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Short forms of the "reference-" and "working-memory" Morris water maze for assessing age-related deficits
M D Lindner1, A H Balch, C P VanderMaelen
1Department of Neuropharmacology, Bristol-Myers Squibb Pharmaceutical Research Institute, Wallingford, Connecticut 06492.
Abstract:
Short forms of the reference- and working-memory versions of the Morris water maze, each limited to 10 trials, were examined for their reliability and sensitivity to age-related deficits in 16- and 24-month F-344 rats, relative to 2- to 2.5-month young controls. The reference-memory task used long intertrial intervals of 23 h, but required learning only one target location, while the working-memory task used shorter intertrial intervals of 60 min but required learning many different target locations. The reference-memory task was very reliable, revealed large age-related deficits, and correctly identified almost all aged rats as impaired relative to young controls. The working-memory task was less reliable, revealed smaller deficits than the reference memory task at 24 months, and did not discriminate as well between 2.5- and 24-month rats. Furthermore, in the working-memory task 16- and 24-month rats had longer swim paths than 2- to 2.5-month rats on the first trial of each trial pair, which is suggestive of a deficit in processing spatial information and raises questions about the validity of this test as a specific test of working memory. Although the working-memory procedures may be preferable under certain conditions, perhaps as a measure specific to hippocampal dysfunction, the reference-memory task seems more sensitive to age-related deficits and more accurately identifies older rats as impaired. These results are consistent with previous reports that age-related deficits in acquiring spatial learning tasks are common and that the magnitude of the deficit increases as the length of the retention interval increases.
Insights
The reference-memory Morris water maze is more reliable for detecting age-related spatial learning deficits in rats than the working-memory version. It accurately identifies impaired older rats, unlike the working-memory task.
Area of Science:
- Neuroscience
- Gerontology
- Behavioral Science
Background:
- Aging is associated with cognitive decline, particularly in spatial learning and memory.
- The Morris water maze is a common tool for assessing spatial learning in rodents.
- Shortened versions of cognitive tasks are often used to increase efficiency but may impact reliability and sensitivity.
Purpose of the Study:
- To evaluate the reliability and sensitivity of short-form reference-memory and working-memory Morris water maze tasks.
- To assess age-related spatial learning deficits in aged F-344 rats compared to young controls.
- To determine which task version is more effective in identifying cognitive impairment in aging rats.
Main Methods:
- Utilized 16- and 24-month-old F-344 rats as aged groups and 2- to 2.5-month-old rats as young controls.
- Administered a 10-trial reference-memory task with a 23-hour intertrial interval and a single target location.
- Administered a 10-trial working-memory task with a 60-minute intertrial interval and multiple changing target locations.
Main Results:
- The reference-memory task demonstrated high reliability and identified significant age-related deficits, accurately classifying most aged rats as impaired.
- The working-memory task showed lower reliability and detected smaller deficits in 24-month-old rats, with less discrimination between age groups.
- Aged rats in the working-memory task exhibited longer swim paths on initial trials, suggesting potential spatial processing deficits rather than specific working memory impairment.
Conclusions:
- The reference-memory version of the Morris water maze is more sensitive to age-related spatial learning deficits in rats.
- The working-memory task's validity as a specific measure of working memory in aged rats is questioned due to observed spatial processing issues.
- Longer retention intervals in spatial learning tasks appear to exacerbate age-related performance deficits.