The long-term objective of this work is to study the integration of visual and motor signals to produce appropriate and accurate eye movements, specifically saccadic eye movements. Saccadic eye movements are necessary for directing gaze towards objects of interest in the visual world and are fundamentally important during many simple behaviors (e.g. reading). Damage to the central nervous system or errors in the development of the visual pathways can result in deficits in the visual- oculomotor system and an inability to direct gaze accurately. It is known that the generation, direction and control of saccades are mediated by various cortical, thalamic and brainstem structures; however the mechanisms by which saccades are generated and their accuracy maintained are not fully understood. Evidence suggests that the pregeniculate nucleus (PGN) of the thalamus may play a role in saccadic eye movements. The PGN is reciprocally connected to the superior colliculus (SC) and the nucleus of the optic tract (NOT), structures that are known to contribute to visual oculomotor control. Saccade-related activity has been recorded previously in PGN neurons. Therefore the specific aims of this project are to determine the role of the PGN in saccadic behavior and to characterize the relationship of the PGN with other oculomotor structures, such as the SC and NOT. To define the functional connectivity of the PGN with the SC, we will antidromically activate physiologically characterized SC and NOT neurons from the PGN (or, in related experiments, from the adjacent dorsal lateral geniculate nucleus) as well as characterized PGN neurons from the SC. The anatomical connections of the PGN with other brainstem structures will be defined using a variety of anterograde and retrograde tracers in combination with immunocytochemical staining for various neurotransmitters. To determine the role of the PGN in the control of saccades, the effect of electrical stimulation or pharmacological manipulation of the PGN on saccadic eye movements will be assessed. To study further the role of the PGN in saccadic visual-motor behaviors, we will record the activity of single PGN neurons in trained animals, during visual and oculomotor testing, including the generation of saccadic eye movements.
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