This Research Topic is part of the Memory Processes in Medial Temporal Lobe series:

Memory Processes in Medial Temporal Lobe: Experimental, Theoretical and Computational Approaches

The medial temporal lobe (MTL) includes the hippocampus, amygdala and parahippocampal regions, and is crucial for episodic and spatial memory. MTL memory function consists of distinct processes such as encoding, consolidation and retrieval. Encoding is the process by which perceived information is transformed into a memory trace. After encoding, memory traces are stabilized by consolidation. Memory retrieval (recall) refers to the process by which memory traces are reactivated to access information previously encoded and stored in the brain. Although underlying neural mechanisms supporting these distinct functional stages remain largely unknown, recent studies have indicated that distinct oscillatory dynamics, specific neuron types, synaptic plasticity and neuromodulation, play a central role. The theta rhythm is believed to be crucial in the encoding and retrieval of memories. Experimental and computational studies indicate that precise timing of principal cell firing in the hippocampus, relative to the theta rhythm, underlies encoding and retrieval processes. On the other hand, sharp-wave ripples have been implicated in the consolidation through the “replay” of memories in compressed time scales.

The neural circuits and cell types supporting memory processes in the MTL areas have only recently been delineated using experimental approaches such as optogenetics, juxtacellular recordings and optical imaging. Principal (excitatory) cells are crucial for encoding, storing and retrieving memories at the cellular level, whereas inhibitory interneurons provide the temporal structures for orchestrating the activities of neuronal populations of principal cells by regulating synaptic integration and timing of action potential generation of principal cells as well as the generation and maintenance of network oscillations (rhythms). In addition, neuromodulators such as acetylcholine alter dynamical properties of neurons and synapses, and modulate oscillatory state and rules of synaptic plasticity and their levels might tune MTL to specific memory processes.

The goal of the research topic is to offer a snapshot of the current stateof-the-art on how memories are encoded, consolidated, stored and retrieved in MTL structures. Particularly welcome will be studies (experimental or computational) focusing on the structure and function of neural circuits, their cellular components (principal cell and inhibitory interneurons), synaptic plasticity rules involved in these memory processes, network oscillations such as theta and sharp-wave ripples, and role of neuromodulators.

Key research questions are:

(1) Which areas or pathways within the MTL support encoding/consolidation/retrieval?

(2) What neural activity defines specific memory processes?

(3) What are the roles of neuromodulators in defining/switching these memory processes?

(4) Could the role of synaptic plasticity be different in different memory processes?

(5) What functional roles do the various inhibitory interneurons support during the encoding/consolidation/retrieval processes?

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