Eye Movements and Visuo-spatial Perception

This research aims to highlight the key roles of the cerebellar and cortical fronto-parietal networks in the coupling of eye movements with visual perception and visuo-spatial attention.

The first axe of this research focuses on the role of the cerebellum which has a major contribution to sensorimotor adaptation and more precisely in saccadic adaptation but the nature of this contribution is still debated. A classical assumption stipulates cerebellum has an exclusive action on saccadic burst generator in the brainstem whereas recent data increasingly support the view that cerebellum could also modulates cerebral cortex through a cerebello-thalamo-cortical pathway. On the other hand, several studies have shown that modification of saccade amplitude by saccadic adaptation leads to a distortion of the visual localization of briefly flashed spatial probes but no study to date has tested, the contribution of the cerebellum in these adaptation-induced mislocalizations. The main objective of this axe is to define the role of the cerebellum not only in saccadic adaptation, but also in mislocalizations which occur after adaptation. Moreover, in testing this assumption, arguments in favour -or in disfavor- of the action of the cerebellum on cortical stages dedicated to visuo-spatial perceptual processing will be provided. Besides, variability of cerebellar lesion (or cerebellar dysfunction) location in patients can lead to different pattern in saccadic adaptation and localization task performances. Identification of dissociations between these two abilities in some patients will define more precisely the role of the cerebellum in the coupling between saccadic adaptation and visuo spatial perception as an oculomotor plasticity territory and / or as a territory underlying the error signal coding generating this type of plasticity.

This second axe of this research aims to apply basic findings in healthy subject on the coupling between oculomotor plasticity and spatial attention to patients with parietal lesion, in order to evaluate a rehabilitation procedure for neglect patients. Habchi and colleagues showed that the adaptation of reactive saccades in the left hemifield has a boosting effect on attentional performance in the same hemifield. The coupling between these two mechanisms highlighted in healthy subjects can be used as fundamentals in the elaboration of a rehabilitation procedure for attentional disorders in the neglect syndrome. This syndrome is mainly observed after cerebral lesions in the right hemisphere, and is characterized by very disabling cognitive disorders such as an alteration of the spatial representation of left hemi-space and/or left hemi-body. stimulation of sensorimotor plasticity thanks to prismatic adaptation could be used as a rehabilitation procedure for this syndrome. Being another efficient way to stimulate sensorimotor plasticity, the equip believe that saccadic adaptation can also be used as a rehabilitation procedure for neglect patients. Moreover, due to its tight coupling with visual attention, the benefits of saccadic adaptation could be even stronger and longer lasting than the visuo-manual plasticity induced by prismatic adaptation.

Eligibility Criteria:
Inclusion Criteria:

* Age : from 18 to 80 ans included
* Visual acuity monocularly at distance and near corrected : \> 5/10
* Possible understanding of experimental guidelines
* Possible respect for sustained seated position
* Subject covered by social security
* Agreement of the subject

Inclusion Criteria, specific to Axe 1:

* Cerebellar patients - Cerebellar degenerative disease (group A) or stroke (group B, délai depuis l'AVC : delay from the stroke : at least 1 month)

  * Scanner or MRI showing diffuse atrophy (group A) or focal cerebellar lesion (group B)
* Healthy subjects

  * Absence of known ophtalmological or neurological pathology

Inclusion Criteria, specific to Axe 2:

* Stroke patients - ischemic or hemorrhagic stroke

  * Encephalic MRI or CT scan showing an unique lesion
  * Minimal delay of one year after the stroke

Exclusion Criteria:

* Visual acuity monocularly \< 5/10
* Language disorder restricting oral and reading comprehension of the study
* Severe disability limiting the maintenance of sitting position and concentration capacities for a period of 30 minutes consecutive
* Poor French language skills
* Non-stabilized medical condition
* Psychotropic medication intake
* Pregnant and / or nursing women
* Subject under guardianship or curatorship
* Subject frequently in healthcare or social care for purposes other than research
* Subject deprived of liberty by a judicial or administrative decision

Exclusion Criteria, specific to Axe 1:

• Cerebellar patients

- Disorders prohibiting the correct performance of the task (tremor, ocular instability)

Exclusion Criteria, specific to Axe 2:

• Stroke patients

* Hemianopsia homonima lateral
* Neurological degenerative disease