Cognitive decline associated with normal aging in rats: a neuropsychological approach.

Abstract

The effects of aging on cognitive capacities were examined by comparing the performance of young and old rats on tasks characterized as dependent on different brain systems. This neuropsychological approach was employed to determine the extent to which multiple neural systems are compromised in aging and whether deterioration of one system correlates with that of another. The two tasks used in the present study were an odor-guided recognition memory task, for which different aspects of performance have been shown to be dependent on the integrity of the orbital prefrontal and perirhinal-entorhinal cortex, and the Morris water maze, for which performance depends on the medial prefrontal cortex and hippocampus. Rats were trained on the recognition memory task under minimal memory load and then challenged with longer memory delays and higher levels of inter-item interference. Considerable variation was observed in the performance of aged rats on acquisition of the recognition memory task, and unlike young rats, some aged rats could not acquire the task. Nevertheless, those aged rats who did acquire the cDNM task performed as well as young animals when the memory delay was extended and interference was elevated. In addition, consistent with previous findings, the performance of the same aged rats was highly variable in the Morris water maze task.' Furthermore, although correlations between scores on the two tasks for indiyidual aged rats were not reliable, only those aged rats that performed outside the performance range of young rats in the water maze were impaired on acquisition of the recognition memory task. This pattern of findings is consistent with age-related dysfunction in multiple subdivisions of the prefrontal cortex as well as the hippocampus and suggests that these brain regions may deteriorate in the same subgroup of aged rats.

Brain Aging: Changes in the Nature of Information Coding by the Hippocampus

“…Moreover, when the relationships between distal cues were scrambled, place fields of memory-impaired aged rats often followed the local cues rather than a particular distal cue, although the influence of a single distal cue cannot completely be ruled out, because one distal cue always rotated with the local set. These results and earlier findings (Zyzak et al, 1995) indicate that the old animals have no difficulty in detecting and using local olfactory cues. Distal cues are certainly sufficient to solve spatial problems (Morris, 1984;O'Keefe and Speakman, 1987) and would provide information for guiding movements from any location in a large environment, and this would not be true of local cues perceived only in particular parts of the maze.…”

“…Finally, to test whether indifference of aged place cells to local cue scramble could be attributable to impaired olfaction in these rats, four of the aged rats were tested in a simple olfactory discrimination task (Zyzak et al, 1995). Two old memory-intact rats discriminated 95% correctly with undiluted odors, 80% correctly with 1:10 dilutions, and 85% correctly with 1:100 dilutions.…”

Cognitive aging is linked to social role in honey bees (Apis mellifera)

“…Previously, progressive behavioral senescence has been demonstrated in the fly Drosophila melanogaster (for review, see Grotewiel et al, 2005), the nematode Caenorhabditis elegans (Murakami and Murakami, 2005), rats (Zyzak et al, 1995), primates (Price et al, 1991) and humans (Perlmutter et al, 1981). This phenomenon appears to reflect a general pattern of life history in these species, but the progressive nature of their aging makes it difficult to separate effects of chronological aging from those of physiological aging.…”

Individual differences in neurocognitive aging of the medial temporal lobe

“…Such evidence has been garnered in the study population that has been the focus of our work; reliable individual differences in a range of aging-sensitive behavioral measures, e.g., cued reaction time and diurnal behavior, have been dissociated from cognitive decline Burwell et al 1992;Gallagher and Burwell, 1989). Even within the broad scope of cognitive abilities that are affected by aging, dissociations have been shown between functions that depend on different neural systems, e.g., medial temporal lobe and prefrontal cortex (Barense et al 2002;Glisky et al 1995;Schoenbaum et al 2002;Zyzak et al 1995). Such dissociations support the general concept of modeling the effects of aging on the brain in a system-specific manner.…”