2026 Theses Doctoral

Switching between internal and external attention

Poskanzer, Craig

As we navigate our daily lives, we direct our attention both internally to our memories and thoughts, and externally to encode the stimuli around us into lasting memory traces. Adaptive behavior may rely on either external or internal attention independently, or on both processes concurrently, as in complex behaviors like driving a car or studying for an exam. While complementary, external and internal attention depend on distinct and opposing brain states.

The question at the heart of this dissertation is: how do we balance the need to direct our attention externally and internally, both in the brain and in behavior? I focus primarily on memory encoding as an index of external attention, and memory retrieval as a type of internal attention. Across three Chapters, I ask how encoding and retrieval are balanced using a combination of behavioral studies, computational modeling, and functional neuroimaging (fMRI).

Chapter 1 presents a series of novel behavioral experiments demonstrating that, despite relying on opposing states, successful retrieval can facilitate successful encoding. Chapter 2 leverages a biologically plausible computational model of the hippocampus (C-HORSE) to explain divergent patterns of behavior by varying the dynamics of hippocampal attention states. Finally, Chapter 3 uses neuroimaging data to show how the hippocampus supports distinct attentional demands for internally and externally oriented processing by dynamically switching its functional interactions with the dorsal attention network and cholinergic basal forebrain. Across these three chapters, I highlight how dynamic interactions between internal and external states govern behavior and how the hippocampus plays a central role in balancing our ability to encode and retrieve memories.