Journal of Neurophysiology, Vol 52, Issue 4 743-761, Copyright © 1984 by APS

ARTICLES

Neural control of vergence eye movements: activity of abducens and oculomotor neurons

L. E. Mays and J. D. Porter

Single-unit recordings were made from neurons with horizontal eye position sensitivity in the oculomotor and abducens nuclei in alert monkeys. The animals were trained to perform a visual tracking task that resulted in conjugate eye movements or symmetrical vergence movements. Scatterplots were obtained for unit firing rate as a function of the position of the ipsilateral eye for both types of movement. The slopes of the linear regression line were computed for conjugate (kc) and vergence movements (kv). Previous recording studies implied that kv should be equal to kc for most, if not all, abducens and oculomotor neurons. Other lines of evidence suggested that kv should be zero for a substantial proportion of abducens neurons. In the abducens nucleus, we found some cells for which kv matched kc, and a few cells with a kv value of zero. However, the majority of abducens units had vergence signals that were neither equal to zero nor to their conjugate signals. Overall, kv/kc was 0.62, and the correlation between kv and kc was not significantly different from zero. Similarly, in the oculomotor nucleus, kv was significantly different from kc for a majority of the cells. A few units had kv values less than or equal to zero, whereas other cells had very high kv values. Overall, the kv/kc for oculomotor units was nearly unity (0.94), and the correlation between kv and kc was 0.31. These results confirm previous reports that most neurons in the abducens and oculomotor nuclei with a horizontal eye position sensitivity carry both conjugate and vergence eye movement signals. We do not find that the relative magnitudes of these signals are closely matched for most neurons. It is more likely that vergence and conjugate signals are matched globally, for an entire nucleus, rather than for individual motoneurons. This view is consistent with the hypothesis that conjugate and vergence signals are generated independently and combined for the first time at the motoneurons. Our results also imply that some motoneurons play a more important role than others in either vergence or conjugate movements.

This article has been cited by other articles:

				M. R. Van Horn, P. A. Sylvestre, and K. E. Cullen The Brain Stem Saccadic Burst Generator Encodes Gaze in Three-Dimensional Space J Neurophysiol, May 1, 2008; 99(5): 2602 - 2616. [Abstract] [Full Text] [PDF]

				M. Wei, G. C. DeAngelis, and D. E. Angelaki Do Visual Cues Contribute to the Neural Estimate of Viewing Distance Used by the Oculomotor System? J. Neurosci., September 10, 2003; 23(23): 8340 - 8350. [Abstract] [Full Text] [PDF]

				P. A. Sylvestre, J. T. L. Choi, and K. E. Cullen Discharge Dynamics of Oculomotor Neural Integrator Neurons During Conjugate and Disjunctive Saccades and Fixation J Neurophysiol, August 1, 2003; 90(2): 739 - 754. [Abstract] [Full Text] [PDF]

				J. L. Demer, R. Kono, and W. Wright Magnetic Resonance Imaging of Human Extraocular Muscles in Convergence J Neurophysiol, April 1, 2003; 89(4): 2072 - 2085. [Abstract] [Full Text] [PDF]

				P. A. Sylvestre and K. E. Cullen Dynamics of Abducens Nucleus Neuron Discharges During Disjunctive Saccades J Neurophysiol, December 1, 2002; 88(6): 3452 - 3468. [Abstract] [Full Text] [PDF]

				J. M. Miller, C. J. Bockisch, and D. S. Pavlovski Missing Lateral Rectus Force and Absence of Medial Rectus Co-Contraction in Ocular Convergence J Neurophysiol, May 1, 2002; 87(5): 2421 - 2433. [Abstract] [Full Text] [PDF]

				P. Dean, J. Porrill, and P. A. Warren Optimality of Position Commands to Horizontal Eye Muscles: A Test of the Minimum-Norm Rule J Neurophysiol, February 1, 1999; 81(2): 735 - 757. [Abstract] [Full Text] [PDF]

				P. Dean Simulated Recruitment of Medial Rectus Motoneurons by Abducens Internuclear Neurons: Synaptic Specificity vs. Intrinsic Motoneuron Properties J Neurophysiol, September 1, 1997; 78(3): 1531 - 1549. [Abstract] [Full Text] [PDF]