Single-Neuron Representations of Spatial Targets in Humans

The hippocampus and surrounding medial-temporal-lobe (MTL) structures are critical for both memory and spatial navigation (Scoville and Milner, 1957; Morris et al., 1982). Much research has focused on neurons that activate according to an animal’s own spatial properties, such as “place cells” that represent the current location (O’Keefe and Dostrovsky, 1971), or “head-direction cells” that code for the current heading (Taube et al., 1990). In addition to representing the current spatial setting, these same MTL structures are important for other behaviors such as memory, which can involve remote locations among other contextual information (Schiller et al., 2015; Epstein et al., 2017). However, the human cellular representations that underlie our ability to form memories that involve remote locations are unclear. We recorded single-neuron activity from neurosurgical patients playing Treasure Hunt (TH), a virtual-reality object–location memory task. We found that the activity of many MTL neurons was significantly modulated by the position of the to-be-remembered object. In addition, we observed neurons whose firing rates during navigation were explained by the subject’s heading direction, and others that predicted subsequent memory performance. By showing evidence for neurons encoding remote locations that are the targets of memory encoding, our results suggest that the human MTL represents to-be-remembered locations in service of memory formation.