Coordination of eye and head components of movements evoked by stimulation of the paramedian pontine reticular formation.
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.
Gandhi
Neeraj J
NJ
Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA. neg8@pitt.edu
Barton
Ellen J
EJ
Sparks
David L
DL
D000818:Animals; D001288:Attention / Q000502:physiology; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D005133:Eye Movements / Q000502:physiology*; D007839:Functional Laterality; D019416:Head Movements / Q000502:physiology*; D008253:Macaca mulatta; D009046:Motor Neurons / Q000528:radiation effects; D011597:Psychomotor Performance / Q000502:physiology*; D012154:Reticular Formation / Q000502:physiology* / Q000528:radiation effects