| Abstract No.: | B-D2134 |
| Country: | Canada |
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| Title: | THE ROSTRAL SUPERIOR COLLICULUS ENCODES TARGET LOCATION IN RELATION TO AN INDIVIDUAL EYE |
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| Authors/Affiliations: | 1 Marion Van Horn*; 1 Kathleen Cullen;
1 McGill University, Montreal, QC, Canada
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| Content: | Objectives: Recent work in monkeys has revealed that neurons located in the superior colliculus (SC) are involved in encoding the distance between the eye and a target (Bergeron and Guitton 2002). In particular, fixation neurons in the rostral SC (SCFN) are maximally activated once the eye has reached its desired location (Choi and Guitton 2007). The SC receives visual information about target location from numerous cortical structures including areas that have been shown to discharge in association with vergence movements (e.g., FEF). These known anatomical connections, in conjunction with the findings that electrical microstimulation at the rostral pole of the SC can modify the trajectory of combined saccade-vergence movements (Chaturvedi and van Gisbergen 1999) suggests that the SC is involved in controlling eye movements in 3 dimensions. Here, we explore the rostral SC for evidence of signals related to vergence during symmetric vergence and saccade-vergence interactions.
Material and Methods: In the present study we recorded single neurons in the rostral zone of the superior colliculus in one monkey. The anatomical location was verified by low current (40µA) electrical stimulation, which resulted in a complete interruption of saccades for up to 1sec. The monkey, implanted with eye coils in each eye, was trained to fixate targets presented at different eccentricities and depths. In particular, targets were presented in front of one eye in order to generate ‘monocular’ saccades in which the movement of one eye is substantially reduced.
Results: We identified neurons in the rostral pole of the SC that were indistinguishable from the classic fixation neurons when recorded during conjugate saccades. The neurons fired tonically during fixation of a visual target and paused during saccades. Interestingly, the activity of these same neurons changed when the monkey fixated targets located at different depths. In particular, when the monkey performed combined saccade-vergence movements, where one eye was aligned with the target the neuron fired almost exclusively for when one individual eye was on, or very close to target. For example, during monocular saccades when the non-preferred eye was aligned on the target, the neuron remained silent until the “preferred” eye reached the target.
Conclusion: In summary, we have indentified neurons in the rostral pole of the SC tuned to the movements of an individual eye. Overall, these findings strongly suggest that the superior colliculus encodes signals associated with 3-D fixation.
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