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Ziad M. Hafed, Richard J. Krauzlis; Activity of superior colliculus neurons during parafoveal pursuit. Journal of Vision 2005;5(8):578. doi: 10.1167/5.8.578.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The rostral superior colliculus (SC), which represents the central visual field, has been shown to be involved in smooth pursuit. However, it is not clear whether pursuit-related activity arises rostrally in the SC because the stimuli used to guide pursuit are typically foveal or because the gaze errors during pursuit are typically small. We investigated caudal and rostral SC buildup neurons in a task that dissociated the goal of pursuit from the visual stimuli driving it.
Methods: One monkey was presented with two moving bars (3º−5.6º high × 0.44º−0.9º wide) placed 13º−25º apart at symmetrically opposite locations in space. The bars were oriented perpendicular to the axis connecting the center of the screen with the bars' centers and translated together along this axis in a sinusoidal fashion (trajectory amplitude and frequency: 4º and 0.7Hz). In tracking trials, the monkey was required to maintain its gaze within 2.5º of the midpoint between the moving bars. In fixation trials, the monkey fixated a stationary spot and ignored the bars. For caudal sites, one bar was placed in the neuron's response field; for rostral ones, the bars were placed as eccentric as possible. For all our sites, visual stimuli guiding pursuit never came closer than 4º to the monkey's gaze.
Results: Neurons in the caudal SC with no visual responses did not respond during parafoveal pursuit. Caudal neurons with visual responses were active, but not necessarily more so than during passive viewing of similarly placed bar stimuli during fixation. In contrast, rostral buildup neurons were modulated during parafoveal pursuit even though bars placed at the same retinotopic locations during fixation caused little or no change in their activity.
Conclusion: Pursuit-related activity in the SC remains rostral even when the visual stimuli are represented by caudal neurons. Thus, pursuit-related activity in the SC appears to reflect the goal of pursuit, not the stimuli guiding it.
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