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Biomedical subjects

V Henn

Publications and source records attributed to V Henn.

At least 127 records · Page 7Linked to original sources
PubMed1976

Duration and direction of optokinetic after-nystagmus as a function of stimulus exposure time in the monkey.

1. Parameters of the optokinetic after-nystagmus (OKAN) outlasting optokinetic stimulation were studied in monkeys. With constant pattern velocity (60 degrees/s) exposure times were varied between 2 s and 15 min. 2. All monkeys showed a primary after-nystagmus moving in the same direction (OKAN I) as the preceding optokinetic nystagmus, under all conditions tested. A secondary after-nystagmus in the opposite direction (OKAN II), was only observed after exposure times of 30 s or longer. After a 15-min exposure, half of the monkeys showed an early onset of OKAN II in less than 1 min, whereas for the remaining half the transition to OKAN II occurred only after 4 min or not at all. 3. In monkeys showing an early onset of OKAN II, the duration of OKAN I decreased and the maximal slow phase velocity of OKAN II increased consistently with longer exposure times. In several instances OKAN III, moving in the same direction as OKAN I, was seen after OKAN II. 4. Monkeys in which OKAN II was late, or absent, often showed minima and additional maxima of slow phase velocity of OKAN. 5. The results are discussed in terms of two opposing mechanisms underlying the generation of OKAN and their connections to the vestibular system.

Animals↗
PubMed1976

Coding of information about rapid eye movements in the pontine reticular formation of alert monkeys.

Neurons in the rostral paramedian zone of the pontine reticular formation (PRF) have distinct frequency changes prior to and during quick eye movements, but generally little or no tonic activity associated with eye position. Evidence indicates that horizontal saccades and quick phases of nystagmus are generated in this region. Firing of units activated with eye movements (burst units) and of units which are inhibited (pause units) was analyzed. Eye movements were described by a vector having an amplitude (A) and an angle (a). These parameters were related to position changes in certain planes by the equation delta pos = A - cos alpha. In each of 80 cells in the PRF which were encountered, the activity could be related to some parameter of the above equation: change of position (delta pos), amplitude (A), or the cosine of the angle between the direction of movement and a reference direction (cos alpha). Units coding amplitude of eye movement or change in position in a particular plane conveyed the information by number of spikes. Units coding direction of movement did so by frequency. In many units, the information coding was precise so that the direction or amplitude of single eye movements could be predicted from the frequency changes of single units. In other units, this could be determined from averages of the frequency changes. Cells coding direction or change in position had frequency maxima only in planes corresponding to the pulling direction of the eye muscles. The results suggest that a vector description is not only a convenient mathematical tool, but is the way eye movements are coded in the PRF and possibly elsewhere in the central nervous system.

Animals↗
PubMed1975

Ernst Mach on the vestibular organ 100 years ago.

Ernst Mach (1838-1916) performed pioneering research on vestibular function 100 years ago. His experiments were mainly psychophysical and included measurements of threshold and study of the vestibular-visual interaction. Contrary to general belief, he concluded that the adequate stimulus for the semicircular canals must be pressure. He presented evidence specifically against the sustained endolymph flow theory of Breuer (1874) and Crum Brown (1874), with which he is frequently associated. Excerpts from his publications are given and their relevance to current research is discussed.

Germany↗
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

Habituation of the human vestibulo-ocular reflex with low-frequency harmonic acceleration.

Habituation of the human vestibulo-ocular reflex by prolonged low-frequency (0.01 and 0.005 Hz) harmonic (sinusoidal) angular acceleration was assessed by measuring the phase advance of slow-phase eye velocity at 0.01 Hz and the time constant of slow-phase eye velocity decay after impulses of angular acceleration. A single half-hour test session produced increases in low-frequency phase advance and decreases in time constant values in all 16 normal subjects. Although all subjects showed increases in low-frequency advance from the beginning to the end of the initial test session, only a few maintained the increases between test sessions. These changes are qualitatively similar to but quantitatively less than those observed with similar testing in monkeys. For clinical testing, to minimize the effect of habituation during harmonic accelerations, the testing time at low frequencies (i.e., less than 0.1 Hz) should be as short as possible.

Acceleration↗
PubMedDate not supplied

[Morphology and phenomenology of death by kicking (II)].

In the years from 1982 to 1995, 20,504 autopsy cases were examined at the Departments of Forensic Medicine in Hamburg and Greifswald. In 103 cases death was caused by kicking. In the Greifswald area, the occurrence of kicking as the cause of death could be demonstrated in 68 cases (30% of all homicides), which is in contrast to the observations in Hamburg, were kicking amounted to only 2.5% of the homicides. Most of the victims (average age 44 years) were under the influence of alcohol (mean blood alcohol concentration 1.75/1000), and most were on social support. The victims often showed other signs of blunt trauma such as blows with the fist and strangulation. In a few cases, cutting and stabbing wounds were also found. In the majority of cases death was due to severe haemorrhages and aspiration of blood in addition to the direct effects of the head injuries. The crimes were committed by one person in 46 cases, two in 20 and three in 4 cases. The perpetrators (average age 27.6 years) were always younger than the victims. Case reports show that fatal kicking was mostly triggered by relatively trivial arguments. None of the incidents were preplanned by the perpetrators. In contrast to an expected higher incidence of kicking deaths in the urban area of Hamburg, these crimes occurred ten times more frequently in the rural area of Greifswald.

Adult↗