ARVO 2000 Abstract (Investigative Ophthalmology & Visual Science, Vol. 41, No. 4, p. S315)

 

 

Neural Network Model of Saccade Generation and Control. Z. M. Hafed, J. J. Clark. Center for Intelligent Machines, McGill University, Montreal, Canada.

Purpose: To study the role of the Superior Colliculus (SC) and other brainstem structures in saccade generation. Methods: A biologically plausible model of the oculomotor system was developed. Consistent with recent evidence, the model places the SC inside a local feedback loop controlling saccades, and it prescribes roles for all three known saccade-related cell types in the SC. Burst neurons (BN) encode initial motor error while buildup neurons (BUN), which show shifts of activity during saccades, estimate dynamic error. BNís and BUNís are thus functionally distinct, unlike in (Quaia et al. 1999). Fixation neurons (FN) control saccade initiation through winner-take-all interactions with BNís. Rather than respond directly when the eye stops moving, as is true for brainstem omnipause neurons (OPN), FNís only fire when a target is foveated, suggesting a link to the error estimate provided by BUNís. An integrative process governs the dynamics of both BUNís and FNís. The model was trained using an iterative algorithm like that in (Arai et al. 1994).

Results: A 1-D version of the model was simulated, and it was shown to generate normal and reduced-latency saccades. The model also simulated interrupted saccades, which occur after artificial stimulation of FNís or OPNís. We also illustrated how FN and OPN responses differ during multiple-step gaze shifts (Bergeron and Guitton 1998).

Conclusions: The proposed model is highly consistent with current knowledge about saccade generation, and it is believed to shed some light on the mechanisms governing saccade-related properties like latency.

References: Arai, K., Keller, E. L. & Edelman, J. A. (1994). Two-dimensional neural network model of the primate saccadic system. Neur. Net., 7 (6/7), 1115-1135.

Bergeron, A. & Guitton, D. (1998). Discharge of superior colliculus fixation neurons and brainstem omnipause neurons during multiple-step gaze shifts in head-free cat (Abstract). Soc. Neurosci. Abs., 24, 418.

Quaia, C., LefŤvre, P., & Optican, L. M. (1999). Model of the control of saccades by superior colliculus and cerebellum. J. Neurophys., 82, 999-1018.

CR: None†††††††† Support: Iris/Precarn, Canada