The Object Space Task shows cumulative memory expression in both mice and rats

Abstract

An important aspect of a memory is whether it is representing a specific event or whether it is a representation of knowledge extracted over multiple episodes. To investigate this difference, we developed a new multi-trial behavioral task that can assess memory accumulation in rodents. It makes use of rodents' innate drive to explore novelty and allows for later recordings (e.g. electrophysiology) and interventions. The task consists of three distinct conditions (stable, overlapping, random) that can be repeated within animals. Rodents are exposed to multiple sample trials, in which they explore objects in specific spatial arrangements. In the stable condition, the locations are constant during all sample trials, and one object's location changes during test. In the random condition, object locations are presented without a specific spatial pattern. In the overlapping condition, one location is shared (overlapping) between all trials while the other location changes during sample trials. We show that in the overlapping condition, instead of only remembering the last sample trial, rodents form a cumulative memory of the sample trials. We adapted the task so that it can be learned by both rats and mice, making it suitable for investigating this aspect of memory across species and using a wide array of methods to measure and perturb the neural basis of memory.

Hippocampal subfield‐specific Homer1a expression is triggered by learning‐facilitated long‐term potentiation and long‐term depression at medial perforant path synapses

“…Fear‐association memory can be triggered rapidly and results in profoundly robust memory encoding (Cole et al, 1989; Daumas et al, 2005; Quirk, 2002; Worley et al, 1993) that is accompanied by extensive and potent IEG in the hippocampus (Cole et al, 1990; Garner et al, 2012; Guzowski et al, 1999; Hall et al, 2000; Morgan et al, 1987). By contrast, detailed spatial memory is acquired in a cumulative manner (Genzel et al, 2019) and is accompanied by subtle or moderate IEG expression (Méndez‐Couz et al, 2019). In the past, we have proposed that LTD may serve to modify a neuronal network that has been initially selected by means of LTP (Hagena & Manahan‐Vaughan, 2011; Kemp & Manahan‐Vaughan, 2007; Manahan‐Vaughan, 2018b).…”

Naïve to expert: Considering the role of previous knowledge in memory

“…Another way of evaluating cumulative experience is shown in the object space task (Genzel et al, 2019), where rodents are exposed to a pattern of four possible object locations in an open field throughout the week, with one location that is stable across days, while the others are shifted between the three other possibilities. Based on the natural tendency of rodents to explore novelty in the presence of familiarity, exploration time of the object placed on the stable location should decrease over time.…”

“…Across 20 trials in 1 week, a semantic-like memory is expressed with an extracted pattern of locations, which then guides their behaviour towards exploring the object that was not in the stable location. However, 1 week is not long enough to suppose schema formation or semantic memories per se, thus this task should rather be seen as simple, previous knowledge-based task (Genzel et al, 2019).…”