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Biomedical subjects

V Henn

Publications and source records attributed to V Henn.

At least 91 records · Page 5Linked to original sources
PubMed1983

Spatio-temporal recoding of rapid eye movement signals in the monkey paramedian pontine reticular formation (PPRF).

The integrity of the paramedian pontine reticular formation (PPRF) is necessary for the generation of rapid eye movements. The main saccade-related population is of the burst type with latencies between 0 and 40 ms preceding a saccade, and they can be divided into medium- and long-lead burst neurons. Burst neurons have predominantly spatially coded movement fields in the rostral PPRF, while in the caudal PPRF they increase their burst strength in temporal coding approximately in the pulling directions of extraocular eye muscles (i.e. almost horizontal or vertical). Both neuronal populations have ipsilateral on-directions and contain long-lead burst neurons. In a quantitative analysis the firing patterns of long-lead burst neurons are compared to those of medium-lead burst neurons, which form the predominant output of the saccadic pulse generator to the motoneurons. The firing patterns of temporally coded long-lead bursters are similar to those of medium-lead bursters, except for earlier on-latencies, larger statistical fluctuations, and specializations for small or large saccades in oblique directions. The spatially coded burst neurons form a motor map of saccadic vectors. The diameter of their movement field is often about the size of the saccade vector, and they encode saccadic onset and duration. These results are consistent with a model for visual saccades in eye displacement coordinates, where the spatio-temporal recording of horizontal eye movements is effected by long-lead burst neurons in the PPRF.

Animals↗
PubMed1982

[Acute delirium in bismuth poisoning].

Typical clinical signs and symptoms of bismuth intoxication are illustrated in a cases of a 45-year-old woman. Initially psychasthenia appears followed by acute delirium with ataxia, myoclonic jerks and occasionally coma. If patients survive the acute phase they recover only gradually following discontinuation of bismuth medication. In cases of extreme intoxication, permanent memory deficits may occur. Etiology, pathogenesis, laboratory findings, differential diagnosis and therapy of this rare iatrogenic encephalopathy are discussed.

Bismuth↗
PubMed1982

Eye movement related neurons in the cerebellar nuclei of the alert monkey.

In all cerebellar nuclei saccade related neurons can be recorded. In the alert untrained Rhesus monkey these neurons can be classified into short-lead bursters, complex bursters, and tonic burst neurons. Short-lead bursters can be related to the onset or to the length of saccades and blinks. Complex bursters are active in the early (acceleration) or late (deceleration) phase of saccades. Tonic burst neurons, in addition, display maintained activity which is modulated in a complex manner with eye position, during periods of fixation or slow-phase nystagmus. In agreement with clinical and previous experimental data we view these cerebellar output neurons as elements which are not part of the system which basically generates eye movements, but rather as a system which could influence the execution of movements.

Animals↗
PubMed1982

The primate oculomotor system. I. Motoneurons. A synthesis of anatomical, physiological, and clinical data.

The aim of this paper is to relate recent physiological and anatomical data from Rhesus monkeys to normal function and pathology in the human oculomotor system. 1. Anatomical location of motoneurons in the oculomotor nuclei was investigated with retrograde labelling techniques, and medial rectus motoneurons were found within three different subgroups. 2. Physiological characteristics of motoneurons show a continuous distribution of different types from tonic to phasic, with tonic-phase neurons representing the majority. 3. Quantitative analysis of the firing pattern of motoneurons leads to the construction of iso-frequency curves. They show all possible eye positions for a given firing frequency in a single neuron. They give a quantitative measure for the innervation of a muscle when acting in synergy with all other muscles during fixation. The eye displacement during saccades can be described by a vector represented by a burst discharge in motoneurons, the integral of which can be used to hold the eyes in position. 4. Clinical syndromes will be discussed that can be related to anatomy and physiology.

Abducens Nerve↗
PubMed1982

The primate oculomotor system. II. Premotor system. A synthesis of anatomical, physiological, and clinical data.

Rapid, slow, and vergence eye movements are controlled by neuronal subsystems, which to some extent are anatomically separate. Furthermore, there is a similar separation of the networks controlling horizontal and vertical movements. Therefore, several single systems can be selectively affected in pathology. Anatomical and physiological investigations in monkey have demarcated the paramedian pontine reticular formation and the rostral mesencephalon as areas which generate horizontal and vertical rapid eye movements respectively. The flocculus is an important link for visually mediated movements: foveal pursuit, high velocity optokinetic nystagmus, and the visual suppression of vestibular nystagmus. The function of these structures is discussed with respect to oculomotor control, and their dysfunction related to specific neurological deficits.

Adaptation, Physiological↗
PubMed1981

Habituation of the vestibulo-ocular reflex (VOR) in the monkey during sinusoidal rotation in the dark.

In experimentally naive monkeys the horizontal vestibulo-ocular-reflex (VOR) has a time constant which is in the range of 40--60 s. It can be measured as the nystagmus decline after pulses of angular acceleration, or from the transfer functions obtained from sinusoidal rotation with different frequencies. When frequencies below 0.1 Hz are applied, sinusoidal rotation leads to a pronounced phase advance, a decrease in gain and a shortening of the pre- and post-rotatory nystagmus time constant. Even very low frequencies (e.g., 0.002 Hz) are effective where the phase advance of eye relative to head velocity is already 90 degrees in the naive animal. Exposing the animal to stimulation only at a single frequency shifts the whole frequency curve towards a greater phase advance. These results are consistent with habituation experiments in which steps of angular velocity have repeatedly been applied. In these experiments nystagmus duration is shortened, whereas the initial response at the end of acceleration does not change. This corresponds to a phase shift and a gain reduction in the low frequency range (below 0.1 Hz) which we have also observed during sinusoidal rotation.

Animals↗
PubMed1981

Visual-vestibular interaction in the flocculus of the alert monkey. I. Input activity.

Neuronal activity in the flocculus of alert Rhesus monkeys was recorded during vestibular stimulation (rotation of the monkey about a vertical axis in complete darkness), optokinetic stimulation (rotation of the visual surround around the stationary monkey), combined visual-vestibular stimulation (rotation of the monkey inside the stationary surround in light), and conflicting visual-vestibular stimulation (rotation of the monkey together with the visual surround in the same direction). The input to the flocculus was recorded as non-Purkinje cell (non-P-cell) activity. Ninety per cent of the non-P-cells which were modulated during our stimulation paradigms carry information similar to that in the neurons of vestibular nuclei. This suggests that the main mossy fiber input to the flocculus originates in the vestibular nuclei. A second input of unknown origin conveys visual information about retinal slip. Thus, part of the flocculus -- as further discussed elsewhere (Waespe and Henn 1981) -- may be specialized to subserve visual-vestibular interaction to improve the nystagmus response.

Animals↗
PubMed1981

Visual-vestibular interaction in the flocculus of the alert monkey. II. Purkinje cell activity.

The activity of Purkinje cells (P-cells) was recorded in the flocculus of alert Rhesus monkeys under different conditions of visual-vestibular stimulation. Stimulations conditions were vestibular, optokinetic, combined and conflicting. About 10--20% of all P-cells were activated in their simple spike activity during conflicting stimulation to the recording side (type I) and gave no response or much less during vestibular stimulation. About half of these P-cells were also activated during optokinetic stimulation to the recording side at velocities above 40--60 deg/s. Simple and complex spike activity behaved in a reciprocal way with overlapping but not identical working ranges. Simple spike modulation was unidirectional, complex spike activity always bidirectional. Modulation of simple spike activity cannot be related to one single parameter of the sensory input or the oculomotor output. The hypothesis is put forward that the vestibular nuclei and the flocculus behave in a complementary fashion in processing visual-vestibular information, the flocculus being specialized for high velocity optokinetic nystagmus and suppression of vestibular nystagmus.

Animals↗
PubMed1981

Circularvection: psychophysics and single-unit recordings in the monkey.

In psychophysical experiments, human subjects indicated the amount of circularvection (CV) that experienced during sinusoidal rotation (0.01-5 Hz) of the visual surround. Accelerations varied between 5 and 160 degrees/second2; maximal velocities did not exceed 160 degrees/second. Below 0.1 Hz and 20 degrees/second2, most subjects experienced full CV; above, CV was only partial. Subjects then perceived a combination of CV and object motion. All subjects still had some CV at 2 Hz. The upper frequency limit seemed to occur around 5 Hz. In related neurophysiological studies, single units were investigated in the vestibular cortex (area 2v) of the alert monkey. Neurons responded to animal rotation in the dark as well as to sinusoidal rotation of the visual surround (0.01-1 Hz). Units responded to the visual stimulus in the high-frequency range with a gain increase. These experiments demonstrate the prominent influence of the visual system on vestibular neurons even at high frequencies.

Adult↗
PubMed1981

Vestibular habituation in man and monkey during sinusoidal rotation.

Habituation of the vestibular system by repeated steps of angular velocity leads to a shortening of nystagmus. These steps can be broken down into different frequency sinusoids. High-frequency sinusoidal rotation (above 0.1 Hz) generally was found to be ineffective, while low-frequency stimulation (0.0015-0.05 Hz) led to a dramatic shortening of time constants after only a few cycles of stimulation. In the alert monkey, time constants of vestibular nystagmus and single units, recorded from the vestibular nuclei, are always similar and covary together. Experiments in humans, with measurement of nystagmus and subjective velocity sensation, suggest similar processes for habituation.

Acceleration↗
PubMed1981

Input-output activity of the primate flocculus during visual-vestibular interaction.

In the primate flocculus, unit activity was recorded during vestibular (rotation of the monkey about the vertical axis in complete darkness), optokinetic (rotation of the visual surround around the stationary monkey), and conflicting (rotation of the visual surround and the turntable fixed together) stimulation. Activity indicating two different mossy fiber inputs was recorded. One carried a signal that was similar to that in the vestibular nuclei: during optokinetic stimulation, neurons saturated at a velocity of 60 degrees/second; and during conflicting stimulation, neuronal activity was attenuated only at low accelerations. This input combines vestibular, visual, and oculomotor information. Another mossy fiber input carried information about visual image slip only. This input indicates instances when nystagmus is not compensatory. Purkinje cells were modulated in their simple spike activity during optokinetic stimulation only at high stimulus velocities of 40-60 degrees/second and above, and during conflicting stimulation at high accelerations. This suggests a complementary information processing of the flocculus and the vestibular nuclei during visual-vestibular stimulation. The findings are corroborated by lesion studies in primates.

Animals↗
PubMed1981

Frequency response of the vestibulo-ocular reflex (VOR) in the monkey.

The frequency response of the vestibulo-ocular reflex has been investigated in the alert monkey during sinusoidal rotation about a vertical axis ina frequency range of 0.001-0.5 Hz. Phase and gain of nystagmus slow phase velocity was determined. In the frequency range above 0.1 Hz, nystagmus slow phase velocity was in phase with (compensated for) head velocity. At lower frequencies, an increasing phase lead was present which could reach more than 90 degrees. Gain fell off correspondingly at low frequencies. Calculated time constants were 10-40 s in different monkeys. Animals which had been exposed to numerous previous rotary stimuli in the laboratory showed much shorter time constants than did "naive" monkeys.

Animals↗