Rapid and independent memory formation in the parietal cortex

Abstract

Previous evidence indicates that the brain stores memory in two complementary systems, allowing both rapid plasticity and stable representations at different sites. For memory to be established in a long-lasting neocortical store, many learning repetitions are considered necessary after initial encoding into hippocampal circuits. To elucidate the dynamics of hippocampal and neocortical contributions to the early phases of memory formation, we closely followed changes in human functional brain activity while volunteers navigated through two different, initially unknown virtual environments. In one condition, they were able to encode new information continuously about the spatial layout of the maze. In the control condition, no information could be learned because the layout changed constantly. Our results show that the posterior parietal cortex (PPC) encodes memories for spatial locations rapidly, beginning already with the first visit to a location and steadily increasing activity with each additional encounter. Hippocampal activity and connectivity between the PPC and hippocampus, on the other hand, are strongest during initial encoding, and both decline with additional encounters. Importantly, stronger PPC activity related to higher memory-based performance. Compared with the nonlearnable control condition, PPC activity in the learned environment remained elevated after a 24-h interval, indicating a stable change. Our findings reflect the rapid creation of a memory representation in the PPC, which belongs to a recently proposed parietal memory network. The emerging parietal representation is specific for individual episodes of experience, predicts behavior, and remains stable over offline periods, and must therefore hold a mnemonic function.long-term memory | posterior parietal cortex | precuneus | memory systems consolidation | virtual reality L earning enables adaptive and effective interaction with the environment based on past experience. How this essential capability of the brain to encode, store, and later retrieve new information is implemented on the systems level has been the focus of many studies. However, although there is consistent evidence that specific brain regions are involved in learning and memory, the interactions between these regions and their temporal dynamics remain unclear. For declarative memory, one influential model proposes complementary roles of the hippocampus and neocortex in supporting memory representations (1-3). It assumes that the highly plastic hippocampus serves as a fast learner, transiently storing newly encountered information. Later on, this information is gradually integrated into more stable neocortical networks (4).Many experiments in animals and humans have confirmed decreased hippocampal but increased neocortical contributions to memory retrieval with longer consolidation intervals (5-7). Concerning the time frame during which hippocampal independence of a memory is established, accounts diverge widely. In the case of patients with medial temporal lobe (MTL) dama...

Increased hippocampal excitability and altered learning dynamics mediate cognitive mapping deficits in human aging

“…Previous research indicates that RSC is primarily 25 involved in the processing of landmark permanence, whereas POS may relate landmarks to certain 26 locations and might show a different time-course of its involvement during spatial learning(Auger et 27 al., 2015). In the present study, we found a learning-related activity increase in RSC proper as well as 28 in clusters in the POS, located very closely to previously reported activations(Brodt et al, 2016; 29 Wolbers & Büchel, 2005). Disentangling the respective role of different parts of RSC and POS during 30 spatial navigation in the aging brain would be an important topic for future research.31 Notably, an age-related hyperactivity in the hippocampus has been observed in several 32 studies investigating age-related deficits in pattern separation in humans (Reagh et al, 2018; Yassa 33 et al, 2011), as well as in rodent and non-human primate studies on age-related changes in spatial 34 navigation (Thomé et al, 2016; Wilson et al, 2005).…”

Hard decisions shape the neural coding of preferences

“…In addition, while preference changes were absent at the behavioural level for correct guesses, a significant neural effect for spread of alternatives in this condition could nevertheless be observed in the precuneus. This region has been associated with the rapid formation and retrieval of episodic memory (Brodt et al, 2016), with self-relevant processing (Kircher et al, 2002) and with decisions based on guessing (Bode, Bogler, and Haynes, 2013). The precuneus might therefore be involved in less certain retrieval processes for items, which only lead to smaller, behaviourally sub-threshold choice-induced preference change effects.…”

Cerebellar‐hippocampal processing in passive perception of visuospatial change: An ego‐ and allocentric axis?

“…As already pointed out in Section 1, the medial parietal cortex has recently been found to likely complement the hippocampus in the establishment of memory representations, as it is sensitive to repetitions but suppressed during initial encoding of novel information (Brodt et al, ; Brodt et al, ; Gilmore et al, ; Schott et al, ). We did not find that the activity in the parietal cortex could be explained by the number of repetitions preceding the deviants, suggesting that the activity we see here is not merely a reflection of this reinstatement‐dependent behavior.…”