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Biomedical subjects

Thomas Brandt

Publications and source records attributed to Thomas Brandt.

At least 37 records · Page 2Linked to original sources
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

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↗
PubMed2005

Medial vestibular nucleus lesions in Wallenberg's syndrome cause decreased activity of the contralateral vestibular cortex.

Three patients with the clinical diagnosis of Wallenberg's syndrome caused by acute unilateral ischemic infarctions, which included the vestibular nucleus in the medullary brain stem and afferent vestibular pathways, were examined by positron emission tomography (PET) during caloric vestibular stimulation. They all had typical signs of vestibular dysfunction such as transient rotatory vertigo with vomiting at the onset, ipsiversive body and ocular lateropulsion, and a complete ocular tilt reaction with tilts of the subjective visual vertical. Compared with healthy volunteers, who show activation in a network of temporoparietal vestibular areas within both hemispheres, especially in the posterior insula and retroinsular region that contains the human homologue of the parietoinsular vestibular cortex (PIVC) in monkeys, the activation pattern of the patients with Wallenberg's syndrome was typically changed. During caloric irrigation of the ear ipsilateral to the side of the lesion, they showed no or significantly reduced activation in the contralateral hemisphere, whereas the activation pattern in the ipsilateral hemisphere appeared "normal." These results are compatible with bilateral ascending vestibular pathways from the vestibular nuclei to the vestibular cortex. The novel finding in all three patients was that the activation patterns were compatible with the assumption that only the crossing fibers from the medial vestibular subnucleus to the contralateral medial longitudinal fascicle were affected, but the ipsilateral vestibular thalamocortical projections via the superior vestibular subnucleus were spared. Thus, the activation pattern in the PET study may reflect the vestibular tonic imbalance within the vestibular nuclei circuitry at the cortical level.

Adult↗
PubMed2005

Effect of 4-aminopyridine on upbeat and downbeat nystagmus elucidates the mechanism of downbeat nystagmus.

The potassium channel blocker 4-aminopyridine (4-AP) restored vertical smooth pursuit and gaze holding in light in one patient with upbeat (UBN) and in one with downbeat nystagmus (DBN). Without a visible target, however, 4-AP had no effect on UBN, but DBN vanished. We hypothesize that this difference in the effects of 4-AP, which is known to increase the excitability of cerebellar Purkinje cells, can be attributed to the different lesion sites involved in UBN and DBN.

4-Aminopyridine↗
PubMed2004

Areas MT/V5 and their transcallosal connectivity in cortical dysplasia by fMRI.

A patient with unilateral focal cortical dysplasia with a significant impairment of visual motion perception within the contralateral hemifield was examined with fMRI. During hemifield visual motion stimulation primary visual cortex areas were activated contralaterally and deactivated ipsilaterally to the stimulated hemifield. Transcallosal visuo-visual interaction was further evident as bilateral activation in temporo-occipital areas that best correspond to the motion sensitive areas MT/V5. MT/V5 was displaced anteriorly, superiorly, and medially within the dysplastic hemisphere and separated into two distinct activation clusters. During visual motion stimulation the parieto-insular vestibular cortex showed signal decreases that agree with the concept of inhibitory visuo-vestibular interaction. Thus, fMRI is a suitable tool for detecting preserved function and transcallosal connections in patients with focal cortical dysplasia.

Adult↗
PubMed2004

Methylprednisolone, valacyclovir, or the combination for vestibular neuritis.

BACKGROUND: Vestibular neuritis is the second most common cause of peripheral vestibular vertigo. Its assumed cause is a reactivation of herpes simplex virus type 1 infection. Therefore, corticosteroids, antiviral agents, or a combination of the two might improve the outcome in patients with vestibular neuritis. METHODS: We performed a prospective, randomized, double-blind, two-by-two factorial trial in which patients with acute vestibular neuritis were randomly assigned to treatment with placebo, methylprednisolone, valacyclovir, or methylprednisolone plus valacyclovir. Vestibular function was determined by caloric irrigation, with the use of the vestibular paresis formula (to measure the extent of unilateral caloric paresis) within 3 days after the onset of symptoms and 12 months afterward. RESULTS: Of a total of 141 patients who underwent randomization, 38 received placebo, 35 methylprednisolone, 33 valacyclovir, and 35 methylprednisolone plus valacyclovir. At the onset of symptoms there was no difference among the groups in the severity of vestibular paresis. The mean (+/-SD) improvement in peripheral vestibular function at the 12-month follow-up was 39.6+/-28.1 percentage points in the placebo group, 62.4+/-16.9 percentage points in the methylprednisolone group, 36.0+/-26.7 percentage points in the valacyclovir group, and 59.2+/-24.1 percentage points in the methylprednisolone-plus-valacyclovir group. Analysis of variance showed a significant effect of methylprednisolone (P<0.001) but not of valacyclovir (P=0.43). The combination of methylprednisolone and valacyclovir was not superior to corticosteroid monotherapy. CONCLUSIONS: Methylprednisolone significantly improves the recovery of peripheral vestibular function in patients with vestibular neuritis, whereas valacyclovir does not.

Acyclovir↗
PubMed2004

Metabolic changes in vestibular and visual cortices in acute vestibular neuritis.

Five right-handed patients with a right-sided vestibular neuritis were examined twice with fluorodeoxyglucose positron emission tomography while lying supine with eyes closed: once during the acute stage (mean, 6.6 days) and then 3 months later when central vestibular compensation had occurred. Regional cerebral glucose metabolism (rCGM) was significantly increased (p <0.001 uncorrected) during the acute stage in multisensory vestibular cortical and subcortical areas (parietoinsular vestibular cortex in the posterior insula, posterolateral thalamus, anterior cingulate gyrus [Brodmann area 32/24], pontomesencephalic brainstem, hippocampus). Simultaneously, there was a significant rCGM decrease in the visual (Brodmann area 17 to 19) and somatosensory cortex areas in the postcentral gyrus as well as in parts of the auditory cortex (transverse temporal gyrus). Fluorodeoxyglucose positron emission tomography thus allows imaging of the cortical activation pattern that is induced by unilateral peripheral vestibular loss. It was possible to demonstrate that the central vestibular system including the vestibular cortex exhibits a visual-vestibular activation-deactivation pattern during the acute stage of vestibular neuritis similar to that in healthy volunteers during unilateral labyrinthine stimulation. Contrary to experimental vestibular stimulation, the activation of the vestibular cortex was not bilateral but was unilateral and contralateral to the right-sided labyrinthine failure.

Aged↗
PubMed2004

Rollvection versus linearvection: comparison of brain activations in PET.

We conducted a PET study to directly compare the differential effects of visual motion stimulation that induced either rollvection about the line of sight or forward linearvection along this axis in the same subjects. The main question was, whether the areas that respond to vection are identical or separate and distinct for rollvection and linearvection. Eleven healthy volunteers were exposed to large-field (100 degrees x 60 degrees ) visual motion stimulation consisting of (1) dots accelerating from a focus of expansion to the edge of the screen (forward linearvection) and (2) dots rotating counterclockwise in the frontal plane (clockwise rollvection). These two stimuli, which induced apparent self-motion in all subjects, were compared to each other and to a stationary visual pattern. Linearvection and rollvection led to bilateral activations of visual areas including medial parieto-occipital (PO), occipito-temporal (MT/V5), and ventral occipital (fusiform gyri) cortical areas, as well as superior parietal sites. Activations in the polar visual cortex around the calcarine sulcus (BA 17, BA 18) were larger and more significant during linearvection. Temporo-parietal sites displayed higher activity levels during rollvection. Differential activation of PO or MT/V5 was not found. Both stimuli led to simultaneous deactivations of retroinsular regions (more pronounced during linearvection); this is compatible with an inhibitory interaction between the visual and the vestibular systems for motion perception.

Adult↗
PubMed2004

Prevalence and distribution of HSV-1, VZV, and HHV-6 in human cranial nerve nuclei III, IV, VI, VII, and XII.

The etiology of idiopathic cranial nerve palsies often remains unresolved. It has been hypothesised that viral reactivation of herpesviruses in the corresponding nuclei in the brainstem is the cause. We investigated the distribution of herpes simplex virus type 1 (HSV-1) and varicella zoster virus (VZV) in nuclei that are associated with peripheral sensory ganglia [oculomotor (nIII), facial (nVII) nuclei] and in nuclei that are not associated with peripheral sensory ganglia [trochlear (nIV), abducens (nVI), and hypoglossal (nXII) nuclei] of five human brainstems. Samples of the cranial nerve nuclei and adjacent control tissue were taken from histological sections after precise identification of every single nucleus and control tissue. DNA and RNA amplification methods were used to determine the prevalence and distribution of HSV-1 and VZV. The distribution of human herpes virus type 6 (HHV-6) was also determined and served as a control, since HHV-6 infection has never been associated with idiopathic cranial nerve palsies. HSV-1 was distributed at random in all cranial nerve nuclei and control tissue, whereas VZV DNA was not detected in any of the samples examined. Surprisingly, HHV-6 was present in almost all samples where HSV-1 was also present, however, the latency associated transcript (LAT) of HSV-1 was not found in any of the samples positive for HSV-1 DNA. The absence of LAT in the samples positive for HSV-1 and the distribution of HSV-1 and HHV-6 do not support the hypothesis that idiopathic cranial nerve palsies result from viral reactivation in the brainstem nuclei.

Abducens Nerve↗
PubMed2004

Eyes open and eyes closed as rest conditions: impact on brain activation patterns.

The patterns of associated brain activations during eyes-open and eyes-closed states in complete darkness considerably differ in fMRI. An "interoceptive" state with the eyes closed is characterized by visual cortex activation, while an "exteroceptive" state with the eyes open is characterized by ocular motor system activity. The impact of the chosen rest condition (eyes open or eyes closed in complete darkness) on the pattern of brain activations during visual stimulation was evaluated in 14 healthy volunteers. During fixation or dim light room illumination, the activation of the visual cortex was larger with the eyes-open rest condition than with the eyes-closed rest condition; however, activation of the lateral geniculate nucleus was smaller. Activations that can be attributed to ocular motor structures, such as the prefrontal cortex, parietal and frontal eye fields, cerebellar vermis, the thalamus, and basal ganglia were larger with the eyes-closed rest condition than with the eyes-open rest condition. BOLD signal decreases of cortical areas that represent visual, somatosensory, auditory, and vestibular functions were seen in the comparison fixation of light emitting diode (LED) minus eyes closed. Thus, the choice of rest condition (either eyes closed or eyes open) is critical for stimulus-induced brain activation patterns. Activity of the ocular motor system as well as deactivation of sensory cortical areas may go undetected with eyes open as rest condition.

Adolescent↗
PubMed2004

Brain activation patterns during imagined stance and locomotion in functional magnetic resonance imaging.

Posture and gait are sensorimotor actions that involve peripheral, spinal, and supraspinal structures. To investigate brain activity during stance and locomotion, 13 healthy subjects were asked to stand, walk, run, and lie down; subsequently, they were trained to imagine standing, walking, running, and lying [imagined lying as rest condition in functional magnetic resonance imaging (fMRI)]. Separate and distinct activation/deactivation patterns were found for the three imagined conditions: (1) standing imagery was associated with activation in the thalamus, basal ganglia, and cerebellar vermis; (2) walking imagery was associated with activation in the parahippocampal and fusiform gyri (areas involved in visuospatial navigation), occipital visual areas, and in the cerebellum; (3) running imagery caused a predominantly cerebellar activation in the vermis and adjacent hemispheres (six times larger than during imagination of walking or standing), but activations in the parahippocampal and fusiform gyri were smaller than during walking. Deactivations were found for walking and running, but not for standing imagery. They were located in the vestibular (posterior insula, superior temporal gyrus, supramarginal gyrus) and somatosensory (postcentral gyrus) cortex with right-hemispheric dominance. These findings support the concept of a hierarchical organization of posture and locomotion. Automated locomotion, for example, running, is based on spinal generators whose pace is driven by the cerebellar locomotor region. Deactivation in the vestibular and somatosensory cortex prevents adverse interactions with the optimized spinal pattern and sensory signals; this confirms earlier findings of a multisensory inhibition during unhindered locomotion. During slow walking, spatial navigation, mediated by the parahippocampal cortex, becomes more important. Postural control during standing involves a low intensity cerebellar activity and sensorimotor control via the thalamus and basal ganglia.

Adult↗
PubMed2003

Inverse U-shaped curve for age dependency of torsional eye movement responses to galvanic vestibular stimulation.

To investigate age dependent changes we analysed torsional eye movement responses to binaural and monaural galvanic vestibular stimulation (GVS) in 57 healthy subjects (20-69 years old). GVS (1-3 mA) induced torsional eye movements consisting of static torsion toward the anode (amplitude 1-6 degrees ) and superimposed torsional nystagmus (slow phase velocity 0.5-3 degrees /s, quick phase amplitude 0.5-2 degrees, nystagmus frequency 0.75-1.5 s-1). Static ocular torsion and torsional nystagmus increased from the third to the sixth decade and decreased in older subjects, e.g. slow phase velocity increased from 1.5 degrees /s (20-29 years) to 2.9 degrees /s (50-59 years) and decreased to 2.5 degrees /s for the seventh decade (60-69 years). Thus, an inverse U-shaped curve was found for the dependence of torsional eye movement responses on age. All structures relevant for vestibular function degenerate with age, but at varying times. Since hair cell loss precedes those seen in the vestibular nerve and Scarpa's ganglion, the decrease in hair cell counts could be compensated for by increased sensitivity of afferent nerve fibres or central mechanisms. Increased sensitivity could thus maintain normal function despite reduced peripheral input. As GVS acts at the vestibular nerve (thereby bypassing the hair cells), electrical stimulation should be more efficient in subjects with the beginning of hair cell degeneration, as seen in our data up to the sixth decade. The degeneration of nerve fibres, ganglion cells and central neurons becomes evident at older ages. Thus, the compensatory increase in sensitivity breaks down and GVS-induced eye movements decline-a finding that is reflected by the inverse U-shaped curve for age dependency presented in this study.

Adult↗
PubMed2003

Dually infected (HSV-1/VZV) single neurons in human trigeminal ganglia.

Human trigeminal ganglia were tested by double fluorescence in situ hybridization for the presence and distribution of herpes simplex virus type 1 (HSV-1) and varicella-zoster virus (VZV) latency. Latency transcripts of both viruses were detected in common areas within the ganglia. Also, a few single neurons were shown to harbor HSV-1 and VZV together.

Adolescent↗