INAUGURAL ARTICLE by a Recently Elected Academy Member:The hippocampal formation and action at a distance

The question of why our conceptions of space and time are intertwined with memory in the hippocampal formation is at the forefront of much current theorizing about this brain system. In this article I argue that animals bridge spatial and temporal gaps through the creation of internal models that allow them to act on the basis of things that exist in a distant place and/or existed at a different time. The hippocampal formation plays a critical role in these processes by stitching together spatiotemporally disparate entities and events. It does this by 1) constructing cognitive maps that represent extended spatial contexts, incorporating and linking aspects of an environment that may never have been experienced together; 2) creating neural trajectories that link the parts of an event, whether they occur in close temporal proximity or not, enabling the construction of event representations even when elements of that event were experienced at quite different times; and 3) using these maps and trajectories to simulate possible futures. As a function of these hippocampally driven processes, our subjective sense of both space and time are interwoven constructions of the mind, much as the philosopher Immanuel Kant postulated.

Action at a distance in physics involves the nonlocal interaction of objects separated in space and/or time. It has a long and checkered history and is frequently discussed in terms of quantum entanglement, which Einstein famously called “spooky.” Philosophers talk about action at a distance whenever there is a spatial or temporal gap (or both) between a cause and its effect. Controversy arises with regard to the notion of unmediated action at a distance, involving a gap between cause and effect with no obvious intermediaries filling the gap. There is little argument with examples of mediated action at a distance, where spatially and temporally continuous events stretch across time and space to fill an apparent gap.Mediated action at a distance is central to much of what psychologists care about, given that behavior is frequently motivated by things that are at a spatial and/or temporal remove from the here and now. I will argue that mediating action at a distance is so important that a brain system, centered on the hippocampal formation, is largely devoted to carrying it out. Staresina and Davachi (1) pointed to a role for this brain region in “minding” the small spatial and temporal gaps they manipulated in their stimulus displays. Expanding on this idea, I will assert that animals, including humans, bridge large spatial and temporal gaps through the creation of internal models that allow them to act on the basis of things that exist in a distant place, and/or existed at a different time. But not only to act: Humans often think about, and plan for, the future. The hippocampal formation also plays a role in imagining places and times in the future (2). Memory, in this view, serves to bridge these extensive spatiotemporal gaps, providing the mechanistic basis for action at an apparent distance. In brief, the hippocampal formation accomplishes the goal of stitching together spatiotemporally disparate entities and events by 1) constructing cognitive maps that represent extended spatial contexts, incorporating and linking aspects of an environment that may never have been experienced together; 2) creating neural trajectories that link the parts of an event, whether they occur in close temporal proximity or not, enabling the construction of event representations even when elements of that event were experienced at quite different times; and 3) using these maps and trajectories to simulate possible futures. As a function of these hippocampally driven processes, our subjective sense of both space and time are interwoven constructions of the mind, much as the philosopher Kant postulated.The question of why our conceptions of space and time are intertwined with memory in the hippocampal formation is at the forefront of much current theorizing about this brain system (e.g., refs. 3 –7). I will suggest that what distinguishes its involvement from that of most other brain systems engaged with space, time and memory is its role in mediating action at a distance. Without a hippocampal formation, I will argue, organisms are largely incapable of escaping the here and now—a state of being captured quite well in the title of Suzanne Corkin’s book (8) about the famous amnesic patient H.M.: “Permanent Present Tense.” This assertion leads to a number of implications, which I consider, albeit briefly, in the conclusion.