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Biomedical subjects

David S Zee

Publications and source records attributed to David S Zee.

35 records · Page 2Linked to original sources
PubMed2003

Neck muscle vibration alters visually perceived roll in normals.

The objective of this study was to determine whether vibration of dorsal neck muscles or of the mastoid bone or of both modified the perception of visual orientation in the head roll-tilt plane in normal subjects. Measurements of the subjective visual vertical (SVV) were obtained from 26 normal human subjects. Subjects reported the SVV in the upright and in the left and right 30 degrees static head roll-tilt positions. Subjects then reported the SVV while vibration was applied to the left or right dorsal neck or left or right mastoid. Both head position and vibration independently modified settings of the SVV. In head-tilted positions, vibration of the upper dorsal neck muscles (on the side of the head opposite to the head tilt) caused a significantly greater shift of the SVV in the opposite direction of head roll-tilt compared to vibration of the lower dorsal neck muscles or of the mastoid. These results support a role for cervical somatosensory information in perception of visual orientation in the roll plane. Our findings may help explain the differences observed in visual orientation perception in normal subjects between head alone and whole-body roll-tilt. Finally, vibration of neck muscles in the head roll-tilted plane may be a useful method to test cervical somatosensory function possibly by increasing their response to external stimulation.

Adult↗
PubMed2003

Vergence-dependent adaptation of the vestibulo-ocular reflex.

The gain of the vestibulo-ocular reflex (VOR) normally depends on the distance between the subject and the visual target, but it remains uncertain whether vergence angle can be linked to changes in VOR gain through a process of context-dependent adaptation. In this study, we examined this question with an adaptation paradigm that modified the normal relationship between vergence angle and retinal image motion. Subjects were rotated sinusoidally while they viewed an optokinetic (OKN) stimulus through either diverging or converging prisms. In three subjects the diverging prisms were worn while the OKN stimulus moved out of phase with the head, and the converging prisms were worn when the OKN stimulus moved in-phase with the head. The relationship between the vergence angle and OKN stimulus was reversed in the fourth subject. After 2 h of training, the VOR gain at the two vergence angles changed significantly in all of the subjects, evidenced by the two different VOR gains that could be immediately accessed by switching between the diverged and converged conditions. The results demonstrate that subjects can learn to use vergence angle as the contextual cue that retrieves adaptive changes in the angular VOR.

Adaptation, Physiological↗
PubMed2003

Ocular motor responses to abrupt interaural head translation in normal humans.

We characterized the interaural translational vestibulo-ocular reflex (tVOR) in 6 normal humans to brief (approximately 200 ms), high-acceleration (0.4-1.4g) stimuli, while they fixed targets at 15 or 30 cm. The latency was 19 +/- 5 ms at 15-cm and 20 +/- 12 ms at 30-cm viewing. The gain was quantified using the ratio of actual to ideal behavior. The median position gain (at time of peak head velocity) was 0.38 and 0.37, and the median velocity gain, 0.52 and 0.62, at 15- and 30-cm viewing, respectively. These results suggest the tVOR scales proportionally at these viewing distances. Likewise, at both viewing distances, peak eye velocity scaled linearly with peak head velocity and gain was independent of peak head acceleration. A saccade commonly occurred in the compensatory direction, with a greater latency (165 vs. 145 ms) and lesser amplitude (1.8 vs. 3.2 deg) at 30- than 15-cm viewing. Even with saccades, the overall gain at the end of head movement was still considerably undercompensatory (medians 0.68 and 0.77 at 15- and 30-cm viewing). Monocular viewing was also assessed at 15-cm viewing. In 4 of 6 subjects, gains were the same as during binocular viewing and scaled closely with vergence angle. In sum the low tVOR gain and scaling of the response with viewing distance and head velocity extend previous results to higher acceleration stimuli. tVOR latency (approximately 20 ms) was lower than previously reported. Saccades are an integral part of the tVOR, and also scale with viewing distance.

Acceleration↗
PubMed2003

Influence of target size on vertical gaze palsy in a pathologically proven case of progressive supranuclear palsy.

We document a new oculomotor phenomenon in a patient with pathologically proven progressive supranuclear gaze palsy (PSP), namely that vertical gaze excursion improves with larger pursuit targets. We used computerised video-oculography during vertical smooth pursuit eye movements (SPEM) of circular targets of diameter 0.16 degrees and 16 degrees, sinusoidally oscillating at 0.08 Hz (peak-to-peak amplitude 49 degrees). Increasing target size improved vertical gaze excursion from 10 degrees to 25 degrees. There was no concomitant increase in slow phase eye velocity. The findings could be explained by a potentiation of the position control mechanism of pursuit by target size due to increased activation of brainstem pursuit-optokinetic pathways and to higher order attentional mechanisms. This observation may be useful in the clinical assessment of PSP patients with severe neck rigidity in whom the doll's head-eye manoeuvre cannot be performed by comparing the degree of vertical gaze palsy during smooth pursuit testing between at least two differently sized targets and observing whether there is a larger excursion in response to a large target such as a newspaper.

Aged↗
PubMed2003

Effects of lesions of the cerebellar oculomotor vermis on eye movements in primate: binocular control.

The effects of lesions of the dorsal 'oculomotor' cerebellar vermis on binocular oculomotor functions in three monkeys were examined. Prominent findings included (1) a convergence bias during monocular fixation, i.e., an 'esodeviation' in the absence of disparity cues, (2) a loss of comitancy, i.e., alignment varies more with orbital position, (3) abnormal saccade yoking producing saccade disconjugacy, and (4) defects in prism-induced phoria adaptation. There was also a suggestion of a disturbance in the dynamic properties of disparity-induced vergence. These findings point to a role for the 'oculomotor' vermis in binocular aspects of the control of eye movements.

Adaptation, Physiological↗
PubMed2003

Evaluating the dizzy patient: bedside examination and laboratory assessment of the vestibular system.

Dizziness and imbalance are common presenting complaints to the neurologist. The lack of a systematic approach to the examination and laboratory evaluation of the vestibular system often leads to incorrect diagnoses and suboptimal care. With a basic understanding of vestibular physiology and proper examination techniques, a correct diagnosis can generally be made at the bedside. We review the principles of the neuro-otological examination, including assessment for static vestibular imbalance, dynamic vestibular function, provocative maneuvers, ocular motor examination, and vestibulospinal testing. The use of additional vestibular laboratory testing and neuroimaging is then considered to further localize and quantify abnormalities.

Dizziness↗
PubMed2003

Primary position and listing's law in acquired and congenital trochlear nerve palsy.

PURPOSE: In ocular kinematics, the primary position (PP) of the eye is defined by the position from which movements do not induce ocular rotations around the line of sight (Helmholtz). PP is mathematically linked to the orientation of Listing's plane. This study was conducted to determine whether PP is affected differently in patients with clinically diagnosed congenital (conTNP) and acquired (acqTNP) trochlear nerve palsy. METHODS: Patients with unilateral conTNP (n = 25) and acqTNP (n = 9) performed a modified Hess screen test. Three-dimensional eye positions were recorded with dual search coils. RESULTS: PP in eyes with acqTNP was significantly more temporal (mean: 21.2 degrees ) than in eyes with conTNP (6.8 degrees ) or healthy eyes (7.2 degrees ). In the pooled data of all patients, the horizontal location of PP significantly correlated with vertical noncomitance with the paretic eye in adduction (R = 0.59). Using a computer model, PP in acqTNP could be reproduced by a neural lesion of the superior oblique (SO) muscle. An additional simulated overaction of the inferior oblique (IO) muscle moved PP back to normal, as in conTNP. Lengthening the SO and shortening the IO muscles could also simulate PP in conTNP. CONCLUSIONS: The temporal displacement of PP in acqTNP is a direct consequence of the reduced force of the SO muscle. The reversal of this temporal displacement of PP, which occurs in some patients with conTNP, can be explained by a secondary overaction of the IO muscle. Alternatively, length changes in the SO and IO muscles, or other anatomic anomalies within the orbit, without a neural lesion, may also explain the difference in location of PP between conTNP and acqTNP.

Adaptation, Ocular↗
PubMed2003

Ocular motor behavior of children with neurofibromatosis 1.

Patients with neurofibromatosis 1 show neurocognitive deficits including abnormal visuospatial performance, but oculomotor behavior has not been studied. We recorded saccades in neurofibromatosis 1 and normal children, ages 6 to 12 years. Patients showed increased latency and diminished amplitude to more eccentric targets for both visually guided and memory-guided saccades. Subtracting the latencies of visually guided saccades from memory-guided saccades produced no differences between groups. For predictive saccades (0.5 Hz), patients with neurofibromatosis 1 generated fewer anticipatory saccades than normal subjects, but patients with neurofibromatosis 1 made more direction errors in an antisaccade task. Patients with neurofibromatosis 1 show saccade abnormalities that are not easily ascribed to dysfunction within single cortical areas. Rather, the findings likely reflect (1) partial involvement of different components of a widely distributed cerebral network that controls saccades, (2) impaired visuomotor maturation in a brain abnormal early in development, and (3) excessive gamma-aminobutyric acid-mediated inhibition, which could influence basal ganglia pathways that modulate superior colliculus activity.

Basal Ganglia↗
PubMed2003

Short-term adaptation of the VOR: non-retinal-slip error signals and saccade substitution.

We studied short-term (30 min) adaptation of the vestibulo-ocular reflex (VOR) in five normal humans using a "position error" stimulus without retinal image motion. Both before and after adaptation a velocity gain (peak slow-phase eye velocity/peak head velocity) and a position gain (total eye movement during chair rotation/amplitude of chair motion) were measured in darkness using search coils. The vestibular stimulus was a brief ( approximately 700 ms), 15 degrees chair rotation in darkness (peak velocity 43 degrees /s). To elicit adaptation, a straight-ahead fixation target disappeared during chair movement and when the chair stopped the target reappeared at a new location in front of the subject for gain-decrease (x0) adaptation, or 10 degrees opposite to chair motion for gain-increase (x1.67) adaptation. This position-error stimulus was effective at inducing VOR adaptation, though for gain-increase adaptation the primary strategy was to substitute augmenting saccades during rotation while for gain-decrease adaptation both corrective saccades and a decrease in slow-phase velocity occurred. Finally, the presence of the position-error signal alone, at the end of head rotation, without any attempt to fix upon it, was not sufficient to induce adaptation. Adaptation did occur, however, if the subject did make a saccade to the target after head rotation, or even if the subject paid attention to the new location of the target without actually looking at it.

Adaptation, Physiological↗
PubMed2003

Context-specific adaptation and its significance for neurovestibular problems of space flight.

It has been demonstrated that various vestibular and oculomotor responses can be adapted in a context-specific manner: different adapted states are associated with different states of a prevailing context cue, and a change in the context state triggers a change in the response such that each adapted state is associated with a given context state. We review selected literature on context-specific adaptation, including our own recent results on adaptation of saccades, pursuit, and the linear and angular vestibulo-ocular reflexes (LVOR and AVOR), and suggest some ways in which context-specific adaptation might be useful as a countermeasure to the adverse neurovestibular effects of space flight.

Adaptation, Physiological↗
PubMed2002

Motor mechanisms of vertical fusion in individuals with superior oblique paresis.

PURPOSE: We wanted to determine the mechanisms of motor vertical fusion in patients with superior oblique paresis and to correlate these mechanisms with surgical outcomes. METHODS: Ten patients with superior oblique paresis underwent 3-axis, bilateral, scleral search coil eye movement recordings. Eye movements associated with fusion were analyzed. RESULTS: Six patients had decompensated congenital superior oblique paresis and 4 had acquired superior oblique paresis. All patients with acquired superior oblique paresis relied predominantly on the vertical rectus muscles for motor fusion. Patients with congenital superior oblique paresis were less uniform in their mechanisms for motor fusion: 2 patients used predominantly the oblique muscles, 2 patients used predominantly the vertical recti, and 2 patients used predominantly the superior oblique in the hyperdeviated eye and the superior rectus in the hypodeviated eye. The last 2 patients developed the largest changes in torsional eye alignment relative to changes in vertical eye alignment and were the only patients to develop symptomatic surgical overcorrections. CONCLUSION: There are 3 different mechanisms for vertical fusion in individuals with superior oblique paresis, with the predominant mechanism being the vertical recti. A subset of patients with superior oblique paresis uses predominantly the superior oblique muscle in the hyperdeviated paretic eye and the superior rectus muscle in the fellow eye for fusion. This results in intorsion of both eyes, causing a large change in torsional alignment. The consequent cyclodisparity, in addition to the existing vertical deviation, may make fusion difficult. The differing patterns of vertical fusional vergence may have implications for surgical treatment.

Adolescent↗
PubMed2002

Isolated acquired unilateral horizontal gaze paresis from a putative lesion of the abducens nucleus.

In three patients, acute horizontal gaze pareses developed that could not be overcome with the oculocephalic maneuver, indicating a putative lesion of the ipsilateral abducens nerve nucleus. None of the patients had a facial nerve paresis or evidence of a trigeminal sensory neuropathy. Although most lesions that affect the abducens nerve nucleus also damage the ipsilateral fasciculus of the facial nerve, small lesions in this region can produce an isolated horizontal gaze paresis.

Abducens Nerve Diseases↗
PubMed2002

The cerebellar contribution to eye movements based upon lesions: binocular three-axis control and the translational vestibulo-ocular reflex.

The study of human cerebellar patients and monkeys with experimental cerebellar lesions has taught us much about the role of the cerebellum in normal ocular motor control. Here we emphasize recent findings that point to a role for the cerebellum in (1) the control of the three-dimensional axis about which the eye rotates in response to visual and vestibular stimuli, and (2) the generation of the translational VOR. Findings in cerebellar patients include abnormalities of eye torsion during attempted fixation that suggest a cerebellar role in the control of torsion so that Listing's law is obeyed. Abnormal torsion during vertical pursuit suggests that central processing of information for smooth pursuit may be based upon a phylogenetically old, semicircular canal coordinate scheme. Inappropriate and disconjugate vertical and torsional eye movements ("cross-coupling") occur during brief, high-acceleration rotations of the head. This suggests a role for the cerebellum in the binocular control of the rotation axis of the VOR. Finally, abnormalities of the modulation of the translational VOR with near viewing in cerebellar patients, but with sparing of the very initial 25-30 msec of response, suggests an important role for the cerebellum in the translational VOR.

Animals↗
PubMed2002

Changes in Listing's plane after sustained vertical fusion.

PURPOSE: To determine whether prolonged fusion of an imposed vertical disparity leads to a change in the orientation of Listing's plane, even when measured during monocular viewing. METHODS: Four normal subjects (age range, 24-37 years) wore Fresnel prisms of increasing power for 72 hours to produce a final left-over-right disparity (range, 7-11 prism diopters [approximately 3.9 - 6.2 degrees]) that was still fusible. Eye movements were measured binocularly, using three-axis search coils, as subjects fixed on an array of light-emitting diodes (LEDs) arranged on a flat screen, 124 cm away. A regression was used to fit the data points to a plane (Listing's plane) during monocular and binocular viewing. From each planar fit, the horizontal and vertical components of primary position (the direction of gaze that is perpendicular to Listing's plane) were calculated. Baseline data were collected in the unadapted state, either just before or at least 4 days after wearing the prisms. RESULTS: After the period of viewing through the prisms, there was a change in vertical phoria (prism adaptation) ranging from 1.6 to 3.3. There was a significant (P < 0.01) shift of the relative orientation of the vertical component of primary position between the two eyes of 6.3 +/- 1.7 degrees (right eye value minus left eye, up being positive, each measured during monocular viewing). There was no consistent pattern of change in the horizontal component of primary position. CONCLUSIONS: Prolonged fusion of a vertical disparity is associated with a change in the orientation of Listing's plane that persists under monocular viewing. Possible mechanisms include phoria adaptation, the prolonged fusional effort itself, and the residual disparity that must be overcome by sensory mechanisms.

Adult↗