Distinct Neural Circuits for the Formation and Retrieval of Episodic Memories

Abstract

The formation and retrieval of a memory is thought to be accomplished by activation and reactivation, respectively, of the memory-holding cells (engram cells) by a common set of neural circuits, but this hypothesis has not been established. The medial temporal-lobe system is essential for the formation and retrieval of episodic memory for which individual hippocampal subfields and entorhinal cortex layers contribute by carrying out specific functions. One subfield whose function is poorly known is the subiculum. Here, we show that dorsal subiculum and the circuit, CA1 to dorsal subiculum to medial entorhinal cortex layer 5, play a crucial role selectively in the retrieval of episodic memories. Conversely, the direct CA1 to medial entorhinal cortex layer 5 circuit is essential specifically for memory formation. Our data suggest that the subiculum-containing detour loop is dedicated to meet the requirements associated with recall such as rapid memory updating and retrieval-driven instinctive fear responses.

A Hippocampus-Accumbens Tripartite Neuronal Motif Guides Appetitive Memory in Space

“…Furthermore, dCA1 inputs to dSub are dispensable for CPP memory retrieval but contribute to (unconditioned) spatial novelty detection, consistent with a role of dSub in the encoding of new spatial memories (Cembrowski et al., 2018, Morris et al., 1990). Our findings join recent work revealing dissociable information streams in the hippocampal formation (Cembrowski et al., 2018, Roy et al., 2017), which develop upon the canonical view of the hippocampal formation acting as a simple chain of connected circuits processing information in series. Instead, these results support the exciting perspective that the hippocampal formation hosts a complex set of cell-type- and circuit-selective pathways processing multiple, parallel information streams to serve distinct behavioral and mnemonic roles.…”

Separate cortical and hippocampal cell populations target the rat nucleus reuniens and mammillary bodies

“…While these topographies help to separate many efferent pathways, some subiculum efferents have collateral projections to more than one site (Calderazzo; Donovan & Wyss, ; Kinnavane; Swanson, Sawchenko, & Cowan, ). Two relevant examples concern the subicular projections to the mammillary bodies, some of which collateralize to reach the entorhinal cortices (Donovan & Wyss, ; Roy et al., ) or the retrosplenial cortex (Kinnavane et al., ).…”

“…Two relevant examples concern the subicular projections to the mammillary bodies, some of which collateralize to reach the entorhinal cortices (Donovan & Wyss, 1983;Roy et al, 2017) or the retrosplenial cortex (Kinnavane et al, 2018).…”

“…The same thalamic nucleus then provides much of the anterior thalamic nuclei inputs to the prelimbic and infralimbic cortices (Hoover & Vertes, 2007). This connectivity has potential relevance for the recent suggestion that projections from the subiculum to the mammillary bodies play a role in autonomic responses following fear-place conditioning (Roy et al, 2017; see also Krieckhaus, 1964). Both the dorsal peduncular and the infralimbic cortex are highly connected to autonomic areas and have been considered to be viscero-motor areas involved in the control of autonomic function (Frysztak & Neafsey, 1991Heidbreder & Groenewegen, 2003).…”

MIN1PIPE: A Miniscope 1-Photon-Based Calcium Imaging Signal Extraction Pipeline

“…Recent advances in single-photon-based miniscope technology have further enabled imaging of neural ensemble activities in freely moving animals (Cai et al, 2016; Flusberg et al, 2008; Ghosh et al, 2011), thereby allowing circuits involved in a rich repertoire of animal behaviors to be examined. For example, this technology has been successfully used in probing dynamics of neural circuits involved in innate behaviors (Betley et al, 2015; Douglass et al, 2017; Jennings et al, 2015), decision making (Pinto and Dan, 2015; Carvalho Poyraz et al, 2016), motor control (Klaus et al, 2017), learning and memory (Grewe et al, 2017; Kamigaki and Dan, 2017; Kitamura et al, 2017; Roberts et al, 2017; Roy et al, 2017; Xu et al, 2016), social memory (Okuyama et al, 2016), hippocampal place coding (Ziv et al, 2013), sleep (Cox et al, 2016; Weber and Dan, 2016), bird song (Markowitz et al, 2015), and pathological processes (Berdyyeva et al, 2016). …”