Hippocampal neurons code individual episodic memories in humans
Luca D. Kolibius, Frédéric Roux, George Parish, Marije Ter Wal, Mircea van der Plas, Ramesh Chelvarajah, Vijay Sawlani, David T. Rollings, Johannes Lang, Stephanie Gollwitzer, Katrin Walther, R. Hopfengärtner, Gernot Kreiselmeyer, Hajo M. Hamer, Bernhard P. Staresina, Maria Wimber, Howard Bowman, Simon Hanslmayr
Abstract
The hippocampus is an essential hub for episodic memory processing. However, how human hippocampal single neurons code multi-element associations remains unknown. In particular, it is debated whether each hippocampal neuron represents an invariant element within an episode or whether single neurons bind together all the elements of a discrete episodic memory. Here we provide evidence for the latter hypothesis. Using single-neuron recordings from a total of 30 participants, we show that individual neurons, which we term episode-specific neurons, code discrete episodic memories using either a rate code or a temporal firing code. These neurons were observed exclusively in the hippocampus. Importantly, these episode-specific neurons do not reflect the coding of a particular element in the episode (that is, concept or time). Instead, they code for the conjunction of the different elements that make up the episode.