The effects of aging on memory for sequentially presented objects in rats.

Abstract

The current study investigated memory for sequentially presented objects in young rats 6 months of age (n=12) and aged rats 24 months of age (n=12). Rats were tested on a task involving three exploratory trials and one probe test. During the exploratory trials, the rat explored a set of three sequentially presented object pairs (A-A, B-B, and C-C) for 5 min per pair with a 3 min delay between each pair. Following the exploratory trials, a probe test was conducted where the rat was presented simultaneously with one object from the first exploratory trial (A) and one object from the third exploratory trial (C). Results from the three exploratory trials showed no significant age-related differences in exploration, indicating that 24 month old rats explored the object pairs as much as 6 month old rats. Results from the probe test demonstrated that 6 month old rats spent significantly more time exploring object A compared to object C, indicating that young rats show intact memory for the temporal order of the exploratory trial objects. In contrast, 24 month old rats showed no preference for object A and spent a relatively equal amount of time exploring objects A and C. The results suggest that temporal order memory may decline as a result of age-related changes in the rodent brain. In addition, the findings may reflect differences in attraction to objects with different memory strengths. Since no significant age-related differences were detected during the exploratory trials, age-related differences on the probe trial were not due solely to decreased exploration, motivation, or locomotion in aged rats.

Age-related changes in detection of spatial novelty

“…For example, aged nonhuman primates and rodents demonstrate parallel impairments to animals with hippocampal damage on a variety of memory tasks, including tasks measuring spatial memory [19–24], temporal order memory [25], contextual memory [26], delayed recognition memory [27–29], odor memory [30], and transitive inference [31]. …”

“…Various visually dissimilar objects 10–15 cm in height were used for the task, for example a toy truck, rubber duck, water bottle, and dog toy. The objects were similar to those used in previously published experiments [3,25]. Objects were mounted on metal washers and held in place on the apparatus using magnets to prevent a rat from displacing the objects.…”

Spontaneous object recognition memory in aged rats: Complexity versus similarity

“…First, there is a great variety of objects used and they are not always well defined. They could be classified as standard objects, such as elemental everyday and junk objects (Aggleton et al 1989;Lukaszewska and Radulska 1994;Liu et al 2004;Hauser et al 2009;Da Silva Costa-Aze et al 2011), solid geometric forms including cubes, pyramids, and cylinders (Willig et al 1987;Scali et al 1994;Bartolini et al 1996;Vannucchi et al 1997;Pitsikas et al 2005), and complex objects built of Lego blocks (de Lima et al 2005;Pieta Dias et al 2007;de Lima et al 2008;Leite et al 2011). Thus, it is difficult to evaluate the degree of dissimilarity and the difficulty level of the discrimination.…”

“…In Experiment 1 we used standard objects that differed in material, shape, size, and color. Aging studies using SOR tasks have applied a great variety of standard objects (Aggleton et al 1989;Lukaszewska and Radulska 1994;Liu et al 2004;Hauser et al 2009), since the use of clearly different elemental stimuli is common (Cavoy and Delacour 1993;Burke et al 2010;Bergado et al 2011). However, they are often poorly described and not easily found all over the world, rendering it difficult to replicate the experiments.…”

Neural Basis of Object Recognition

“…Object discrimination requires the integrity of cortical cholinergic system; in rodents the cortex-hippocampus circuitry consents to distinguish individual objects such as different shapes [Hauser et al, 2009].…”