Functional MRI of macaque monkeys during task switching

The ability to switch from one task to another is central to intelligent behavior, as it allows an organism to cope efficiently with the demands of swiftly changing environments. Human functional magnetic resonance imaging (fMRI) studies have indicated the importance of prefrontal (PFC) and anterior cingulate cortex (ACC) during task switching (Liston et al., 2006; Woodward et al., 2006; Wylie et al., 2004). In addition, lesion and inactivation studies in monkeys have demonstrated impairments in task switching following both PFC (Dias et al., 1996) and ACC (Rushworth et al., 2003; Shima and Tanji, 1998) lesions. Except for set-shifting (Nakahara et al., 2002) and visual search experiments (Wardak et al., 2010), no task switching paradigms, particularly those requiring shifts in operant behavior, have been used during fMRI in monkeys. In our study, macaque monkeys (N=2) were trained to switch between saccades and arm movements. After a brief period of fixation, a blue or green target appeared. A separate go-cue (brightening of a spot) instructed the monkey to make either a saccade to the green target, or to move the arm ipsilateral to the blue target (Premereur et al., 2015). Furthermore, we used a fixation task in which the monkeys had to fixate centrally while a grey distractor appeared at the same position as the target. We performed a contrast-agent enhanced fMRI experiment (3T, 1.25 mm isotropic voxels, 2s TR). Each run contained all tasks, randomly presented in 40s blocks. Switch trials were defined as the first trial of a block requiring another operant behavior compared to the previous block. Note that only correctly performed switch trials were included. Stay trials were defined as a correct trial (immediately following another correct trial), randomly chosen from the same blocks from which the switch trials were selected. Data were collected in 102 runs for monkey R (903 switch and stay trials, each) and 111 runs for monkey U (632 trials). We compared the activation for Switch vs Stay trials (conjunction analysis for both animals; p