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Mark H. Histed, Earl K. Miller; Sef microstimulation reorders spatial memories in a convergent manner. Journal of Vision 2005;5(8):102. doi: 10.1167/5.8.102.
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Saccadic eye movements can be elicited by microstimulation of the supplementary eye field (SEF), an area on the dorsomedial surface of the frontal lobe. In contrast to the frontal eye fields (FEF) and the superior colliculus, saccades evoked from the SEF are often convergent: stimulation causes saccades to a single final target, or termination zone, from many initial eye positions. Because recent work suggests that the SEF may also play a role in the control of sequential movements, we explored the effect of microstimulation on monkeys' ability to remember and execute a sequence of two saccades.
While a monkey fixated a central target, two peripheral locations were cued in sequence. After a memory delay, the animal was required to make a saccade to those two locations in the same order as they were cued. Six pairs of targets were used in each experiment. During the delay, we microstimulated the SEF at currents below the threshold for evoking saccades, typically at 50µA. At 23 of 34 sites (68%), this stimulation biased the order in which animals saccaded to the targets — the animals made saccades to the two cued locations, but in the wrong order. Saccade metrics and latencies were not affected.
The direction of bias was systematic: stimulation biased the animals' responses such that the final endpoint of the set of saccades was contraversive. Furthermore, across different pairs of targets, biases were convergent: the final endpoints favored by stimulation lay near one another. This data relates the prior observed roles of the SEF in convergent saccadic movements and sequential movement control.
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