Can you guess the colour of this moving object? A dissociation between colour and motion in blindsight.

Blindsight has been primarily and extensively studied by Lawrence Weiskrantz. Residual visual abilities following a hemispheric lesion leading to homonymous hemianopia encompass a variety of visual-perceptual and visuo-motor functions. Attention blindsight produces the more salient subjective experiences, especially for motion (Riddoch phenomenon). Action blindsight illustrates visuo-motor abilities despite the patients' feeling that they produce random movements. Perception blindsight seems to be the weakest residual function observed in blindsight, e.g. for wavelength sensitivity. Discriminating motion produced by isoluminant colours does not give rise to blindsight for motion but the outcome of the reciprocal test is not known. Here we tested whether moving stimuli could give rise to colour discrimination in a patient with homonymous hemianopia. It was found that even though the patient exhibited nearly perfect performances for motion direction discrimination his colour discrimination for the same moving stimulus remained at chance level. It is concluded that easily discriminated moving stimuli do not give rise to colour discrimination and implications for the 3 levels of blindsight taxonomy are discussed.

Main inherited neurodegenerative cerebellar ataxias, how to recognize them using magnetic resonance imaging?

Ataxia is a neurodegenerative disease resulting from brainstem, cerebellar, and/or spinocerebellar tracts impairments. Symptoms onset could vary widely from childhood to late-adulthood. Autosomal cerebellar ataxias are considered as one of the most complex group in neurogenetics. In addition to their genetic heterogeneity, there is an important phenotypic variability in the expression of cerebellar impairment, complicating the genetic mutation research. A pattern recognition approach using brain MRI measures of atrophy, hyperintensities and iron-induced hypointensity of the dentate nuclei, could be therefore helpful in guiding genetic research. This review will discuss a pattern recognition approach that, associated with the age at disease onset, and clinical manifestations, may help neuroradiologists differentiate the most frequent profiles of ataxia.

Are Covert Saccade Functionally Relevant in Vestibular Hypofunction?

The vestibulo-ocular reflex maintains gaze stabilization during angular or linear head accelerations, allowing adequate dynamic visual acuity. In case of bilateral vestibular hypofunction, patients use saccades to compensate for the reduced vestibulo-ocular reflex function, with covert saccades occurring even during the head displacement. In this study, we questioned whether covert saccades help maintain dynamic visual acuity, and evaluated which characteristic of these saccades are the most relevant to improve visual function. We prospectively included 18 patients with chronic bilateral vestibular hypofunction. Subjects underwent evaluation of dynamic visual acuity in the horizontal plane as well as video recording of their head and eye positions during horizontal head impulse tests in both directions (36 ears tested). Frequency, latency, consistency of covert saccade initiation, and gain of covert saccades as well as residual vestibulo-ocular reflex gain were calculated. We found no correlation between residual vestibulo-ocular reflex gain and dynamic visual acuity. Dynamic visual acuity performance was however positively correlated with the frequency and gain of covert saccades and negatively correlated with covert saccade latency. There was no correlation between consistency of covert saccade initiation and dynamic visual acuity. Even though gaze stabilization in space during covert saccades might be of very short duration, these refixation saccades seem to improve vision in patients with bilateral vestibular hypofunction during angular head impulses. These findings emphasize the need for specific rehabilitation technics that favor the triggering of covert saccades. The physiological origin of covert saccades is discussed.

The Attentional Fields of Visual Search in Simultanagnosia and Healthy Individuals: How Object and Space Attention Interact.

Simultanagnosia is a deficit in which patients are unable to perceive multiple objects simultaneously. To date, it remains disputed whether this deficit results from disrupted object or space perception. We asked both healthy participants as well as a patient with simultanagnosia to perform different visual search tasks of variable difficulty. We also modulated the number of objects (target and distracters) presented. For healthy participants, we found that each visual search task was performed with a specific "attentional field" depending on the difficulty of visual object processing but not on the number of objects falling within this "working space." This was demonstrated by measuring the cost in reaction times using different gaze-contingent visible window sizes. We found that bilateral damage to the superior parietal lobule impairs the spatial integration of separable features (within-object processing), shrinking the attentional field in which a target can be detected, but causing no deficit in processing multiple objects per se.

Effects of structural and functional cerebellar lesions on sensorimotor adaptation of saccades.

The cerebellum is critically involved in the adaptation mechanisms that maintain the accuracy of goal-directed acts such as saccadic eye movements. Two categories of saccades, each relying on different adaptation mechanisms, are defined: reactive (externally triggered) saccades and voluntary (internally triggered) saccades. The contribution of the medio-posterior part of the cerebellum to reactive saccades adaptation has been clearly demonstrated, but the evidence that other parts of the cerebellum are also involved is limited. Moreover, the cerebellar substrates of voluntary saccades adaptation have only been marginally investigated. Here, we addressed these two questions by investigating the adaptive capabilities of patients with cerebellar or pre-cerebellar stroke. We recruited three groups of patients presenting focal lesions located, respectively, in the supero-anterior cerebellum, the infero-posterior cerebellum and the lateral medulla (leading to a Wallenberg syndrome including motor dysfunctions similar to those resulting from lesion of the medio-posterior cerebellum). Adaptations of reactive saccades and of voluntary saccades were tested during separate sessions in all patients and in a group of healthy participants. The functional lesion of the medio-posterior cerebellum in Wallenberg syndrome strongly impaired the adaptation of both reactive and voluntary saccades. In contrast, patients with lesion in the supero-anterior part of the cerebellum presented a specific adaptation deficit of voluntary saccades. Finally, patients with an infero-posterior cerebellar lesion showed mild adaptation deficits. We conclude that the medio-posterior cerebellum is critical for the adaptation of both saccade categories, whereas the supero-anterior cerebellum is specifically involved in the adaptation of voluntary saccades.

Acquired visual field defects rehabilitation: critical review and perspectives.

Visual field deficit (VFD) is one of the most commonly observed symptoms following brain injury. Persistent VFD and defective exploratory oculomotor scanning patterns often cause severe impairment in daily activities, particularly as regards visual exploration and reading. Homonymous hemianopia is consequently a powerful negative predictor of patient outcome. In spite of these quantitative and qualitative factors, there currently exists no consensus on rehabilitative therapy and treatment. Different approaches have nevertheless been developed, all of them having one therapeutic principle in common; repeated practice of a specific visual task, with the hope/expectation that improved performance will extend to a wide range of ecologically useful visual functions. The four main available methods aim at replacing part of the intact visual field with part of the damaged visual field (optical therapy using prisms), at partially restoring the lost visual field region (restorative therapies), at stimulating detection capacities in the blind field (stimulation or blindsight) or at substituting for the lost region by reorganizing the control of visual information processing and eye movements (compensatory therapies). This review explores the key data relative to these different approaches in terms of behavioral or imagery results. It also aims at critically analyzing the advantages and limits of each one. The importance of strict assessment in terms of deficiencies or disabilities is underlined. Finally, upon consideration of these data taken as a whole, it is suggested that efficient treatment would probably have to associate general components and more specific elements, according to what may be done with regard to other aspects of cognitive rehabilitation.

[Saccadic system plasticity mechanisms in Parkinson disease patients]. / Mécanismes de plasticité saccadique chez les patients atteints de maladie de Parkinson.

INTRODUCTION: Voluntary or reactive saccades predominate in rapid eye movements. Their goal is to preserve an active and optimal visual perception of the environment. Saccades cannot be guided once launched. Oculomotor plasticity, or saccadic adaptation, is still partially unknown, in particular the role played by the basal ganglia. New neuro-ophthalmological rehabilitation techniques require understanding the neurophysiological basis and demonstrating the neuronal structures involved in this plasticity. OBJECTIVES: This study assessed the reactive saccade adaptation in patients with idiopathic Parkinson disease, as a model of basal ganglia dysfunction. We predicted that saccadic adaptation would be preserved in this pathology. PATIENTS AND METHODS: Five patients with mild idiopathic hemi-Parkinson disease were included, as well as four age-matched controls. Reactive saccade adaptation was studied using the double-step target paradigm, in patients with OFF-Dopa treatment and in controls. RESULTS: Group analysis demonstrated that patients had a lower level of adaptation than the controls (p<0.05). Individually, two patients did not adapt for bilateral saccades and one for ipsilateral (compared to Parkinson motor clinical syndrome) saccades. Two additional patients adapted on both sides but with a deficit in contralateral saccades when compared to the control group. DISCUSSION: These preliminary results suggest basal ganglia involvement in reactive saccadic adaptation, which remains to be clarified.

Facial macrosomatognosia and pain in a case of Wallenberg's syndrome: selective effects of vestibular and transcutaneous stimulations.

Macro- and micro-somatognosia refer to rare disorders of the cerebral representation of the body whereby patients perceive body parts as disproportionately large or small. Here we report the experimental study of a patient who, following a left lateral medullary stroke (Wallenberg's syndrome, including vestibular deficits) complained of a persistent somatosensory illusory sensation of swelling, confined to the left side of his face (i.e., left macrosomatognosia). This hemifacial somatosensory distortion was associated with a left facial anesthesia, and a neuropathic pain affecting the three branches of the left trigeminal nerve. In this study, we first document quantitatively the patient's somatosensory illusion by using a somatosensory-to-visual matching task in which the patient modified the picture of his own face to fit his left-sided somatosensory misperception. The patient's performance revealed that macrosomatognosia was confined to the second branch of the left trigeminal nerve. Perception of the size of visual objects was comparatively preserved. Second, we investigated the effects of two peripheral stimulations, which may affect the spatial component of somatosensory deficits (caloric vestibular stimulation, CVS; transcutaneous electrical nervous stimulation, TENS) and pain (TENS). Left CVS abolished the facial somatosensory illusion, for about 30min, but had no effect on the left facial pain. Conversely, left TENS substantially reduced the neuropathic pain during stimulation, but had no effect on macrosomatognosia, indicating a double dissociation between the two disorders. These results reveal that facial macrosomatognosia may be regarded as a high-order deficit of somatosensory perception of the shape and volume of the face, which fits the definition of 'hyperschematia' (i.e., when the body takes up too much room) originally proposed by Bonnier (1905). Our data also indicate that CVS may favor the restoration of the conscious representation of the shape and size of the face. Overall, these findings lend support to the view that afferent inputs from the vestibular system can affect in a specific fashion the activity of cerebral structures involved in the building up and updating of the topological description of body parts.

Detection of mild papilloedema using spectral domain optical coherence tomography.

OBJECTIVE: To propose a method of diagnosis of mild papilloedema (PO) using peripapillary total retinal (PTR) thickness measurement by spectral domain optical coherence tomography (OCT). METHODS: 24 eyes in 24 patients with PO caused by increased intracranial pressure and 22 eyes in 22 normal subjects were studied. OCT high-quality fundus images were analysed and graded by three masked observers using the Modified Frisén Scale. Eyes with PO were divided into two subgroups: those with mild PO (n=18) and those with moderate-severe PO (n=6). Two methods of measurements were evaluated and compared: retinal nerve fibre layer (RNFL) thickness measurements using standard optic disc cube 200 × 200 acquisition protocol and PTR thickness measurements using the 'macular' cube 512 × 128 acquisition protocol centred on the optic disc. Thickness values were calculated globally and for each quadrant (temporal, superior, nasal, inferior) and compared among the three groups (control, mild PO, moderate-severe PO). The main outcome measures were RNFL and PTR thickness. RESULTS: Average RNFL and PTR thickness in the moderate-severe PO, mild PO and control groups were 299.3 ± 10.9, 112.4 ± 6.3, 96 ± 5.7 and 804.5 ± 17, 463.1 ± 9.8 and 332.4 ± 8.9 µm, respectively. Moderate-severe PO differed from mild PO and control groups using both RNLF thicknesses and PTR thicknesses measurements. Mild PO did not differ from controls using RNLF thickness measurement (p=0.17), but was statistically different using PTR thickness measurement (p<0.001). CONCLUSION: PTR thickness measurement increases the sensitivity of detection of mild PO compared with conventional RNFL measurement. This new way of using OCT may be useful for clinicians to detect mild PO.

Persistent ocular motor manifestations and related visual consequences in multiple sclerosis.

Abnormal eye movements in multiple sclerosis (MS) are often persistent and known to be associated with general disability. However, there is no precise knowledge concerning their incidence and resulting visual handicap. The aim of our study was to describe the persistent ocular motor manifestations in MS and relate them to visual functions tested with visual acuity and with a vision-related questionnaire. We selected 24 MS patients complaining of persistent visual disability associated with ocular motor manifestations without any anterior visual pathway deficit. Internuclear ophthalmoplegia was the most frequently observed symptom, followed by gaze-evoked nystagmus, saccadic hypermetria, and then pendular nystagmus. Pendular nystagmus, saccadic hypermetria, and the association of internuclear ophthalmoplegia and gaze-evoked nystagmus were associated with decreased visual acuity and visual functional scores. There was a correlation between the number of abnormal eye movements and visual functions. This study demonstrates that ocular motor dysfunction in MS induces specific visual dysfunction and handicap.

Acquired pendular nystagmus in multiple sclerosis and oculopalatal tremor.

OBJECTIVE: Acquired pendular nystagmus occurs mainly in multiple sclerosis (MS) and focal brainstem lesions. In the later case, it is part of the syndrome of oculopalatal tremor. Even though pathophysiology of acquired pendular nystagmus has been clearly characterized experimentally in both etiologies, there is a persisting ambiguity in clinical literature, which leads one to consider both clinical conditions as a common entity. The objective of our work was to compare in a prospective study clinical features, eye movement recording, and functional consequences of acquired pendular nystagmus in 14 patients with oculopalatal tremor and 20 patients with MS. METHODS: Besides complete neurologic evaluation, evaluation of visual function, 3-dimensional eye movement recording, and functional scores of the Visual Function Questionnaire were recorded. RESULTS: One patient with oculopalatal tremor and 15 patients with MS disclosed signs of optic neuropathy. The nystagmus in the oculopalatal group showed significant larger mean amplitude (8 deg vs 1 deg), higher mean peak velocity (16 deg/s vs 6 deg/s), lower mean frequency (1-3 Hz vs 4-6 Hz), and larger asymmetry and irregularity of ocular oscillations compared to the MS group. The vision-specific health-related quality of life was more deteriorated in the oculopalatal tremor group than in the MS group. CONCLUSIONS: This study emphasizes the need to consider acquired pendular nystagmus in MS and oculopalatal tremor as 2 different clinical entities. This is of particular importance regarding the future evaluation of potential specific effects of pharmacologic agents.

[Idiopathic vasospastic angiopathy of the internal carotid arteries: A rarely recognized cause of ischemic stroke in young individuals]. / Angiopathie vasospastique idiopathique de l'artère carotide interne : une cause peu connue d'accident vasculaire du sujet jeune.

INTRODUCTION: Idiopathic vasospastic angiopathy of the internal carotid arteries is a rare and largely unknown cause of ischemic stroke. METHODS: We report the case of a 39-year-old man with migraine treated by beta-blockers, who had been suffering from progressive right visual impairment and headache for one week. He then experienced a seizure and left hemiparesis. Ophthalmological examination revealed right retinal ischemia and partial left homonymous hemianopia. MRI revealed a long stenosis of both carotid arteries and a recent ischemic stroke in the territory of the right middle cerebral artery. The diagnosis of vasospastic angiopathy of the internal carotid arteries was made based on a second MRI and colored duplex sonography which showed a decrease in the stenosis and no intraparietal hematoma confirming the vasospasm mechanism for stenosis. The clinical course was favorable with calcium channel blockers and aspirin. Use of vasoconstrictor treatments was contraindicated. DISCUSSION/CONCLUSION: Idiopathic vasospastic angiopathy of the internal carotid arteries has been rarely documented. Association with migraine has been mentioned but remains unclear in the literature. This etiology for stroke is probably under-diagnosed due to lack of rapid and repeated examinations of the cervical arteries (angio-MR and colored duplex sonography) to confirm the vasospasm mechanism. Recurrences have been reported justifying a specific secondary preventive treatment to induce vasodilatation. Vasoconstrictor treatments should be contraindicated.

Sensorimotor adaptation of saccadic eye movements.

Sensory-motor adaptation mechanisms play a pivotal role in maintaining the performance of goal-directed movements. The saccadic system, used to explore the visual environment through fast and accurate shifts of the eyes (saccades), is a valuable model for studying adaptation mechanisms. Significant progresses have been recently made in identifying the properties and neural substrates of saccadic adaptation elicited by the double-step target paradigm. Behavioural data collected in healthy and brain-damaged subjects, and neurophysiological data from non human primates, will be reviewed in an attempt to build a coherent picture of saccadic adaptation mechanisms. Emphasis will further be put on the contextual factors of saccadic adaptation, and on the link between adaptive changes of oculomotor commands and visual perception. It will be shown that saccadic adaptation relies on multiple mechanisms according to experimental contexts, time-scales, saccade categories, and direction of adaptive changes of saccade amplitude (shortening versus lengthening). Taking into account this complexity will be a key toward a comprehensive understanding of the physiopathology of saccadic adaptation and toward the development of possible rehabilitation procedures.

[Motorocular syndromes due to neurogenic hyperactivity and their treatment]. / Les syndromes oculomoteurs par hyperactivité neurogène et leur traitement.

In this chapter we describe a variety of rare but clinically identifiable ocular motor syndromes, including ocular neuromyotonia, superior oblique myokymia, ocular motor synkinesis, third nerve palsy with cyclic spasms, and paroxysmal manifestations of multiple sclerosis. These syndromes share many characteristics. They result from neurogenic hyperactivity, causing episodic spasms of one or several extraocular muscles. The pathophysiology is not fully understood, but it usually includes both a focal and partial lesion of one of the ocular motor nerves and a central rearrangement of neuronal activity in the ocular motor nuclei. Treatment with membrane-stabilizing agents, such as carbamazepine, is usually effective to reduce the symptoms. The above-mentioned syndromes result from a number of different diseases. A proportion of apparently idiopathic cases may be related to a neurovascular compression syndrome.