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Biomedical subjects

V Henn

Publications and source records attributed to V Henn.

At least 109 records · Page 6Linked to original sources
PubMed1980

Nystagmus slow-phase velocity during vestibular, optokinetic, and combined stimulation in the monkey.

In Rhesus monkeys the slow-phase velocity of nystagmus was measured during optokinetic, vestibular, and combined stimulation. Accelerations and decelerations of 2.5--40 degrees/s2, and rotation at constant velocities of 70-160 degrees/s were applied. During combined visual-vestibular stimulation, nystagmus slow-phase velocity is a function only of the instantaneous stimulus velocity: It has a gain near unity and is independent of the duration and value of the acceleration. The limited linear working range of the vestibular or optokinetic system is thus extended. During deceleration an inappropriate nystagmus response is elicited only when the previous constant velocity rotation was above the saturation velocity of optokinetic nystagmus (OKN). These results are related to single neuron activity recorded in the vestibular nuclei and the flocculus under identical stimulus conditions.

Acceleration↗
PubMed1980

Subjective velocity estimation during conflicting visual-vestibular stimulation.

Human subjects continuously estimated their position during and after steps of angular acceleration in complete darkness. These estimations were compared with the same vestibular stimulation in the light while subjects gazed at a striped cylinder which completely enclosed them and was mechanically fixed to the turntable. Rotation with such a fixed visual surround created a sensory conflict: the acceleration is sensed by the vestibular end organs, while the visual system senses no displacement. Accordingly, during the conflict stimulation, the estimation of rotational velocity and its duration is markedly reduced. These findings in humans compare well with nystagmus and single neuron recordings in the vestibular nuclei of alert monkeys.

Acceleration↗
PubMed1979

The velocity response of vestibular nucleus neurons during vestibular, visual, and combined angular acceleration.

In alert Rhesus monkeys neuronal activity in the vestibular nuclei was measured during horizontal angular acceleration in darkness, acceleration of an optokinetic stimulus, and combined visual-vestibular stimulation. The working ranges for visual input velocity and acceleration extend up to 60 degrees/s and 5 degrees/s2. The corresponding working range for vestibular input acceleration is wider and time-dependent. During combined stimulation, that is acceleration of the monkey in the light, a linear relation between neuronal activity and velocity could be established for all neurons. Type I vestibular plus eye movement neurons displayed the greatest sensitivity and had a small linear range of operation. Other vestibular neurons were less sensitive but had a larger range of linear response to different values of acceleration. Accelerating the animal and visual surround, simultaneously but in opposite directions, results in neuronal activity proportional to relative velocity over a limited range.

Acceleration↗
PubMed1978

Conflicting visual-vestibular stimulation and vestibular nucleus activity in alert monkeys.

In alert Rhesus monkeys (Macaca mulatta) neuronal activity of vestibular nuclei was recorded during pure vestibular and conflicting visual-vestibular stimulation. Pure vestibular stimulation consisted of rotating the monkey about the vertical axis in complete darkness. During conflicting visual-vestibular stimulation the monkeys were rotated in the light within a vertically striped cylinder mechanically coupled to the turntable. The conflict is that although the monkey is accelerated, there is no relative movement between visual surrounding and the animal. In the conflict situation thresholds of neuronal modulation and of nystagmus were raised compared with those during pure vestibular stimulation. Nystagmus slow-phase velocity could always be dissociated from the neuronal activity, the nystagmus often being totally suppressed whereas the neuronal activity was only attenuated. This suggests a further information processing between vestibular and oculomotor nuclei in the generation of nystagmus.

Animals↗
PubMed1978

Dynamic changes of optokinetic after-nystagmus (OKAN) caused by brief visual fixation periods in monkey and in man.

Optokinetic nystagmus (OKN) continues after the cessation of visual stimulation in complete darkness as primary optokinetic after-nystagmus (OKAN I). After variable periods of time, it is followed by secondary OKAN (OKAN II). Short periods of visual fixation during OKAN I in monkey and in man inhibit OKAN I, but enhance OKAN II. The enhanced OKAN II starts earlier, lasts longer, and often reaches higher slow-phase velocities than in control experiments. Therefore, OKAN II depends not on the ocurrence or strength of OKAN I, but mainly on parameters of the preceding optokinetic stimulus. Results suggest that OKAN I duration is partially determined by the development of OKAN II.

Adult↗
PubMed1978

Reciprocal changes in primary and secondary optokinetic after-nystagmus (OKAN) produced by repetitive optokinetic stimulation in the monkey.

In six rhesus monkeys (Macaca mulatta) the effect of repetitive periods of whole-field optokinetic stimulation upon the different phases of optokinetic after-nystagmus (OKAN) was studied. The precedings optokinetic stimulus consisted of rotating a striped cylinder around the stationary monkey. Experiments were performed on up to 8 successive days. The results demonstrate that OKAN I and OKAN II are affected in a reverse manner by repeated optokinetic stimulation: The duration of OKAN I strongly decreases, whereas OKAN II increases in duration and intensity. The mechanisms under lying the generation of OKAN I and OKAN II and the role of OKAN II in the habituation process are discussed.

Animals↗
PubMed1978

Transfer characteristics of neurons in vestibular nuclei of the alert monkey.

1. In the alert monkey, 74 neurons in the vestibular nuclei were investigated during sinusoidal rotation about a vertical axis at frequencies between 0.003 and 0.5 Hz. Phase and gain were determined by a fast Fourier analysis program. 2. Phase advance, relative to turntable velocity, was small between 0.05 and 0.5 Hz. At lower frequencies phase advance increased to 45 degrees at 0.007--0.02 Hz, and 90 degrees at 0.003--0.005 Hz. In agreement with the phase characteristics, a gain decrease of -3 dB was determined between 0.007 and 0.02 Hz. Assuming a linear system, time constants of 9.5, 11.9, and 24.5 s were calculated for three different monkeys. 3. Simultaneously recorded nystagmus exhibited similar time constants as the central vestibular neurons for each monkey. 4. Frequency responses of 11 neurons were recorded from the same monkeys while they were under general anesthesia and the time constants were reduced to 4--7 s. This is the range of time constants seen in the peripheral nerve. 5. The longer time constants in the alert state are due to an integration process, which provides a low-frequency compensation, and is thought to be achieved through a feedback loop involving the reticular formation. 6. In the alert and anesthetized state, monkeys were also exposed to velocity trapezoids. Time constants of decay of neuronal activity were in good agreement with the data obtained during sinusoidal stimulation. 7. A transfer function of the primary vestibular afferents is expanded to include the described low-frequency compensation found in central vestibular neurons in the alert animals.

Anesthesia, General↗
PubMed1977

Vestibular nuclei activity during optokinetic after-nystagmus (OKAN) in the alert monkey.

Neurons which receive an input from the horizontal semicircular canals were recorded from the vestibular nuclei in chronically prepared monkeys (Macaca mulatta) during optokinetic after-nystagmus (OKAN). In complete darkness the vestibular neurons showed activity changes which closely paralleled the strength of nystagmus. The activity of vestibular units returned to baseline levels of spontaneous discharge only when all after-nystagmus had ceased, or when it was inhibited by stationary visual stimuli. The possible role of vestibular neurons in the generation of OKAN and its significance in vestibulo-visual interaction is discussed.

Animals↗
PubMed1977

Vestibular-related neuronal activity in the thalamus of the alert monkey during sinusoidal rotation in the dark.

1. In the alert monkey neuronal activity was recorded in the ventro-posterior nucleus (VP) of the thalamus in the dark during sinusoidal rotation over a frequency range from 0.01-1 Hz. 2. From 57 neurons 38 (67%) were activated with rotation to the ipsilateral side (type I) and 19 (33%) to the contralateral side (type II). The spontaneous activity was low (average 10.1 imp/sec) and irregular. No activity changes were found with eye movements. 3. At 0.2-0.1 Hz neuronal activity showed a phase lead of 10-20 degrees relative to chair velocity. At the lowest frequency (0.01 Hz) the phase lead was only slightly higher (about 30 degrees). Accordingly the decrease in gain was only moderate. 4. At lower frequencies the simultaneously recorded eye movements (nystagmus) showed an increase in phase lead comparable to the values for the neuronal activity in the thalamus. For both neuronal activity in the thalamus and nystagmus a time constant between 25-35 sec was calculated. 5. The data are compared with vestibular nerve and nuclei recordings. It is argued that the time constants of vestibular neurons in the thalamus are very similar to the time constants of neurons in the vestibular nuclei in alert animals.

Animals↗
PubMed1977

Vertical eye movement related unit activity in the rostral mesencephalic reticular formation of the alert monkey.

Eye movement related unit activity was recorded in the rostral mesencephalic reticular formation (MRF) of the alert monkey. Most units (78 out of 117) were activated with a short activity burst starting before the eye movement and were otherwise silent. The activity was the same whether movements occurred spontaneously in the light or dark, or were fast phases of vestibular or optokinetic nystagmus, and could be related to parameters of a vector representing the eye movement such as amplitude, position changes along certain planes or direction of movements. Units coding position changes or direction of movement had their preferred direction always close to the vertical. Other units (18 out of 117) showed some tonic activity, which was also only related to vertical eye position. It is suggested that this region of the rostral MRF acts an an immediate supranuclear structure, mediating eye movements in the vertical plane.

Action Potentials↗
PubMed1977

Neuronal activity in the vestibular nuclei of the alert monkey during vestibular and optokinetic stimulation.

Recordings from neurons of the vestibular nuclei were performed in alert monkeys. Type I and type II units were identified by rotating the monkey about a vertical axis. Al neurons responded also when only the visual surround was rotated around the stationary monkey. The combination of visual and vestibular stimulation points towards non-algebraic summation characteristics for the two inputs, with each input dominating the response over a certain range.

Animals↗