Title

Neurons in the central mesencephalic reticular formation and paramedian pontine reticular formation related to the control of eye movement

Date of Completion

January 2006

Keywords

Biology, Neuroscience|Health Sciences, Ophthalmology|Psychology, Cognitive

Degree

Ph.D.

Abstract

The precise control of eye position is of critical importance for proper vision. The eyes must be quickly and accurately shifted to view different objects in the environment and once targets are acquired, fixation must be maintained. Accordingly, deficits in ocular-motility have pronounced effects on patients and knowledge of the neurobiology of the oculomotor system can be critical in their treatment. The immediate motor structures involved in ocular control (the eye muscles and the motor neurons innervating them) and the brain regions involved in the selection of the target of an upcoming gaze shift are well understood. However, there is still significant debate about how the brain transforms the location of a selected target into the motor activity necessary to place the eyes onto that target. This function is undoubtedly mediated by brain stem oculomotor centers. Thus, extracellular single unit neuronal recordings were performed in a number of oculomotor regions including the central mesencephalic reticular formation (cMRF), paramedian pontine reticular formation (PPRF), superior colliculus (SC), raphe interpositus (RIP), and abducens nucleus. The primary goal of these studies was to understand the role of cMRF neurons in saccadic control by comparing their responses to those of more well understood components of the oculomotor system. To identify whether cMRF neurons encode the metrics of eye movement, neuronal responses during behaviors that caused the eyes to move at different velocities were compared. Subsequently, cMRF and PPRF neuronal activity was examined during a series of oblique saccades that caused the duration of horizontal eye velocity to be prolonged, allowing neurons influenced by the vectorial (overall) saccade velocity to be dissociated from those related only to horizontal component velocity. Finally, neurons across all of the recorded brain regions were examined during various behavioral tasks to assess their roles in oculomotor control, loss of function due to permanent cMRF lesion is detailed, and experiments examining the interconnections of the examined structures are described.^