Abstract:
Neuroimaging and neuropsychological research has established that our capacity to imagine future events is dependent on our capacity to remember the past. Both tasks engage a common core network of brain regions including the medial prefrontal, medial parietal, and medial temporal cortices, which suggests that they share similar underlying neural and cognitive processes. The hippocampus, a medial temporal lobe structure known to be critical for episodic memory, has a controversial role in imagining the future. The hippocampus might serve to encode and store imagined future events in memory, just as it does for real-life events. However, the encoding and retention of imagined future events has yet to be systematically investigated. The studies in this thesis use both fMRI and novel behavioural methods to provide insight into how imagined future events are encoded. Study 1 reveals that the hippocampus contributes to the encoding of imagined events, as both its anterior and posterior extents are more active while participants are imagining events that they will later remember than while imagining events that they will later forget. Study 2 clarifies that the interaction of the hippocampus with a wider whole-brain network is important for the imagination of future events, and that this connectivity is modulated by encoding success. Study 3 demonstrates that recall rates are higher for imagined events rated by participants as being more detailed and more plausible, and for those rated as involving more familiar people and places. Finally, as subjective participant ratings are widely used in studies of episodic future thinking, including Studies 1 and 3, the validity of participant ratings for their imagined future events was explored in Study 4. Specifically, the study shows that subjective participant ratings predict objective measures of the episodic content of participants' imagined future events, as quantified in an adapted version of the Autobiographical Interview. Broadly, these findings expand our knowledge of the role of the hippocampus in the encoding of episodic representations, including future simulations. They also highlight the contributions of the episodic system to our ability to make, encode and execute plans for the future.