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Activity in the Primate Rostral Superior Colliculus during the “Gap Effect” for Pursuit and Saccades
Author(s) -
KRAUZLIS RICHARD J.,
DILL NATALIE,
KORNYLO KRISTA
Publication year - 2002
Publication title -
annals of the new york academy of sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.712
H-Index - 248
eISSN - 1749-6632
pISSN - 0077-8923
DOI - 10.1111/j.1749-6632.2002.tb02842.x
Subject(s) - neuroscience , psychology
The latencies of both pursuit and saccadic eye movements are reduced when a fixat- ed visual target is extinguished several hundred milliseconds before a new target ap- pears.1-6 One possible neural substrate for this "gap effect" is the rostral superior colliculus (SC), which has recently been shown to participate in pursuit eye move- ments, in addition to its established role in the control of saccades. The discharge rate of buildup neurons in the rostral SC (rSC) is related to the retinal position of tar- gets during pursuit, as well as during the preparation and execution of saccades.7,8 In addition, microstimulation of the rSC disrupts the initiation of both types of eye movements.9 To test whether these rostral buildup neurons could underlie the "gap effect," we have now studied their activity with this paradigm during both pursuit and saccades. Monkeys tracked a target stimulus that appeared either immediately after the off- set of the fixation spot (no-gap trials) or 200 msec after the offset of the fixation spot (gap trials). On saccade trials, the target stimulus was stationary and was presented at an eccentricity of 3.5o along the horizontal meridian. On pursuit trials, the target stimulus appeared at an eccentricity of 2o and moved toward the center of the dis- play at 15o/sec. We adjusted the starting position of the stimulus to produce saccade- free pursuit and chose neurons with appropriate response fields. We identified the neurons in our sample (n = 72) as rostral buildup neurons on the basis of criteria de- scribed previously.7 The activity of most rostral buildup neurons showed a "gap effect" for both pur- suit and saccades. For example, on no-gap trials, the firing rate of the neuron illus- trated in FIGURE 1 remained nearly constant at 25 spikes/sec until 50-100 msec after target onset, at which point the firing rate increased to more than 100 spikes/sec. However, on gap trials, the firing rate of this neuron increased after the offset of the fixation spot, reaching a firing rate of 40-50 spikes/sec. These changes in activity