A Snapshot seminar hosted by the School of Physiology, Pharmacology and Neuroscience

Abstract: In this talk I will present two strands of studies where we investigated two prominent mechanisms suggested to underlie human episodic memory. First, Hebbian learning (i.e “fire-together, wire together”) or Spike-Timing-Dependent-Plasticity (STDP), which posits that the firing of neurons in close temporal proximity is crucial for laying down a memory trace. Recording the co-firing of single-neuron in epilepsy patients in the medial-temporal-lobe during a memory task we found results that are consistent with STDP (1). I will also show results from rhythmic stimulation studies demonstrating that the manipulation of temporal patterns in the range of milliseconds modulates episodic memory formation (2). A second idea that has influenced memory research is the “Indexing Theory” (3) which posits that the human hippocampus stores episodic memories via an Index – a conjunctive type of code that points to the different elements that belong to the episode. I will present recent evidence from human single neuron recordings (4) where we found neurons that are consistent with such an indexing function. I will also present unpublished results from an ultra-highfield fMRI at 7T which supports these human single unit findings, and suggest that the Index is predominantly located in the hippocampal subfield CA3. I will close the talk by presenting a recent theoretical framework (5) where we integrate these findings with Concept Cells (so-called Jennifer Anniston cells; (6)) and the Engram Allocation Theory (7). At the end I will speculate how these findings could lead to the development of Neural Memory Prosthesis.