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W H Zangemeister

Publications and source records attributed to W H Zangemeister.

At least 19 recordsLinked to original sources
PubMed2003

The effect of transcranial magnetic stimulation over the cerebellum on the synkinesis of coordinated eye and head movements.

We made a study of coordinated saccadic eye and head movements following random and predictable horizontal visual targets by applying transcranial magnetic stimulation (TMS) over the cerebellum before the start of the gaze movement. We have found three effects of TMS on eye/head movements under these conditions. SACCADIC LATENCY-EFFECT: When stimulation took place shortly before movements commenced, significantly shorter latencies were found between target presentation and commencement of saccades: For predictable, to a lesser extent for random targets and TMS up to 75 ms before start of the saccade, latencies were significantly decreased when compared with no application of TMS. Without stimulation, latencies to random targets were within a range of 120-200 ms. EYE-HEAD INTERACTION-EFFECT: Without TMS, for amplitudes greater than 25 degrees, head movements usually preceded eye movements, as expected, especially for predictive responses. With the application of TMS shortly after the target display, the number of eye movements which preceded head movements, was significantly increased (p<0.001), and the delay between eye and head movements was reduced or reversed (p<0.001), compared with gaze movements without the use of TMS. SACCADIC PEAK VELOCITY-EFFECT: Applying transcranial magnetic stimulation at 5-25 ms after the position change of the 60 degrees target, and 50-5 s before the start of eye movement, mean peak velocity of synkinetic saccades increased up to 600 degrees/s, compared with 350-400 degrees/s without the use of TMS. We conclude that transient functional cerebellar deficits caused by the application of TMS can change the central synkinesis of eye-head coordination.

Adult↗
PubMed2001

Visual imagery in hemianopic patients.

In this article we report some findings about visual imagery in patients with stable homonymous hemianopia compared to healthy control subjects. These findings were obtained by analyzing the gaze control through recording of eye movements in different phases of viewing and imagery. We used six different visual stimuli for the consecutive viewing and imagery phases. With infrared oculography, we recorded eye movements during this presentation phase and in three subsequent imagery phases in absence of the stimulus. Analyzing the basic parameters of the gaze sequences (known as "scanpaths"), we discovered distinct characteristics of the "viewing scanpaths" and the "imagery scanpaths" in both groups, which suggests a reduced extent of the image within the cognitive representation. We applied different similarity measures (string/vector string editing, Markov analysis). We found a "progressive consistency of imagery," shown through raising similarity values for the comparison of the late imagery scanpaths. This result suggests a strong top-down component in picture exploration: In both groups, healthy subjects and hemianopic patients, a mental model of the viewed picture must evolve very soon and substantially determine the eye movements. As our hemianopic patients showed analogous results to the normal subjects, we conclude that these patients are well adjusted to their deficit and, despite their perceptual defect, have a preserved cognitive representation, which follows the same top-down vision strategies in the process of visual imagery.

Adult↗
PubMed2001

Transcranial magnetic stimulation over the cerebellum delays predictive head movements in the coordination of gaze.

We investigated coordinated saccadic eye and head movements following predictive horizontal visual targets at +/- 30 degrees by applying transcranial magnetic stimulation (TMS) over the cerebellum before the start of the gaze movement in 10 young subjects. We found three effects of TMS on eye-head movements: 1. Saccadic latency effect. When stimulation took place shortly before movements commenced (75-25 ms before), significantly shorter latencies were found between predictive target presentation and initiation of saccades. Eye latencies were significantly decreased by 45 ms on average, but head latencies were not. 2. Gaze amplitude effect. Without TMS, for the 60 degrees target amplitudes, head movements usually preceded eye movements, as expected (predictive gaze type 3). With TMS 5-75 ms before the gaze movement, the number of eye movements preceding head movements by 20-50 ms was significantly increased (p < 0.001) and the delay between eye and head movements was reversed (p < 0.001), i.e. we found eye-predictive gaze type 1. 3. Saccadic peak velocity effect. For TMS 5-25 s before the start of head movement, mean peak velocity of synkinetic eye saccades increased by 20-30% up to 600 degrees/s, compared to 350-400 degrees/s without TMS. We conclude that transient functional cerebellar deficits exerted by means of TMS can change the central synkinesis of eye-head coordination, including the preprogramming of the saccadic pulse and step of a coordinated gaze movement.

Adult↗
PubMed1999

Prolonged postexcitatory inhibition after transcranial magnetic stimulation of the motor cortex in patients with cerebellar ataxia.

Postexcitatory inhibition after transcranial magnetic stimulation of the motor cortex (silent period, SP) is supposed to be predominantly mediated by the activation of inhibitory cortical interneurons. Cortical excitability seems to be reduced in patients with cerebellar ataxia. Motor threshold, central motor conduction time and the duration of the silent period after a single magnetic stimulus to the motor cortex on both sides were measured in five patients with cerebellar ataxia of different origin and 18 healthy controls. Duration of SP was highly significantly prolonged in patients compared with controls (P<0.001) while motor threshold and central motor conduction times were not different. Fifteen of 18 control subjects showed late EMG responses after magnetic stimulation but none of the patients did (P<0.001). These findings support the hypothesis that cerebellar lesions activate inhibitory cortical interneurons or cause a disruption of a normally tonic cerebellar excitation to the motor cortex. Silent period measurement appears to be a sensitive diagnostic tool in the neurophysiological examination of cerebellar diseases.

Adult↗
PubMed1999

[Infrared pupillography in patients with diabetes mellitus].

AIM: To examine effects of diabetes mellitus on the pupillary light reflex it was analysed using a new compact integrated infrared pupillograph (CIP). PATIENTS AN METHODS: We examined 52 patients with diabetes mellitus and 21 control subjects. The initial pupillary diameter was diminished in the group of the diabetics. This was the only parameter that was significantly diminished in the group of all patients with diabetes mellitus. The maximal constriction velocity, the maximal velocity of the first part of the redilation, the reflex amplitude and the latency time were significantly reduced only in those patients showing also signs of autonomic neuropathy of the cardiovascular system. The amplitude and the velocities however, measured as part of the initial pupillary diameter showed no significant reduction. CONCLUSION: This leads to a very crucial question when examining the pupillary reflex of diabetics. Which alterations are due to the pathological small pupil and which are directly due to autonomic neuropathy. This study shows that the diminished pupillary diameter after adaptation to the dark is an early sign of autonomic neuropathy; other alterations in the pupillary reflex can be seen after other symptoms of the autonomic neuropathy are shown as well.

Adult↗
PubMed1998

Disturbances of antagonistic neck innervation in patients with cerebellar deficits.

Fast 60 degree head rotations of nine patients with cerebellar deficits were analysed and compared with those of nine normal subjects. The surface EMG activity from both Splenii capitis muscles were recorded. The triphasic pattern of reciprocal innervated neck muscles with regard to the duration, amplitude and onset of the pulses were analysed together with the dynamic features of head rotation, i.e. position and acceleration profiles. The deviation of the onset of the antagonistic (B) pulse of the EMG-pattern flow was substantially increased. In most cases the onset of the B-pulse was delayed, less premature and sporadic regular onsets occurred. The number of co-contractions and multiple antagonistic pulses was significantly increased. Half of the movements of patients were found to be dysmetric, with an irregular flow of position and acceleration functions. From these, mainly hypermetric movements occurred. The number of irregular pulse patterns was higher than the number of dysmetrias. In this context cocontractions, multiple antagonistic pulses and cortical control can be discussed as strategies of the cerebellar patients to improve their dynamic output. Our experiments support the notion of the cerebellum playing an important part in the temporal integration of an antagonistically innervated movement. The measurement of electromyographic burst patterns can be used as a clinical tool to demonstrate an insufficient timing of the activities of muscles involved.

Adult↗
PubMed1996

Anticipatory smooth eye movements of high velocity triggered by large target steps: normal performance and effect of cerebellar degeneration.

We studied frequencies and dynamic characteristics of anticipatory smooth eye movements (ASEM) in humans who were tracking step target movements of 20-70 deg amplitude. During presentation of periodic steps of constant amplitude healthy subjects showed frequent high velocity ASEM reaching maximal peak velocities of 5-40 deg/sec. There was no effect of ASEM on the frequency of anticipatory saccades. Randomization of target step amplitude or onset reduced the frequency of ASEM but did not completely abolish fast ASEM. In patients with cerebellar degeneration who exhibited impaired smooth pursuit, fast ASEM were absent and the number of slow ASEM was minimal. In conclusion, large sequential target steps can elicit much higher ASEM velocities than typically described in the literature. Similar to slow ASEM triggered by small steps, these fast ASEM do not require specific training and are not canceled by unpredictable step target motion. However, fast ASEM depend on the intact function of the cerebellum which gives further evidence of their generation by the smooth pursuit oculomotor subsystem.

Adolescent↗
PubMed1996

Target predictability influences the distribution of coordinated eye-head gaze saccades in patients with homonymous hemianopia.

In hemianopic patients target predictability plays a differential role for the distribution of different types of initial saccades. A linear correlation was shown to exist between the adaptive state of reading capability and the probability of a correct initial eye-head gaze saccade that hit the target accurately. A constant target frequency of 0.8 Hz was found to be the optimum frequency for hemianopic patients to follow square step targets with an eccentricity of +/- 20 degrees. Variability of the compensatory eye movement velocity gain was lowest at this frequency. We were able to use this target frequency as a test for a clinical classification of the status of adaptation of hemianopic patients in combination with simple reading tests. The repetition of this manoeuvre could correct the synkinesis and the balance of the VOR during active gaze of hemianopic patients.

Adaptation, Physiological↗
PubMed1995

Frontal and parietal transcranial magnetic stimulation (TMS) disturbs programming of saccadic eye movements.

Transcranial magnetic stimulation (TMS) of human motor cortex typically evoked motor responses. TMS has failed to elicit eye movements in humans, whereas prolongations of saccadic latency have been reported with TMS. In previous studied we demonstrated that saccades can be abolished or saccadic trajectories can be changed through TMS in the 100 msec before saccade onset. This effect was especially marked when TMS was applied parietally. TMS never influenced a saccade in flight. Simulations of predictive experimental saccades that were impaired through TMS of the frontal or parietal cortex demonstrated especially that the dynamics of small saccades were markedly influenced, resulting in a significant decrease in acceleration and amplitude, or an almost complete inhibition. The impact of inhibition through TMS was critically dependent on timing: early TMS (-70 msec) had a much larger inhibitory effect than late TMS (-20 msec) on experimental saccades. Differential timing of TMS in influencing the cortical control signal is demonstrated through simulations of a reciprocally innervated eye movement model that paralleled empirically determined changes in eye movement dynamics after real TMS. There is a reasonable match between the model and the experimental data. We conclude that the inhibitory action of a presaccadic disturbance, such as a TMS pulse, on saccadic programming is inversely related to timing and amplitude of the predicted saccade.

Computer Simulation↗
PubMed1995

Evidence for a global scanpath strategy in viewing abstract compared with realistic images.

Scanpaths, the repetitive sequences of saccadic eye movements, occurred when subjects viewed slide projections of both realistic and abstract art. Variance analysis demonstrated that global/local eye movement indices were lower for local scanning by professional art viewers who relied on more global viewing, particularly in abstract images. Non-professional, unsophisticated subjects carried their local scanpath patterns from realistic images on to abstract images. The blink rate of professional subjects viewing abstract images was also significantly lower, indicating increased visual effort. Non-professional viewers showed no difference in blink rates.

Adult↗
PubMed1995

Parameter identification of a neurological control model for the pathological head movements of cerebellar patients.

The objective of this research is to explore the role of the cerebellum in the human motor control system. The present study quantitatively compares the neurological control signals effecting fast, horizontal head rotations in normal subjects to those in patients with a cerebellar lesion. The method involves the use of a computer simulation model for one degree-of-freedom movements. A method for unconstrained global optimization, first proposed by Hans Bremermann (1970), is used to identify the timing and magnitudes of the input neurological control signals to the model, which are compared to recorded electromyograms (EMGs). Experimentally recorded kinematics from cerebellar patients and from normal subjects were used to drive the parameter search. These simulations found that cerebellar patients' neurological control signals were altered with respect to those of normal subjects, and suggest that the electromyographic activity of cerebellar patients may comprise at least five bursts of activity whereas normal subjects typically exhibit only three. The results are discussed with respect to the hypothesis that the cerebellum may be involved in both the timing and magnitudes of the neurological control signals effecting voluntary movement.

Algorithms↗
PubMed1995

The efferent innervation of outer hair cells in humans: physiological investigations.

We report on a case of reversible pontine deafness caused by multiple sclerotic lesions in the pons, and describe six experiments in humans, in whom we recorded transient otoacoustic emissions and distortion products. Our findings indicate an inhibitory effect of efferent innervation on the motility of outer hair cells in humans. Otoacoustic emissions increased in patients with unilateral deafness after the central part of the efferent pathway was destroyed (pontine deafness). Otoacoustic emissions also increased in patients with myasthenia gravis after the administration of an acetylcholinesterase inhibitor. General myotonia (Batter-Curschmann-Steinert Syndrome) resulted in mild sensorineural hearing loss, and in the absence of contralateral inhibition of otoacoustic emissions. Otoacoustic emissions decreased gradually under general anesthesia with muscle relaxation. Contralateral acoustic stimulation was seen during anaesthesia with muscle relaxation.

Acoustic Stimulation↗
PubMed1995

Short-term adaptation of eye movements in patients with visual hemifield defects indicates high level control of human scanpath.

In continuation of earlier studies, we recorded gaze movements in patients with hemianopic visual field defects primarily due to stroke. Use of high resolution infrared oculography enabled us to record and analyze a variety of tasks including paradigms of visual search, reading, and scanpath eye movements. The tasks were recorded several times in sequential order. Through these sequences, we observed short-term adaptation, i.e., training effects of eye movement strategies to improve the initially deficient results on the side of the blind hemifield with respect to the relative difficulty of the specific task. This quantitative and statistically confirmed finding adds new evidence for the top-down control of the human scanpath even in hemianopic patients.

Adaptation, Ocular↗
PubMed1993

Preview control of gaze saccades: efficacy of prediction modulates eye-head interaction during human gaze saccades.

Healthy human subjects made orienting saccades towards visual target stimuli, either with the head fixed or during intended time optimal head movements. Four experimental paradigms were used to study the influence of target predictability on eye-head coordination. They represented different sequences of horizontal target steps, that were varied in amplitude, direction and frequency. In some subjects midflight perturbations of the active head movements were applied to examine the intrasaccadic vestibulo-ocular reflex (VOR). In coordinated gaze saccades, latencies and dynamics of the eye saccade and the additional head trajectory demonstrated specific task-related changes with respect to the head fixed condition. Highly predictable target steps result in the relatively earlier onset of the head movement and an increase of the intrasaccadic head contribution to the overall gaze displacement. Differences in the level of VOR suppression became significant when gaze amplitudes exceeded 60 degrees. Consequently, an effective speed up of large gaze saccades was found with increased target predictability. We concluded, that eye-head coordination during human gaze saccades underlies high level preview control mechanisms. A parametric modulation of the intrasaccadic VOR maintains gaze accuracy, although the actual contribution of the more flexible head motor system varied, depending on gaze amplitude and prediction. The efficacy of preview control depends on interaction of these factors.

Adult↗
PubMed1992

Sensitivity coefficients, trajectories and graphs of a human head-movement model.

With time as the criterion to be optimized, the divergences from optimal head movements show systematic differences in their control signal variables with respect to single behaviours. To clarify these relationships, this study applies manipulation and mathematical analysis of the 6th-order nonlinear head movement model, using the three-fold approach of sensitivity analysis. The sensitivity analysis of the improved and refined head movement model explains the different tasks of the control parameters and their relation to the plant. It shows that width more than height of the agonistic and antagonistic pulses dominate the important behaviours of the movement: acceleration, magnitude and duration.

Head↗
PubMed1991

Normal gait is differentially influenced by the otoliths.

Postural control depends on the integration of vestibular, somatosensory and visual orientation signals. The otolith contribution to postural control is achieved by the integration of otolith inputs and peripheral afferent inputs involved in crossed reflex pathways. This study shows that a functional linkage between otolith signals and activity in lower limb muscles is detectable in normal human gait. The otolith input appears to dominate particularly the neck proprioceptive and gaze motor influences during normal gait. This is demonstrated by an increase of tibialis anterior muscle activity during retroflexion of the head/neck, leading to an increased stability and counteracting possible perturbations. It is also shown by decrease of coordination during the movement caused by larger displacement of the centre of gravity demonstrated in vector diagrams.

Biomechanical Phenomena↗
PubMed1991

Cerebral potentials evoked by painful, laser stimuli in patients with syringomyelia.

Brief cutaneous heat stimuli generated by a CO2 laser were used to elicit late somatosensory evoked cerebral potentials (SEPc) in 10 patients with syringomyelia. For comparison, early and late cerebral potentials in response to electrical nerve stimuli (SEPn) were recorded in the same session. In 8 patients with localized impairment of pain and temperature sensitivity we found complete absence of SEPc after stimulation of the affected area; in another patient with similar sensory deficits, the SEPc was grossly attenuated and delayed. In 1 patient with intact pain sensitivity but absent temperature sensitivity, a well defined SEPc could be recorded. Both early cortical SEPn and late SEPn in response to conventional nerve stimuli were normal in all patients and thus did not differentiate control and affected areas. These data indicate that alteration of SEPc correlates with altered pain sensitivity in patients with a circumscribed spinal lesion. SEPc may thus be used as a neurophysiological test in the assessment of hypalgesic dermatomes.

Brain↗