Citation

Ramakrishnan A, Chokhandre S, Murthy A. J. Neurophysiol. 2010; 103(5): 2400-2416.

Affiliation

National Brain Research Centre.

Copyright

(Copyright © 2010, American Physiological Society)

DOI

10.1152/jn.00843.2009

PMID

20164397

Abstract

Although the nature of gaze control regulating single saccades is relatively well documented, how such control is implemented to regulate multi-saccade gaze shifts is not known. We used highly eccentric targets to elicit multi-saccade gaze shifts and tested the ability of subjects to control the saccade sequence by presenting a second target on random trials. Their response allowed us to test the nature of control at many levels - before, during and in-between saccades. While the saccade sequence could be inhibited before it began, we observed clear signs of truncation of the first saccade, which confirmed that it could be inhibited in mid-flight as well. Using a race model that explains the control of single saccades, we estimated that it took ~100 ms to inhibit a planned saccade but took ~150 ms to inhibit a saccade during its execution. Although the time taken to inhibit was different, the high subject-wise correlation suggests a unitary inhibitory control acting at different levels in the oculomotor system. We also frequently observed responses that were comprised of hypometric initial saccades, followed by secondary saccades to the initial target. Given the estimates of the inhibitory process provided by the model that also took into account the variances of the processes as well, the secondary saccades (average latency ~215ms) should have been inhibited. Failure to inhibit the secondary saccade suggests that the intersaccadic interval in a multi-saccade response is a ballistic stage. Collectively these data indicate that the oculomotor system can control a response until a very late stage in its execution. However, if the response consists of multiple movements then the preparation of the second movement becomes refractory to new visual input, either because it is part of a preprogramed sequence or as a consequence of being a corrective response to a motor error.

Language: en