From Correlation to Causation: Understanding Episodic Memory Networks

Episodic memory refers to our ability to recall specific past events and experiences, a process supported by the intricate interplay between multiple distant brain regions, including structures in the medial temporal lobe (MTL) -particularly the hippocampus- and areas of the frontal and parietal cortices. Understanding how these brain regions work together to encode, consolidate, and retrieve episodic memories is one of the foremost questions in cognitive neuroscience. Traditional approaches for investigating episodic memory, such as lesion studies and neuroimaging, have been advanced by the introduction of non-invasive brain stimulation (NIBS) methods, especially transcranial magnetic stimulation (TMS). By applying magnetic fields to precise areas of the brain, TMS provides a causally oriented approach to understand different aspects of episodic memory. This review begins by delineating the evolving understanding of episodic memory from both psychological and neurobiological perspectives and discusses the brain networks supporting episodic memory processes. Then, we review studies that employed TMS to modulate episodic memory, with the aim of identifying potential cortical regions that could be used as stimulation sites to modulate episodic memory networks. We finally discuss implications of stimulation studies on advancing the understanding of the neural mechanisms of episodic memories, as well as the future directions of using non-invasive brain stimulation for the modulation of episodic memory.