Monkey dorsolateral prefrontal cortex represents abstract visual sequences during a no-report task

Abstract

Monitoring sequential information is an essential component of our daily lives. Many of these sequences are abstract, in that they do not depend on the individual stimuli, but do depend on an ordered set of rules (e.g., chop then stir when cooking). Despite the ubiquity and utility of abstract sequential monitoring, little is known about its neural mechanisms. Human rostrolateral prefrontal cortex (RLPFC) exhibits specific increases in neural activity (i.e., "ramping") during abstract sequences. Monkey dorsolateral prefrontal cortex (DLPFC) has been shown to represent sequential information in motor (not abstract) sequence tasks, and contains a sub-region, area 46, with homologous functional connectivity to human RLPFC. To test the prediction that area 46 may represent abstract sequence information, and do so with parallel dynamics to those found in humans, we conducted functional magnetic resonance imaging (fMRI) in monkeys. When monkeys performed no-report abstract sequence viewing, we found that right area 46 responded to both abstract sequential rule and number changes. Interestingly, left area 46 exhibited ramping activation similar to that observed in humans that also indicated abstract sequential rule changes. Together, these results indicate that monkey DLPFC monitors abstract visual sequential information, and may do so through unique, hemisphere-specific neural mechanisms. More generally, these results show that abstract sequences are represented in functionally homologous regions across monkeys and humans.