Human Thought and the Lateral Prefrontal Cortex

Human thought is a remarkable evolutionary achievement and one of our species’ defining abilities. It has been closely linked to the prefrontal cortex (PFC) by converging evidence from a wide range of disciplines, from phylogenetic and ontogenetic development, to patient studies and single-cell recordings, to modern neuroimaging. Here I review work on the links between the lateral PFC and two different forms of thought: goal-directed and spontaneous. A special emphasis is placed on the anterior (rostral or frontopolar) lateral PFC, which supports some of the most complex and uniquely human forms of thought, such as reasoning about multiple relations and introspective cognition, and also becomes recruited during the kind of unconstrained thought processes that occurs during rest. I outline an organizational view of the lateral prefrontal cortex which recognizes different lateral prefrontal subregions as functionally distinct and arranged in a rostrocaudal gradient of complexity in processing and representational abstraction, with higher abstraction in thought corresponding to more anterior lateral PFC regions. Furthermore, it appears that the functions of lateral PFC extend beyond goal-directed thinking, to include more spontaneous, free-flowing mental cognition. Unlike goal-directed thought, however, spontaneously occurring thought appears to draw most heavily upon resources outside the PFC, including lateral and medial temporal lobe regions. The nature of interactions between lateral PFC and the temporal lobe remains an important topic for future research that promises to help elucidate some of the most intriguing aspects of human thought, including its spontaneous generation.