Oculomotor control after hemidecortication: One hemisphere encodes normal ipsilateral oblique anti-saccades

A critical question in neurology is how the brain reorganizes its structure and function following injury. Here, we consider oculomotor control following a massive brain lesion, a hemispherectomy. We used the oblique anti-saccade task which requires the suppression of a saccade towards a visual cue, flashed anywhere in a patient's seeing hemifield, and the generation, in the dark, of an anti-saccade to a task-dependent location in the opposite blind hemifield; inverting either the horizontal or both horizontal and vertical components. Anti-saccades require a visuo-motor vector inversion that normally involves bilateral interactions between frontal, parietal and subcortical structures across both hemispheres. Here, oblique anti-saccades presented a major challenge to the patient's single hemisphere, requiring one site in visual cortex to communicate with an instruction-dependent site in oculomotor cortex. Patients with discrete frontal lobe damage can be strongly impaired in anti-saccades. By contrast, hemispherectomy patients performed oblique anti-saccades normally, contrasting with their permanent contralesional hemianopia and severe hemiparesis.