Spatial navigation–episodic memory task with embedded temporal memory

In the treasure hunt task, the patients sat in bed and performed a hybrid spatial navigation–episodic memory task running on a laptop. The task was adapted from previous studies (9, 25) and implemented using Unity3D (Unity Technologies, San Francisco, CA, USA). The virtual environment was designed to resemble a beach, enclosed by a circular wooden fence with a diameter of 100 virtual units (vu). Navigation was restricted to the area inside the fence. There were no landmarks within the environment itself, but, some landmarks, such as palm trees and barrels, were positioned just outside the fence. One side of the beach bordered the sea, and the background featured mountains, palm trees, and the sky (Fig. 1A-C). Patients completed up to 40 trials per session. At the start of each trial, they were placed at a random location on the virtual beach (“passive home base transport”; Fig. 1A) and remained there until they initiated the trial by pressing a button. They then navigated to a series of treasure chests that appeared one after another on the beach (“navigation–encoding period”; Fig. 1A). Participants were encouraged to reach the chests as quickly as possible to earn bonus points for efficient navigation. Upon reaching a chest, they were automatically rotated to face it, and the chest opened to reveal an object and its name (Fig. 1A-C). After 1500 ms, the chest and object disappeared. Each trial involved visiting 2 or 3 chests, and across 40 trials, patients encountered 100 chests in total. After visiting the final chest in a trial, patients were passively transported to one of two elevated positions where they had an overhead view of the environment (“passive tower transport”; Fig. 1A-C). They then played a distractor game in which they tracked which of three moving boxes contained a coin. After the distractor game, the recall phase of the trial began. During the recall phase, patients either completed location-cued object recall or object-cued location recall on a trial by trial basis. We did not analyze these recall parts in this study. After recalling all locations and objects from a trial, patients completed a temporal order judgment task, where they were asked to decide which of two objects they had encountered later. Thus, the recall phase tested all components of episodic memory: object, location, and temporal information. At the end of the trial, patients received feedback on their performance, including points for correct object, location and temporal order recalls. Patients navigated the virtual environment using a game controller (forward, turn left, turn right), and their virtual positions and heading directions were recorded at 60 Hz. We synchronized the behavioral and electrophysiological data using triggers sent from the task paradigm to the recording system.