Thinking about the future versus the past in personal and non-personal contexts.

The ability to ponder the future is a hallmark of human imagination. Neuroimaging research so far has focused on episodic prospection, or thinking about hypothetical future personal events. What has received no attention is semantic prospection or contemplating hypothetical future world events. Using functional magnetic resonance imaging (fMRI), we show a number of functional dissociations in the brain when comparing future and past thinking across personal and non-personal conceptual domains. In the prefrontal cortex, the processes of information integration and self-referential thinking in the anterior medial prefrontal cortex were differentiated from those pertaining to generative construction along the dorsal medial prefrontal cortex and adjoining regions in the superior frontal gyrus. Dorsal parts of the lateral inferior parietal lobe showed lateralization effects as a function of the divergent or convergent nature of the retrieval process corresponding to whether the accessed information referred to hypothetical or real events. While ventral parts of the bilateral inferior parietal lobe were preferentially engaged during both personal past and personal future thinking, dissociations between the areas involved in personal past versus personal future thinking were found along the medial parietal wall. All in all, these findings provide novel and critical insights into the complex interactions between different processes involved in prospective and retrospective thought as modulated by the type of processed content.