Age-related changes in contextual associative learning

Abstract

The hippocampus plays a critical role in processing contextual information. Although age-related changes in the hippocampus are well documented in humans, nonhuman primates, and rodents, few studies have examined contextual learning deficits in old rats. The present study investigated age-related differences in contextual associative learning in young (6 mo) and old (24 mo) rats using olfactory stimuli. Stimuli consisted of common odors mixed in sand and placed in clear plastic cups. Testing was conducted in two boxes that represented two different contexts (Context 1 and Context 2). The contexts varied based on environmental features of the box such as color (black vs. white), visual cues on the walls of the box, and flooring texture. Each rat was simultaneously presented with two cups, one filled with Odor A and one filled with Odor B in each context. In Context 1, the rat received a food reward for digging in the cup containing Odor A, but did not receive a food reward for digging in the cup containing Odor B. In Context 2, the rat was rewarded for digging in the cup containing Odor B, but did receive a reward for digging in the cup containing Odor A. Therefore, the rat learned to associate Context 1 with Odor A and Context 2 with Odor B. The rat was tested for eight days using the same odor problem throughout all days of testing. The results showed no significant difference between young and old rats on the first two days of testing; however, young rats significantly outperformed old rats on Day 3. Young rats continued to maintain superior performance compared to old rats on Days 4-8. The results suggest that aging results in functional impairments in brain regions that support memory for associations between specific cues and their respective context.

Olfactory Dysfunction in the Elderly: Basic Circuitry and Alterations with Normal Aging and Alzheimer’s Disease

“…Odor discrimination, which involves processing in the OB and higher, is less consistently affected by age (Enwere et al 2004, Prediger et al 2006, Patel and Larson 2009, Kramer and Apfelbach 2004, Luu et al 2008). Odor habituation and dishabituation, which depend on piriform cortex function, were examined in one study of rats, which found intact habituation but impaired dishabituation at 22 months (Guan and Dluzen 1994).…”

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]. …”

“…Therefore, age-related changes in the hippocampus may contribute to the present findings in 25 mo old rats. Furthermore, prior studies have reported age-related impairment on other hippocampal dependent spatial tasks in rodent models of aging [19–23,25,26]. The encoding of contextual information may be critical to the formation of episodic memories due to the need to form associations among stimuli, actions, and places that compose an event [36].…”

Context Processing in Aging: Older Mice Are Impaired in Renewal of Extinguished Fear

“…Occasion setting can also be studied under conditions in which contextual cues indicate the circumstances under which a CS is associated with a rewarding US. One very recent and intriguing report finds that aged rats are unable to utilize context cues as occasion setters in an appetitive olfactory task (Luu, Pirogovsky, & Gilbert, 2008). To date, there are only a very small number of papers in the literature that examine renewal in mice.…”