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Biomedical subjects

Thomas Brandt

Publications and source records attributed to Thomas Brandt.

At least 19 recordsLinked to original sources
PubMed2006

Artificial neural network: a new diagnostic posturographic tool for disorders of stance.

OBJECTIVE: To determine the accuracy of diagnoses made with artificial neural network techniques (ANNW) that identify postural sway patterns typical for balance disorders. METHODS: Body sway was measured by means of posturography during 10 test conditions of increasing difficulty. From a database of 676 subjects 60 training cases (TCs) and 60 validation cases (VCs) were selected in which the following diagnoses had been established clinically: normal subject (NS), postural phobic vertigo (PPV), anterior lobe cerebellar atrophy (CA), primary orthostatic tremor (OT), and acute unilateral vestibular neuritis (VN). A standard 3-layer feed-forward ANNW, using the backpropagation algorithm, was trained with TCs, validated with VCs, and its accuracy tested on 5 new cases. RESULTS: ANNW differentiated the established diagnoses with an overall sensitivity and specificity of 0.93. Sensitivity and specificity were 1 for NS and OT; for PPV, 0.87 and 0.96; for CA, 1 and 0.98; and for VN, 0.8 and 0.98, respectively. New subjects were identified with ANNW output variables of the true diagnoses between 0.73 and 1. CONCLUSIONS: ANNW differentiates postural sway patterns of several distinct clinical balance disorders with high sensitivity and specificity. Once designed and tested ANNW could be considered a black box, which each examiner can apply to predict a specific diagnosis even without a clinical examination. SIGNIFICANCE: A promising diagnostic tool for disorders of upright stance in selected neurological disorders.

Adolescent↗
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

A clinical test of otolith function: static ocular counterroll with passive head tilt.

When roll-tilted around the naso-occipital axis, humans exhibit compensatory torsional rotation of the eyes in the opposite direction owing to the torsional vestibulo-ocular reflex. In the static condition (sustained head roll), the utricles act as responsible sensors for 'static ocular counterroll'. Contributions of cervico-ocular reflexes remain unknown. To find an easy, clinically useful test of utricular function, we induced ocular counterroll in 10 healthy study participants (two men, mean age 27+/-2 years) under three stimulation conditions (active/passive head tilt and passive whole body tilt in roll plane), used three-dimensional video-oculography to measure it, and compared values. Active head-tilt-induced ocular counterroll varied most and was thus less reliable than passive head and body tilt-induced ocular counterroll. Utricular function can thus be tested simply by measuring passive head tilt with video-oculography.

Adult↗
PubMed2006

Eccentric eye and head positions in darkness induce deviation from the intended path.

Head and gaze are aligned with the actual path during locomotion. Before a turn is made, gaze changes in the direction of the planned trajectory. We investigated whether eccentric horizontal head and/or eye position without vision causes deviations from the intended straight path. Twenty blindfolded healthy volunteers were asked to walk toward a previously seen target 10 m straight ahead. Various combinations of head and eye positions were tested (eye-in-head gaze straight ahead or 35 degrees left or right with head straight ahead or 70 degrees left or right). Head rotation to the left caused a gait deviation to the right (3.7 degrees ) and head rotation to the right caused a deviation to the left (2.7 degrees ; F(2,40) = 34.966; P < 0.00001). Eye position also showed a tendency to cause gait deviations opposite in direction to gaze, which was, however, not significant. Deviations from the intended straight path were largest with head rotation and eyes straight ahead (gaze 70 degrees off target) or eyes opposite to head rotation (gaze 35 degrees off target). Notably, when lateral eye deviation added to head rotation (gaze 105 degrees off target), i.e., gaze is directed backward, mean deviations decreased (2.3 degrees to the right and 1.2 degrees to the left). Thus, we show that (1) eccentric head positions induce direction-specific gait deviations that are independent of concurrent environmental visual information, and (2) that gait deviations are contraversive to eye-head gaze rather than ipsiversive as reported by others for visually controlled locomotion. The direction of deviation may reflect the compensation of an expected or perceived deviation in the direction of gaze.

Adolescent↗
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↗
PubMed2006

Benign paroxysmal positioning vertigo: a long-term follow-up (6-17 years) of 125 patients.

CONCLUSIONS: The study disclosed a few predictive factors for benign paroxysmal positioning vertigo (BPPV) recurrences, which are clinically relevant and essential for patient awareness of the often long-term course of the condition. OBJECTIVES: To determine the long-term recurrence rate of posterior canal BPPV after successful liberatory maneuvers. METHODS: A retrospective self-evaluation questionnaire with a structured interview was conducted 6-17 years after assessment of the diagnosis in 125 patients. RESULTS: The recurrence rate in patients with a mean follow-up of 10 years was 50%. Most recurrences (80%) were within the first year after treatment, irrespective of the liberatory maneuver applied. None of the patients observed a recurrence after a symptom-free period of 8 years. Recurrences were seen significantly more often in women (58% versus 39%). The recurrence rate of patients in the seventh decade was half that of those in the sixth decade (p=0.0009). A history of three or more BPPV attacks prior to treatment indicated a higher risk of impending multiple recurrences in about two-thirds of the patients.

Adolescent↗
PubMed2006

Latency of alpha-herpes viruses is accompanied by a chronic inflammation in human trigeminal ganglia but not in dorsal root ganglia.

The immune response to latent herpesvirus infections was compared in human trigeminal ganglia (TG) and dorsal root ganglia (DRG) of 15 dead individuals. On the basis of our previous findings, we hypothesized that T-cells would be attracted to sensory neurons latently infected with herpes simplex virus type 1 (HSV-1), but not to those harboring latent varicella zoster virus (VZV). We showed that the TG contain a positive hybridization signal for HSV-1 latency-associated transcript (LAT), whereas the DRG from the same individuals lack detectable LAT. In contrast, immunohistochemistry revealed that latent VZV protein 62 stained positive in the vast majority of all tested TG and DRG. T-cell infiltrates prominently surrounded individual neurons in the TG but not in the DRG. TaqMan polymerase chain reaction also showed higher expression of CD8 and RANTES transcripts in the TG versus DRG. Only the infiltrates in the TG, but not in the DRG, produced RANTES at the protein level. Because it has been shown that RANTES protein is produced only after T-cell receptor stimulation, we assume that T-cell infiltration is associated with antigen recognition in the TG but not in the DRG.

Adolescent↗
PubMed2006

Pharmacological advances in the treatment of neuro-otological and eye movement disorders.

PURPOSE OF REVIEW: First, to describe the current pharmacological treatment options for peripheral and central vestibular, cerebellar, and ocular motor disorders. Second, to identify vestibular and ocular motor disorders in which treatment trials are warranted. RECENT FINDINGS: Peripheral vestibular disorders: In vestibular neuritis recovery of the peripheral vestibular function can be improved by treatment with oral corticosteroids. In Ménière's disease treatment strategies range from low-salt diet, diuretics, and betahistine, to intratympanic injection of corticosteroids or gentamicin. Unfortunately most of the trials on Ménière's disease do not have an up-to-date design. In bilateral vestibulopathy steroids do not seem to improve vestibular function.Central vestibular, cerebellar, and ocular motor disorders: The use of aminopyridines introduced a new therapeutic principle in the treatment of downbeat and upbeat nystagmus and episodic ataxia type 2 (EA2). These potassium channel blockers presumably increase the activity and excitability of cerebellar Purkinje cells, thereby augmenting the inhibitory influence of these cells on vestibular and cerebellar nuclei. A few studies showed that baclofen improves periodic alternating nystagmus, and gabapentin and memantine, pendular nystagmus. Many other eye movement disorders, however, such as ocular flutter, opsoclonus, central positioning, or see-saw nystagmus are still difficult to treat. SUMMARY: Although progress has been made in the treatment of vestibular neuritis, downbeat and upbeat nystagmus, as well as EA2, state-of-the-art trials must still be performed on many vestibular and ocular motor disorders, namely Ménière's disease, bilateral vestibulopathy, vestibular paroxysmia, vestibular migraine, and many forms of central eye movement disorders.

Animals↗
PubMed2006

Documentation and teaching of surgery with an eye movement driven head-mounted camera: see what the surgeon sees and does.

A first proof of concept was developed for a head-mounted video camera system that is continuously aligned with the user's orientation of gaze. In doing so, it records images from the user's perspective that can document manual tasks during, e.g., surgery. Eye movements are tracked by video-oculography and used as signals to drive servo motors that rotate the camera. Thus, the sensorimotor output of a biological system for the control of eye movements evolved over millions of years is used to move an artificial eye. All the capabilities of multi-sensory processing for eye, head, and surround motions are detected by the vestibular, visual, and somatosensory systems and used to drive a technical camera system. A camera guided in this way mimics the natural exploration of a visual scene and acquires video sequences from the perspective of a mobile user, while the oculomotor reflexes naturally stabilize the camera on target during head and target movements. Various documentation and teaching applications in health care, industry, and research are conceivable.

Documentation↗
PubMed2005

Vestibular loss causes hippocampal atrophy and impaired spatial memory in humans.

The human hippocampal formation plays a crucial role in various aspects of memory processing. Most literature on the human hippocampus stresses its non-spatial memory functions, but older work in rodents and some other species emphasized the role of the hippocampus in spatial learning and memory as well. A few human studies also point to a direct relation between hippocampal size, navigation and spatial memory. Conversely, the importance of the vestibular system for navigation and spatial memory was until now convincingly demonstrated only in animals. Using magnetic resonance imaging volumetry, we found that patients (n = 10) with acquired chronic bilateral vestibular loss (BVL) develop a significant selective atrophy of the hippocampus (16.9% decrease relative to controls). When tested with a virtual variant (on a PC) of the Morris water task these patients exhibited significant spatial memory and navigation deficits that closely matched the pattern of hippocampal atrophy. These spatial memory deficits were not associated with general memory deficits. The current data on BVL patients and bilateral hippocampal atrophy revive the idea that a major--and probably phylogenetically ancient--function of the archicortical hippocampal tissue is still evident in spatial aspects of memory processing for navigation. Furthermore, these data demonstrate for the first time in humans that spatial navigation critically depends on preserved vestibular function, even when the subjects are stationary, e.g. without any actual vestibular or somatosensory stimulation.

Adult↗
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

Assessment of potential cardiotoxic side effects of mitoxantrone in patients with multiple sclerosis.

Previous studies showed that mitoxantrone can reduce disability progression in patients with multiple sclerosis (MS). There is, however, concern that it may cause irreversible cardiomyopathy with reduced left ventricular (LV) ejection fraction (EF) and congestive heart failure. The aim of this prospective study was to investigate cardiac side effects of mitoxantrone by repetitive cardiac monitoring in MS patients. The treatment protocol called for ten courses of a combined mitoxantrone (10 mg/m(2) body surface) and methylprednisolone therapy. Before each course, a transthoracic echocardiogram was performed to determine the LV end-diastolic diameter, the end-systolic diameter and the fractional shortening; the LV-EF was calculated. Seventy-three patients participated (32 males; age 48 +/- 12 years, range 20-75 years; 25 with primary progressive, 47 with secondary progressive and 1 with relapsing-remitting MS) who received at least four courses of mitoxantrone. Three of the 73 patients were excluded during the study (2 patients discontinued therapy; 1 patient with a previous history of ischemic heart disease developed atrial fibrillation after the second course of mitoxantrone). The mean cumulative dose of mitoxantrone was 114.0 +/- 33.8 mg. The mean follow-up time was 23.4 months (range 10-57 months). So far, there has been no significant change in any of the determined parameters (end-diastolic diameter, end-systolic diameter, fractional shortening, EF) over time during all follow-up investigations. Mitoxantrone did not cause signs of congestive heart failure in any of the patients. Further cardiac monitoring is, however, needed to determine the safety of mitoxantrone after longer follow-up times and at higher cumulative doses.

Adult↗
PubMed2005

Comparison of tap-evoked and tone-evoked postural reflexes in humans.

To find an easy clinical test of postural reflexes, we compared tone and tap stimuli for eliciting postural reactions in leg muscles in 13 healthy subjects during upright stance. Tones (1000 Hz, 90 dB nHl) were presented monaurally via headphones; taps were applied with a reflex hammer to the forehead. Surface EMG was recorded from the medial gastrocnemius and the sternocleidomastoid muscles, and rectified and averaged. Tapping the forehead of a standing subject evoked leg muscle reflexes that began 50 ms after the stimulus in all subjects. Tone-evoked leg muscle reflexes behaved differently, i.e., they had smaller amplitudes and could be recorded in only 5 of 13 subjects. However, this same acoustic stimulus elicited reflex activity in the neck muscles of all subjects. There were also other differences (amplitudes, dependence on pre-activation) between these two reflexes. Tone-evoked leg muscle responses and tone-evoked neck muscle responses seem to be mediated by different structures, i.e., the latter by an oligosynaptic pathway and the former by polysynaptic neural circuits. We conclude that tap-evoked leg muscle responses are not or not solely mediated by saccular receptors but other receptors (i.e., proprioceptors, semicircular canals) are probably also involved.

Acoustic Stimulation↗
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

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

General vestibular testing.

A dysfunction of the vestibular system is commonly characterized by a combination of phenomena involving perceptual, ocular motor, postural, and autonomic manifestations: vertigo/dizziness, nystagmus, ataxia, and nausea. These 4 manifestations correlate with different aspects of vestibular function and emanate from different sites within the central nervous system. The diagnosis of vestibular syndromes always requires interdisciplinary thinking. A detailed history allows early differentiation into 9 categories that serve as a practical guide for differential diagnosis: (1) dizziness and lightheadedness; (2) single or recurrent attacks of vertigo; (3) sustained vertigo; (4) positional/positioning vertigo; (5) oscillopsia; (6) vertigo associated with auditory dysfunction; (7) vertigo associated with brainstem or cerebellar symptoms; (8) vertigo associated with headache; and (9) dizziness or to-and-fro vertigo with postural imbalance. A careful and systematic neuro-ophthalmological and neuro-otological examination is also mandatory, especially to differentiate between central and peripheral vestibular disorders. Important signs are nystagmus, ocular tilt reaction, other central or peripheral ocular motor dysfunctions, or a unilateral or bilateral peripheral vestibular deficit. This deficit can be easily detected by the head-impulse test, the most relevant bedside test for the vestibulo-ocular reflex. Laboratory examinations are used to measure eye movements, to test semicircular canal, otolith, and spatial perceptional function and to determine postural control. It must, however, be kept in mind that all signs and ocular motor and vestibular findings have to be interpreted within the context of the patient's history and a complete neurological examination.

Humans↗