Coordinated activities of retrosplenial ensembles during resting-state encode spatial landmarks

Abstract

The brain likely uses offline periods to consolidate recent memories. One hypothesis holds that the hippocampal output provides a unique, global linking or ‘index’ code for each memory, and that this code is stored in the cortex in association with locally encoded attributes of each memory. Activation of the index code is hypothesized to evoke coordinated memory trace reactivation thus facilitating consolidation. Retrosplenial cortex (RSC) is a major recipient of hippocampal outflow and we have described populations of neurons there with sparse and orthogonal coding characteristics that resemble hippocampal ‘place’ cells, and whose expression depends on an intact hippocampus. Using two-photon Ca 2+ imaging, we recorded ensembles of neurons in the RSC during periods of immobility before and after active running on a familiar linear treadmill track. Synchronous bursting of distinct groups of neurons occurred during rest both prior to and after running. In the second rest epoch, these patterns were associated with the locations of tactile landmarks and reward. Complementing established views on the functions of the RSC, our findings indicate that the structure is involved with processing landmark information during rest. This article is part of the Theo Murphy meeting issue ‘Memory reactivation: replaying events past, present and future’.

Memories replayed: reactivating past successes and new dilemmas

“…(d) Finally, dimensionality reduction techniques such as principle component analysis (PCA) can also be used to identify cell groups and then be used to track the cell group activity across time (for example, see [26,27]). For examples of unsupervised-learning machine learning techniques that are used for memory reactivation analysis please see [17] issue [18,20,21,36,[45][46][47][48][49]). Yet at present, the information being processed during reactivation can at best be deduced based upon the subsequent offline changes in a memory.…”

“…issue [18,20,21,36,[45][46][47][48][49]). Yet at present, the information being processed during reactivation can at best be deduced based upon the subsequent offline changes in a memory.…”

Thalamus and claustrum control parallel layer 1 circuits in retrosplenial cortex

“…Activity in the granular retrosplenial cortex (RSG) is correlated with a wide variety of behaviors, including spatial navigation, learning, memory, fear conditioning, imagination, and planning for the future ( Alexander et al, 2020 ; Alexander and Nitz, 2017 ; Chang et al, 2020 ; Chrastil, 2018 ; Hinman et al, 2018 ; Mao et al, 2018 ; Miller et al, 2021 ; Miller et al, 2019 ). The RSG is also among the most densely connected regions of the brain, integrating inputs from a bevy of cortical and subcortical sources and serving as part of the default mode network ( Greicius et al, 2009 ; Kaboodvand et al, 2018 ; Liu et al, 2019 ; Whitesell et al, 2021 ).…”

Thalamus and claustrum control parallel layer 1 circuits in retrosplenial cortex

“…Activity in the granular retrosplenial cortex (RSG) is correlated with a wide variety of behaviors, including spatial navigation, learning, memory, fear conditioning, imagination, and planning for the future (Alexander et al, 2020; Alexander and Nitz, 2017; Chang et al, 2020; Chrastil, 2018; Hinman et al, 2018; Mao et al, 2018; Miller et al, 2020, 2019). The RSG is also among the most densely connected regions of the brain, integrating inputs from a bevy of cortical and subcortical sources and serving as part of the default mode network (Greicius et al, 2009; Kaboodvand et al, 2018; Liu et al, 2019; Whitesell et al, 2021).…”