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Biomedical subjects

J R Hotson

Publications and source records attributed to J R Hotson.

At least 19 recordsLinked to original sources
PubMed1996

Anticipatory smooth eye movements and predictive pursuit after unilateral lesions in human brain.

Anticipatory smooth eye movements precede expected changes in target motion. It has been questioned whether anticipatory smooth eye movements are a component of the smooth pursuit system. Five subjects with unilateral brain lesions and five control subjects were tested with predictable double-ramp stimuli to determine whether these lesions have a similar effect on horizontal, visually guided smooth pursuit, anticipatory smooth eye movements, and the predictive component of smooth pursuit. All four subjects with a brain lesion involving the parietal or parietal-frontal lobe had parallel velocity asymmetries in all three forms of smooth eye movements, with lowest velocities toward the side of the lesion. A similar uniformity and magnitude of smooth eye movement directional asymmetries were not found in control subjects. Unidirectional attenuation of these three forms of smooth eye movements provides evidence that they are part of a unified smooth eye movement system.

Brain↗
PubMed1995

Prolonged confusion with nocturnal wandering arising from NREM and REM sleep: a case report.

A 51-year-old man with Machado-Joseph disease had a 3-year history of prolonged confusion following nightly nocturnal wandering. Polysomnography with videotape monitoring revealed 19- to 120-minute sleepwalking episodes emerging from non-rapid eye movement (NREM) sleep and occasionally from rapid eye movement (REM) sleep, followed by 22-47 minutes of prolonged confusion and disorientation. The patient also had a periodic limb movement disorder and obstructive sleep apnea syndrome. Excessive daytime sleepiness was evident by results from the Epworth Sleepiness Scale and Multiple Sleep Latency Test. A sleep-deprived electroencephalogram (EEG) and a polysomnogram with an expanded EEG montage before and during these episodes revealed no epileptiform activity. A contrast-enhanced brain magnetic resonance imaging (MRI) scan demonstrated findings consistent only with Machado-Joseph disease. The patient improved with a combination of temazepam and carbidopa-levodopa.

Cerebellum↗
PubMed1992

Predictive smooth pursuit eye movements near abrupt changes in motion direction.

The stimulus-response characteristics of predictive smooth pursuit eye movements near the time of predictable, abrupt changes in target motion direction were studied. Expectations about the speed and direction of target motion both before and after the direction change affected specific components of the predictive pursuit responses. We propose that, when the direction of target motion is expected to change, the cessation of motion in one direction and the initiation of motion in a new direction are separately anticipated and that predictive pursuit movements are summated responses to these two events.

Adult↗
PubMed1991

Differential diagnosis of choreiform tardive dyskinesia.

Orofacial dyskinesias and choreiform movements of limbs occur with moderate frequency among psychiatric patients. Abnormal involuntary movements are symptoms of a wide variety of neurological and medical disorders. For both therapeutic and medicolegal reasons, psychiatric patients should be thoroughly evaluated before being given the diagnosis of tardive dyskinesia. This review presents the differential diagnosis of disorders associated with orofacial and appendicular choreiform involuntary movements. In addition, this paper provides a guide to the clinical and laboratory evaluation of patients with these symptoms.

Athetosis↗
PubMed1991

Memory-contingent saccades and the substantia nigra postulate for essential blepharospasm.

Essential blepharospasm and cranial dystonia are related focal dystonias of unknown aetiology. Blepharospasm induced by acute dopamine depletion in parkinsonism restricts saccade initiation possibly via the substantia nigra pars reticulata (SNpr). If essential blepharospasm and cranial dystonia similarly restrict saccades, then a selective, somatotopically arranged pathway such as the SNpr may be involved. To test this possibility memory-contingent and visually-guided saccades were measured in patients with essential blepharospasm and cranial dystonia. The latency of both forms of saccades was either significantly prolonged or excessively variable, while the accuracy and peak velocity of these fast eye movements were similar to age-matched control subjects. Essential blepharospasm and cranial dystonia alter the initiation of saccadic eye movements. Subcortical brain regions or pathways where eyelid, saccade and cranial/cervical motor control are somatotopically approximated, such as the SNpr, may be involved in blepharospasm.

Blepharospasm↗
PubMed1989

Motion perception prominence alters anticipatory slow eye movements.

Perceived motion may be a stimulus for anticipatory slow eye movements. To test this possibility, the production of anticipatory slow eye movements in humans was studied using apparent motion stimuli. Short range apparent motion was produced with random dot stimuli and the anticipatory slow eye movements were isolated from the smooth pursuit responses by occasionally including trials in which the random dot stimulus did not appear. Long range apparent motion was produced with subjective contour stimuli. Both short range and long range apparent motion were found to be effective stimuli for anticipatory slow eye movements. The prominence of perceived motion was altered by changing the spatiotemporal displacement intervals in the short range apparent motion stimuli. Changing the subjective contours also changed the motion percepts of the long range apparent motion stimuli. With both stimuli, the peak anticipatory slow eye velocities that were achieved decreased as the prominence of the motion percepts decreased, while the time-course of the anticipatory responses were similar under the different conditions. These findings indicate that the expectation of perceived motion is necessary for anticipatory slow eye movements.

Adult↗
PubMed1988

Stimulus conditions that enhance anticipatory slow eye movements.

Anticipatory slow eye movements are predictive responses that occur prior to both ramp and step target motions. These low velocity eye movements are enhanced and can be studied in isolation by transient target disappearance before ramp motion onset. Slow eye velocities also decrease prior to the termination of target motion. In experiments using a bistable apparent motion stimulus, it was found that perceived motion is a stimulus for anticipatory slow eye movements. This relationship between motion perception and anticipatory slow eye movements can explain previously noted differences between these predictive movements and the predictive component of smooth pursuit.

Adult↗
PubMed1988

Neurologic complications of cardiac transplantation.

The neurologic evaluation of an individual cardiac transplant recipient often does not lead to a succinct bedside diagnosis. There are few consistent clinical observations. The onset of seizures in the early postoperative period is associated with embolic cerebral infarction. Seizures occur most commonly, however, as a neurotoxic manifestation of cyclosporine. The onset of an acute delirium or psychosis in the first week after cardiac transplantation usually has multiple causative factors and is reversible. A postoperative brachial plexopathy or mononeuropathy can be identified with a neurologic examination, confirmed by appropriate electrophysiologic testing and is usually reversible. The onset of periorbital inflammation, ophthalmoplegia, and nasal turbinate or sinus invasion and necrosis is consistent with phycomycosis. Most patients, however, present with nonspecific findings of impaired mentation with or without focal neurologic signs. These patients require a fairly systematic search for potentially treatable neurologic complications (see Table 3). In a medically stable patient an aggressive diagnostic approach, at times including stereotaxic brain aspirate or biopsy, is indicated. In the severely ill patient with multiple organ failure, empirical therapy for the most probable treatable disorder is justified.

Brain Abscess↗
PubMed1987

The search for a physiologic marker of Machado-Joseph disease.

Machado-Joseph disease is a dominantly inherited, multisystem, degenerative disorder that lacks a proven genetic marker. Peripheral nerve conduction-refractory period, sensory evoked potentials, and quantified oculomotor recordings were studied in nine patients affected with this disease to look for a potential physiologic marker. Only the oculomotor measurements of saccade and smooth pursuit gain were consistently abnormal in all patients. Identical eye movement recordings in 12 asymptomatic individuals at risk for Machado-Joseph disease revealed findings typical of affected patients in only 1 individual. Quantified oculomotor studies may contribute to the early confirmation of the disease, primarily in individuals at risk with minor or equivocal neurologic signs.

Adolescent↗
PubMed1986

Saccade responses to dopamine in human MPTP-induced parkinsonism.

Depletion of dopamine content in the substantia nigra resulting from 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP) toxicity produces parkinsonism. Management of 3 patients with MPTP-induced parkinsonism required drug holidays during which there was a state of dopamine depletion followed by dopamine replacement. We used this opportunity to study the effect of the selective loss of pars compacta dopaminergic cells on vertical and horizontal saccade (fast) eye movements. During the drug holidays, visually guided saccades were hypometric and had long latencies but retained a normal saccade velocity-amplitude relationship. Dopamine agonists or precursors improved the accuracy and reaction times of saccades in all directions, but not their velocity. Two of the three patients also had intermittent blepharospasm during dopamine depletion. During the episodes of blepharospasm, saccade responses became slow eye movements. MPTP causes a dopaminergic-responsive disorder of saccade initiation that is similar to idiopathic parkinsonism. The inhibition of voluntary eyelid opening during MPTP-induced blepharospasm further increases this impairment of fast eye movements and altered saccade velocity, presumably via the pars reticulata of the substantia nigra.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1986

Regional cooling of human nerve and slowed Na+ inactivation.

Regional cooling of human sensory nerves increases the amplitude and surface area of an evoked sensory compound action potential (SCAP). It has been proposed that these changes are due to cold-induced slowing of Na+ inactivation. Na+ inactivation is also the main voltage-dependent event that underlies the refractory period in myelinated nerve. Therefore, if slowed Na+ inactivation causes the increased SCAP amplitude and area seen in focal cooling, a parallel temperature-dependent change should also occur in the SCAP refractory period. We compared the duration and magnitude of the relative refractory period to the total surface of a median nerve SCAP at 5 intervals of increasing temperature, from 24 degrees C to 36 degrees C. In 5 control subjects, the SCAP surface area and the relative refractory period increased 4-5-fold in parallel and revealed a non-linear relation to temperature change. Prolongation of the duration of individual nerve fiber potentials from slowed Na+ inactivation is proposed as one explanation of these temperature-related changes.

Electroencephalography↗
PubMed1984

Convergence-initiated voluntary flutter: a normal intrinsic capability in man.

The proposal that there is an inherent capability in humans to produce bursts of fluttering saccades was tested by comparing Purkinje image eye movement recordings in subjects with voluntary nystagmus and control subjects. Voluntary nystagmus is composed of recurrent saccades without an intersaccade interval and has been proposed to be an inherited event. No difference in saccade peak velocity-amplitude curves or microsaccades during visual fixation was found between the two groups. With training control subjects learned to produce runs of saccadic flutter identical to voluntary nystagmus. This learned flutter was composed of recurrent complete saccades rather than saccades interrupted in midflight. Voluntary flutter is thus not a genetic trait but a learned event that is usually undeveloped in man. These observations can be explained by the Robinson model of saccade generation and indicate that similar models must have an inherent ability to produce saccadic flutter.

Adolescent↗
PubMed1984

Clinical detection of acute vestibulocerebellar disorders.

The acute onset of vertigo, nystagmus and postural instability, without brain-stem signs, is commonly attributed to a disorder of the labyrinth, the vestibular, sensory end organ. Identical symptoms can occur, however, with discrete infarctions or hemorrhages involving the central vestibulocerebellum. Whereas acute labyrinthine disorders are usually benign and self-limited, vascular injuries of the cerebellum may produce swelling, compression of the brain stem and acute hydrocephalus one to four days after the onset of symptoms. Therefore it is important to accurately distinguish between labyrinthine and vestibulocerebellar disorders with the neurologic examination. Acute labyrinthine disease causes unidirectional nystagmus with past-pointing and falling in the opposite direction of the nystagmus, environmental vertigo in the same direction and suppression of the nystagmus with visual fixation. Disorders of the vestibulocerebellum do not produce this consistent pattern of findings.

Cerebellar Diseases↗
PubMed1983

Hyperviscosity-induced dementia.

Dementia was the presenting symptom in a patient with increased serum viscosity secondary to multiple myeloma. Plasmapheresis led to complete resolution of the neurologic syndrome. Serum hyperviscosity should be added to the growing list of reversible causes of dementia. When hyperviscosity-associated dementia is suspected, both serum and whole blood viscosity determinations are indicated.

Aged↗
PubMed1982

Cerebellar control of fixation eye movements.

Human subjects normally have miniature eye movements during tasks that require steady visual fixation. These eye movements were compared in 12 control subjects and 4 patients with degenerative cerebellar disorders. Slow drifts, small fixation saccades, square waves, saccadic oscillations, flutter, and vertical nystagmus occurred in both control subjects and patients. In the patients, however, fixation eye movements were enlarged and square waves and saccadic oscillations were more frequent. It appears that some forms of pathologic fixation instability are due to defective cerebellar control of fixation eye movements, and that precise measurements of these eye movements may quantitate disorders of cerebellar function.

Adolescent↗
PubMed1981

Penicillin- and barium-induced epileptiform bursting in hippocampal neurons: actions on Ca++ and K+ potentials.

Both barium (Ba++) and penicillin produce spontaneous epileptiform burst generation in hippocampal neurons in vitro. Recent investigations suggest that Ba++ acts by both adding to a calcium (Ca++)-mediated depolarization and reducing potassium (K+) conductance. In contrast, it has been proposed that penicillin produces burst generation by attenuating inhibitory postsynaptic potentials. However, some evidence suggests that penicillin may also directly alter intrinsic membrane properties. We therefore compared the actions of penicillin and Ba++ on three intrinsic Ca++- or K+-mediated membrane events, namely, CA++ spikes, Ca++-dependent anomalous rectification, and K+-dependent afterhyperpolarization. Ba++ augmented the Ca++ potentials and attenuated the K+-dependent afterhyperpolarization; penicillin had no demonstrable effect on these events. Ba++ produced rhythmical burst firing and oscillations of the membrane potentials, while penicillin caused sporadic burst generation followed by a longlasting afterhyperpolarization. Synchronized, orthodromically evoked burst firing occurred after exposure to penicillin but not to Ba++. Ba++ and penicillin are prototypes of agents which induce epileptogenesis in mammalian cortical neurons by two different but probably interrelated mechanisms. Ba++ causes burst generation by disrupting a delicate balance between depolarizing Ca++ potentials and repolarizing, hyperpolarizing K+ potentials. Penicillin does not affect Ca++- or K+-mediated membrane events; other data suggest that it produces burst generation in hippocampal pyramidal neurons by attenuating gamma-aminobutyric acid-mediated synaptic inhibition, which in turn ordinarily limits intrinsic bursting.

Action Potentials↗
PubMed1981

Modern neurosyphilis: a partially treated chronic meningitis.

Approximately 5,000 new cases of neurosyphilis may occur in the United States each year. General paresis and tabes dorsalis, however, have become relatively rare since the introduction of penicillin. Seizures, neuro-ophthalmologic symptoms, stroke and acute meningoencephalitis are currently the most common manifestations of neurosyphilis. In more than a third of patients with neurosyphilis, nontreponemal tests for syphilis (such as VDRL) are negative and should not be used to exclude the diagnosis. Specific treponemal tests are more sensitive and more specific. Examination of the cerebrospinal fluid may show no abnormalities in neurosyphilis and is not an infallible guide to the activity of the infection. Penicillin is the only proven antibiotic treatment of neurosyphilis. However, low-dose regimens do not produce spirocheticidal concentrations in the brain, and high-dose penicillin therapy is recommended to insure eradication of the spirochetes. Doxycycline, a tetracycline derivation that achieves relatively high concentration in the brain, may also be effective.

Adolescent↗