Abstract
INTRODUCTION: The common marmoset has garnered significant interest in recent years as a model system for studying vision in the non-human primate. However, it has been thought that their less driven temperament and lower cognitive capabilities would prevent them from performing cognitive and memory tasks developed in the rhesus macaque, especially tasks requiring delaying responses to salient stimuli. We sought to test whether marmosets could perform classical memory-guided saccades and compare their performance with rhesus macaques performing the same task. METHODS: Marmosets begin by fixating on a central target for 150–300 ms, initiating a cue period. The target to be remembered appears 4.5–5.5 degrees (roughly half their comfortable oculomotor range) from the central target in a random direction for 100–250 ms. The animals maintain fixation for 600–1000 ms until the central target is extinguished. The animal then saccades to the remembered location of the cue. With only small tweaks to standard macaque operant training, marmosets readily learn this task. RESULTS: We demonstrate that marmosets can be trained to perform memory-guided saccades, which allows us to compare their performance quantitatively to a rhesus macaque performing the same task. We show that, within their more limited oculomotor range, marmosets have comparable performance to the macaque. Marmosets are significantly more accurate than chance, with a median saccadic error of 2.25°, compared to 5° expected for random guesses. Macaques, with a larger oculomotor range, exhibit proportionally larger median error, but also a greater difference between shuffled and unshuffled target-saccade distances (indicating higher accuracy). Marmosets exhibited substantial completion rates for the longest delay periods tested (1 sec). Combined with techniques for stitching together electrophysiological data from multiple recording sessions, we demonstrate the feasibility of studying the neural basis of persistent activity in this species, with tight connections to the better-studied rhesus macaque.
Acknowledgement: National Institutes of Health