Hippocampal theta sequences reflect current goals

Abstract

Hippocampal information processing is discretized by oscillations, and the ensemble activity of place cells is organized into temporal sequences bounded by theta cycles. Theta sequences represent time-compressed trajectories through space. Their forward-directed nature makes them an intuitive candidate mechanism for planning future trajectories, but their connection to goal-directed behavior remains unclear. As rats performed a value-guided decision-making task, the extent to which theta sequences projected ahead of the animal’s current location varied on a moment-by-moment basis depending on the rat’s goals. Look-ahead extended farther on journeys to distant goals than on journeys to more proximal goals and was predictive of the animal’s destination. On arrival at goals, however, look-ahead was similar regardless of where the animal began its journey from. Together, these results provide evidence that hippocampal theta sequences contain information related to goals or intentions, pointing toward a potential spatial basis for planning.

Hippocampal Mechanisms for the Segmentation of Space by Goals and Boundaries

“…2). Thus, in addition to the goal being represented at late theta phases (Wikenheiser and Redish 2015), our findings show that the start location is represented at early phases. Combining these observations, the phase code is defined by the current location in the context of a past bounded by a journey's beginning and a future bounded by the journey's end.…”

“…To dissociate these two possibilities, rats were trained to traverse around a circular track, collecting rewards by waiting a variable amount of time at each of three locations (Wikenheiser and Redish 2015). Rats had a choice to stay and wait for a reward or run to the next location, which was the optimal strategy if the wait time for reward at the more distant site was shorter (Wikenheiser et al 2013).…”

“…As an extension to existing theories, we propose that the clustering of cells within theta periods defines event segmentation (Gupta et al 2012;Wikenheiser and Redish 2015). In building this argument, we first discuss the influence that goals and landmarks have on the hippocampal representation of space.…”

Characterization of exploratory activity and learning ability of healthy and “schizophrenia-like” rats in a square corridor system (AMBITUS)

“…Searching for food is also a naturally motivated behavior; thus, rodents are able to learn to retrieve food rewards located in different setups (Post et al, 2011;Vorhees & Williams, 2014). Some researchers have used a circular corridor with a few (3) side boxes (only in the outer side) with food rewards to investigate the learning capability of rodents (Wikenheiser et al, 2013;Wikenheiser & Redish, 2015;Wikenheiser & Redish, 2011). The AMBITUS system is a combination of the hole-board and the corridor tests; since similarly to the hole-board, it offers the animals the opportunity of exploring a new environment and finding several food rewards, but no open field is available.…”

“…It is well-known that in contrast to a hole-board with an open field, where the rats can show significant anxiety, rats prefer the narrow tunnels (Kimchi & Terkel, 2004). Based on this assumption, some laboratories have applied a circular corridor with or without a few side-boxes containing food rewards to evaluate the exploratory activity and/or learning abilities with a video-tracking system (Nadal, Rotllaant, Marquez, & Armario, 2005;Wikenheiser, Stephens, & Redish, 2013;Wikenheiser & Redish, 2015;Wikenheiser & Redish, 2011;Monaco, Rao, Roth, & Knierim, 2014;Newman, Climer, & Hasselmo, 2014). Unfortunately, both methods may require time-consuming data collection and/or they need long training sessions, or the commercial video-tracking systems (e.g., EthoVision XT) require special softwares which can analyze precisely the behavior of the animals.…”