Journal
EXPERIMENTAL BRAIN RESEARCH
Volume 189, Issue 1, Pages 35-47Publisher
SPRINGER
DOI: 10.1007/s00221-008-1401-1
Keywords
Gaze shifts; PPRF; saccade; superior colliculus; head movements; spinal cord
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Funding
- NEI NIH HHS [F32 EY007001, R01 EY001189, EY007001, R01 EY015485, T32 EY007001, EY001189, EY007009, F32 EY007009, EY015485] Funding Source: Medline
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Constant frequency microstimulation of the paramedian pontine reticular formation (PPRF) in head-restrained monkeys evokes a constant velocity eye movement. Since the PPRF receives significant projections from structures that control coordinated eye-head movements, we asked whether stimulation of the pontine reticular formation in the head-unrestrained animal generates a combined eye-head movement or only an eye movement. Microstimulation of most sites yielded a constant-velocity gaze shift executed as a coordinated eye-head movement, although eye-only movements were evoked from some sites. The eye and head contributions to the stimulation-evoked movements varied across stimulation sites and were drastically different from the lawful relationship observed for visually-guided gaze shifts. These results indicate that the microstimulation activated elements that issued movement commands to the extraocular and, for most sites, neck motoneurons. In addition, the stimulation-evoked changes in gaze were similar in the head-restrained and head-unrestrained conditions despite the assortment of eye and head contributions, suggesting that the vestibulo-ocular reflex (VOR) gain must be near unity during the coordinated eye-head movements evoked by stimulation of the PPRF. These findings contrast the attenuation of VOR gain associated with visually-guided gaze shifts and suggest that the vestibulo-ocular pathway processes volitional and PPRF stimulation-evoked gaze shifts differently.
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