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Biomedical subjects

M Dieterich

Publications and source records attributed to M Dieterich.

At least 37 records · Page 2Linked to original sources
PubMed2001

The spectrum of vascular lesions in the mammary skin, including angiosarcoma, after breast conservation treatment for breast cancer.

BACKGROUND: With the general acceptance of lumpectomy, axillary staging, and radiotherapy as local treatment for infiltrating breast cancer, an appreciation is evolving for the spectrum of vascular lesions that occur in the mammary skin after this treatment. Most of these lesions develop within the prior radiation field after breast conservation treatment. STUDY DESIGN: A retrospective chart and slide review was conducted, consisting of five patients with cutaneous vascular lesions after breast conservation treatment for infiltrating breast cancer. RESULTS: The latent time interval from definitive treatment of breast cancer to the clinical recognition of vascular lesions ranged from 5 to 11 years. Two patients did not have either arm or breast edema, two patients had breast edema, and the fifth patient had arm edema. Lesions arising in the irradiated mammary skin included extensive lymphangiectasia (one), atypical vascular lesions (two), and cutaneous angiosarcoma (four). CONCLUSIONS: Atypical vascular lesions at the skin margins of mastectomy may be predictive of recurrence after resection of angiosarcoma. Excision of skin from the entire radiation field may be necessary to secure local control of the chest wall in patients with cutaneous angiosarcoma after therapeutic breast radiotherapy.

Aged↗
PubMed2001

Modeling the role of the interstitial nucleus of Cajal in otolithic control of static eye position.

Previous models of ocular counterroll assumed that static eye position was controlled by direct brainstem pathways from the vestibular nuclei via the ocular motor nuclei to the extraocular eye muscles. However, recent experimental evidence has shown that the interstitial nucleus of Cajal (INC), known as the vertical-torsional velocity-to-position integrator, plays a crucial role in torsional otolith-dependent eye position, i.e. for the modification of Listing's plane by static head tilts. To evaluate possible mechanisms by which otolithic input may influence eye position via the INC, we constructed a 3D mathematical model of saccade and nystagmus generation. The model includes the burst generators located in the rostral interstitial nucleus of the medial longitudinal fasciculus (MLF) and paramedian pontine reticular formation and the velocity-to-position integrators located in the INC and prepositus hypoglossi. The model simulations suggest that otolith pathways to the neural integrator that adjust Listing's plane may involve the cerebellum.

Humans↗
PubMed2001

Multisensory cortical signal increases and decreases during vestibular galvanic stimulation (fMRI).

Functional magnetic resonance imaging blood-oxygenation-level-dependent (BOLD) signal increases (activations) and BOLD signal decreases ("deactivations") were compared in six healthy volunteers during galvanic vestibular (mastoid) and galvanic cutaneous (neck) stimulation in order to differentiate vestibular from ocular motor and nociceptive functions. By calculating the contrast for vestibular activation minus cutaneous activation for the group, we found activations in the anterior parts of the insula, the paramedian and dorsolateral thalamus, the putamen, the inferior parietal lobule [Brodmann area (BA) 40], the precentral gyrus (frontal eye field, BA 6), the middle frontal gyrus (prefrontal cortex, BA 46/9), the middle temporal gyrus (BA 37), the superior temporal gyrus (BA 22), and the anterior cingulate gyrus (BA 32) as well as in both cerebellar hemispheres. These activations can be attributed to multisensory vestibular and ocular motor functions. Single-subject analysis in addition showed distinctly nonoverlapping activations in the posterior insula, which corresponds to the parieto-insular vestibular cortex in the monkey. During vestibular stimulation, there was also a significant signal decrease in the visual cortex (BA 18, 19), which spared BA 17. A different "deactivation" was found during cutaneous stimulation; it included upper parieto-occipital areas in the middle temporal and occipital gyri (BA 19/39/18). Under both stimulation conditions, there were signal decreases in the somatosensory cortex (BA 2/3/4). Stimulus-dependent, inhibitory vestibular-visual, and nociceptive-somatosensory interactions may be functionally significant for processing perception and sensorimotor control.

Acoustic Stimulation↗
PubMed2001

Central positional nystagmus simulated by a mathematical ocular motor model of otolith-dependent modification of Listing's plane.

To find an explanation of the mechanisms of central positional nystagmus in neurological patients with posterior fossa lesions, we developed a three-dimensional (3-D) mathematical model to simulate head position-dependent changes in eye position control relative to gravity. This required a model implementation of saccadic burst generation, of the neural velocity to eye position integrator, which includes the experimentally demonstrated leakage in the torsional component, and of otolith-dependent neural control of Listing's plane. The validity of the model was first tested by simulating saccadic eye movements in different head positions. Then the model was used to simulate central positional nystagmus in off-vertical head positions. The model simulated lesions of assumed otolith inputs to the burst generator or the neural integrator, both of which resulted in different types of torsional-vertical nystagmus that only occurred during head tilt in roll plane. The model data qualitatively fit clinical observations of central positional nystagmus. Quantitative comparison with patient data were not possible, since no 3-D analyses of eye movements in various head positions have been reported in the literature on patients with positional nystagmus. The present model, prompted by an open clinical question, proposes a new hypothesis about the generation of pathological nystagmus and about neural control of Listing's plane.

Animals↗
PubMed2001

Ocular motor system: anatomy and functional magnetic resonance imaging.

This article reviews current positron emission tomography and functional MR imaging (fMRI) studies of brain activation and indicates some of the insights they provide into the neuronal network mediating motion-perception and ocular motor control. The complexity of the network and the activation of the entire system seemingly independent of the specific ocular motor task performed makes functional interpretation extremely difficult. At the same time, however, the complexity illustrates the dilemma of associating a particular locus with one specific function. Caution is required to differentiate specific from nonspecific effects, to identify activations and deactivations, and to distinguish which of the systems has been activated inadvertently through poor stimulus control. The next step required for meaningful correlations of structure with function is for fMRI studies to test neurologic patients with distinct and separate lesions of the network. Such a comparison must evaluate the effect of the ocular motor deficit on the lesion site and the connected network in the acute stage and then following functional recovery caused by plasticity and neuronal repair.

Brain↗
PubMed2001

Vestibular system: anatomy and functional magnetic resonance imaging.

In this article, the authors present evidence that the multisensory parietoinsular cortex in humans is involved in perceiving both verticality and self-motion. This evidence is based on (a) lesional studies in patients who have acute unilateral infarctions and (b) positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) evidence of cerebral activation by use of vestibular caloric stimulation, galvanic stimulation, and optokinetic stimulation.

Animals↗
PubMed2000

A placebo-controlled crossover trial of creatine in mitochondrial diseases.

To test the efficacy and safety of creatine (Cr) monohydrate in mitochondrial diseases, 16 patients with chronic progressive external ophthalmoplegia or mitochondrial myopathy were randomized in a crossover design to receive double-blind placebo or 20 g Cr/day for 4 weeks. Cr was well tolerated, but there were no significant effects with regard to exercise performance, eye movements, or activities of daily life. The power of this pilot study was limited and future multicenter trials are needed.

Adult↗
PubMed2000

Hemifield visual motion stimulation: an example of interhemispheric crosstalk.

Coherent motion stimulation of the right or left visual hemifield was performed in nine healthy volunteers in order to investigate interhemispheric visuo-visual interaction by means of functional magnetic resonance imaging. The vertical edge of the motion pattern field was located 8 degrees distant from the fixation point to avoid stimulating the vertical meridian, which is represented retinotopically in both hemispheres. Bilateral activation was significant in the middle occipital gyrus (motion-sensitive middle temporal/middle superior temporal areas; BA 19/37). A negative signal change was found in the primary visual cortex including the lingual and fusiform gyri (BA 18/17) and the occipital white matter containing the optic radiation contralateral to the stimulated hemisphere. These data are most compatible with an interhemispheric transfer of visual motion information, most likely through the corpus callosum. Transcallosal transfer of visual motion information, evident as increases (BA 19/37) and decreases (BA 18/17) of the fMRI signals, may be functionally significant for the processing of motion perception.

Adult↗
PubMed2000

Differential effects of vestibular stimulation on walking and running.

Prompted by our recent observation that an acute vestibular tone imbalance causes less deviation from the intended path when running than when slowly walking, we examined 10 healthy subjects when walking or running at different step frequencies during galvanic vestibular stimulation. Blindfolded subjects were asked to walk (1 Hz step frequency) or run (3 Hz step frequency) straight ahead toward a previously seen target. The mean gait deviation after 10 s was 6.0 +/- 2.4 degrees at 1 Hz and 2.8 +/- 1.8 degrees at 3 Hz step frequency (n = 10; p < 0.001, paired t-test). In a second experiment walking and running in place were investigated. There was no significant difference in body displacement. Walking and running are highly automated processes based on spinal locomotor generators that are under supraspinal control. We conclude that vestibular input is differentially regulated depending on the locomotion speed and pattern used.

Adult↗
PubMed2000

Central processing of human ocular torsion analyzed by galvanic vestibular stimulation.

We examined the dynamics of human ocular torsion (OT) responses to sinusoidal galvanic vestibular stimulation (GVS) (0.005-1.67 Hz). The tonic OT showed a lowpass characteristic with a time constant of 1.74 s and a gain of 0.93 deg/mA. In two subjects, nystagmus dominated the observable OT pattern at frequencies <0.1 Hz. The nystagmus slow phases showed an exponential trajectory with a time constant of 1.49 s. The dynamics of both tonic OT and torsional nystagmus in our study were similar to the dynamics of OT induced by rotation and linear acceleration found in the literature. We propose a model for the central processing of torsional eye movements that is based on a common neural integration of semicircular canal (SC) and utricular inputs as well as nystagmus bursts. The sensitivity of all vestibular afferents to GVS was derived to be 0.76 spikes/s/mA. SC effects on OT are at least 3.5 times higher than utricular effects.

Acceleration↗
PubMed2000

Patients with somatoform phobic postural vertigo: the more difficult the balance task, the better the balance performance.

The objective was to test, whether the increased body sway activity, shown in patients with phobic postural vertigo (PPV) in a previous posturographic study, impairs postural balance during demanding balance tasks. In 17 patients with PPV and 15 normal subjects body sway was analyzed for two standing positions on a foam rubber-padded posturographic platform with the eyes open or closed: (a) normal upright stance, (b) tandem stance. During normal upright stance patients showed an increase in body sway activity between 0.1 and 19 Hz and in sway path values for lateral and fore/aft directions. During the most difficult balance task, i.e. tandem stance with the eyes closed, body sway activity and sway path values did not differ between patients and controls. Objective balance skills were not impaired in patients with PPV during balance tasks at the limits of postural control.

Adult↗
PubMed2000

[Detecting phobic vertigo!].

The syndrome of phobic postural vertigo is characterized by a combination of non-rotational dizziness, subjective disturbance in the upright stance and gait, despite normal clinical balance tests. Phobic postural vertigo most frequently occurs in form of attacks. It may be accompanied by anxiety and panic symptoms. It is almost invariably associated with particular constellations of perceptual stimuli or social situations. There is a tendency for rapid conditioning, generalization, and avoidance behavior to develop. Frequently, onset of condition follows periods of particular psychosocial stress. Despite a considerable rate of improvement in vertigo complaints, a psychiatric comorbidity in a subgroup of patients must be respected during the course of illness. Educative information on the mechanism and possible releasing factors and behavioural therapeutic techniques with self-controlled exposure behaviour are the main therapeutic approaches.

Adolescent↗
PubMed2000

Cerebellar activation during optokinetic stimulation and saccades.

OBJECTIVE: To investigate the activation pattern of cerebellar structures during small-field optokinetic stimulation (OKN) by functional MRI (fMRI) and compare it with that obtained during voluntary saccades and fixation suppression of OKN. METHODS: Functional images were acquired from oblique transverse slices of eight healthy, right-handed volunteers using a radio frequency-spoiled, single-slice, fast low-angle shot (FLASH) pulse sequence with high-spatial resolution. RESULTS: Horizontal OKN and saccades were associated with bilateral activity in the cerebellar hemispheres (superior semilunar lobule, simple lobule, quadrangular lobule, inferior semilunar lobule), the middle cerebellar peduncle, the dentate nucleus, and medially in the culmen and uvula of cerebellar nuclei. The pattern and extent of activation were independent of the stimulus direction for OKN and saccades. During fixation suppression, the extent of activation was significantly diminished (hemispheres) or even absent (uvula, culmen). CONCLUSION: The differential effects of fixation suppression on this complex pattern of cerebellar activation in part allow us to separate visual and attentional from ocular motor processing. Our data agree with behavioral and physiologic animal data about ocular motor processes and motor learning in the vestibulospinal and optokinetic reflex. This suggests that hemispheric cerebellar activity may be mainly associated with changes in attention, whereas vermal activity seems to be associated with ocular motor control, and activity of the dentate nuclei and the cerebellar peduncles seems to be associated with both.

Adult↗
PubMed2000

Brain activation studies on visual-vestibular and ocular motor interaction.

Despite their different sensorimotor functions, saccades, pursuit eye movements, small-field optokinetic nystagmus and visual motion stimulation with the eyes stationary evoke a common complex pattern of activation in various cortical, basal ganglia, brain-stem and cerebellar areas. On closer inspection, however, typical subregions can be delineated that allow differentiation of adjacent but separate loci for specific functions (e.g. the separation of the two parallel corticocortical systems to control saccades and pursuit in the cortical eye fields). It is becoming increasingly clear that stimulation of one sensory system affects other sensory systems, and generally this is via an inhibitory reciprocal mode of interaction. For example, vestibular stimulation deactivates the visual cortex and visual stimulation deactivates the vestibular cortex.

Animals↗
PubMed2000

Perceived vertical and lateropulsion: clinical syndromes, localization, and prognosis.

We present a clinical classification of central vestibular syndromes according to the three major planes of action of the vestibulo-ocular reflex: yaw, roll, and pitch. The plane-specific syndromes are determined by ocular motor, postural, and perceptual signs. Yaw plane signs are horizontal nystagmus, past pointing, rotational and lateral body falls, deviation of perceived straight-ahead to the left or right. Roll plane signs are torsional nystagmus, skew deviation, ocular torsion, tilts of head, body, and perceived vertical in a clockwise or counterclockwise direction. Pitch plane signs are upbeat/downbeat nystagmus, forward/backward tilts and falls, deviations of the perceived horizon. The thus defined vestibular syndromes allow a precise topographic analysis of brainstem lesions according to their level and side. Special emphasis is placed on the vestibular roll plane syndromes of ocular tilt reaction, lateropulsion in Wallenberg's syndrome, thalamic and cortical astasia and their association with roll plane tilt of perceived vertical. Recovery is based on a functionally significant central compensation of a vestibular tone imbalance, the mechanism of which is largely unknown. Physical therapy may facilitate this central compensation, but this has not yet been proven in prospective studies.

Animals↗
PubMed1999

Galvanic stimulation in bilateral vestibular failure: 3-D ocular motor effects.

Bilateral galvanic vestibular stimulation (GVS) with current intensity of 3 mA was applied at mastoid level in 11 patients with chronic bilateral vestibular failure, in order to determine ocular motor responses by 3-D video-oculography. The following abnormal features were found: (1) a predominantly torsional or mixed torsional-horizontal nystagmus at the onset of stimulation with lower current intensities (1.0-3.0 mA) in nine patients; (2) a reduced amplitude of tonic ocular torsion by about 50% in nine patients (1.3 +/- 0.6 degrees at 3 mA); (3) a nystagmus in the opposite direction at stimulation offset in five patients (rebound); (4) no eye movements at all in a patient with bilateral nerve failure. GVS stimulates the vestibular nerve, thus allowing differentiation of nerve failure from labyrinthine failure. The low thresholds for initiating nystagmus and the rebound, which appear to be the most typical features of bilateral labyrinthine failure, can be explained by central compensation mechanisms.

Acceleration↗