Single-neuron representations of spatial targets in humans

Abstract

The hippocampus and surrounding medial-temporal-lobe (MTL) structures are critical for both memory and spatial navigation, but we do not fully understand the neuronal representations used to support these behaviors. Much research has examined how the MTL neurally represents spatial information, such as with "place cells" that represent the current location or "head-direction cells" that code for the current heading. In addition to behaviors that require an animal to attend to the current spatial location, navigating to remote destinations is a common part of daily life. To examine the neural basis of these behaviors we recorded single-neuron activity from neurosurgical patients playing Treasure Hunt, a virtual-reality spatial-memory task. By analyzing how the activity of these neurons related to behavior in Treasure Hunt, we found that the firing rates of many MTL neurons during navigation significantly changed depending on the position of the current spatial target. In addition, we observed neurons whose firing rates during navigation were tuned to specific heading directions in the environment, and others whose activity changed depending on the timing within the trial. By showing that neurons in our task represent remote locations rather than the subject's own position, our results suggest that the human MTL can represent remote spatial information according to task demands.

Predictive Representations in Hippocampal and Prefrontal Hierarchies

“…They can also test the dynamics of goal and subgoal representation more closely. This analysis would complement previous electrophysiology and neuroimaging work showing goal representation in the hippocampus (Brown et al, 2016;Howard et al, 2014;Sarel et al, 2017;Tsitsiklis et al, 2019) . Future studies with larger graphs-with multiple paths leading from one location to others-will be better suited to investigate the specifics of similarity to goal findings in hippocampal-prefrontal hierarchies.…”

Context Reinstatement

“…Broadly, there are two categories of spatial information to which our memory systems are sensitive. First, within a single visual scene (e.g., a photograph or our visual perspective from a single viewpoint), we leverage the relative positions and spatial relations between different scene elements in remembering what we see and in integrating across memories of different scenes (Robin and Olsen, 2019;Tsitsiklis et al, 2019). Second, within our broader environment, our own spatial location at the time we experience a stimulus or event becomes part of that memory's context and affects how we organize and relate our corresponding memories of those stimuli or events (Miller et al, 2013a), and of the spatial layout of the environment (Manning et al, 2014).…”

OpenMaze: An Open-Source Toolbox for Creating Virtual Navigation Experiments

“…Game development engines offer the greatest flexibility in terms of both stimulus creation (e.g., environment and objects) and task design. Two of the most popular options among researchers are Unity software (Unity Technologies; example experiments: Nadasdy et al, 2017;Starrett et al, 2019;Tsitsiklis et al, 2019) and Unreal software (Epic Games, Inc; example experiments: Deuker et al, 2014;Steemers et al, 2016;West et al, 2017). Both engines provide built-in, dragand-drop/point-and-click graphical user interfaces (GUIs) for creating highly customizable environments and stimuli.…”

“…Even more appealing, many of these engines are free to access. Indeed, game engines have been successfully used to build custom VE experiment tasks (examples include: Deuker et al, 2016;Starrett et al, 2019;Tsitsiklis et al, 2019).…”