Dynamic modification of the vestibulo-ocular reflex by the nodulus and uvula.

The time constant of the decay of slow-phase eye velocity of postrotatory nystagmus or optokinetic after-nystagmus is reduced during exposure to a stationary visual surround (visual suppression). It is also reduced after tilting the head (tilt suppression). A "dump" mechanism in the vestibulo-ocular reflex has been proposed to rapidly discharge activity from the central vestibular system during both types of suppression. Monkeys lost this mechanism after lesions of the nodulus and uvula. They also lost the ability to habituate the time constant of nystagmus on repeated exposure to optokinetic and vestibular stimuli. Periodic alternating nystagmus, which is believed to represent an instability in the vestibulo-ocular reflex, was observed in two of three monkeys. These data indicate that the nodulus and uvula play an important role in suppressing, habituating, and stabilizing the vestibulo-ocular reflex.

Oculomotor functions of the flocculus and the vestibular nuclei after bilateral vestibular neurectomy.

Ito's hypothesis of an important role of the flocculus of the vestibulocerebellum in the immediate visual control of the VOR during visual-vestibular interaction has received substantial support. Nevertheless, several parts in this hypothesis are unclear, at least in primates. In normal monkey, vestibularly driven neurones in the vestibular nuclei do not carry signals which are adequate to account for the full range of eye movement responses during optokinetic tracking (OKN) and different situations of visual-vestibular interaction (especially VOR-suppression). Thus these neurones seem not to be located at the final stage where floccular "gaze-velocity" Purkinje cells (PCs) exert their control function on the three-neurone-reflex arc. The signals of these "central" vestibular neurones (if relevant for the oculomotor output) must further be processed. After bilateral vestibular neurectomy (BVN) only a small number of vestibular nuclei neurones were found with eye velocity sensitivities during smooth pursuit tracking (SP) and OKN in the range of those of floccular PCs (also after BVN), and with the appropriate polarity of modulation. Our difficulties in finding neurones in the vestibular nuclei which, according to their neurophysiological behaviour, could be main target cells of floccular PCs, either in normal or in BVN monkeys, are discussed.

Input-output activity of the primate flocculus during visual-vestibular interaction.

In the primate flocculus, unit activity was recorded during vestibular (rotation of the monkey about the vertical axis in complete darkness), optokinetic (rotation of the visual surround around the stationary monkey), and conflicting (rotation of the visual surround and the turntable fixed together) stimulation. Activity indicating two different mossy fiber inputs was recorded. One carried a signal that was similar to that in the vestibular nuclei: during optokinetic stimulation, neurons saturated at a velocity of 60 degrees/second; and during conflicting stimulation, neuronal activity was attenuated only at low accelerations. This input combines vestibular, visual, and oculomotor information. Another mossy fiber input carried information about visual image slip only. This input indicates instances when nystagmus is not compensatory. Purkinje cells were modulated in their simple spike activity during optokinetic stimulation only at high stimulus velocities of 40-60 degrees/second and above, and during conflicting stimulation at high accelerations. This suggests a complementary information processing of the flocculus and the vestibular nuclei during visual-vestibular stimulation. The findings are corroborated by lesion studies in primates.

Canal and otolith afferent activity underlying eye velocity responses to pitching while rotating.

Pitching the head while rotating (PWR) combines periodic activation of the semicircular canals and the otoliths to generate pitch and roll eye deviations and continuous horizontal nystagmus. Monkeys were tested after individual pairs of semicircular canals were plugged and single units were recorded in the vestibular nerve while the animals were sinusoidally pitched 20-40 deg about a spatial horizontal axis with 5- and 16-s periods and simultaneously rotated about a spatial vertical axis at 30-120 deg/s. As previously shown, the steady-state horizontal response disappeared after plugging the vertical semicircular canals, but was maintained when the lateral canals were plugged. When the left anterior and right posterior canal (LARP) pair was left intact, the steady-state response depended on the axis about which the pitching took place. When the axis was normal to the LARP plane, there was no steady-state response. When the pitching axis was perpendicular to the LARP normal, the response was maximal. Firing rates of otolith units were approximately in phase with pitch position, and the addition of rotation about a vertical axis did not change the response. Lateral canal units did not have a steady-state modulation during pitch or constant velocity rotation. During PWR, they oscillated at twice the pitch frequency. This corresponded to the frequency at which the canal was maximally activated as it aligned with the plane of rotation. The amplitude of modulation increased proportionally to rotational velocity, but the phase remained the same. These characteristics were unchanged during roll while rotating (RWR), which induces little continuous nystagmus. Anterior and posterior canal units were maximally excited near pitch-velocity maxima and minima, respectively, during pure pitching. During PWR, however, the phases of both components simultaneously shifted toward each other and toward being in phase with otolith units. The peak excitation tended toward a forward-pitch position when the rotation was to the ipsilateral side, and toward a backward pitch position when the rotation was to the contralateral side. With 120-deg/s rotation during a 16-s pitch period, the phase difference between anterior and posterior canal units was as small as 17 deg. These data support the postulate that the correlation between vertical canal and otolith units is the critical factor in generating continuous unidirectional horizontal nystagmus during PWR.

[Postpartum footdrop due to compression of the lumbosacral trunk]. / Geburtstraumatische Fussheberpareseinfolge einer pelvinen Nervenschädigung.

We report on a rare peripartal neuropathy of the leg caused by pro longed difficult labor in which forceps were used or caesarean sec tion was performed. Immediately after delivery, the 2 patients corn plained of a unilateral footdrop and numbness in the leg. The foot drop was most likely due to a compression of the lumbosacral trunl exposed to the fetal head. This trunk contains fibres from the lumba roots L4 and L5 and connects the lumbar with the sacral plexus. The outcome was favourable in both patients. If subsequent pregnancies occur, caesarean section may be indicated.

[Imminent paraplegia]. / Die drohende Querschnittslähmung.

Acute and subacute paraparesis are discussed, using case reports. Some important anamnestic, anatomic and clinical investigational features to be considered in patients with lesions of the spinal cord are emphasized. Most frequent and for the practitioner most important are lesions due to compression, mainly localized in the thoracic cord. Such lesions need rapid evaluation.

[Herpes-simplex encephalitis: case example, diagnosis and therapy]. / Die Herpes-simplex-Enzephalitis: Fallbeispiel, Diagnose und Therapie.

Herpes simplex encephalitis (HSE) is the most common nonepidemic cause of acute viral encephalitis. Since successful therapy depends on a high level of suspicion that HSE is present and on the early administration of antiviral treatment, knowledge of clinical and laboratory findings of HSE is of great importance. The clinical hallmark of HSE are signs of both focal and diffuse neurologic involvement. Our case report exemplifies the diagnostic problems that can occur in HSE-patients. The validity of the different ancillary examinations is discussed. Up to the present time brain biopsy has been the method of choice for a reliable early diagnosis of HSE. In the foreseeable future early diagnosis is likely to become available in a non-invasive way by the polymerase-chain reaction. Immediate antiviral therapy with acyclovir in HSE has proved to be useful in rigorously controlled trials. The clinical picture of the acyclovir-induced encephalopathy represents a disorder that can be probably avoided by means of a sufficient hydration.

[Fever, headache and paralysis of the left leg]. / Status febrilis, Cephalaea und Parese des linken Beins.

A 17 year old man was hospitalized because of fever, headache and a paresis of his left leg. Radiologic findings demonstrated a subdural interhemispheric empyema on the right side as a complication of ipsilateral pansinusitis. Streptococcus milleri was cultured as the only pathogen from maxillary sinus suppuration. Pathogenesis and therapy of subdural empyema are discussed. Cure was achieved with ceftriaxone, flucloxacilline and ornidazole during one week followed by ceftriaxone as monotherapy during further five weeks. The importance of streptococcus milleri as causing agent of purulent lesions in internal organs is stressed.

Eye movement disorders.

The past year's literature on eye movements is characterized by two trends: first by the examination of eye movement organization in the three planes of eye rotation in normal subjects (there is yet no publication about abnormalities of this three-dimensional organization in patients) and second by the increasing awareness of clinicians that the characteristics of saccades are highly task-dependent, and that the saccadic performance of patients must be tested under various conditions. Several papers try to establish a correlation between the site of a lesion and abnormalities of specific parameters of task-dependent saccades. For a better understanding, the different experimental tasks for the elicitation of saccades are explained in the text.

[Benign postural vertigo and nystagmus of the horizontal semicircular canal]. / Der gutartige Lagerungsschwindel und -nystagmus des horizontalen Bogenganges.

Benign paroxysmal vertigo and nystagmus are induced not only by the posterior but also by the horizontal semicircular canal. Benign positional nystagmus of the horizontal canal is more often observed than was previously thought. In 10 patients we analyzed the characteristics and the variability of nystagmus which accompanies positional vertigo of the horizontal canal. There are two forms of nystagmus: primary-geotropic, most often paroxysmal nystagmus (7 patients), and primary-apogeotropic, non-paroxysmal nystagmus (3 patients). Interestingly, in 2 patients with the primary-apogeotropic form the nystagmus converted during the examination into the primary-geotropic form. The reverse was not observed. We discuss the possible pathophysiological mechanisms which could be relevant for provoking manoeuvres.

[Benign paroxysmal postural vertigo: basis and its therapy in clinical practice]. / Der gutartige paroxysmale Lagerungsschwindel: Grundlagen und seine Therapie in der Praxis.

The theory of canalolithiasis assumes that benign paroxysmal vertigo and nystagmus is due to particles within the semicircular canal which move freely in the endolymph under gravitational forces, thereby deflecting its cupula. According to this theory the particles could be removed from the posterior canal by manoeuvres applying a succession of different head positions. We describe the pathophysiological mechanism of benign paroxysmal vertigo and our experience with one of these manoeuvres, the Semont manoeuvre. The success rate is impressive and the therapy is highly rewarding in a vertigo syndrome which can cause disability in the patients.

The velocity response of vestibular nucleus neurons during vestibular, visual, and combined angular acceleration.

In alert Rhesus monkeys neuronal activity in the vestibular nuclei was measured during horizontal angular acceleration in darkness, acceleration of an optokinetic stimulus, and combined visual-vestibular stimulation. The working ranges for visual input velocity and acceleration extend up to 60 degrees/s and 5 degrees/s2. The corresponding working range for vestibular input acceleration is wider and time-dependent. During combined stimulation, that is acceleration of the monkey in the light, a linear relation between neuronal activity and velocity could be established for all neurons. Type I vestibular plus eye movement neurons displayed the greatest sensitivity and had a small linear range of operation. Other vestibular neurons were less sensitive but had a larger range of linear response to different values of acceleration. Accelerating the animal and visual surround, simultaneously but in opposite directions, results in neuronal activity proportional to relative velocity over a limited range.

Reciprocal changes in primary and secondary optokinetic after-nystagmus (OKAN) produced by repetitive optokinetic stimulation in the monkey.

In six rhesus monkeys (Macaca mulatta) the effect of repetitive periods of whole-field optokinetic stimulation upon the different phases of optokinetic after-nystagmus (OKAN) was studied. The precedings optokinetic stimulus consisted of rotating a striped cylinder around the stationary monkey. Experiments were performed on up to 8 successive days. The results demonstrate that OKAN I and OKAN II are affected in a reverse manner by repeated optokinetic stimulation: The duration of OKAN I strongly decreases, whereas OKAN II increases in duration and intensity. The mechanisms under lying the generation of OKAN I and OKAN II and the role of OKAN II in the habituation process are discussed.

Neurotoxicity of antituberculous drugs in a patient without active tuberculosis.

A 56-year old patient presented 3 months after initiation of an antituberculous regimen with Isoniacid (INH, 5 mg/kg daily), Ethambutol (20 mg/kg daily) and Rifampicin (675 mg daily) a mild sensory polyneuropathy and a bilateral retrobulbar neuritis which progressed to a severe optic atrophy. Multiple hyperintense foci were detected with NMR-imaging in the cerebral white matter suggestive of demyelination. INH and Ethambutol are known for their neurotoxic effects but suggestion was made that neurologic signs may not be due to drug neurotoxicity but could be induced by immunological processes initiated by the tubercle bacillus. In the reported patient the suspected tuberculosis of the urogenital tract was never proved histologically. Most likely his neurological symptoms were therefore cause by the administration of INH and Ethambutol. Patients with a low serum zinc level and a slow acetylation of INH are reported to be at special risk; both factors were present in our patient.

[Rapid eye movements (saccades): review of their physiological and anatomical basis and their clinical significance]. / Rasche Augenbewegungen (Sakkaden): Uberblick über die physiologischen und anatomischen Grundlagen und ihre klinische Bedeutung.

Our understanding of the organization of eye movements has been greatly expanded in recent years, mainly due to studies in animals. A review of the clinically important neurophysiological and anatomical aspects of the organization of rapid eye movements (saccades) is presented. A knowledge of these basic aspects will assist the clinician's investigation and understanding of pathologic eye movements in patients.

[Epidural anesthesia in a patient with Friedreich's ataxia]. / Epiduralanaesthesie bei einer Patientin mit Friedreichscher Ataxie.

Friedreich's ataxia (FA), a hereditary disease with degenerative changes localized chiefly in the spinal cord and cerebellum, is characterized clinically by ataxia, absence of tendon reflexes, loss of proprioceptive sensation, and extensor plantar responses. There are only a few reports on anesthesia for patients with FA. General but not regional anesthesia is usually recommended because a persistent aggravation of symptoms is feared with regional anesthesia. We report a 31-year-old gravida 1 para 0 patient with FA who was admitted at the 20th week of gestation for induced abortion, curettage and tubal ligation. Familial FA was diagnosed at the age of 15, and since the age of 23 the patient had been confined to a wheelchair. As she strictly declined general anesthesia, epidural analgesia with 0.125% bupivacaine and morphine was used for 14 h, during which period induced abortion by prostaglandin was performed. This was followed by epidural anesthesia with 2% lidocaine for curettage and laparoscopic tubal ligation. A reduced dosage of local anesthetics, as commonly recommended during pregnancy, was used. Neurological consultation before and 1 day, 6 weeks, and 7 months after operation revealed no undue exacerbation of symptoms. Our case report suggests that epidural anesthesia can safely be administered to a patient with FA.

Optokinetic nystagmus (OKN) and optokinetic after-responses after bilateral vestibular neurectomy in the monkey.

The superior branch of the vestibular nerve containing peripheral axons of primary afferents originating in the lateral and anterior semicircular canals was cut bilaterally in three monkeys (vestibular neurectomy). Vertical and horizontal components of eye position were monitored by electro-oculography (EOG) during different stimulus and behavioral paradigms. Postoperatively, monkeys were unable to hold their eyes in eccentric lateral positions in complete darkness. The eyes drifted slowly back to the primary position where eye drift was minimal (null-zone). After vestibular neurectomy the time constant of the eye position integrator in darkness was 4-8 s. Constant velocity optokinetic stimuli produced peak velocities of horizontal OKN that were similar to those before operation. Consistent optokinetic after-responses could not be observed after neurectomy for stimulus durations of less than 60 s. However, with stimulus periods greater than 60-120 s a drift near the primary position of the eyes appeared in darkness which had the same direction as the slow phases of the preceding OKN. Drift velocity was too high to be explained by drift due to the imperfect eye position integrator alone. We assume that drift after prolonged optokinetic stimulation is a combination of an after-response similar as it can be observed after smooth pursuit and of drift due to an imperfect eye position integrator. Secondary optokinetic after-nystagmus was not observed after neurectomy.