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.
Highlights
That memory is not a unitary process is well accepted and several forms of memory have been described in the literature [1,2,3] and can be traced back to the antiquity [4]
We used two delayed-non-match-to-place WM radial maze tasks designed in our laboratory [28,35,36], and we showed that when the repetitiveness of the task is increased, the content of WM can be kept in memory for days, impairing rats’ performance after several days of training by generating long-term proactive interference (PI)
Post hoc analyses revealed that performance of rats trained in the High interference working memory (HIWM) task was lower on Trial 4 as compared to Low interference working memory (LIWM) trained rats (p = 0.0109)
Summary
That memory is not a unitary process is well accepted and several forms of memory have been described in the literature [1,2,3] and can be traced back to the antiquity [4]. In 1968, Atkinson and Shiffrin described short-term memory as a simple storage system through which information would transit before being eventually transferred into a more durable long-term memory [7]. It is to solve this issue that the term "working memory" was coined by Miller, Galenter and Pribram [8] based on the idea that the mind functions like a computer [4], a prevalent analogy in the 1960’s. These authors defined WM as a quick-access memory used to execute a certain plan of actions, guiding our behavior according to our general knowledge of the world. WM and short-term memory have rarely been considered independent and the two terms have often been used synonymously [9] ( see [10])
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