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Biomedical subjects

V Henn

Publications and source records attributed to V Henn.

At least 73 records · Page 4Linked to original sources
PubMed1986

Sensory input modifying central motor actions.

Motor output is often initiated by sensory stimuli and continuously monitored during execution by sensory input, except for the fastest movements. Recent experiments in animals explored the interaction between classical sensory and motor areas of the central nervous system during motor tasks. In man, evoked potentials can give an estimate of involvement of these structures. In analogy, nystagmus has been analyzed in primates, where a more complete description of the sensorimotor process is possible.

Animals↗
PubMed1985

Frontal eye field projection to the paramedian pontine reticular formation traced with wheat germ agglutinin in the monkey.

Injections of the retrograde tracer [125I]wheat germ agglutinin have been placed in different areas of the paramedian pontine reticular formation (PPRF), a well known premotor center for gaze control. Experiments in 5 monkeys revealed 3 major sources of input: (1) bilateral projections from the so-called frontal eye field (FEF), which is situated in the frontal cortex around the arcuate sulcus; (2) the intermediate and deep layers of mainly the contralateral superior colliculus; and (3) ipsilateral projections from brainstem structures such as the accessory oculomotor nuclei (nucleus interstitialis of Cajal, nucleus of Darkschewitsch, and nucleus of the posterior commissure), the mesencephalic reticular formation, the vestibular nuclei, the nucleus prepositus hypoglossi, and the cerebellar fastigial nucleus. The results are compared with previous anatomical investigations and confirm the electrophysiologically demonstrated FEF-PPRF-abducens disynaptic pathway.

Animals↗
PubMed1985

Vestibulo-ocular reflexes after selective plugging of the semicircular canals in the monkey--response plane determinations.

The contribution from different pairs of semicircular canals to the generation of horizontal vestibular nystagmus was examined in monkeys. Animals with different pairs of semicircular canals surgically plugged were accelerated sinusoidally at 1 Hz (a predictive stimulus) or with steps of angular velocity (a non-predictive stimulus) about an earth vertical axis while the head was placed in various static pitch positions. In normal animals, and in animals with only the lateral canals intact, horizontal nystagmus elicited with angular velocity steps is maximal at a static pitch angle of 15 degrees nose-down (relative to the horizontal stereotaxic plane). The response follows a cosine function of the pitch angle, approaches zero at an angle of 90 degrees to the optimal orientation, and finally reverses. In animals with only the vertical canals operating, direction specific horizontal nystagmus can still be elicited. Using velocity steps, a null plane at which nystagmus reverses can be determined. It is found at about 32 degrees nose-down and thus is different from the optimal plane of the lateral canals. Consequently, it is not possible to stimulate the lateral canals maximally without stimulating the vertical canals simultaneously. Using sinusoidal rotation, nystagmus is attenuated at the static pitch position of 32 degrees nose-down, but does not reverse direction with further pitching.

Animals↗
PubMed1985

ISO-frequency curves of oculomotor neurons in the rhesus monkey.

Static firing frequencies have been determined in extraocular motoneuronal discharge patterns for different eye positions within +/- 30 deg around the primary position. From these data iso-frequency curves were plotted stating all possible eye positions for a given firing rate. Such curves have been constructed for the lateral, medial, and inferior recti, the superior oblique and for the upward pulling muscles (without distinguishing superior rectus and inferior oblique). Fixation of eye position always involved natural synergistic action of all muscles. The iso-frequency curves of individual motoneurons are a family of almost parallel curves with mainly horizontal or vertical gradients. Especially for the superior oblique, the innervation gradients depend strongly on eye position. Motoneurons subserving the same muscle can have different innervation gradients at the same eye position.

Action Potentials↗
PubMed1984

The sleep-wake transition in the oculomotor system.

Eye and head position, EEG, and activity of oculomotor and vestibular neurons in the brainstem were recorded during alertness and at the transition to light sleep. Characteristic changes of firing patterns were found in many neuronal populations at the sleep-wake transition and could be related to disruption of fixation and rapid and compensatory eye movement generation. Motoneurons decreased their firing rate by 20 to 50%, and their eye velocity coding deteriorated. Burst neurons had a significant drop in maximum firing rates and often showed continuous activity unrelated to rapid eye movements, but responded to vestibular stimuli. Pause neurons went completely silent. Neurons in the vestibular nuclei often reduced their level of activity, but still responded qualitatively unchanged to semicircular canal stimulation. In the framework of current models of oculomotor organization, the sleep-wake transition can be interpreted as a non-equilibrium phase transition which is driven by specific inputs and nonspecific activating systems.

Animals↗
PubMed1984

Experimental gaze palsies in monkeys and their relation to human pathology.

Lesions were placed in the paramedian pontine reticular formation ( PPRF ) of monkeys and the resulting gaze palsies studied. Brainstem regions were identified by single cell recordings before kainic acid was injected to selectively destroy neuronal cell bodies in the vicinity. Unilateral PPRF lesions led to a loss of all rapid eye movements towards the ipsilateral side. Deficits were identical to those after experimental electrolytic lesions in monkeys, or structural lesions in humans. Bilateral PPRF lesions produced two different syndromes. Rostral PPRF lesions led to a selective loss of horizontal rapid eye movements leaving vertical movements intact. Caudal PPRF lesions led in addition to a severe disruption of vertical rapid eye movements.

Animals↗
PubMed1984

E. Mach on the analysis of motion sensation.

Ernst Mach (1838-1916) in his many and widely read publications contributed to physics, physiology, and philosophy. His work on the analysis of motion sensation is discussed in the light of contemporary ideas and modern concepts of vestibular physiology.

Acceleration↗
PubMed1983

Horizontal and vertical vestibulo-ocular and cervico-ocular reflexes in the monkey during high frequency rotation.

In the alert monkey the horizontal vestibulo-ocular reflex (VOR) is basically compensatory over the range of 0.5 to 6 Hz with a gain near unity, and with the phase of the compensatory eye position having a minimal lag with respect to head position. Typical frequency-dependent eye movement patterns were observed. Vertical VOR is also compensatory having the same phase relations but with a reduced gain (-2.5 to -3.7 dB). In this range, vestibular input appears to be the predominant sensory influence on reflex eye movements. Additional optokinetic reflexes do not improve the VOR above 0.5 Hz. The horizontal cervico-ocular reflex (COR) is minimal or absent in normal monkeys.

Afferent Pathways↗
PubMed1983

Nystagmus generated by sinusoidal pitch while rotating.

Sinusoidal pitch while rotating about a vertical axis in darkness causes continuous horizontal compensatory nystagmus in the monkey which persists for the duration of stimulation. The steady-state velocity sums with post-rotatory nystagmus to reduce or cancel it, suggesting involvement of the velocity storage mechanism. Analysis of the labyrinthine excitation during pitch while rotating suggests that the vertical canals play a predominant role in generating the response. Effects of selective labyrinthine lesions are in agreement with this hypothesis. Plugging the lateral canals, leaving the vertical canals intact, blocked the initial rapid response at the onset of rotation, but did not interrupt the continuous nystagmus induced by pitch while rotating. On the other hand, plugging the vertical canals abolished the response. If the lateral canal nerves were cut so that the velocity storage mechanism was inactivated, the continuous response to pitch while rotating also disappeared. The dominant labyrinth activation responsible for the nystagmus during pitching while rotating appears to arise in the vertical semicircular canals and to couple to the oculomotor system through the velocity storage mechanism.

Animals↗