Consensus paper: roles of the cerebellum in motor control--the diversity of ideas on cerebellar involvement in movement

Considerable progress has been made in developing models of cerebellar function in sensorimotor control, as well as in identifying key problems that are the focus of current investigation. In this consensus paper, we discuss the literature on the role of the cerebellar circuitry in motor control, bringing together a range of different viewpoints. The following topics are covered: oculomotor control, classical conditioning (evidence in animals and in humans), cerebellar control of motor speech, control of grip forces, control of voluntary limb movements, timing, sensorimotor synchronization, control of corticomotor excitability, control of movement-related sensory data acquisition, cerebro-cerebellar interaction in visuokinesthetic perception of hand movement, functional neuroimaging studies, and magnetoencephalographic mapping of cortico-cerebellar dynamics. While the field has yet to reach a consensus on the precise role played by the cerebellum in movement control, the literature has witnessed the emergence of broad proposals that address cerebellar function at multiple levels of analysis. This paper highlights the diversity of current opinion, providing a framework for debate and discussion on the role of this quintessential vertebrate structure.

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.

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.

[Idiopathic vasospastic angiopathy of the internal carotid arteries: A rarely recognized cause of ischemic stroke in young individuals]

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.

Separate neural substrates in the human cerebellum for sensory-motor adaptation of reactive and of scanning voluntary saccades

Sensory-motor adaptation processes are critically involved in maintaining accurate motor behavior throughout life. Yet their underlying neural substrates and task-dependency bases are still poorly understood. We address these issues here by studying adaptation of saccadic eye movements, a well-established model of sensory-motor plasticity. The cerebellum plays a major role in saccadic adaptation but it has not yet been investigated whether this role can account for the known specificity of adaptation to the saccade type (e.g., reactive versus voluntary). Two patients with focal lesions in different parts of the cerebellum were tested using the double-step target paradigm. Each patient was submitted to two separate sessions: one for reactive saccades (RS) triggered by the sudden appearance of a visual target and the second for scanning voluntary saccades (SVS) performed when exploring a more complex scene. We found that a medial cerebellar lesion impaired adaptation of reactive-but not of voluntary-saccades, whereas a lateral lesion affected adaptation of scanning voluntary saccades, but not of reactive saccades. These findings provide the first evidence of an involvement of the lateral cerebellum in saccadic adaptation, and extend the demonstrated role of the cerebellum in RS adaptation to adaptation of SVS. The double dissociation of adaptive abilities is also consistent with our previous hypothesis of the involvement in saccadic adaptation of partially separated cerebellar areas specific to the reactive or voluntary task (Alahyane et al. Brain Res 1135:107-121 (2007)).

[Vertigo treatment according to their mechanisms]

Vertigo is an illusion of rotatory or linear movement that demonstrates a functional or lesional disturbance of the vestibular system, from periphery to central connections. According to the ANAES report (1997), benign paroxysmal positional vertical vertigo, vestibular neuronitis and Ménière's disease account for 40-50% of all mixed vertigo etiologies. Central etiologies may account for 20-40% of causes and 10-40% remain more difficult to classify, and are usually classified under the term of "peripheral vestibulopathy." These include vertigo due to neurovascular compression syndrome of the VIIIth nerve. Clinical manifestations, differential diagnosis, and treatment of the main etiologies of vertigo will be developed in this chapter. A specific section will discuss the subject of neurovascular compression syndrome of the VIIIth nerve. Even though some publications should be challenged, it appears that neurovascular compression syndrome of the VIIIth nerve might explain some cases of vertigo or chronic instability, with or without cochlear signs. The diagnosis is difficult and must be established on multiple clinical, electrophysiological and radiological arguments. A therapeutic test with antiepileptic drugs is helpful. The treatment includes these drugs as a first option but may require a neurosurgical approach if medical treatment fails.

[Motorocular syndromes due to neurogenic hyperactivity and their treatment]

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.

[Clinical and functional assessment of the vestibular nerve]

Clinical and functional assessment of the vestibular nerve is fundamental in demonstrating vestibular signs and searching for associated otological and neurological signs. This may help orient topographic diagnosis toward central or peripheral syndrome and etiologic diagnosis.

[Functional anatomy of the vestibular nerve]

The vestibular system detects head movements such as angular rotation, translation, and head position relative to gravity. It acts to stabilize the eyes and posture through subcortical reflexes. Its signals are also integrated at the cortical level to participate in the elaboration of a body scheme, used for different functions such as spatial orientation and motor control. The vestibular nerve shows a resting discharge rate that is modulated up or down according to head motion or position. Central functioning depends on the detection of an asymmetry between signals coming from a pair of peripheral sensors, one on either side. In pathological cases, unilateral peripheral dysfunction is interpreted by the central system as an asymmetry resulting from a change in head position leading to nystagmus, postural disturbances, and vertigo. The dysfunction can be either a deficit, such as observed in vestibular neuronitis, or hyperactivity such as observed in neurovascular compression syndrome of the VIIIth nerve. Anatomically, the VIIIth nerve has a long Root Entry Zone (REZ) that extends over 10mm before entering the brainstem. The VIIIth nerve is also physiologically close to numerous vessels at the pontocerebellar angle and internal auditory meatus. Therefore, vestibular syndrome resulting from neurovascular compression syndrome of the VIIIth nerve may exist, but it is very difficult to prove using radiological imagery.