Representation of Object-Centered Space by Neurons of the Supplementary Eye Field

The supplementary eye field (SEF) is a region of cortex located on the dorsomedial shoulder of the frontal lobe, considered to be involved in the control of eye movements. SEF neurons show spatially selective activity during visually- and memory-guided saccades. The selectivity exhibited by SEF neurons has been described as being related to an eye- or head-centered reference frame. We have previously shown that SEF neurons exhibit selectivity in an object-centered reference frame: neurons will fire selectively when saccades are directed to one end of a bar or another, irrespective of the absolute location of the bar in space.It is not well known how SEF neurons display selectivity for object-centered locations. In order to better understand the mechanism of this phenomenon, we performed three studies. In the first study, we asked how SEF neurons encode locations in both egocentric and object-centered reference frames. We recorded from single SEF neurons while monkeys performed tasks requiring spatial representation in either eye-centered or object-centered reference frames. Different SEF neurons encoded locations in eye-centered coordinates only, object-centered coordinates only, or in complex combinations of the two.In the second study, we tested whether object-centered selectivity is an innate property of SEF neurons or whether it is acquired through learning. We recorded the activity of SEF neurons before and after training monkeys to perform an object-centered task. Some SEF neurons exhibited object-centered selectivity before training. Following training, this number was increased, as was the intensity of object-centered spatial selectivity.In the third study, we investigated whether the object-centered selectivity seen in SEF neurons during performance of an object-centered task is reduced during performance of a non-object-centered task. We recorded from SEF neurons while monkeys performed either an object-centered task or a color matching task with an object as a target. An equivalent number of neurons showed object-centered selectivity in both tasks, but the strength of selectivity was slightly higher during performance of the object-centered task. We conclude from the results of these studies that neurons in the SEF are critically involved in the dynamic representation of locations using multiple spatial reference frames