Recurrent exertion-induced spinal cord ischemia due to infrarenal aortic occlusion.
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Adult↗
Biomedical subjects
Thomas Brandt
Publications and source records attributed to Thomas Brandt.
Latent herpesvirus infection in human trigeminal ganglia causes chronic immune response.
The majority of trigeminal ganglia (TGs) are latently infected with alpha-herpesviruses [herpes simplex virus type-1 (HSV-1) and varicella-zoster virus (VZV)]. Whereas HSV-1 periodically reactivates in the TGs, VZV reactivates very rarely. The goal of this study was to determine whether herpesvirus latency is linked to a local immune cell infiltration in human TGs. T cells positive for the CD3 and CD8 markers, and CD68-positive macrophages were found in 30 of 42 examined TGs from 21 healthy individuals. The presence of immune cells correlated constantly with the occurrence of the HSV-1 latency-associated transcript (LAT) and only irregularly with the presence of latent VZV protein. In contrast, uninfected TGs showed no immune cell infiltration. Quantitative RT-PCR revealed that CD8, interferon-gamma, tumor necrosis factor-alpha, IP-10, and RANTES transcripts were significantly induced in TGs latently infected with HSV-1 but not in uninfected TGs. The persisting lymphocytic cell infiltration and the elevated CD8 and cytokine/chemokine expression in the TGs demonstrate for the first time that latent herpesviral infection in humans is accompanied by a chronic inflammatory process at an immunoprivileged site but without any neuronal destruction. The chronic immune response seems to maintain viral latency and influence viral reactivation.
Adolescent↗
Eye closure in darkness animates sensory systems.
Single subject and group analyses (n = 12) showed that the eyes-open and eyes-closed states in complete darkness considerably and consistently differ in the patterns of associated brain activation in fMRI. During nonchanging external stimulation, ocular motor and attentional systems were activated when the eyes were open; the visual, somatosensory, vestibular, and auditory systems were activated when the eyes were closed. These data suggest that there are two different states of mental activity: with the eyes closed, an "interoceptive" state characterized by imagination and multisensory activity and with the eyes open, an "exteroceptive" state characterized by attention and ocular motor activity. Our study also shows that the chosen baseline condition may have a considerable impact on activation patterns and on the interpretation of brain activation studies.
Adult↗
Mathematical model predicts clinical ocular motor syndromes.
Clinical ocular motor syndromes were compared with ocular motor syndromes simulated by a mathematical model of the vestibuloocular reflex. The mathematical sensorimotor feedforward model of otolith control of three-dimensional binocular eye position is based on relevant anatomical connections of the vestibuloocular reflex from the utricles to extraocular eye muscles. This is the first attempt to simulate static ocular motor syndromes for unilateral utricular or vestibular nerve failure, lesions of the vestibular nucleus, and lesions of the ascending vestibuloocular reflex pathways. Comparison of the predicted syndromes with those found in patients with unilateral disorders of the vestibular nerve (herpes zoster neuritis), the vestibular nucleus (medullary infarction), and the medial longitudinal fasciculus (pontine infarction) showed good agreement as regards the direction of horizontal, vertical, and torsional eye deviations. The ability of the model to simulate complete or incomplete failures of single elements or entire pathways allows us to pose direct clinical questions about as yet unknown ocular motor syndromes or about the localization of the damage as well as the mechanism involved in syndromes already known.
Aged↗
Inhibitory interhemispheric visuovisual interaction in motion perception.
Findings of an earlier functional magnetic resonance imaging (fMRI) study that coherent motion stimulation of the right or left visual hemifield exhibited negative signal changes (deactivations) in the primary visual cortex and the lateral geniculate nucleus contralateral to the stimulated hemisphere were evaluated to determine the functional significance of this contralateral inhibition of the visual system. Fourteen subjects participated in a psychophysical study on the perception of single object motion (0.4 degrees /s) in one visual hemifield with or without concurrent coherent motion stimulation of the contralateral hemifield. Mean detection times for horizontal object motion (0.5 +/- 0.19 vs. 0.61 +/- 0.22 s) and vertical object motion (0.53 +/- 0.19 vs. 0.72 +/- 0.34 s) were significantly prolonged during concurrent motion pattern stimulation in the contralateral hemifield. These data support the interpretation that the deactivation of neuronal activity in the visual system found by fMRI is associated with a functional decrement in the sensitivity needed to perceive motion and may reflect transcallosal attentional shifts between the two hemispheres.
Adult↗
Spatial memory deficits in patients with chronic bilateral vestibular failure.
The role of the vestibular system for navigation and spatial memory has been demonstrated in animals but not in humans. Vestibular signals are necessary for location-specific "place cell" activity in the hippocampus which provides a putative neural substrate for the spatial representation involved in navigation. To investigate the spatial memory in patients with bilateral vestibular failure due to NF2 with bilateral neurectomy, a virtual variant (on a PC) of the Morris water task adapted to humans was used. Significant spatial learning and memory deficits were shown in 12 patients as compared to 10 healthy controls. These data suggest that functional hippocampal deficits manifest due to a chronic lack of vestibular input in these patients. These deficits can even be demonstrated with the subjects stationary, i.e., without any actual vestibular or somatosensory stimulation.
Adult↗
Eye movements and balance.
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Eye Movements↗
Torsional eye movement responses to monaural and binaural galvanic vestibular stimulation: side-to-side asymmetries.
Vestibular stimulation by head accelerations always involves multisensory activation of the vestibular, somatosensory, and visual systems. Over the past few years, galvanic vestibular stimulation (GVS) has become increasingly popular for testing vestibular function for clinical and research purposes. Although GVS provides a nonphysiological stimulation, it is more selective than natural head accelerations and is thus an attractive tool for such tests. Eye movement responses elicited by GVS mainly consist of torsional and horizontal components, as first described by Hitzig in 1871. Animal experiments have shown that GVS increases the vestibular afferent spike frequency at the cathodal site and decreases it at the anodal site of stimulation. As a continuation of a study on age-dependency of eye movement responses to GVS, we analyzed side-to-side asymmetries in healthy subjects. It is necessary to know the normal range of asymmetry between left- and right-sided stimulation to interpret GVS responses in patients with vestibular diseases.
Adult↗
Both actual and imagined locomotion suppress spontaneous vestibular nystagmus.
Acute unilateral vestibulopathy is characterized by a combination of signs and symptoms including spontaneous nystagmus, postural imbalance and gait disturbance. A functional link between these vestibulo-ocular and vestibulo-spinal motor responses has been demonstrated. These responses use common vestibular input and partially overlapping neuronal networks, but it is not known if and to what extent they are linked or operate separately. We found that slow phase velocity of spontaneous vestibular nystagmus in patients with acute vestibulopathy was suppressed by 26% during actual walking (ANOVA p< 0.02, = 6). It was also suppressed by imagined locomotion: by 26% during the imagination of walking and by 42% during the imagination of running ( p< 0.003, = 10). The suppression of vestibular nystagmus might be beneficial for patients, for it alleviates the disturbing impression of movement of the visual scene (oscillopsia) caused by involuntary eye movements.
Adult↗
fMRI signal increases and decreases in cortical areas during small-field optokinetic stimulation and central fixation.
Small-field optokinetic nystagmus (OKN) was performed in seven healthy volunteers in order to analyze the activation and deactivation patterns of visual motion, ocular motor, and multisensory vestibular cortex areas by means of fMRI during coherent visual motion stimulation. BOLD signal decreases (deactivations) were found in the first and second long insular gyri and retroinsular areas (the human homologue of the parietoinsular vestibular cortex and the visual posterior sylvian area in the monkey) of both hemispheres, extending into the transverse temporal gyrus and inferior-anterior parts of the superior temporal gyrus (BA 22), and the precentral gyri at two separate sites (BA 4 and 6). Further deactivations were found in cranioposterior parts of the superior temporal gyrus (BA 22) and the adjacent inferior parietal lobule (BA 40), anterior cingulate gyrus, hippocampus, and corpus callosum. Most of these BOLD signal decreases involved parts of the "multisensory vestibular cortical circuit". These findings support the concept of a reciprocally inhibitory visual-vestibular interaction that has now been demonstrated not only for large-field visual motion stimulation that induces vection (without eye movements) but also for optokinetically induced eye movements (without vection). The functional significance of this concept may be related to the perception of self-motion, since both large-field visual motion stimulation and optokinetic nystagmus are linked to the visual control of self-motion. With respect to activation of the cortical ocular motor system two separate and distinct areas of activations were delineated in the precentral sulcus of both hemispheres, one ventrolaterally (in BA 9) and the other dorsomedially at the junction of the superior frontal sulcus with the precentral sulcus (in BA 6). Both probably correspond to different subregions of the frontal eye field and the premotor cortex for the ocular motor performance of OKN.
Adult↗
Phobic postural vertigo. Body sway during visually induced roll vection.
Patients with phobic postural vertigo (PPV) often report a particularly increased unsteadiness when looking at moving visual scenes. Therefore, the differential effects of large-field visual motion stimulation in roll plane on body sway during upright stance were analyzed in 23 patients with PPV, who had been selected for the integrity of their vestibular and balance systems, and in 17 healthy subjects. Visual motion stimulation induced a sensation of apparent body motion (roll vection) in all patients and normal subjects. Normal subjects showed an increased lateral sway path with a lateral shift of the center of pressure (COP) in stimulus direction (mean 1.67 cm, SD 1.63). The patients also exhibited an increase in sway path during visual motion stimulation; however, their body sway differed from that of normals in that there was no lateral displacement of COP (mean 0.19 cm, SD 0.73). The lateral displacement of COP and the increase in RMS of body sway during visual motion stimulation were significantly greater in normals than in the patients ( p<0.05). The patients' increased body sway without COP deviation does not imply an increased risk of falling. Two explanations are conceivable for this increased body sway without body deviation in patients with PPV: (a) the patients rely more on proprioceptive and vestibular rather than on visual cues to regulate upright stance; or (b) they depend on visual, vestibular, and proprioceptive information, but the threshold at which they initiate a compensatory body sway opposite in direction to a perceived body deviation is lower than in normal subjects. The data support the second explanation.
Adult↗
Cranial nerve palsies: herpes simplex virus type 1 and varizella-zoster virus latency.
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Cranial Nerve Diseases↗
Changes in cerebellar activation pattern during two successive sequences of saccades.
The changes in the cerebellar activation pattern of two successive fMRI scanning runs were determined for visually guided to-and-fro saccades in 12 healthy volunteers familiar with the study paradigm. Group and single subject-analyses revealed a constant activation of the paramedian cerebellar vermis (uvula, tonsils, tuber, folium/declive), which reflects constant ocular motor activity in both runs. A significant decrease in activation of the cerebellar hemispheres found in the second run is best explained by either a decrease in attention or the effects of motor optimization and learning. The significant, systematic changes of the cerebellar activation pattern in two successive runs were not expected, because the ocular motor task was simple, familiar, and highly automated. These findings indicate that similar effects may bias other cerebellar activation studies, in which sensorimotor tasks are repeated in a single session.
Action Potentials↗
Sensory system interactions during simultaneous vestibular and visual stimulation in PET.
The patterns of regional cerebral blood flow (rCBF) increases and decreases in PET were compared for unimodal vestibular, unimodal visual, and for simultaneous vestibular and visual stimulation. Thirteen healthy volunteers were exposed to a) caloric vestibular stimulation, b) small-field visual motion stimulation in roll, c) simultaneous caloric vestibular and visual pattern stimulation. Unimodal vestibular stimulation led to activations of vestibular cortex areas, in particular the parieto-insular vestibular cortex (PIVC), and concurrent deactivations of visual cortical areas [Brodmann area (BA) 17-19]. Unimodal visual motion stimulation led to activations of the striate visual cortex and the motion-sensitive area in the middle temporal/middle occipital gyri (BA 19/37) with concurrent deactivations in the PIVC. Simultaneous bimodal stimulation resulted in activations of the cortical representation of both sensory modalities. In the latter condition activations and deactivations were significantly smaller compared to unimodal stimulation. The findings are consistent with the concept of an inhibitory reciprocal vestibulo-visual interaction in all three stimulus conditions.
Adult↗
Vestibular brainstem disorders: clinical syndromes in roll plane and their model simulation.
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Animals↗
Lid closure mimics head movement in fMRI.
Motion correction algorithms are commonly used to correct for involuntary head motions in fMRI. We found that lid closure increased signal intensity of the eyes by a factor of 1.6 to 2 in EPI-fMRI. If the eyes were included in the scanning volume, transitions from eyes open to eyes closed in darkness were regularly associated with erroneously detected head translations along the z-axis and head rotations around the x-axis in Talairach's coordinate system. These artefacts could be avoided by masking the eyes in the images during the estimation of movement parameters.
Adult↗
Suppression of eye movements improves balance.
The aim of this study was to investigate the possible interaction of vestibulo-ocular and vestibulo-spinal functions. Spontaneous eye movements and anterior-posterior and lateral body sway were recorded simultaneously in 10 patients with vestibular neuritis (Experiment 1) and in 11 healthy subjects (Experiment 2) while all subjects wore a mask that allowed fixation of a head-fixed target. For the healthy subjects, there was no significant difference in postural sway for the conditions of eyes open in darkness and fixation of the head-fixed target. For the patients, the question was whether transient suppression of the spontaneous nystagmus by fixating the target affected excessive body sway or whether modulation of nystagmus and postural sway were largely independent. The mean peak slow-phase velocity of the spontaneous nystagmus decreased from 13.5 +/- 5.6 to 4.3 +/- 2.4 degrees /s during fixation. The suppression of nystagmus also reduced postural sway while standing on foam rubber. Mean value decreased from 25.2 +/- 7.6 to 16.2 +/- 7.7 mm (right-left root mean square values; ANOVA, P = 0.003). Since a head-fixed target was used to suppress spontaneous eye movements, the data cannot be explained by any stabilizing effect of afferent visual cues. Instead, ocular motor efference copy signals or reafferences may have contributed to the postural instability of patients with vestibular neuritis, which would explain the reduction of postural sway during fixation suppression of the nystagmus. Thus, ocular motor signals rather than afferent visual cues about retinal slip are used for visual control of postural sway, at least in this experimental paradigm.
Adult↗
Visual-vestibular and visuovisual cortical interaction: new insights from fMRI and pet.
PET and fMRI studies have revealed that excitation of the vestibular system by caloric or galvanic stimulation not only activates the parietoinsular vestibular cortex but also bilaterally deactivates the occipital visual cortex. Likewise, visual motion stimulation not only activates the visual cortex but also deactivates the parietoinsular vestibular cortex. These findings are functionally consistent with the hypothesis of an inhibitory reciprocal visual-vestibular interaction for spatial orientation and motion perception. Transcallosal visuovisual interaction between the two hemispheres was found by using half-field visual motion stimulation: activation of motion-sensitive areas hMT/V5 and deactivations of the primary visual cortex contralateral to the stimulated hemisphere. The functional significance of these inter- and intra-sensory interactions could be that they (A) allow a shift of the sensorial weight between two incongruent sensory inputs and (B) ensure a correspondence of the two hemispheres during evaluation of contradictory motion stimulation of the right and left hemifields. In terms of mathematical modeling, these findings may reflect the concepts of a sensory conflict mechanism or a mismatch between expected and actual sensory input.
Animals↗