Vestibulo-ocular Responses Research Articles

Bilateral Vestibulopathy

To define clinical and laboratory characteristics of bilateral vestibulopathy (BV) and to propose diagnostic criteria of this disorder based on clinical and laboratory findings. Retrospective case series review. We recruited 108 patients with a clinical suspicion of BV based on presenting symptoms (unsteadiness or oscillopsia during locomotion) and bedside (dynamic visual acuity or head impulse tests) and laboratory (bithermal caloric or rotatory chair tests) findings after excluding the patients with other disorders that may explain the symptoms. Definite diagnosis of BV was made when the patients showed abnormal findings on both bedside and laboratory tests in addition to the symptoms, whereas probable diagnosis was obtained when either the bedside or laboratory findings were abnormal along with the symptoms. All patients had unsteadiness, and 36 (33%) reported oscillopsia. Diminished vestibulo-ocular responses to head impulse in both horizontal directions were present in 45 of the 100 patients evaluated. Dynamic visual acuity was impaired in 65 (95%) of the 68 patients who underwent testing. Fifty-one (57%) patients showed bilateral hyporesponsiveness during bithermal caloric tests. Forty-eight (53%) patients had reduced gain of the vestibulo-ocular reflex during rotatory chair test. By adopting our diagnostic criteria, 93 patients (86%) were diagnosed as having BV, definite in 49 (45%), and probable in 44 (41%). The proposed diagnostic criteria encompass the symptoms and findings of both bedside and laboratory evaluations and may provide a valuable tool for investigating BV.

Can fast-component of nystagmus on caloric vestibulo-ocular responses predict emergence from vegetative state in ICU?

The aim of the study was to determine if bedside caloric vestibulo-ocular responses (VOR) are able to predict consciousness recovery from clinically determined vegetative state (VS) in the ICU. Twenty-six severely brain injured patients that were clinically in VS were included. Horizontal VOR were tested at bedside by cold-water irrigation of the external auditory canal. Visual inspection evaluated the presence of a slow drift toward the side of stimulation (slow-component of nystagmus or tonic deviation) as well as the presence of a rapid compensatory movement/jerk back to the midline (fast-component of nystagmus). Patients were then divided into two groups according to whether they eventually regained consciousness or not. Patients were 59 ± 21 years old. Thirteen out of 26 patients ultimately recovered consciousness and 13 remained unconscious. Thirteen patients (100%) presented a slow-component of nystagmus during VOR testing in the group that recovered consciousness and 11 (85%) in the group that remained unconscious. All the patients that recovered consciousness (13, 100%) presented a fast-component of nystagmus during VOR testing compared to only one of 11 patients (8%) in the group that remained unconscious. Sensitivity of fast-component of nystagmus during VOR testing to predict recovering of consciousness was 1.00, specificity was 0.92, positive predictive value was 0.93 and negative predictive value was 1.00. Bedside VOR testing in clinically VS patients seems able to predict consciousness recovery from vegetative state and could help to preclude active medical treatment withdrawal and to indicate the need for further complementary explorations, i.e. event-related potentials, functional MRI or PET-scan.

Automatic classification and robust identification of vestibulo-ocular reflex responses: from theory to practice

The Vestibulo-Ocular Reflex (VOR) stabilizes images of the world on our retinae when our head moves. Basic daily activities are thus impaired if this reflex malfunctions. During the past few decades, scientists have modeled and identified this system mathematically to diagnose and treat VOR deficits. However, traditional methods do not analyze VOR data comprehensively because they disregard the switching nature of nystagmus; this can bias estimates of VOR dynamics. Here we propose, for the first time, an automated tool to analyze entire VOR responses (slow and fast phases), without a priori classification of nystagmus segments. We have developed GNL-HybELS (Generalized NonLinear Hybrid Extended Least Squares), an algorithmic tool to simultaneously classify and identify the responses of a multi-mode nonlinear system with delay, such as the horizontal VOR and its alternating slow and fast phases. This algorithm combines the procedures of Generalized Principle Component Analysis (GPCA) for classification, and Hybrid Extended Least Squares (HybELS) for identification, by minimizing a cost function in an optimization framework. It is validated here on clean and noisy VOR simulations and then applied to clinical VOR tests on controls and patients. Prediction errors were less than 1deg for simulations and ranged from .69deg to 2.1deg for the clinical data. Nonlinearities, asymmetries, and dynamic parameters were detected in normal and patient data, in both fast and slow phases of the response. This objective approach to VOR analysis now allows the design of more complex protocols for the testing of oculomotor and other hybrid systems.

A preformed scleral search coil for measuring mouse eye movements

Mice are excellent subjects for use of genetic-manipulation techniques to study the basis of pathological and normal physiology and behavior; however behavioral analyses of associated phenotypes is often limited. To improve the accuracy and specificity of repeated measurements of vestibular function, we developed a miniaturized, contact-lens scleral search coil to measure mouse eye movements. We describe the physical attributes and document its functionality by measuring vestibuloocular responses in normal mice. This coil should greatly improve the sensitivity and documentation of vestibular dysfunction in mouse models of pathology and dysfunction while allowing screening of significant numbers of subjects.

Pseudonystagmus—clinical features and quantitative characteristics

A 60 year-old woman with multiple sclerosis (MS) and chronic hearing loss presented with head tremor and vestibular hypofunction, the combination of which can produce oscillopsia--a visual sensation that steady objects in the visual field are oscillating. This case highlights the fact that in patients with pseudonystagmus, oscillopsia is attributable to the association of head tremor and vestibular hypofunction. Eye and head movements were measured simultaneously with the search coil technique. Patients with MS can present with oscillopsia, and spontaneous pendular nystagmus is often observed in these individuals. In our patient, the oscillopsia was not due to pendular nystagmus, but rather to pseudonystagmus (of gaze) resulting from diminished compensatory vestibulo-ocular reflex responses to head tremor. A two-step strategy can be used in patients with pseudonystagmus: pharmacological treatment of head tremor, and vestibular rehabilitation to improve balance and diminish oscillopsia associated with head movement. Various health-care providers at other institutes attempted to address our patient's dystonic head tremor with botulinium toxin injections in the neck muscles; the response was unsatisfactory. We offered treatment with baclofen, which the patient did not tolerate. We also discussed the option of vestibular rehabilitation, which the patient did not pursue.

Challenges in diagnosing brain death

Recognizing that the nature of the practice of clinical medicine involves areas of uncertainty, death is one diagnosis that doctors must not be allowed to miss. The concept of brain death, which originates from the Harvard Criteria, has allowed development of cadaveric organ transplantation programs. Over the years, the definition of brain death and the criteria for the neurological determination of death (NDD) have been updated. The Universal Determination of Death Act provides a definition of death but leaves the determination process to accepted medical standards (national, provincial, or even local), which can entail a high variability. In April 2003, in response to a perceived need in the general medical and critical care community, the Canadian Council for Donation and Transplantation (CCDT) held a national forum to revisit the process of declaring brain death and to propose updated recommendations. These are the current guidelines used by organ donation and transplantation organizations across Canada. The CCDT recommendations have the virtue of having brought uniformity to the process of NDD. Still, several of its recommendations are somewhat vague and open the door to clinical judgement and interpretation, a situation that is highly undesirable when facing potential organ donation. In this issue of the Journal, Roberts et al. report two cases where experienced physicians faced challenges in the clinical NDD. In both cases, it appears that several of the criteria for NDD were either misinterpreted or overlooked. Although they are usually not reported in the medical literature, similar incidents occur more than occasionally. This is somewhat disturbing. The existence of cadaveric organ donation and transplantation programs relies on the Dead Donor Rule that dictates that a patient’s death must be confirmed before any attempt at organ preservation or harvesting for the purpose of transplantation. Before a patient is dead, ethical principles mandate that medical care must be directed toward the sole and only benefit of this patient, even in a situation that could be perceived as ‘‘almost dead’’. Brain death is a complex concept that is very difficult for the general public to understand. Patients and their families place their trust in their treating physician. In organ donation, they trust that physicians will strictly abide by the Dead Donor Rule. Therefore, the process for NDD must be watertight. The CCDT recommendations define neurological death as the irreversible loss of all brain stem functions. The minimum criteria for clinical NDD are: 1) an established etiology capable of causing neurological death in the absence of reversible conditions capable of mimicking neurological death; 2) a deep unresponsive coma with bilateral absence of motor responses (excluding spinal reflexes); 3) absent brain stem reflexes, as defined by absent gag and cough reflexes, and the bilateral absence of corneal responses, pupillary responses to light (with pupils at mid-size or greater), and vestibulo-ocular responses; 4) absent respiratory effort based on the apnea test; and 5) absence of any confounding factors. Minimum means that at least all of these criteria must be met for clinical NDD. Confusion may arise regarding the first criterion. An etiology ‘‘capable of causing’’ neurological death is not the same as ‘‘sufficient to account for’’ the absence of clinical signs of brain function. For example, brain trauma is an M. R. Lessard, MD (&) J. G. Brochu, MD Department of Anesthesia and Critical Care, Centre hospitalier affilie universitaire de Quebec, Universite Laval, 1401, 18e rue, Quebec, QC G1J 1Z4, Canada e-mail: martin.lessard@anr.ulaval.ca

Peaks and Troughs of Three-Dimensional Vestibulo-ocular Reflex in Humans

The three-dimensional vestibulo-ocular reflex (3D VOR) ideally generates compensatory ocular rotations not only with a magnitude equal and opposite to the head rotation but also about an axis that is collinear with the head rotation axis. Vestibulo-ocular responses only partially fulfill this ideal behavior. Because animal studies have shown that vestibular stimulation about particular axes may lead to suboptimal compensatory responses, we investigated in healthy subjects the peaks and troughs in 3D VOR stabilization in terms of gain and alignment of the 3D vestibulo-ocular response. Six healthy upright sitting subjects underwent whole body small amplitude sinusoidal and constant acceleration transients delivered by a six-degree-of-freedom motion platform. Subjects were oscillated about the vertical axis and about axes in the horizontal plane varying between roll and pitch at increments of 22.5° in azimuth. Transients were delivered in yaw, roll, and pitch and in the vertical canal planes. Eye movements were recorded in with 3D search coils. Eye coil signals were converted to rotation vectors, from which we calculated gain and misalignment. During horizontal axis stimulation, systematic deviations were found. In the light, misalignment of the 3D VOR had a maximum misalignment at about 45°. These deviations in misalignment can be explained by vector summation of the eye rotation components with a low gain for torsion and high gain for vertical. In the dark and in response to transients, gain of all components had lower values. Misalignment in darkness and for transients had different peaks and troughs than in the light: its minimum was during pitch axis stimulation and its maximum during roll axis stimulation. We show that the relatively large misalignment for roll in darkness is due to a horizontal eye movement component that is only present in darkness. In combination with the relatively low torsion gain, this horizontal component has a relative large effect on the alignment of the eye rotation axis with respect to the head rotation axis.Electronic supplementary materialThe online version of this article (doi:10.1007/s10162-010-0210-y) contains supplementary material, which is available to authorized users.

Synchronised Paroxysmal Ocular Tilt Reaction and Limb Dystonia

ABSTRACTA case of paroxysmal ocular tilt reaction due to a midbrain cavernoma showing co-existing limb dystonia is described with particular reference to the synchronisation of eye and limb paroxysms. The single case has been observed over a 20-year period with video documentation of eye and limb movements. The function of the relevant neuro-anatomical circuits have been investigated. The now 51-year-old female patient suffered from a right midbrain haemorrhage 20 years earlier. She developed a synchronized paroxysmal ocular tilt reaction and focal limb dystonia, associated with a unilateral startle-like response. Video-oculography and electromyography during paroxysms demonstrated left forearm electromyography spikes time locked with bursts of ocular torsion. Whilst the ocular tilt reaction may be explained by a single irritative lesion of the right interstitial nucleus of Cajal, additional involvement of the right rostral interstitial nucleus of the medial longitudinal fasciculus was suggested by abnormal binocular scleral coil recordings of the torsional vestibulo ocular response. There was a marked unilateral acoustic startle-like response, not explained by damage to either nucleus. Treatment with acetazolamide abolished the attacks. The observations suggest that the coexistence of skew deviation, conjugate ocular torsion and limb dystonia in meso-diencephalic lesions may occur because neural centres controlling these eye and limb movements are closely related anatomically, rather than through the activation of a “hard wired” physiological synkinesis. We propose that the paroxysms are generated within the zona incerta where excitatory auditory, somatosensory and motor neurons are densely packed and extensively project to centres of gaze and motor control.

Vestibulo-ocular (oVEMP) responses produced by bone-conducted sound stimuli applied to the mid-sagittal plane of the head

Recently several studies have yielded evidence that impulses of bone-conducted (BC) sound can produce short-latency myogenic responses in the extraocular muscles, which are probably mediated by otolithic afferents. These responses, although miniscule, can be recorded with surface electrodes and are termed ocular vestibular evoked myogenic potentials (oVEMP). It is assumed that in response to low-frequency BC-sound stimuli the head moves predominantly along the axis from the site of the applied stimulus to the opposite side. Thus, oppositely-directed accelerations along a particular axis would produce oppositely-directed compensatory vestibulo-ocular responses (VOR) and oVEMPs. The aim of this study was to investigate whether the oVEMPs would reflect these direction-dependent VOR responses. Single cycles of 125 and 250 Hz BC tones were applied to opposite sides of two approximately orthogonal, naso-occipital (x) and vertical (z) axes of the head. oVEMP responses were recorded with standard bilateral vertical EOG montages. The responses in all twelve healthy subjects showed consistent differences with regard to the latency and/or shape of the response to stimuli applied to opposite sides of the head. These differences likely reflect different patterns of electro-myographic activity of the extraocular muscles, which may be mediated by groups of vestibular (probably otolithic) afferents with differently-orientated spatial polarization vectors.

The human sound-evoked vestibulo-ocular reflex and its electromyographic correlate

Objective Sound and vibration evoke a short-latency eye movement or “sound-evoked vestibulo-ocular reflex” (VOR) and an infraorbital surface potential: the “ocular vestibular-evoked myogenic potential” (OVEMP). We examined their relationship by measuring the modulation of both responses by gaze and stimulus parameters. Methods In seven subjects with superior semicircular-canal dehiscence (SCD) and six controls, the sound-evoked VOR was measured in 3D using scleral search coils. OVEMPs were recorded simultaneously, using surface electromyography. Results Eye movement onset (11.6 ± 0.8 ms) coincided with the OVEMP peak (12.1 ± 0.35 ms). OVEMP and VOR magnitudes were 5–15 times larger in SCD compared with controls. OVEMP amplitudes were maximal on upgaze and abolished on downgaze; VOR magnitudes were unaffected. When stimulus type was changed from sound to vibration, OVEMP and VOR changed concordantly: increasing in controls and decreasing in SCD. OVEMP and VOR tuned to identical stimulus frequencies. OVEMP and VOR magnitudes on upgaze were significantly correlated ( R = 0.83–0.97). Conclusion Selective decrease of the OVEMP upon downgaze is consistent with relaxation or retraction of the inferior oblique muscles. The temporal relationship of OVEMP and VOR and their identical modulation by external factors confirms a common origin. Significance Sound-evoked OVEMP and VOR represent the electrical and mechanical correlates of the same vestibulo-ocular response.

Vestibulo-Ocular Responses Evoked Via Bilateral Electrical Stimulation of the Lateral Semicircular Canals

We investigated the vestibulo-ocular responses (VORs) evoked by bilateral electrical stimulation of the nerves innervating horizontal semicircular canals in squirrel monkeys and compared these responses to those evoked by unilateral stimulation. In response to sinusoidal modulation of the electrical pulse rate, the VOR for bilateral stimulation roughly equals the addition of the responses evoked by unilateral right ear and unilateral left ear stimulation; the VOR time constants were about the same for bilateral and unilateral stimulation and both were much shorter than for normal animals. In response to individual pulse stimulation, the VOR evoked by bilateral stimulation closely matches the point-by-point addition of responses evoked by unilateral right ear and unilateral left ear stimulation. We conclude that, to first order, the VOR responses evoked by bilateral stimulation are the summation of the responses evoked by unilateral stimulation. These findings suggest that--from a physiologic viewpoint--unilateral and bilateral vestibular prostheses are about equally viable. Given these findings, one possible advantage of a bilateral prosthesis is higher gain. However, at least for short-term stimulation such as that studied herein, no inherent advantage in terms of the response time constant ("velocity storage") was found.

Differential Dynamic Processing of Afferent Signals in Frog Tonic and Phasic Second-Order Vestibular Neurons

The sensory-motor transformation of the large dynamic spectrum of head-motion-related signals occurs in separate vestibulo-ocular pathways. Synaptic responses of tonic and phasic second-order vestibular neurons were recorded in isolated frog brains after stimulation of individual labyrinthine nerve branches with trains of single electrical pulses. The timing of the single pulses was adapted from spike discharge patterns of frog semicircular canal nerve afferents during sinusoidal head rotation. Because each electrical pulse evoked a single spike in afferent fibers, the resulting sequences with sinusoidally modulated intervals and peak frequencies up to 100 Hz allowed studying the processing of presynaptic afferent inputs with in vivo characteristics in second-order vestibular neurons recorded in vitro in an isolated whole brain. Variation of pulse-train parameters showed that the postsynaptic compound response dynamics differ in the two types of frog vestibular neurons. In tonic neurons, subthreshold compound responses and evoked discharge patterns exhibited relatively linear dynamics and were generally aligned with pulse frequency modulation. In contrast, compound responses of phasic neurons were asymmetric with large leads of subthreshold response peaks and evoked spike discharge relative to stimulus waveform. These nonlinearities were caused by the particular intrinsic properties of phasic vestibular neurons and were facilitated by GABAergic and glycinergic inhibitory inputs from tonic type vestibular interneurons and by cerebellar circuits. Coadapted intrinsic filter and emerging network properties thus form dynamically different neuronal elements that provide the appropriate cellular basis for a parallel processing of linear, tonic, and nonlinear phasic vestibulo-ocular response components in central vestibular neurons.

Otolith-ocular responses in Meniere's patients before and after endolymphatic shunt operation

Caloric testing in prone/supine position and constant velocity off-vertical axis rotation (OVAR) in yaw axis (rotate-then-tilt paradigm) can evaluate labyrinth function and vestibular-ocular reflex (VOR) behaviour before and after endolymphatic shunt surgery (ESS). Preoperative and postoperative otolith dysfunction can be documented by constant velocity OVAR, before the VOR is modulated by the vestibular compensation. Vestibulo-ocular responses in prone/supine position and linear VOR (lVOR) OVAR responses were observed in 10 patients before and after ESS. Ipsilateral caloric reaction in prone/supine position was reduced after ESS. Otolith-ocular function and canal-otolith-interaction were improved postoperatively. Meniere's patients with bias component opposite to normal when rotating towards the lesioned ear showed relief of symptoms postoperatively. The bias component returning to normal can help to identify the relief of Meniere's attacks after ESS. The canal-otolith interaction can be observed pre- and postoperatively by means of caloric reaction in prone/supine position as part of the clinical routine.

Evoked potential testing in neuro-otology

To outline clinically applicable and evolving evoked potential techniques in neuro-otology. Vestibular evoked potentials can be recorded from the averaged electromyogram of actively contracting sternocleidomastoid muscles (cervical vestibular evoked myogenic potentials) using air-conducted sound, bone-conducted vibration or direct current stimulation of the mastoid. Typical cervical vestibular evoked myogenic potential changes in common peripheral and central vestibulopathies are now known. A sound or vibration evoked vestibulo-ocular response has recently been recorded from averaged extra-ocular muscle electromyograms using surface recordings beneath the eye (ocular vestibular evoked myogenic potentials). Both techniques enable assessment of otolith function, and are sensitive screening tests for the superior canal dehiscence syndrome presenting with sound and pressure sensitivity. Vestibular evoked potentials recorded from human masseter muscles and from scalp electrodes are new techniques whose characteristics are still being explored. Vestibular evoked potentials to nonphysiological stimuli can be recorded from cervical and extra-ocular muscles. They enable assessment of otolith organs, complement conventional tests of semicircular canal function and can be easily established in a neurology or otology practice.

Vestibulo-ocular responses to vertical translation in normal human subjects

Prior studies of the human translational vestibulo-ocular reflex (tVOR) report that eye rotations amount to less than 60% of those required to keep the eyes pointed at a stationary visual target, unlike the angular VOR (aVOR) which is optimized to maintain stable gaze. Our first goal was to determine if the performance of the tVOR improves when head translations are combined with head rotations in ambient lighting. A second goal was to measure tVOR during vertical head translations (bob), which has not received systematic study. We measured tVOR alone and in combination with the aVOR in 20 normal human subjects, aged 25-72 years, as they sat on a moving platform that bobbed at 2.0 Hz while rotating horizontally (yaw) at 1.0 Hz. When subjects viewed a visual target at 2 m, median "compensation gain" (eye rotational velocity/required eye rotational velocity to maintain foveal target fixation) was 0.52 during pure bob and 0.59 during combined bob-yaw; during viewing of a near target at approximately 17 cm, compensation gain was 0.58 for pure bob and 0.60 for combined bob-yaw. Mean phase lag of eye-in-head velocity for the tVOR was approximately 19 degrees with respect to the ideal compensatory response, irrespective of whether translation was accompanied by rotation. Thus, the tVOR changed only slightly during translation-rotation versus pure translation, and our subjects' ocular rotations remained at about 60% of those required to point the eyes at the target. Comparison of response during binocular or monocular viewing, and ambient or reduced illumination, indicated that relative image motion between the target and background was an important determinant of tVOR behavior. We postulate that tVOR evolved not to stabilize the image of the target on the fovea, but rather to minimize retinal image motion between objects lying in different planes, in order to optimize motion parallax information.

Translational motion perception and vestiboocular responses in the absence of non-inertial cues

Path integration studies in humans show that we have the ability to accurately reproduce our path in the absence of visual information. It has been suggested that this ability is supported by acceleration signals, as transduced by the otolith organs, which may then be integrated twice to produce path excursion. Vestibuloocular responses to linear translations (LVOR), however, show considerable frequency dependence, with substantial attenuation in response to low frequency translational motion. If otolith information were processed similarly by path integration mechanisms, the resulting signal would not be sufficient to account for robust path integration for stimuli typically used in such studies. We hypothesized that such behavior relies upon cognitive skill and transient otolith cues, typically combined with non-directional cues of motion, such as vibration and noise produced by the mechanics apparatus used to produce linear motion. Continuous motion estimation tasks were used to assess translation perception, while eye movement recordings revealed LVOR responses, in 12 normal and 2 vestibulopathic human subjects while riding on a sled designed to specifically minimize non-directional motion cues. In the near absence of such cues, perceptual responses, like the LVOR, showed high-pass characteristics. This implies that otolith signals are not sufficient to support previously observed path integration behaviors, which must be supplemented by non-directional motion cues.

Modified dynamic visual acuity tests after acoustic neuroma resection

Conclusion. These data suggest that visual acuity during quiet sitting is dynamic, requiring full body interaction of vestibulo-ocular and postural responses. These findings may have practical implications for seating design and design of tasks requiring good visual acuity while seated. Objectives. Looking at something during quiet sitting is usually assumed to be a static activity. We tested the idea that visual acuity during quiet sitting is dynamic, requiring integration of whole body responses as well as intact vestibulo-ocular reflexes. Materials and methods. Normal subjects and patients scheduled for acoustic neuroma resection were tested preoperatively. Patients were then tested during the four in-patient postoperative days. Testing was done while seated, with or without head and back support, while reading numbers from slides on a laptop computer at eye level, in font sizes from 20pt to 12pt. The dependent measure was percent correct per font size. Results. In both groups scores while sitting unsupported were significantly higher than with full support or only back support. In patients, scores were significantly decreased on postoperative day 1 and gradually increased toward normal but maintained the pattern of better scores when sitting unsupported than with head or back support.

Effect of high-dose methyl-prednisolone on brainstem encephalopathy and basal ganglia impairment complicating cat scratch disease

Cat scratch disease (CSD) is a zoonotic illness caused by the Gram negative bacillus Bartonella henselae characterized by a small skin lesion at the site of a bite, lick or scratch by a cat, commonly followed by regional lymphadenopathy 1 or 2 weeks later. We report herein on severe neurological complications of CSD combining brainstem encephalopathy and basal ganglia impairment. This 12-year-old female acutely presented to a local hospital with profound coma and a prolonged tonic posturing of extremities. On the neurological examination she was deeply comatose with pin-point pupils and lack of vestibulo-ocular responses, suggestive of brainstem encephalopathy, along with marked rigid hypertonicity suggestive also of basal ganglia impairment. Initially suspecting Herpes simplex encephalitis or acute disseminated encephalomyelitis she was promptly started with high-dose methyl-prednisolone and acyclovir. Her parents apparently reported that she was scratched by a kitten some 4 weeks prior to her present admission and as such, suspecting CSD, she was begun with doxycycline and rifampicin. Her serology had proven positive for IgM antibodies to Bartonella henselae establishing the diagnosis. She regained consciousness after 4 days and the signs of brainstem and extra-pyramidal impairment also gradually abated and disappeared after 10 days. A follow-up exam after a month disclosed mild extra-pyramidal abnormalities which disappeared after 3 months. Although extremely rare, CSD should be also considered in a patient presenting with a severe encephalopathy and associated basal ganglia impairment. The prompt administration of high-dose methyl-prednisolone upon admission may have contributed to the favorable outcome in our patient and therefore should be advocated in any patient presenting with profound encephalopathy regardless the underlying etiology recovered later.

Selective Engagement of Plasticity Mechanisms for Motor Memory Storage

The number and diversity of plasticity mechanisms in the brain raises a central question: does a neural circuit store all memories by stereotyped application of the available plasticity mechanisms, or can subsets of these mechanisms be selectively engaged for specific memories? The uniform architecture of the cerebellum has inspired the idea that plasticity mechanisms like cerebellar long-term depression (LTD) contribute universally to memory storage. To test this idea, we investigated a set of closely related, cerebellum-dependent motor memories. In mutant mice lacking Ca(2+)/calmodulin-dependent protein kinase IV (CaMKIV), the maintenance of cerebellar LTD is abolished. Although memory for an increase in the gain of the vestibulo-ocular reflex (VOR) induced with high-frequency stimuli was impaired in these mice, memories for decreases in VOR gain and increases in gain induced with low-frequency stimuli were intact. Thus, a particular plasticity mechanism need not support all cerebellum-dependent memories, but can be engaged selectively according to the parameters of training.

Valores poblacionales de referencia para videooculografía en el test de agitación cefálica y la prueba calórica bitérmica

ObjectiveTo obtain reference values for the vestibulo-ocular reflex response to the head-shaking nystagmus and the bithermal caloric test in the spanish population Patients and methods: DesingA descriptive study. Set up: General hospital Set upGeneral hospital IndividualsOne hundred and seven healthy sex and age stratified voluntiers were included. The final sample included 97 individuals over 18 years of age InterventionSpontaneous nystagmus (SN), head-shaking nystagmus (HSN) and caloric induced nystagmus were explored. The eyes movement was recorded by a video-oculographic system. The SN or HSN was considered significant when at least 6 consecutive beats with a slow phase velocity of 2º/sec were detected. The caloric test was performed with water flow at 250mL/20 s at 30ºC and 44ºC with an interval of 10 minutes between irrigations. The percentage of canal paresis (CP) and directional preponderance (DP) was calculated using maximum slow phase velocity and the Jongkees index formula Main outcome measurementsPresence of SN, horizontal and vertical SHN, percentage of CP and DP ResultsSN was found in 10,3% individuals (6 women and 4 men). Horizontal HSN was also observed in 9 women and 10 men (19,5%), and vertical HSN in 8 women and 10 men (18,6%). The mean and 95 percentil for CP were 13,10 and 28,60 in women and 11,02 and 27,30 in men. For DP, the mean and 95 percentil were 11,76 and 35,80 in women and 11,58 and 28,65 in men. The 5 percentils for slow phase velocity of nystagmus after each irrigation were 6,30; 5,14; 5,96; 4,02 º/s (left ear 44º, right ear 44º, left ear 30º, right ear 30º, respectively) in the group of women; and 5,82; 6,99; 5,67; 4,55 º/s in men (with the same irrigation sequence) ConclusionResults presented should be considered as a population-based norms and may be useful as references for water bithermal test for VOG studies. The SN or HSN could be observed in subjects without vestibular pathology