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Biomedical subjects

V Henn

Publications and source records attributed to V Henn.

At least 55 records · Page 3Linked to original sources
PubMed1992

Pathophysiology of rapid eye movements in the horizontal, vertical and torsional directions.

Saccades and fast phases of optokinetic or vestibular nystagmus are rapid eye movements which are generated in the reticular formation of the brain stem. Palsies of rapid eye movement generation therefore always point towards an infratentorial lesion. Two cell assemblies are responsible for the generation of rapid eye movements: the PPRF, which triggers all rapid eye movements and in this sense plays an important coordinating role in addition to generating movements with a horizontal movement component, and the riMLF in the mesencephalon for movements which have a vertical or torsional direction component. As neurone populations are anatomically segregated according to their respective on-directions, focal lesions lead to the loss of rapid eye movements in particular directions (Table 2). Such palsies of rapid eye movement generation which are direction specific can be distinguished from dysmetria, which points towards a cerebellar lesion, or the difficulty to trigger a saccade to a particular target, which can involve cortical systems.

Animals↗
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

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

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↗
PubMed1990

[Sleep disorders from the neurological viewpoint].

Sleep can be measured by EEG or a monitor which records motor activity. In this way objective data on sleep behavior can be obtained from patients. Total sleep time over 24 hours remains remarkably constant above age 20. Therefore, any changes in total sleep time can be considered to be pathologic. A true shortening of sleep time is rare and is usually associated with a psychosis. More often "common sleep disorders" are encountered, which show a normal total sleep time per 24 hours. Prolonged sleep, usually associated with increased day-time somnolence, is often caused by chronic meningitis or intracranial space occupying lesions. Narcolepsy is a separate entity which has no connection with epilepsy, in which the different physiological components of sleep are desynchronized.

Adult↗
PubMed1990

Delta-9-tetrahydrocannabinol shows antispastic and analgesic effects in a single case double-blind trial.

A double-blind study was performed comparing 5 mg delta-9-tetrahydrocannabinol (THC) p.o., 50 mg codeine p.o., and placebo in a patient with spasticity and pain due to spinal cord injury. The three conditions were applied 18 times each in a randomized and balanced order. Delta-9-THC and codeine both had an analgesic effect in comparison with placebo. Only delta-9-THC showed a significant beneficial effect on spasticity. In the dosage of THC used no altered consciousness occurred.

Adult↗
PubMed1990

Caloric nystagmus in three dimensions under otolithic control in rhesus monkeys. A preliminary report.

The caloric nystagmus of rhesus monkeys in the 'optimum' supine or prone position was recorded three-dimensionally using magnetic search coils. The horizontal component of the nystagmus was in the direction expected from the convection flow theory of Bárány. The torsional component changed its direction according to the side of caloric stimulation independent of head position with regard to gravity, i.e., counterclockwise nystagmus by right ear stimulation and clockwise nystagmus by left ear stimulation both in the supine or in the prone positions. The direction of the vertical component depended upon the head position and not upon the side of stimulation, i.e., up-beating nystagmus in the supine position and down-beating nystagmus in the prone position. The durations and the contours of slow phase velocity of the horizontal, vertical and torsional components were different from each other. The origins of the first phase of caloric nystagmus in three dimensions may be explained by activation of all the three semicircular canals. As for the second phase of caloric nystagmus in the supine or in the prone position, the torsional component was comparatively strong and lasted the longest among the three components. The second phase of caloric nystagmus was markedly modified by head position with regard to gravity. These findings suggest that it is the otolithic organs that determine the moving plane of second phase caloric nystagmus.

Animals↗
PubMed1989

On the generation of vertical and torsional rapid eye movements in the monkey.

The role of the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) in generating the vertical and torsional components of rapid eye movements was examined. The on-directions of burst neurons in the riMLF of alert Rhesus monkeys were obtained during quick phase nystagmus in three dimensions. The distinguishing feature of these burst neurons was the torsional component of their on-directions; neurons on the right side exhibited a clockwise component, from the point of view of the subject, while those on the left had a counterclockwise component. Vertical components could have up or down directions. This organization was verified by means of unilateral reversible inactivation of the riMLF using Muscimol. An injection in the right riMLF impaired the generation of quick phases with clockwise components while one on the left impaired counterclockwise components.

Action Potentials↗
PubMed1989

How could canal-pluggings result in intensive direction changing type of positional nystagmus?

The objectives of this study in Rhesus monkeys is to observe the sequences which appear in the oculo-spinal-motor system after selected semicircular canals had been plugged. The left anterior and the right posterior canals in a monkey "LARP", the left anterior and posterior canals in "LALP", and the left lateral canal in "LL" were plugged under intubation general anesthesia. Three-dimensional eye recordings were performed, using two scleral coils. Behavior, posture, and vestibulo-ocular reflex were studied. Compensation was established in the light within 2 days. In darkness, no spontaneous nystagmus was recorded in the sitting position. The monkey "LALP" developed marked positional nystagmus. When the head position was changed up to 360 degrees in 15 degrees steps, horizontal, vertical and torsional eye movements showed remarkable changes. Spontaneous direction changing nystagmus in darkness was also recorded in "LALP". To conclude, direction changing positional nystagmus, which was seen for several months after the canal plugging, was difficult to explain by the damage to the adjacent ampullary and/or otolithic endorgans, but may be explained by the limited otolithic compensation in the earth parallel plane for the defective dynamic canal inputs. These observations and conclusions were from experiments using three monkeys only and should still be confirmed in more extended experiments.

Animals↗
PubMed1989

Vestibular habituation in student pilots.

The dynamics of vestibular nystagmus were measured in 42 military student pilots (age 19 to 21). Their responses were compared with 40 non-flying subjects of similar age who were also fulfilling requirements for the mandatory Swiss military service. The following differences emerged: the time constant of the nystagmus response after vestibular stimulation was shorter (p less than 0.001; t-test) in student pilots, whereas the gain tended to be higher (p less than 0.025). These changes in the response dynamics are attributed to habituation. Student pilots were additionally tested with conflicting visual-vestibular stimulation. Nystagmus response was delayed and attenuated when compared to stimulation in darkness. Under these conditions motion sickness occurred in one third of the subjects. We found no relation between the occurrence of motion sickness and the value of the time constant or gain of vestibular nystagmus. Results show that there is no single "normal" value of vestibular nystagmus. This becomes important when defining "normal" values as opposed to pathological values in vestibular testing.

Acceleration↗
PubMed1989

Rapid eye movement generation in the primate. Physiology, pathophysiology, and clinical implications.

The trajectories of rapid eye movements are usually described in a Cartesian coordinate frame with a horizontal, vertical and torsional component. The sensory to motor coordinate transformations for horizontal components of rapid eye movements can be localized to neurons of the paramedian pontine reticular formation (PPRF), where long-lead and short-lead burst neurons are found. The equivalent area for recoding of vertical and torsional movement components is situated in the rostral interstitial nucleus of the MLF (rostral iMLF). Pause cells in caudal midline structures of the PPRF help to coordinate the various movement components. Experimental inactivation of these different neuron population lead to palsies of rapid eye movement generation. A unilateral PPRF lesion leads to a loss of all horizontal rapid eye movements towards the ipsilateral side. A bilateral PPRF lesion involving caudal midline structures leads to a bilateral horizontal gaze palsy in addition to a severe disruption of vertical and torsional eye movements. A bilateral rostral iMLF lesion leads to a loss of all rapid eye movements with a vertical or torsional movement component. A unilateral iMLF lesion leads to a loss of all rapid eye movements with an ipsilateral torsional component.

Animals↗
PubMed1987

[Conservative therapy of chronic subdural hematomas].

Between 1975 and 1984, subdural hematoma was diagnosed in 66 patients at the Department of Neurology, University Hospital, Zürich. In this report we evaluate the therapeutic results retrospectively. In 13 patients treatment was surgical, while 53 patients were treated medically, i.e. with bedrest and corticosteroids. Three surgery patients developed a recurrence which was then also treated medically. Of this total number of 56 patients in the medically treated group, 8 had to undergo surgery later and two patients died. Soporose patients with distinct focal symptoms and comatose patients with incipient herniation received immediate surgical treatment. Of the 46 medically treated patients, 83% were symptom-free and 17% showed residual symptoms. Comparing these results with those of surgical treatment in the literature, conservative treatment can be recommended if strict guidelines are observed.

Aged↗