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Biomedical subjects

M Fetter

Publications and source records attributed to M Fetter.

At least 37 records · Page 2Linked to original sources
PubMed1999

Autosomal dominant cerebellar ataxia type I: oculomotor abnormalities in families with SCA1, SCA2, and SCA3.

Forty-six patients suffering from autosomal dominant cerebellar ataxia type I (ADCA I) underwent to a genotype-phenotype correlation analysis by molecular genetic assignment to the spinocerebellar ataxia type 1, 2, or 3 (SCA1, SCA2, SCA3) genetic locus and electro-oculography. Oculomotor deficits that are attributed to dysfunction of cerebellar structures occurred in all three mutations without major differences between the groups. Gaze-evoked nystagmus, however, was not found to be associated with SCA2. Square wave jerks were exclusively observed in SCA3. The gain in vestibulo-ocular reflex was significantly impaired in SCA3 and SCA1. In SCA3 the severity of vestibular impairment increased with CAG repeat length. Severe saccade slowing was a highly characteristic feature of SCA2. In SCA3 saccade velocity was normal to mildly reduced while SCA1 fell into an intermediate range. The present data show that each mutation is associated with a distinct syndrome of oculomotor deficits. Reduced saccade velocity and the absence of both square-wave jerks and gaze-evoked nystagmus allow one SCA2 to be distinguished from SCA3 patients in almost all cases. The eye movement disorder of SCA1 patients, however, overlaps with both SCA2 and SCA3.

Adult↗
PubMed1999

Persistent cerebellar deterioration in a patient with lobar pneumonia under lithium, carbamazepine, and trifluperidol treatment.

We report on a patient with schizoaffective disorder who was on combination therapy of lithium, carbamazepine, and the neuroleptic trifluperidol. He experienced a lobar pneumonia and developed an acute and persistent cerebellar deterioration which was most likely due to lithium toxicity, while the serum lithium level was within the therapeutic range. The combination of lithium, carbamazepine, and neuroleptics is common, and is generally considered to be safe. The reported case suggests that this regimen might increase the risk of intoxication with potentially disabling side-effects.

Anti-Bacterial Agents↗
PubMed1999

3D eye movements--basics and clinical applications.

The eye muscles in humans are arranged such that they allow rotations of the globe about any axis in three-dimensional space. Only 3D analysis techniques will suffice to describe the sometimes complex dependencies between the elicited eye movements and the stimulation conditions. With the recent availability of modern 3D eye movement measurement techniques and the further development of appropriate mathematical descriptions, we are now able to study eye movements in all three degrees of freedom. This article describes the basic mathematical tools for 3D eye movement analysis like rotation vectors, reference frames, coordinate systems, and the concept of Listing's law. In a second part some clinical applications are presented. The close coupling between the vestibular and the oculomotor system suggests that by observing spontaneous and elicited eye movements in the case of an acute unilateral vestibular pathology we might be able to find out which parts of the vestibular system (that is, which of the semicircular canals or which of the otoliths) are affected. The rationale of such an analysis is based on the observation that electrical stimulation of single semicircular canal afferents in animals induces eye movements that lie roughly in the plane of the canal. It is, therefore, possible to deduce which canals cause the eye movements observed when only some parts of the vestibular system are defective. Thus, the analysis of 3D movements not only provides an improved understanding of how the brain organizes movement in 3D space, but also has the potential to significantly improve our diagnostic capabilities.

Electronystagmography↗
PubMed1998

Optimizing gaze control in three dimensions.

Horizontal and vertical movements of the human eye bring new objects to the center of the visual field, but torsional movements rotate the visual world about its center. Ocular torsion stays near zero during head-fixed gaze shifts, and eye movements to visual targets are thought to be driven by purely horizontal and vertical commands. Here, analysis of eye-head gaze shifts revealed that gaze commands were three-dimensional, with a separate neural control system for torsion. Active torsion optimized gaze control as no two-dimensional system could have, stabilizing the retinal image as quickly as possible when it would otherwise have spun around the fixation point.

Adult↗
PubMed1998

Association between angiotensin I-converting enzyme genotypes, extracranial artery stenosis, and stroke.

The insertion(I)/deletion(D) polymorphism of the angiotensin-converting-enzyme (ACE) gene has been associated with an increased risk of myocardial infarction, lacunar stroke, and with an increased intimal-medial thickness in several populations. The aim of this study was to evaluate whether the ACE I/D genotype is associated with stenosis of extracranial arteries and stroke in middle-aged and aged men and women. We studied 388 patients (247 male, 141 female) using Doppler and Duplex ultrasound of the extracranial arteries. Patients' history was obtained by standard questionnaire and by the hospital case records. Genomic DNA was analyzed by polymerase chain reaction (PCR) to identify the I/D polymorphism, with a second insertion specific PCR in samples classified as homozygous DD genotypes to prevent mistyping. The ACE genotype groups (DD 132, ID 164, II 92) were well matched for the basic characteristics. The DD genotype was more common in patients with extracranial artery stenosis > or = 50%, compared with patients without stenosis (59/147 versus 73/241, odds ratio 1.54, 95%-CI 1.01-2.37), but was not associated with a history of stroke (30/91 versus 102/297, odds ratio 0.94, 95%-CI 0.57-1.54). The association of the DD genotype with extracranial artery stenosis was also present in hypertensive subjects (n = 206, odds ratio 1.76, 95%-CI 0.99-3.17). In the whole group multiple logistic regression analysis revealed that the association of the DD genotype with extracranial artery stenosis was independent of age, gender, hypertension, hyperlipidemia, and diabetes. In conclusion, the ACE DD genotype is a weak risk factor for hemodynamically relevant stenosis of extracranial arteries, but not for stroke.

Adult↗
PubMed1998

Contribution of the vertical semicircular canals to the caloric nystagmus.

Modulation of the caloric nystagmus in response to repositioning the plane of one vertical semicircular canal from gravitational horizontal to vertical during continuous caloric stimulation was used to measure the vertical canal's contribution to the nystagmus. The rationale was to examine the thermovective response from one vertical canal at a time, after a temperature gradient had been established across its two limbs. The nystagmus was measured and analysed in three dimensions using orthogonal head-referenced coordinates. The magnitude of each semicircular canal's contribution to the overall caloric response, the canal vector, was determined in non-orthogonal, contravariant semicircular canal plane coordinates. By using the canal plane reorientation technique and contravariant canal plane coordinates, we were able to measure the proportional thermovective response magnitude generated by each vertical canal during caloric stimulation. We found that the anterior canal contributed about one-third and the posterior canal about one-tenth as much as the lateral canal did to the overall caloric response magnitude when it was reoriented from horizontal to vertical. Comparison of the eye rotation axis before and after each vertical canal plane reorientation, with the geometry of the stimulated semicircular canals, also showed directional modulation of the caloric nystagmus by the vertical canal response. When one vertical canal plane was horizontal during caloric stimulation, the eye rotation axis aligned with the resultant of the other vertical canal and the lateral canal response axes. After vertical canal plane reorientation, the eye rotation axis realigned towards the resultant of the maximally stimulated vertical canal and the lateral canal, by 55.2+/-33.9 degrees (mean+/-SD) after anterior canal plane reorientation and by 32.3+/-21.2 degrees after posterior canal reorientation.

Adult↗
PubMed1998

Smooth pursuit eye movements and otolith-ocular responses are differently impaired in cerebellar ataxia.

Horizontal and vertical smooth pursuit was compared with otolith-ocular responses in 11 patients with cerebellar ataxia and 21 normal subjects using three-dimensional magnetic search coil eye movement recordings. Otolith-ocular responses were investigated during off-vertical axis rotation. This stimulus induces nystagmus consisting of the exponentially decaying canalicular response, and an eye-velocity modulation and offset which arise from the excitation of the otoliths by the gravity vector, which lasts as long as the rotation continues. Otolith-ocular reflexes are intimately interrelated with visual tracking when real targets are viewed during linear motion. The responses of both the translational vestibulo-ocular reflex and the pursuit system have been shown to be linearly dependent on the inverse of the viewing distance, so that a common central pathway for the two systems has been suggested, probably travelling through the cerebellum. Thus, the aim of the study was to evaluate to what extent these reflexes are disturbed in cerebellar disease. The results confirm the earlier notion that in normal subjects pursuit performance is better for horizontal than for vertical tracking, and that it is better for upward than for downward tracking. This pattern is also found in patients. In addition, smooth pursuit performance is clearly degraded in patients, but the modulation of eye-velocity during off-vertical axis rotation is enhanced. Since the amount of this enhancement does not correlate with the amount of pursuit impairment, degradation of smooth pursuit and pathological enhancement of otolith-ocular responses seem to be independent effects of cerebellar degeneration. Thus, the increase in the otolith-ocular response in patients cannot be attributed to adaptational mechanisms trying to overcome the smooth pursuit deficiency; it is more likely to represent pathological disinhibition of otolith derived responses. The absence of compensatory eye-velocity offset during off-vertical axis rotation may reflect the fact that in patients the otolith signals are not utilized in computations thought to be important for spatial orientation mechanisms arising from the interaction of vestibular, visual and somatosensory signals.

Adult↗
PubMed1998

Acute disseminated encephalomyelitis following Pontiac fever.

We report the case of a 35-year-old woman who developed headache and psychosis and gradually became comatose within 3 weeks after a flu-like infection. MRI revealed bifrontal demyelination consistent with acute disseminating encephalomyelitis (ADEM). Two different cerebrospinal fluid samples were positively tested for Legionella cincinnatiensis by direct sequencing of a PCR-amplified Legionella-specific fragment. This result made it possible to interpret the initial symptoms as Pontiac fever. We think it most likely that this is a case of ADEM following the very rare situation of a systemic infection with L. cincinnatiensis. A review of the literature on Legionella-associated encephalopathy suggests that some of these cases may also have had ADEM.

Adult↗
PubMed1998

Disentangling gravitational, environmental, and egocentric reference frames in spatial neglect.

Previous studies in neglect patients using rotation of the body around the roll-axis revealed neglect of visual stimuli not only in the egocentric, body-centered left but also in the environmental left. The latter has been taken as evidence for a gravity-based environment-centered component of neglect occurring independently of the subject's actual body orientation. However, by using visual stimuli in a normally lightened room, the studies confounded the gravitational upright with the visible upright of the surround. Thus, it is possible that the visible upright of the environment may have served the role of the gravitational upright relative to which neglect occurred. The present experiment evaluated the influence of gravity on contralateral neglect when no visual information was presented. In complete darkness, neglect patients' exploratory eye movements were recorded in five experimental conditions: body in normal upright position, body titled 30 degrees to the left and 30 degrees to the right, and body pitched 30 degrees backward and 30 degrees forward. In the upright orientation, the patients with neglect showed a bias of ocular exploration to the ipsilesional right side. In egocentric body coordinates, we found no significant differences between the orientation of the biased search field in the different experimental conditions showing that the search field shifted with the orientation of the body. No significant decrease or enhancement of neglect was observed when body orientation was varied in the different conditions. In conclusion, the present results revealed that the modulation of gravitational forces has no significant influence on the exploratory bias of these patients. When visual information was excluded and only graviceptive information was available, the patients' failure to explore the contralesional part of space appeared purely body-centered. The results argue against a disturbed representation of space in neglect that encodes locations in a gravity-based reference system.

Aged↗
PubMed1998

Three-dimensional eye movement analysis during caloric stimulation used to test vertical semicircular canal function.

HYPOTHESIS AND BACKGROUND: Quantitative caloric testing is considered to be one of the most sensitive parameters in the diagnosis of peripheral vestibular disorders. In the past, because of limitations in the methods, the evaluation of the caloric response was restricted to mainly lateral semicircular canal functions. In this study, the authors tried to extend caloric testing to the function of all semicircular canals by using three-dimensional (3-D) analysis techniques. METHODS: The authors studied in seven normal subjects 3-D eye movement responses to air caloric of the right ear with the subjects positioned in standard caloric position (lateral semicircular canal vertical) or such that one of the three semicircular canals of the right side was horizontal. Movement of the left eye was measured in 3-D with a dual-magnetic search coil. During stimulation, 10 seconds of maximum response were selected and desaccaded to yield the slow-phase velocity profile. From this profile, the average magnitude and direction of the eye rotation axis (velocity vector) were calculated in head coordinates. RESULTS: In all subjects, in standard caloric position, warm caloric produced eye velocity vectors that clustered closely along the direction expected from an excitation of the right lateral semicircular canal. When the subjects were positioned with one of the vertical semicircular canals horizontal, the orientation of the velocity vectors shifted toward a direction expected from the combined excitation of the lateral and the other vertical semicircular canal and vice versa. CONCLUSIONS: The 3-D eye movement recordings during caloric stimulation in different head positions allow the evaluation of the function of all semicircular canals.

Adult↗
PubMed1997

Dissociation between the perception of body verticality and the visual vertical in acute peripheral vestibular disorder in humans.

Estimates of the subjective visual and postural vertical were obtained from five patients with acute peripheral vestibular lesions and 20 normal subjects. The visual vertical was assessed by asking the subjects to align a target line to earth vertical by means of remote control. Postural vertical judgments were obtained by exposing them to rotational displacements in the roll plane while sitting on a motor-driven chair and requiring them to align their body to vertical using a joystick control. While the patients showed strong deviations of the visual vertical towards the lesion side, their postural vertical judgments remained veridical. We conclude that the above perceptions are not processed identically and that the participating sensory systems are differently weighted during these tasks.

Adult↗
PubMed1997

Saccade velocity in idiopathic and autosomal dominant cerebellar ataxia.

Slow saccades are often found in degenerative ataxia. Experimental studies have shown that horizontal saccades are generated in the paramedian pontine reticular formation and that lesions in this area produce slow saccades. Based on these findings, saccade slowing should be a frequent feature of olivopontocerebellar atrophy, a type of cerebellar degeneration with prominent involvement of the pons. To test this hypothesis, saccade velocity was measured in 31 patients with autosomal dominant cerebellar ataxia (ADCA) and 17 patients with idiopathic cerebellar ataxia (IDCA). Saccade velocity was reduced in most patients with ADCA whereas it was normal in IDCA although olivopontocerebellar atrophy occurred in both groups. Saccade velocities correlated with pontine size in ADCA but not in IDCA. The data disprove the hypothesis that saccadic slowing is a clinical hallmark of olivopontocerebellar atrophy. Instead, only patients with ADCA and morphological features of olivopontocerebellar atrophy have slow saccades.

Adult↗
PubMed1997

Three-dimensional analysis of spontaneous nystagmus in peripheral vestibular lesions.

The direction of spontaneous nystagmus was recorded in three dimensions with scleral dual search coils in three patients after vestibular neurectomy and in seven patients with vestibular neuritis. The rotation vectors of the spontaneous nystagmus clustered along the sensitivity vector of the lateral semicircular canal (SCC). The direction of the spontaneous nystagmus after resection of the whole eighth nerve was not different from that after resection of only the superior branch of the vestibular nerve. Deviations from this direction were observed only after resection of the inferior vestibular nerve and in one patient with vestibular neuritis. The absence of nystagmus components in direction of the vertical SCC reflects an anisotropy of oculomotor efferents of the vestibulo-ocular reflex are rather than a lesion limited to the lateral SCC afferents. Therefore, the three-dimensional analysis of spontaneous nystagmus does not permit accurate localization of a peripheral vestibular lesion.

Adult↗
PubMed1996

Otolith-semicircular canal interaction during postrotatory nystagmus in humans.

The otolith-semicircular canal interaction during postrotatory nystagmus was studied in ten normal human subjects by applying fast, short-lasting, passive head and body tilts (15, 30, 45, or 90 degrees in the roll or pitch plane) 2 s after sudden stop from a constant-velocity rotation (100 degrees/s) about the earth-vertical axis in yaw. Eye movements were measured with three-dimensional magnetic search coils. Following the head tilt, activity in the semicircular canal primary afferents continues to reflect the postrotatory angular velocity vector in head-centered coordinates, whereas otolith primary afferents signal a different orientation of the head relative to gravity. Despite the change in head orientation relative to gravity, postrotatory eye velocity decayed closely along the axis of semicircular canal stimulation (horizontal in head coordinates) for large head tilts (90 degrees) and also for small head tilts (15-45 degrees) for reorientations in the pitch plane. Only for small head tilts (15-45 degrees) in the roll plane was there a reorientation of the eye rotation axis toward the gravitational vector. This reorientation was approximately compensatory for 15 degrees head tilts. For 30 degrees and 45 degrees head tilts the eye rotation axis tilted toward the gravitational vector by about the same amount as for 15 degrees head tilts. These results suggest that, with the exception of small head tilts in the roll plane, there was no compelling data showing a relationship between the eye rotation axis and head tilt and that postrotatory nystagmus is largely organized in head-centered rather than gravity-centered coordinates in humans. This indicates a rudimentary, nonlinear, and direction-specific interaction of semicircular canal and otolith signals in the central vestibular system in humans.

Adult↗
PubMed1996

Ocular exploration of space as a function of neck proprioceptive and vestibular input--observations in normal subjects and patients with spatial neglect after parietal lesions.

We recently argued that the specific compensation of spatial neglect by manipulating neck proprioceptive and vestibular input is due to a central "correction" of the disturbed neural transformation process converting the afferent input coordinates from the peripheral sensory organs into a central representation of egocentric space. Both types of stimulation were proposed to induce a reorientation of the deviated or distorted egocentric spatial reference frame. The aim of the present study was to observe this process of reorientation under a condition in which no visual stimulus can attract the subject's attention and thus influence exploration behaviour from outside. We recorded eye movements of normal subjects and of three patients with spatial neglect after right parietal lesions while searching for a non-existent target in complete darkness. It was assumed that the area of the outer space that subjects spontaneously explore under this condition is a direct function of the subject's representation of egocentric space. Ocular space exploration was biased and confined almost entirely to the right side of the midsagittal plane in patients with neglect. This spatial distribution of exploratory eye movements changed remarkably with left-sided neck muscle vibration as well as with left-sided vestibular stimulation using ice water calorics. The spatial area of exploration was significantly enlarged to the contralesional side and the exploration maximum shifted in the same direction. Whereas with both types of stimulation space exploration of patients with neglect was similar to that of normal subjects when not being stimulated, neck proprioceptive and vestibular stimulation in normal subjects induced a quasi neglect-like exploration pattern, i.e. a bias to one side of the objective midsagittal plane. If ocular space exploration was, however, related to the subjectively perceived position of the midsagittal plane in space, eye movements were symmetrically distributed and carried out to both sides of subjective "straight ahead" in all experimental conditions, in normal subjects as well as in patients with neglect. The present results support the above hypothesis and indicate that neck proprioceptive as well as vestibular input directly contribute to the computation of the subject's central representation of egocentric space used for localizing body orientation and for guiding motor behaviour in space.

Adult↗
PubMed1996

Three-dimensional orientation of the eye rotation axis during the Purkinje sensation.

The otolith-semicircular canal interaction during postrotatory nystagmus was studied in six normal human subjects by applying fast, short-lasting, passive head and body tilts (90 degrees in the roll or pitch plane) 2 s after sudden stop from a constant velocity rotation (100 degrees/s) about the earth-vertical axis in yaw. Eye movements were measured with 3-D magnetic search coils. Following the head tilt, activity in the semicircular canal primary afferents continues to reflect the postrotatory angular velocity vector in head-centered coordinates, whereas otolith primary afferents signal a different orientation of the head relative to gravity. Pitch (roll) tilts away from upright during postrotatory nystagmus after yaw rotation elicited a transient vertical (torsional) VOR. Despite the change in head orientation relative to gravity, postrotatory eye velocity decayed closely along the axis of semicircular canal stimulation (horizontal in head coordinates). These results suggest that postrotary nystagmus is largely organized in head-centered rather than gravity-centered coordinates in humans as suggested by the Purkinje-sensation.

Eye Movements↗
PubMed1996

Vestibular neuritis spares the inferior division of the vestibular nerve.

Acute unilateral vestibulopathy, or vestibular neuritis, is the second most common cause of vertigo. To quantify the involvement of the different semicircular canal (SCC) afferents in this disease, we studied the three-dimensional (3D) properties of the vestibuloocular reflex (VOR) in 16 patients 3-10 days after onset of symptoms. Using 3D magnetic search coil eye movement recordings, we measured the speed and axis of eye rotation during spontaneous nystagmus and during rotation in the planes of the different SCCs. In all patients, spontaneous nystagmus axes clustered between the direction expected with involvement of just one horizontal SCC and the direction expected with combined involvement of the horizontal and anterior SCC on one side. Likewise, dynamic asymmetries were found only during rotations about axes which stimulated the ipsilesional horizontal or ipsilesional anterior SCCs. No asymmetry was found when the ipsilesional posterior SCC was stimulated. Thus, both measurements suggest that vestibular neuritis is a partial and not a complete unilateral vestibular lesion and that this partial lesion affects the superior division of the vestibular nerve which includes the afferents from the horizontal and anterior SCCs.

Adult↗