Long-term effects of interference on short-term memory performance in the rat

Abstract

A distinction has always been made between long-term and short-term memory (also now called working memory, WM). The obvious difference between these two kinds of memory concerns the duration of information storage: information is supposedly transiently stored in WM while it is considered durably consolidated into long-term memory. It is well acknowledged that the content of WM is erased and reset after a short time, to prevent irrelevant information from proactively interfering with newly stored information. In the present study, we used typical WM radial maze tasks to question the brief lifespan of spatial WM content in rodents. Groups of rats were submitted to one of two different WM tasks in a radial maze: a WM task involving the repetitive presentation of a same pair of arms expected to induce a high level of proactive interference (PI) (HIWM task), or a task using a different pair in each trial expected to induce a low level of PI (LIWM task). Performance was effectively lower in the HIWM group than in LIWM in the final trial of each training session, indicative of a “within-session/short-term” PI effect. However, we also observed a different “between-session/long-term” PI effect between the two groups: while performance of LIWM trained rats remained stable over days, the performance of HIWM rats dropped after 10 days of training, and this impairment was visible from the very first trial of the day, hence not attributable to within-session PI. We also showed that a 24 hour-gap across training sessions known to allow consolidation processes to unfold, was a necessary and sufficient condition for the long-term PI effect to occur. These findings suggest that in the HIWM task, WM content was not entirely reset between training sessions and that, in specific conditions, WM content can outlast its purpose by being stored more permanently, generating a long-term deleterious effect of PI. The alternative explanation is that WM content could be transferred and stored more permanently in an intermediary form or memory between WM and long-term memory.

Working and Reference Memory Tasks Trigger Opposed Long-Term Synaptic Changes in the Rat Dentate Gyrus

“…Such difference in the level of performance of rats trained in LIWM and HIWM tasks has systematically been observed in previous studies (Fraize et al, 2016(Fraize et al, , 2017Joseph et al, 2015;Missaire et al, 2017) and likely reflects a non-optimal processing/forgetting of interference in rats training in the HIWM task. This inefficient processing of interference is further revealed by a between-session analysis of performance computed by trials instead of days (Fig.…”

“…2C). Such analysis shows that a difference in performance is observed between the two groups after a 24hperiod of rest on the very first trials completed on Day 2 (Missaire et al, 2017). This result suggests that 24h-old information may impact the recall of recent (Day 2) information.…”

“…To palliate this lack of knowledge, we conducted a long-term electrophysiological study in freely-moving rats using an innovative comparative behavioral approach. Rats were trained in a radial maze in either a long-term -also called "reference"memory (RM) task, or one of two WM tasks: a Low Interference (LIWM) or a High Interference WM task (HIWM) involving variable levels of proactive interference that differentially alter their level of performance (Fraize et al, 2016(Fraize et al, , 2017Joseph et al, 2015;Missaire et al, 2017). Having previously shown that the dentate gyrus (DG) of the dorsal hippocampus (Fraize et al, 2017;Joseph et al, 2015) could play a major role in processing these interference, we performed long-term recordings of fEPSPs at the perforant path (PP) to DG synapse during two consecutive days.…”

Astragaloside IV enhances memory and modulates hippocampal synaptic plasticity by decreasing GABAergic inhibition through EGR-1 mediated BDNF/TrkB signaling pathway in mice

“…Memory formation is a complex process. This is partly due to the information is assumed to be transiently stored in working memory (short-term memory) while it is considered to integrate long-term memory permanently [34]. At present, a lot of knowledge about memory comes from the study of memory impairment, especially amnesia.…”

Astragaloside IV suppressed hippocampal GABAergic synaptic transmission and enhanced memory through EGR-1 mediated BDNF/TrkB signaling pathway in mice

“…Memory formation is a complex process. This is partly due to the information is assumed to be transiently stored in short-term memory while it is considered to integrate long-term memory permanently [38]. At present, a lot of knowledge about memory comes from the study of memory impairment, especially amnesia [39][40][41].…”