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Biomedical subjects

R W Baloh

Publications and source records attributed to R W Baloh.

At least 163 records · Page 9Linked to original sources
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

Quantitative vestibular testing.

Our standard rotational test battery includes tests of optokinetic nystagmus (OKN), the vestibulo-ocular reflex (VOR), and visual-vestibular interaction. Lesions of the peripheral vestibular system characteristically impair only the VOR, whereas lesions of the central system impair OKN and visual-vestibular interaction. The pattern of abnormal responses can help localize lesions within the central vestibular pathways.

Electronystagmography↗
PubMed1984

Low and high frequency sinusoidal rotational testing in patients with peripheral vestibular lesions.

We found a consistent pattern of response to low and high frequency sinusoidal rotational testing in patients with chronic compensated unilateral and bilateral peripheral vestibular lesions. Gain (peak slow phase eye velocity/peak chair velocity) was decreased and phase lead increased at low frequencies but both measurements approached normal at high frequencies. Asymmetries in gain, when present, were approximately the same in the low and high frequency range. These changes can be explained by a simple first order linear model of the vestibulo-ocular reflex if one assumes that the goal of the compensation process is to maintain gain in the high frequency range.

Electrooculography↗
PubMed1983

Eye movements in Friedreich's ataxia.

Twenty-four patients with well-documented Friedreich's ataxia underwent quantitative oculomotor testing. A consistent pattern of eye movement abnormalities was observed. This pattern included fixation instability, inaccurate saccades with normal peak velocity, impaired smooth pursuit and optokinetic slow phases, decreased vestibulo-ocular reflex gain, and impaired visual-vestibular interaction. This pattern corresponds to the known pathologic changes of Friedreich's ataxia and can be useful in the differential diagnosis of cerebellar atrophy.

Adolescent↗
PubMed1983

Analysis of characteristic eye movement abnormalities in internuclear ophthalmoplegia.

Quantitative electro-oculographic recording techniques were used to analyze four characteristic eye movement abnormalities in 21 patients with internuclear ophthalmoplegia (INO). The frequency of each of the abnormalities was determined to suggest a pattern that is the most sensitive in detecting the syndrome of INO. Slowing of the adducting saccade was the most frequently found abnormality, being present in all patients. The other characteristic eye movement disorders were found less frequently: dissociated nystagmus at 30 degrees of eccentric gaze, dysmetria of the abducting eye, and limitation of adduction. The most sensitive pattern for detecting an INO seems to be slowing of the adducting saccade combined with either dissociated nystagmus or dysmetria of the abducting eye. Limitation of adduction was seen much less frequently.

Adult↗
PubMed1983

Influence of vestibulo-ocular reflex gain on human optokinetic responses.

In 15 patients with severe bilateral vestibular impairment (mean vestibulo-ocular reflex (VOR) gain less than 0.05), constant velocity optokinetic nystagmus (OKN) gain, optokinetic after nystagmus (OKAN) initial velocity, and OKAN duration were significantly (p less than 0.0025) lower than in 20 normal subjects of similar age. In the normal subjects VOR gain was significantly correlated (p less than 0.05) with OKAN initial velocity but not with OKAN duration or OKN gain. The results of this study provide additional evidence for the existence in human subjects of an optokinetic pathway whose function, like that of the subcortical optokinetic pathway in animals, varies with VOR gain.

Adult↗
PubMed1983

A comparison of the dynamics of the rabbit and human vestibulo-ocular reflex.

We observed several differences between the dynamics of the vestibulo-ocular reflex (VOR) in rabbits and in human subjects. In the rabbit the "apparent time constant" (time required for the slow phase velocity to reach 37% of the initial value) of postrotatory nystagmus (PRN) increased and the low-frequency phase lead of sinusoidal perrotatory nystagmus decreased with increasing stimulus velocity. In human subjects these measurements did not change with stimulus velocity (for the range of 15 to 120 deg/s). The pattern of PRN decay in the rabbit usually appeared linear whereas in human subjects the decay was usually exponential. After the largest stimulus (120 deg/s) PRN reversals occurred in human subjects but not in rabbits. These differences can be explained on the basis of a simple nonlinearity (saturation of a feedback pathway) present in the rabbit but not in the human VOR.

Animals↗
PubMed1983

The dizzy patient. Symptomatic treatment of vertigo.

Vertigo is a distressing symptom, but in the majority of cases it can be treated effectively. Whenever possible, treatment should be directed at the underlying disorder. Usually, however, symptomatic treatment alone or in combination with specific therapy is effective. Symptomatic treatments include antivertiginous medications, vestibular exercises, and surgical therapy. The choice of medications is determined by the known side effects of the drugs and the time course of symptoms. An early vestibular exercise program ensures a more rapid return to normal physical activity. Surgical therapy is reserved for those patients who fail to respond to medical therapy.

Humans↗
PubMed1983

Acetazolamide-responsive episodic ataxia syndrome.

We studied a kindred with an acetazolamide-responsive, episodic ataxia syndrome. Affected members experienced paroxysmal attacks of ataxia that were precipitated by exertion or stress. All but one young patient had additional neurologic symptoms that included paresthesia, weakness, headache, tinnitus, vertigo, and myotonia. All symptoms were prevented by acetazolamide. Between attacks, serum pyruvate and lactate levels and urinary amino acids were normal, but electroencephalograms showed paroxysmal, high-amplitude, slow and sharp activity. Serum K+ was normal during attacks. The metabolic abnormality seems to affect the cerebellum and brainstem and may involve peripheral nerve and muscle.

Acetazolamide↗
PubMed1983

The dynamics of vertical eye movements in normal human subjects.

We studied the dynamics of horizontal and vertical slow eye movements (vestibular, optokinetic, pursuit, and visual-vestibular) in 10 normal human subjects. Several differences between horizontal and vertical eye movements were found. The time constant (time required for the slow-phase eye velocity to decay to 37% of the peak value) of vertical postrotatory nystagmus (PRN) was, on average, 50% as long as the time constant of horizontal PRN; the mean phase lead of per-rotatory nystagmus during low-frequency sinusoidal rotation in the vertical plane was approximately twice the mean phase lead of per-rotatory nystagmus at the same frequency in the horizontal plane. Vertical optokinetic after-nystagmus (OKAN) was minimal compared to horizontal OKAN. Asymmetries in the dynamics of vertical eye movements were also noted. The mean time constant of PRN with upward slow phases was consistently longer than the mean time constant of PRN with downward slow phases and vertical OKAN only occurred when the optokinetic stimulus moved upward. Upward pursuit was better than downward pursuit and upward slow phases of vestibular nystagmus were poorly inhibited with fixation while downward slow phases were normally inhibited.

Electrooculography↗
PubMed1983

Effect of eccentric gaze on pursuit.

The effect of eccentric gaze on pursuit eye movements was studied with electro-oculography in normal human subjects and a patient with defective pursuit. Sinusoidal target trajectories were centered about the primary position of gaze and eccentric, horizontal positions of gaze. Eccentric gaze decreased pursuit gain (eye velocity/target velocity) when the eyes moved farther eccentrically in the orbits and increased pursuit gain when the eyes moved toward the centers of the orbits. The magnitude of these effects increased with increasing eccentricity of gaze, increasing peak target velocity, and decreasing pursuit gain during tracking of target trajectories centered about the primary position. These effects can be caused by the elastic forces of the extraocular muscles, globe and other orbital tissues. The pursuit subsystem cannot compensate for these factors at high target velocities, or when it is impaired by pathologic lesions.

Cerebellar Diseases↗
PubMed1983

Effects of an optokinetic background on pursuit eye movements.

The effects of an optokinetic background on pursuit eye movements was studied in four normal human subjects and seven patients with impaired pursuit and/or optokinetic nystagmus (OKN). Eye movements were recorded by DC electro-oculography and eye movement velocity was analyzed by a digital, microprocessor system. Tracking of a small laser target was performed against a featureless, white screen, a stationary OKN background that filled the entire visual field and an OKN background moving at constant velocity. The OKN background significantly affected pursuit in all subjects. The stationary background or background moving in the direction opposite to that of the laser target impaired pursuit; whereas, the background moving in the same direction as that of the target improved pursuit. The effects of the background on pursuit were greater in subjects with lower pursuit gains during tracking against the screen. An algebraic summation of independently induced pursuit and OKN eye movements could not account for all of the experimental observations.

Eye Movements↗
PubMed1982

Familial, congenital paralysis of horizontal gaze.

Eye movements were studied in a sister and brother with familial, congenital paralysis of horizontal gaze. Horizontal and vertical eye movements were recorded with DC electro-oculography and analyzed with a laboratory computer. All horizontal, conjugate eye movements were absent (saccades, pursuit, optokinetic nystagmus, vestibulo-ocular response, and visual-vestibular responses). Voluntary vergence eye movements were preserved and were used to track visual targets. An involuntary, horizontal, pendular nystagmus was found to represent disconjugate, smooth, vergence eye movements. Vertical saccades and vestibulo-ocular responses were normal. However, vertical pursuit, optokinetic nystagmus, and suppression of the vestibulo-ocular response by fixation were impaired. A developmental anomaly affecting motor neurons and interneurons in the abducens nuclei is suggested to be the cause of the absence of conjugate, horizontal eye movements.

Abducens Nerve↗
PubMed1982

Myoclonus and ocular oscillations induced by L-tryptophan.

A patient with chronic manic-depressive illness developed generalized myoclonus and spontaneous ocular oscillations after a single 2 gm dose of L-tryptophan. She had been pretreated with both a tricyclic antidepressant and a monoamine oxidase inhibitor. The involuntary movements gradually disappeared within 24 hours after the drugs were discontinued. Electrooculographic recording 7 hours after onset of the abnormal eye movements revealed square-wave jerks and hypometric voluntary saccades. Pursuit as well as optokinetic and vestibular slow phases were normal except for superimposition of the square-wave jerks. Repeat recording 24 hours later was entirely normal.

Adult↗
PubMed1982

Subclinical effects of chronic increased lead absorption--a prospective study. Part IV. Evaluation of heme synthesis effects.

The effects of lead exposure on heme synthesis in workers with subclinical responses and in controls were evaluated. delta-Aminolevulinic acid dehydratase (ALA-d) correlated significantly with blood lead levels in the control group but not with those in the exposed group. Free erythrocyte protoporphyrin correlated significantly with blood lead levels in the exposed group but not with those in the controls and was found to be a good indicator of blood lead history among exposed persons. Hemoglobin values determined at initial employment were not statistically different from those determined during the baseline test for a group of 12 workers with a maximum blood lead level of 86 micrograms/100 ml during their exposure history. The effect such heme inhibition may have on other body functions is uncertain.

Environmental Exposure↗
PubMed1981

Eye movement abnormalities in rod monochromacy.

Eye movements were studied quantitatively using electro-oculography in seven patients with rod monochromacy. Attention was given to eye movement abnormalities that could help to differentiate rod monochromacy from other forms of congenital nystagmus. Horizontal nystagmus in center gaze had pendular and jerk waveforms with much lower amplitude than that in patients with other forms of congenital nystagmus and visual acuity of 20/200-20/400. Slow build-up of slow component velocity over many seconds and directional asymmetry of optokinetic nystagmus (OKN) were observed during monocular optokinetic stimulation. The directional asymmetry of OKN was characterized by a higher OKN gain (eye velocity/OKN drum velocity) during rotation of the OKN drum in the temporal-to-nasal direction in the visual field, than that during drum rotation in the nasal-to temporal direction. Similar directional asymmetry and slow build-up are found in afoveate animals, such as the rabbit, during monocular optokinetic stimulation, but are not found in normal human subjects or in patients with other forms of congenital nystagmus.

Adolescent↗