fMRI in alert, behaving monkeys: an adaptation of the human infant familiarization novelty preference procedure

Functional magnetic resonance imaging (fMRI) is increasingly used in non-human primate research. In the present study, we adapt the familiarization-novelty preference (FNP) procedure used in human infant research to examine visual behavior in alert, unanaesthetized rhesus monkeys that were acclimated to the fMRI environment, but did not undergo behavioral training. In keeping with the typical FNP paradigm, we recorded eye movements (looking time and number of fixations) while monkeys viewed a series of four identical pictures (familiarization phase) followed by two different pictures (novelty phase). Number of fixations and looking time both increased during the novelty phase, thereby demonstrating visual discrimination of the new from the old picture. Importantly, discrimination did not occur on catch trials in which six identical pictures were presented. Moreover, brain activation in the amygdala was more strongly associated with the novelty phase than with the familiarization phase. In addition, magnitude of brain activation in the amygdala was correlated with the behavioral effect of visual discrimination. These findings demonstrate the feasibility of using eye movements as an index of visual discrimination in untrained monkeys during fMRI scanning. This methodological approach helps to extend the repertoire of research tools for fMRI in non-human primates