Evidence That the Superior Colliculus Participates in the Feedback Control of Saccadic Eye Movements

• Published in: Journal of neurophysiology 2002-02, Vol.87 (2), p.679-695
• Main Authors: Soetedjo, Robijanto, Kaneko, Chris R. S, Fuchs, Albert F
• Format: Article
• Language: English
• Subjects: Action Potentials - drug effects; Action Potentials - physiology; Animals; Feedback, Physiological - physiology; GABA Agonists - pharmacology; Macaca mulatta; Male; Muscimol - pharmacology; Neural Pathways; Neurons - physiology; Saccades - drug effects; Saccades - physiology; Superior Colliculi - cytology; Superior Colliculi - physiology
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.00886.2000

  1 Department of Bioengineering,   2 Department of Physiology and Biophysics, and   3 Regional Primate Research Center, University of Washington, Seattle, Washington 98195 Soetedjo, Robijanto, Chris R. S. Kaneko, and Albert F. Fuchs. Evidence That the Superior Colliculus Participates in the Feedback Control of Saccadic Eye Movements. J. Neurophysiol. 87: 679-695, 2002. There is general agreement that saccades are guided to their targets by means of a motor error signal, which is produced by a local feedback circuit that calculates the difference between desired saccadic amplitude and an internal copy of actual saccadic amplitude. Although the superior colliculus (SC) is thought to provide the desired saccadic amplitude signal, it is unclear whether the SC resides in the feedback loop. To test this possibility, we injected muscimol into the brain stem region containing omnipause neurons (OPNs) to slow saccades and then determined whether the firing of neurons at different sites in the SC was altered. In 14 experiments, we produced saccadic slowing while simultaneously recording the activity of a single SC neuron. Eleven of the 14   neurons were saccade-related burst neurons (SRBNs), which discharged their most vigorous burst for saccades with an optimal amplitude and direction (optimal vector). The optimal directions for the 11 SRBNs ranged from nearly horizontal to nearly vertical, with optimal amplitudes between 4 and 17°. Although muscimol injections into the OPN region produced little change in the optimal vector, they did increase mean saccade duration by 25 to 192.8% and decrease mean saccade peak velocity by 20.5 to 69.8%. For optimal vector saccades, both the acceleration and deceleration phases increased in duration. However, during 10 of 14 experiments, the duration of deceleration increased as fast as or faster than that of acceleration as saccade duration increased, indicating that most of the increase in duration occurred during the deceleration phase. SRBNs in the SC changed their burst duration and firing rate concomitantly with changes in saccadic duration and velocity, respectively. All SRBNs showed a robust increase in burst duration as saccadic duration increased. Five of 11 SRBNs also exhibited a decrease in burst peak firing rate as saccadic velocity decreased. On average across the neurons, the number of spikes in the burst was constant. There was no consistent change in the discharge of the three SC neurons that did not exhibit burst