Ventrolateral prefrontal neuronal activity related to active controlled memory retrieval in nonhuman primates

It is controversial whether monkeys, like human subjects, can recall, upon instruction, specific information about an event in memory. We therefore tested macaque monkeys on a task that was originally developed to study such active controlled memory retrieval in human subjects and we were able to demonstrate that monkeys, like human subjects, can retrieve, upon command, specific components of previously encoded events. Furthermore, following earlier functional neuroimaging work with human subjects showing the mid-ventrolateral prefrontal cortex to be involved in such active controlled retrieval, we recorded single-neuron activity within this region of the monkey brain while the monkeys performed the active retrieval task. Neuronal responses were related to the retrieval and the decision whether the retrieved information was the instructed one. These findings demonstrate, for the first time, an impressive capacity by macaque monkeys for controlled memory retrieval and, in addition, provide neurophysiological evidence about the role of the mid-ventrolateral prefrontal cortex in such controlled retrieval.