The prefrontal cortex: from monkey to man

Abstract

Abstract The prefrontal cortex is so important to human beings that, if deprived of it, our behavior is reduced to action-reactions and automatisms, without the ability to make deliberate decisions. Why does the prefrontal cortex hold such importance in humans? To answer this question, this review will draw on the proximity between humans and other primates allowing us, through comparative anatomical-functional analysis, to understand the cognitive functions that we have in common but also to specify those that distinguish humans from their closest cousins. First, the focus will be on the lateral region of the prefrontal cortex to illustrate the existence of a continuum between rhesus monkeys (the most studied primates in neuroscience) and humans for most of the major cognitive functions for which this region of the brain plays a central role. This continuum involves the presence of elementary mental operations in the rhesus monkey (e.g., working memory or response inhibition) constitutive of “macro-functions” such as planning, problem-solving, and even language production. Second, the human prefrontal cortex has developed dramatically compared to that of other primates. This increase seems to concern the most anterior part (the frontopolar cortex). In humans, the development of the most anterior prefrontal cortex is associated with three major and interrelated cognitive changes: i/greater working memory capacities allowing for a greater integration of past experiences and prospective future; ii/a greater capacity to link discontinuous or distant data, whether temporal or semantic; iii/a greater capacity for abstraction allowing humans to classify knowledge in different ways to engage in analogical reasoning or to acquire abstract values that give rise to our beliefs and morals. Together, these new skills enable us, among other things, to develop highly sophisticated social interactions based on language, to dematerialise the world in order to conceive beliefs and moral judgements, and to conceptualise, create and extend our vision of our environment beyond what we can physically grasp. Finally, a model of the transition of the prefrontal functions between human and non-human primates in primates will conclude this review.