Contralesional Direction Research Articles

Effects of cerebellar magnetic stimulation on chronic post-lateral medullary infarction dizziness: A proof-of-principle cohort study

Background and purposeLateral medullary infarction (LMI) sometimes causes long-lasting dizziness. Although the precise mechanism of chronic post-LMI dizziness is unknown, a cerebellar control disorder of the vestibulo-ocular reflex (VOR) has been reported in such patients. We conducted a proof-of-principle cohort study to assess the potential efficacy of cerebellar repetitive transcranial magnetic stimulation (rTMS) as treatment for chronic post-LMI dizziness. MethodsWe first applied cerebellar rTMS in healthy volunteers (n = 11) and showed that cerebellar intermittent theta burst stimulation (iTBS) affected vestibulocerebellar neural activity. Then, between September and December 2015, we enrolled six patients (aged≥20 years) with chronic post-LMI dizziness (duration≥6 months), applied cerebellar rTMS (iTBS for 5 days), and followed these patients up for up to 25 months for clinical symptoms (Dizziness Handicap Inventory [DHI]), signs (nystagmus), and VOR gain. ResultsFour of the six patients completed the study without complications. After rTMS, DHI scores were reduced (mean pre-rTMS DHI score minus post-rTMS DHI score was 13.0 [P = 0.036]) with disappearance of the ipsilesional nystagmus characteristic of the post-LMI dizziness. Reduction in the absolute VOR gain (mean pre- rTMS gain minus post-rTMS gain in the ipsilesional direction was 0.135 [P = 0.036] and that in the contralesional direction was 0.137 [P = 0.031]) were also associated with reduced DHI scores. Relative cerebellar blood flow to the brainstem was increased in four of five patients. The effects of cerebellar rTMS did not always persist, and three of four patients elected to undergo more than one rTMS series. The repeat cerebellar rTMS treatments had same beneficial effects. ConclusionOur study showed, for the first time, the potential efficacy of cerebellar rTMS for treatment of chronic post-LMI dizziness. The short duration of the cerebellar rTMS effects can be compensated for by repeating the rTMS treatment every few months. Further large-scale randomized studies are warranted to confirm our findings.

Isolated Infarction of Anterior Cerebellar Vermis

The anterior cerebellar vermis has been known to act in coordination of gait and postural adjustment of the trunk and legs. However, oculomotor abnormalities in an isolated anterior vermian lesion have not been described in the literature. A 59-year-old man presented with acute non-rotatory dizziness and disequilibrium. Neuro-ophthalmologic examination found impaired smooth pursuit and hypometric saccades in the contralesional direction, and disconjugate ipsiversive ocular torsion, but without spontaneous or gaze-evoked nystagmus. Imaging study showed an infarction restricted to the rostral end of right cerebellar vermis involving the lingual and central lobules. The anterior cerebellar vermis participates in the maintenance of axial posture and gait, and also in the control of ocular motor and vestibular systems. Keywords: Cerebellum; Cerebellar vermis; Gait; Smooth pursuit; Saccades; Ocular torsion 중심 단어: 소뇌, 소뇌충부, 보행, ì›í™œì¶”ì¢ ì•ˆêµ¬ìš´ë™, ì‹ ì†ì•ˆêµ¬ìš´ë™, 안구회ì„

Bilaterally Abnormal Head Impulse Tests Indicate a Large Cerebellopontine Angle Tumor.

Background and PurposeTumors involving the cerebellopontine angle (CPA) pose a diagnostic challenge due to their diverse manifestations. Head impulse tests (HITs) have been used to evaluate vestibular function, but few studies have explored the head impulse gain of the vestibulo-ocular reflex (VOR) in patients with a vestibular schwannoma. This study tested whether the head impulse gain of the VOR is an indicator of the size of a unilateral CPA tumor.MethodsTwenty-eight patients (21 women; age=64±12 years, mean±SD) with a unilateral CPA tumor underwent a recording of the HITs using a magnetic search coil technique. Patients were classified into non-compressing (T1-T3) and compressing (T4) groups according to the Hannover classification.ResultsMost (23/28, 82%) of the patients showed abnormal HITs for the semicircular canals on the lesion side. The bilateral abnormality in HITs was more common in the compressing group than the non-compressing group (80% vs. 8%, Pearson's chi-square test: p<0.001). The tumor size was inversely correlated with the head impulse gain of the VOR in either direction.ConclusionsBilaterally abnormal HITs indicate that a patient has a large unilateral CPA tumor. The abnormal HITs in the contralesional direction may be explained either by adaptation or by compression and resultant dysfunction of the cerebellar and brainstem structures. The serial evaluation of HITs may provide information on tumor growth, and thereby reduce the number of costly brain scans required when following up patients with CPA tumors.

Lying-down nystagmus and head-bending nystagmus in horizontal semicircular canal benign paroxysmal positional vertigo: are they useful for lateralization?

BackgroundLateralization of horizontal semicircular canal benign paroxysmal positional vertigo (HSC-BPPV) is very important for successful repositioning. The directions of lying-down nystagmus (LDN) and head-bending nystagmus (HBN) have been used as ancillary findings to identify the affected sites. This retrospective study was performed to evaluate the lateralizing values of LDN and HBN using clinical and laboratory findings for lateralizing probabilities in patients with HSC-BPPV.MethodsFor 50 HSC-BPPV patients with asymmetric direction-changing horizontal nystagmus (DCHN) during the head-rolling test (HRT) using Frenzel goggles, the directions of LDN and HBN were evaluated and compared to those determined by video-oculography. Directional LDN was defined as the contralesional direction of nystagmus in geotropic types and the ipsilesional direction in apogeotropic types. Directional HBN was defined as the opposite direction relative to directional LDN. We also analyzed LDN and HBN in 14 patients with a history of ipsilesional peripheral vestibulopathy, caloric abnormality or conversion from other types of BPPV (such as probable localized HSC-BPPV, pro-BPPV).ResultsLDN and HBN were seen in 68% (34/50) and 76% (38/50) of patients, respectively. Of these, 19 (55.9%), and 28 (73.7%) patients showed directional LDN and HBN, respectively. The proportion of patients with directional LDN and HBN was much smaller among the pro-BPPV patients (4/12 for LDN, 3/10 for HBN).ConclusionsLDN and HBN did not seem to predict lateralization in patients with HSC-BPPV. To improve the prediction of lateralization of HSC-BPPV, it is necessary to modify the maneuvers used to elicit LDN or HBN, especially in cases of symmetric DCHN during HRT.

Visuomotor Control Post Stroke Can be Affected by a History of Visuospatial Neglect

A frequent consequence of stroke is locomotor disturbance. Locomotor steering, which relies heavily on the use of visual information, can be affected by a stroke but little is known about such disturbance. We investigated the ability of nine chronic stroke patients to steer in response to changes in the optic flow in a single-subject design. Subjects were instructed to walk straight for 5 m in a virtual environment with or without a perturbation of the focus of expansion (FOE), rotating horizontally 40° towards the right or left from the midline. Subjects exhibited 3 distinct behaviours: (I) 4/9 subjects showed no deficits in their locomotor strategy and responded by rotating their head and body in the direction opposite to the FOE shift, as previously reported in healthy individuals: (II) 2/9 subjects showed some degree of steering adjustments in response to the flow but resulted in slightly higher net heading errors; (III) 3/9 showed large net heading errors that were especially pronounced when the FOE was rotated in the contralesional direction. The most important distinction between subjects who performed normally and those who had deficits was that the latter had a history of visuospatial neglect, suggesting that spatial neglect can have a persistent impact on visuomotor control. Our findings also suggest that standard pen-and-paper tests are not sufficient for detecting all forms of neglect and may adequately detect deficits in processing of dynamic visual motion or for stimuli located in far space.

Reversal of Initial Positioning Nystagmus in Benign Paroxysmal Positional Vertigo Involving the Horizontal Canal

In benign paroxysmal positional vertigo (BPPV), spontaneous reversal of the initial positioning nystagmus rarely occurs without further position changes. We analyzed the characteristics of spontaneous reversal of the initial head-turning nystagmus in 21 patients with BPPV involving the horizontal semicircular canal. All patients showed initial geotropic nystagmus (first-phase nystagmus) on head turning to either side while supine, which was followed by spontaneous reversal (second-phase nystagmus). The reversal was either unilateral (n = 16) or bilateral (n = 5). The maximal slow phase velocity (SPV) and duration of the first-phase nystagmus were greater and shorter than those of the second-phase nystagmus. The reversal group showed greater maximal SPVs of the initial nystagmus in either ipsi- or contralesional direction than the control group. BPPV resolved after particle repositioning maneuver (PRM) in most patients. However, one patient showed persistent apogeotropic nystagmus after PRM. Short-term adaptation of the vestibulo-ocular reflex seems to be the main mechanism of spontaneous reversal of the initial positioning nystagmus. However, coexistence of canalo- and cupulolithiasis should be considered in the patient showing bilateral spontaneous reversal.

Perceived gaze direction in faces and spatial attention: a study in patients with parietal damage and unilateral neglect

Perceived gaze in faces is an important social signal that may influence orienting of attention in normal observers. Would such effects of gaze still occur in patients with right parietal damage and left neglect who usually fail to attend to contralesional space? Two experiments tested for effects of perceived gaze on visual extinction. Face or shape stimuli were presented in the right, left, or both hemifields, with faces looking either straight ahead or toward the opposite field. On bilateral trials, patients extinguished a left shape much less often when a concurrent right face looked leftward rather than straight ahead. This occurred, even though gaze was not relevant to the task and processing of facial signals implied attention to a competing ipsilesional stimulus. By contrast, rightward gaze in faces presented on the left side had no effect on extinction, suggesting that gaze cues are not extracted without attention. Two other experiments examined effects of perceived gaze on the detection of peripheral targets. Targets appeared at one of four possible locations to the right or left of a central face looking either toward the target location, another location on the same side, the opposite side, or straight ahead. Face and gaze were not relevant to the task and not predictive of target location. Patients responded faster when the face looked toward the target on both the contralesional and ipsilesional sides. In contralesional space, gaze allowed shifting of attention in a specific quadrant direction, but only to the first target along the scan path when there were different possible locations on the same side. By contrast, in intact ipsilesional space, attention was selectively directed to one among different eccentric locations. Control experiments showed that symbolic arrow cues did not produce similar effects. These results indicate that even though parietal damage causes spatial neglect and impairs the representation of location on the contralesional side, perceived gaze in faces can still trigger automatic shifts of attention in the contralesional direction, suggesting the existence of specific and anatomically distinct attentional mechanisms.

Inactivation of macaque lateral intraparietal area delays initiation of the second saccade predominantly from contralesional eye positions in a double-saccade task.

Previous studies have shown that, although lateral intraparietal (LIP) area neurons have retinotopic receptive fields, the response strength of these cells is modulated by eye position. This combining of retinal and eye position information can form a distributed coding of target locations in a head-centered coordinate frame. Such an implicit head-centered coding offers one mechanism for maintaining spatial stability across eye movements and can be used to compute new oculomotor error vectors after each eye movement. An alternative mechanism is to use eye displacement signals rather than eye position signals to maintain spatial stability. The aim of this study was to distinguish which of these two extra-retinal signals (or perhaps both signals) are employed in a double saccade task, which required the monkey to use extraretinal information associated with the first saccade to localize a remembered target for a second saccade. By varying the direction and the end point of the first saccade and selectively inactivating area LIP in one hemisphere with muscimol injection, we were able to distinguish between the two mechanisms by observing how the second saccade was impaired in this task. The displacement mechanism predicts that, if the first saccade is in the contralesional direction, the second saccade will be impaired, and the end point of the first saccade would not be important. The eye position mechanism predicts that if the first saccade ended in the contralesional head-centered space, the second saccade will be impaired, no matter in which direction the first saccade is made. Results showed that, after area LIP lesion, when the first saccade stepped into the contralesional field, the error rate of the second saccade became higher and the latency longer. However, when the end point of the first saccade was constant, the direction of the first saccade had much less effect on the second saccade. These results suggest that eye position, and not eye displacement, is the more predominant factor in this task. In a different behavioral paradigm, the monkeys performed single visual and memory saccades from different initial eye positions. It was found that the impairment of either the metrics or dynamics of visual and memory saccades did not significantly vary with the different eye positions. It thus appears that the performance of single visual and memory saccades is best described in an oculocentric coordinate frame that does not rely on extraretinal signals. Altogether these results lend further support to the hypothesis that, by combining retinal and eye position signals, area LIP contains concurrent eye-centered and head-centered representations of the visual space. Depending on the task, either representation can be used.

Exploratory saccades show no direction-specific deficit in neglect.

In patients with spatial neglect, contralesional reflexive saccades toward suddenly appearing targets show direction-specific deficits. We examined whether these deficits also occur during free exploration of space. Neglect patients' voluntary eye movements showed reduced amplitudes for saccades in all directions but no direction-specific deficit. The results argue against an interpretation of spatial neglect as a general deficit to disengage attention or to program saccades in contralesional direction.

How many neglects? Some considerations based on anatomy and information processing

Abstract Despite implying a unitary impairment in spatial cognition. the term “neglect” covers numerous behavioural manifestations that are themselves consequent upon damage to distinct neural systems. Aphasia, agnosia, and amnesia have long been acknowledged as heterogeneous conditions, but only recently has spatial cognition proved amenable to similar taxonomic initiatives. Unfortunately, with the advent of a nascent taxonomy, terms have emerged whose meanings have failed to remain consistent. For example, in the motor domain, “directional hypokinesia” originally characterised slowed initiation of contralesional movements (Heilman et al., 1985); subsequently it covered reduced spatial exploration in a contralesional direction (Tegnér & Levander, 1991), or even insufficiently extensive movements in the contralesional direction (Bisiach, Geminiani, Berti, & Rusconi, 1990). Conversely, the implied semantic differences between terms such as “directional motor neglect”, “hemispatial motor neglect” and “hemispatial limb hypometria” may be more apparent than real. In the absence of a precisely defined lexicon devoted to describing spatial cognition, we cannot hope to achieve a principled understanding of its disorders.

Modulation of the Directional Attention Deficit in Visual Neglect by Hemispatial Factors

Using a visuo-spatial cuing paradigm, Posner and collaborators (Posner, Cohen, & Rafal, 1982; Posner, Walker, Friedrich, & Rafal, 1984) reported that subjects with a parietal lobe lesion have difficulty in disengaging their visual attention from an invalidly precued location in the ipsilesional hemifield when the target they have to respond to is presented in the contralesional field. Later, these authors (Posner, Walker, Friedrich, & Rafal, 1987) proposed that this disengagement deficit is one involving spatial shifts of attention in a contralesional direction, irrespective of the visual hemifield in which the target is presented. This proposal of a directional disengagement deficit along the horizontal axis, present in either hemifield, contrasts with a report by Baynes, Holtzman, & Volpe (1986) showing, in right parietal subjects, a disengagement deficit for shifts of attention along the vertical axis that is only manifest in the contralesional hemifield. In the present report, we assessed the disengagement deficit of a neglect subject along the horizontal and vertical axes. Results show a disengagement deficit restricted to shifts of attention in the contralesional direction (horizontal axis), which is significant only in the contralesional visual hemifield. However, there is a clear trend for a directional disengagement deficit in the ipsilateral field. These observations indicate that the attention deficit present in neglect is directional and is modulated either by hemispatial factors or by the lateral target location in the visual field. On the basis of the present results, it is proposed that the deficit of parietal subjects may best be conceptualized as one of attentional capture for stimuli located on the contralesional side of the current focus of attention rather than one of disengagement.