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D Straumann

Publications and source records attributed to D Straumann.

62 records · Page 4Linked to original sources
PubMed1991

Two- rather than three-dimensional representation of saccades in monkey superior colliculus.

Saccades are controlled by neurons in the brainstem reticular formation that receive input from the superior colliculus and cortex. Recently two quantitative models have been proposed for the role of the colliculus in the generation of three-dimensional eye movements. In order to test these models, three-dimensional eye movements were measured in the alert monkey to investigate whether the saccadic motor map of the superior colliculus is two-dimensional, representing retinal target vectors, or three-dimensional, representing three-dimensional motor error for the rotation of the eye. Electrical stimulation of the superior colliculus produced two-dimensional, not three-dimensional, eye movements. It is therefore concluded that the collicular motor map is two-dimensional.

Animals↗
PubMed1991

Listing's law for eye, head and arm movements and their synergistic control.

We have recorded eye, head, and upper arm rotations in five healthy human subjects using the three-dimensional search coil technique. Our measurements show that the coordination of eye and head movements during gaze shifts within +/- 25 deg relative to the forward direction is organized by restricting the rotatory trajectories of the two systems to almost parallel planes. These so-called "Listing planes" for eye-in-space and head-in-space rotations are workspace-oriented, not body-fixed. Eye and head trajectories in their respective planes are closely related in direction and amplitude. For pointing or grasping, the rotatory trajectories of the arm are also restricted to a workspace-oriented Listing plane. During visually guided movements, arm follows gaze, and the nine-dimensional rotatory configuration space for eye-head-arm-synergies (three degrees of freedom for each system) is reduced to a two-dimensional plane in the space of quaternion vectors.

Arm↗
PubMed1991

Smooth pursuit eye movements obey Listing's law in the monkey.

We have tested Listing's law in the monkey using the dual search coil technique to record 3-dimensional eye positions during smooth pursuit and during spontaneous eye movements in the light. Our results indicate that during smooth pursuit the eye positions obey Listing's law with a least the same accuracy as during spontaneous eye movements or during periods of fixations.

Animals↗
PubMed1991

Off-line computing of slow-phase eye velocity profiles evoked by velocity steps or caloric stimulation.

We describe a method to compute the slow-phase eye velocity profile without explicit removal of quick phases. It can be used for off-line analysis of eye movements evoked by angular head velocity steps or caloric stimulation. Zero-crossings of eye velocity from negative to positive values divide the velocity trace into intervals of different length. In each interval, the velocity data points are sorted in an ascending order. The value at the least slope (mode value) is taken as the representative slow-phase velocity for the processed interval. Spline interpolation between the representative points of all intervals results in an envelope that gives an accurate description of the slow-phase velocity over time and is used to determine parameters such as peak slow-phase velocity, time constant etc. The method can easily be implemented on a computer.

Algorithms↗
PubMed1991

Generation of vertical and torsional rapid eye movement in the rostral mesencephalon. Experimental data and clinical implications.

The riMLF is a nucleus in the rostral mesencephalon whose bilateral destruction leads to a palsy of vertical and torsional rapid eye movements. A unilateral lesion leads to a loss of torsional rapid eye movements in only one direction, but vertical rapid movements can still be generated with some reduction in their velocity. Single neuron studies in monkeys and anatomy support the concept that the riMLF together with the PPRF are the critical areas in the brainstem to generate rapid eye movements in 3 dimensions.

Animals↗
PubMedDate not supplied

Effects of alertness on three-dimensional eye movements.

PURPOSE: To investigate effects of alertness on three-dimensional (3D) eye movements. METHODS: During drowsy and alert periods, 3D eye movements were recorded with dual search coils in three normal rhesus monkeys, and in two of these monkeys after placement of bilateral kainic acid lesions of the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF). RESULTS: When the three monkeys were in the normal state, the average plane thickness (standard deviation of all rotation vectors from the regressed plane) during drowsy periods (range, 1.2-1.9 degrees ) increased significantly compared with the plane thickness during alert periods (range, 0.7-0.9 degrees ) in the light (P <.05). The plane thickness increased significantly in the monkey with asymmetric bilateral riMLF-lesions (P <.05); however, the increase was not significant in the monkey with more symmetric bilateral riMLF-lesions. After the bilateral riMLF-lesions, the plane thickness also increased with drowsiness in both monkeys (P <.02), as it had in the normal state. CONCLUSION: The implementation of Listing's law is independent of the presence of vertical-torsional burst neurons in the riMLF. The increase in thickness of Listing's plane during drowsy periods is not due to an imprecise signal from saccadic burst neurons to the 3D velocity-to-position integrator. It is possible that this integrator itself controls Listing's law, depending on the state of alertness.

Animals↗
PubMedDate not supplied

Three-dimensional characteristics of rhesus monkey vestibular nystagmus after velocity steps.

In rhesus monkeys we have investigated 3-dimensional orientations of angular eye velocity vectors during vestibular step responses about an earth-vertical axis. Monkey body position with respect to the rotation axis was systematically changed between upright, 90 degrees ear-down, and supine positions to induce oblique eye movements with horizontal, vertical, and torsional components, respectively. Angular eye velocity axes deviated from stimulus axes due to two types of anisotropies in the vestibulo-ocular reflex, that is, gain anisotropy and velocity-storage anisotropy. Deviations of eye velocity vectors from stimulation axes at peak slow-phase velocity could well be predicted by vectorial summation of gains obtained for the cardinal directions (horizontal, vertical, and torsional). During nystagmus decay, time constants after oblique velocity steps showed a tendency to be similar in participating components. However, this adjustment of time constants was incomplete for horizontal-torsional and horizontal-vertical-down vestibular responses, leading to an orientation change of eye rotation axes during slow-phase velocity decay with a bias toward the horizontal eye movement component.

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