argue that these structures are not strictly 'vestibular' but rather have a multimodal character representing a significant site for the neural transformation of converging vestibular, auditory, neck proprioceptive and visual input into higher order spatial representations. Neurons of these regions provide us with redundant information about the position and motion of our body in space. They seem to play an essential role in adjusting body position relative to external space. This view may initiate further development of those strategies to treat spatial neglect that use routes to rehabilitation based on specific manipulations of sensory input feeding into this system.

Animals↗
PubMed2005

Imaging the visual autokinetic illusion with fMRI.

During fixation of a stationary, dim light-emitting diode (LED) in complete darkness, a subtle, apparent motion is perceived which is called autokinesis. This autokinetic illusion increases with increasing fixation time. Eleven healthy subjects were examined by fMRI while fixating an LED in darkness for 35 s. BOLD signal changes of the first and the second half of the fixation period were compared. While the stimulus was the same for both periods, perception differed in that autokinesis was more pronounced in the second half. This second half of the period was associated with bilateral activations in the motion-sensitive middle occipito-temporal area known as MT/V5. Our finding suggests that area MT/V5 is involved in the mediation of autokinesis.

Adult↗
PubMed2005

Increased incidence of jugular valve insufficiency in patients with transient global amnesia.

OBJECTIVE: While transient global amnesia (TGA) is a clinically well defined disorder, its etiology is poorly understood. Cerebral venous hypertension and subsequent damage to hippocampal and diencephalic structures are among the discussed hypothetical causes. Using a direct method for the study of retrograde flow during a Valsalva maneuver, we determined whether jugular valve insufficiency contributes to cerebral venous hypertension in patients with TGA. METHODS: Jugular valve closure was assessed by duplex sonography in 20 patients with TGA and 20 age and gender matched controls. The diagnosis of valvular insufficiency was made on the basis of recently established criteria. RESULTS: Valvular insufficiency (either left or right-sided, or bilateral) was identified in 85% of patients with TGA,and in 45% of controls (p = 0.008). All patients with involuntary Valsalva episodes immediately prior to TGA developed valvular insufficiency (n = 8; p = 0.13 compared with patients who did not recall such an event). The mean duration of the insufficiency jet did not differ significantly between patients with TGA (3.26 s) and controls (2.78 s; p = 0.315). However, patients with TGA who experienced a trigger event were characterized by significantly longer insufficiency reflux times (3.84 s) than those without (2.55 s; p = 0.03). CONCLUSIONS: TGA is associated with an increase in the prevalence of jugular insufficiency. Valvular insufficiency may lead to increased venous pressure transmission during a Valsalva maneuver and thus contribute to venous ischemia in TGA. The association of valvular insufficiency and longer reflux times with the occurrence of a trigger event further suggests that cerebral venous congestion is an important etiological factor in transient global amnesia.

Aged↗
PubMed2005

Fixation suppression of optokinetic nystagmus modulates cortical visual-vestibular interaction.

Water activation positron emission tomography and statistical group analysis were used to evaluate differences in activation-deactivation patterns during small-field visual motion stimulation, eliciting rightward optokinetic nystagmus and its fixation suppression in 12 healthy volunteers. Bilateral patterns of activation in the visual cortex, including the motion-sensitive area MT/V5, and deactivations in an assembly of vestibular areas (posterior insula, thalamus, anterior cingulate gyrus) during optokinetic nystagmus was markedly diminished or totally absent during its fixation suppression. This finding agrees with the concept of a reciprocal inhibitory interaction between the visual-optokinetic and the vestibular systems, which takes place at a lower level during fixation suppression, because the potential mismatch between the two sensory inputs, visual and vestibular, is then reduced.

Adult↗
PubMed2005

Ultrasound-induced blood clot dissolution without a thrombolytic drug is more effective with lower frequencies.

BACKGROUND AND PURPOSE: Therapeutic ultrasound as stand-alone therapy or in combination with rt-PA has proven to be an effective measure for recanalisation of acute vessel occlusion in different in vitro and in vivo studies. Uncertainty still exists concerning the optimal frequency and intensity with regard to the thrombolytic efficacy of ultrasound. The purpose of this study was a direct comparison of different ultrasound frequencies, when otherwise using identical measurement settings and parameters. METHODS: Ultrasound-induced dissolution of fresh human blood clots was studied in a flow system using low-frequency continuous wave ultrasound of 20, 40 and 60 kHz. After calibration of each ultrasound probe, blood clots were exposed to local time average intensities of either 0.12 or 0.2 W/cm2. Exposure time of the clots to ultrasound was 10 min, the number of treated clots in each experimental group was 12. RESULTS: As tested with 0.2 W/cm2, we found the most pronounced thrombolytic effect with the 20-kHz probe (weight loss of blood clots: 52.4%) and the 40-kHz probe (49.4%), as compared to the 60-kHz probe (21.4%) and the control group (18.5%). The difference between the 20- and 60-kHz probes was statistically significant (p < 0.001). The treatment effect was clearly intensity dependent with a less pronounced, but still significant treatment effect at 0.12 W/cm2 (24.5% at 20 kHz; p < 0.001 compared to 0.2 W/cm2; p = 0.045 compared to controls). CONCLUSIONS: These data show that therapeutic efficacy of ultrasound, in absence of a thrombolytic drug, is frequency and intensity dependent with best results at low frequencies. With continuous wave transmission, the benefit may be limited to the very low frequency range. The results are a basis for further evaluation in animal models.

Anticoagulants↗
PubMed2005

Functional MRI of galvanic vestibular stimulation with alternating currents at different frequencies.

Functional MRI was performed in 28 healthy volunteers to study the effects of galvanic vestibular stimulation with alternating currents (AC-GVS) of different frequencies on brain activation patterns. The aims of this study were (1) to identify specific areas within the vestibular cortical network that are involved in the processing of frequency-specific aspects by correlation analyses, (2) to determine the optimal frequency for stimulation of the vestibular system with respect to perception, and (3) to analyze whether different frequencies of AC-GVS are mediated in different cortical areas or different sites within the vestibular cortex. AC-GVS was performed using sinusoidal stimulation currents with an amplitude of +/-2.5 mA, and frequencies of 0.1 Hz, 0.3 Hz, 0.8 Hz, 1.0 Hz, 2.0 Hz, and 5.0 Hz were applied. Regardless of the applied stimulation frequency, AC-GVS elicited activations within a network of multisensory areas similar to those described in earlier studies using direct currents. No mapping of different stimulation frequencies to different cortical locations was observed. Additional activations of somatosensory cortex areas were observed during stimulation with 5 Hz only. The strongest vestibular sensations were reported during stimulation with 1 Hz and 2 Hz. Correlation analyses between blood oxygenation level dependent (BOLD) signal changes and stimulation frequency revealed a positive dependency in areas of the supramarginal gyrus, posterolateral thalamus, cerebellar vermis, posterior insula, and in the hippocampal region/uncus. These regions represent areas involved in the processing of vestibular information for head and body orientation in space.

Adult↗
PubMed2005

Somatotopic organization of the corticospinal tract in the human brainstem: a MRI-based mapping analysis.

To investigate the incompletely understood somatotopical organization of the corticospinal tract in the human brainstem, we performed a voxel-based statistical analysis of standardized magnetic resonance scans of 41 prospectively recruited patients with pyramidal tract dysfunction caused by acute brainstem infarction. Motor hemiparesis was rated clinically and by the investigation of motor evoked potentials to arms and legs. Infarction affected the pons in 85% of cases. We found the greatest level of significance of affected brainstem areas between the pontomesencephalic junction and the mid pons. Lesion location was significantly more dorsal in patients with hemiparesis affecting more proximal muscles and was significantly more ventral in patients with predominantly distal limb paresis. Comparison of magnetic resonance lesion from patients with paresis predominantly affecting arm or leg did not show significant topographical differences. We conclude that a topographical arm/leg distribution of corticospinal fibers is abruptly broken down as the descending corticospinal tract traverses the pons. Corticospinal fibers, however, follow a somatotopical order in the pons with fibers controlling proximal muscles being located close to the reticular formation in the dorsal pontine base, and thus more dorsal than the fibers controlling further distal muscle groups.

Adult↗
PubMed2005

Immunosuppressive treatment in bilateral vestibulopathy with inner ear antibodies.

CONCLUSIONS: Although vestibular recovery was observed after steroid treatment, it remains uncertain whether this improvement was spontaneous or due to medication. These data do not allow us to generally recommend corticosteroid treatment in patients with BVF and inner ear antibodies. OBJECTIVE: A retrospective study was performed based on the observation of two patients with suspected autoimmune bilateral vestibular failure (BVF) with normal hearing and antilabyrinthine or nervous tissue-specific serum antibodies who showed vestibular recovery after corticosteroid treatment. MATERIAL AND METHODS: Twelve patients with BVF and serum inner ear antibodies who had received imuunosuppressive treatment with corticosteroids were evaluated in terms of medical history, repetitive caloric irrigation and repetitive determination of inner ear antibodies. BVF was complete in four patients and incomplete in eight. RESULTS: After immunosuppressive therapy, four of the 12 patients showed a moderate recovery of the peak slow-phase velocity of horizontal nystagmus induced by bithermal caloric stimulation, which was only transient in two of them.

Adult↗
PubMed2005

Functional and morphological criteria of internal jugular valve insufficiency as assessed by ultrasound.

BACKGROUND AND PURPOSE: Jugular venous valve insufficiency may play a role in different neurological diseases. This study describes the methodology to detect internal jugular valve insufficiency and establishes functional and morphological criteria to discriminate retrograde flow during valve closure from retro grade insufficiency flow. METHODS: Valve closure was assessed in 100 valves (50 healthy volunteers). The valves were visualized in B-mode. During a pressure-controlled Valsalva maneuver, valve closure was monitored by color duplex. The duration and the peak velocity of retrograde flow were determined. RESULTS: Backward flow during valve closure in competent valves was visually clearly discernible from a retrograde flow jet through insufficient valves. Insufficiency was found in 29% of valves. The duration of backward flow in competent valves was between 0.22 and 0.78 seconds (mean = 0.46 +/- 0.14 seconds on Doppler measurements) and in insufficient valves between 1.23 and 6.15 seconds (mean = 2.66 +/- 1.28; P < .0001). Peak velocity of retrograde flow in competent valves was between 12 and 65 cm/s (mean = 26.2 +/- 11.1 cm/s) and between 25 and 160 cm/s (mean = 89.5 +/- 39.3 cm/s; P < .0001) in insufficient valves. On B-mode imaging, the "typical" aspect of an immobile, frozen valve was seen only in 5 cases of insufficient valves; 21 insufficient valves did not display this aspect. CONCLUSION: The duration of retrograde flow clearly discriminates competent and incompetent valves. On the basis of our results, we provide cut off values that help differentiate between physiological and insufficiency reflux. The differences in peak velocity and morphology criteria are helpful but not reliable to predict insufficiency of the valve.

Case-Control Studies↗
PubMed2005

Expectation of sensory stimulation modulates brain activation during visual motion stimulation.

The differential effects of visual hemifield motion stimulation during fixation of a stationary target were compared under two conditions: fixation straight ahead without any further instructions and fixation straight ahead with attention shifted to the "dark hemifield." Data from nine right-handed volunteers revealed that striate and extrastriate right hemispheric visual areas exhibited larger activations during left hemifield motion stimulation when attention was shifted to the right dark hemifield. Montreal Neurological Institute (MNI) coordinates (26, -98, -4) of the additional clusters activated in the latter condition corresponded best to the kinetic occipital region, which is known to process both shape and motion information, and to parts of area V3 posterior to V3A, which has been shown repeatedly to mediate motion perception. A simple computational model of transhemispheric visuovisual interaction is proposed. The basic mechanism of this model is a central predictor formed by a feedback loop that detects a mismatch between input to the two hemispheres. Predicted stimulation is then compared with the actual input. If the sensed motion of a visual hemifield is larger than the predicted net motion in the model, activation of the respective neural population is increased; conversely, a smaller actual motion causes less activation.

Adult↗