Amelioration of an age-related deficit in exploratory behavior by preexposure to the test environment

The effects of age on response time, accuracy, and shoulder/arm kinematics during hammering

The aim of this study was to investigate the effects of age on response time and accuracy during a hammering task. Older male workers aged 51-69 years (older group: OG, n = 23) and younger male reference individuals aged 25-36 years (younger group: YG, n = 16) performed the experiment. Response time, accuracy, and 3D shoulder/arm kinematics were acquired using motion capture. The effects of age were investigated using linear mixed model analysis. Response times were significantly longer for OG compared with YG (P < 0.001) while no marked differences in the accuracy was observed (P = 0.729). OG showed less hammer displacement and smaller range of motion in the shoulder. Although older workers seemed to use a less biomechanical demanding motor strategy, their response times during hammering were about twice that of younger individuals.

Reaction to New Objects and Spatial Changes in Young and Aged Grey Mouse Lemurs (Microcebus murinus)

The exploratory behaviour of young and grey mouse lemurs (Microceb11s murinus) in an experimental enclosure containing various objects was recorded. A new object was added for each test session and could displace an object that had previously been introduced to a new position. For young grey mouse lemurs, there was an obvious preference for new objects and for displaced familiar objects. This indicates that they are able, like other primates, to “map out” and memorize their environment. For the aged grey mouse lemurs, preference for the new objects was very slight. No react ion to changes in the location of familiar objects was noted. Age- related deficits in memory, in particular spatial memory, could account for this lack of response to changes in the environment.

Effect of age and level of cognitive function on spontaneous and exploratory behaviors in the beagle dog

Cognitively characterized young and aged beagle dogs were administered six different spontaneous behavior tests, which provided measures of locomotion, exploration, and social interaction. Consistent with our previous findings, we obtained no overall effect of age on locomotion. We did find, however, that for the aged dogs locomotion correlated with level of cognitive function, being lowest in age-unimpaired dogs and highest in impaired dogs. Exploratory behavior, as measured by response to novelty, varied with age, with young dogs scoring the highest. Young dogs spent more time with novel toys and a person, responded more to a silhouette of a dog, and interacted more with a model dog compared to aged dogs. Among the aged dogs, age-unimpaired dogs spent the greatest amount of time sitting or standing beside a person whereas age-impaired dogs spent the most time reacting to a reflection in a mirror. The age-impaired dogs show undirected, stereotypical types of behavioral patterns. These differences in activity patterns may be linked to underlying age-associated neuropathology.

Differential environmental modulations on locomotor activity, exploration and spatial behaviour in young and old rats

The effects of environmental enrichment on motor activity, exploration and spatial performances were studied in young and old rats. Both young (4 mo old) and old (22 mo old) rats were housed from weaning to testing either in standard or in enriched conditions. All rats were submitted successively to spontaneous alternation test and to object exploration test. Results show that locomotion is decreased by age and enrichment but that the quality of exploration expressed by corrected alternation scores or by the response to spatial change is improved by enrichment sometimes in old, sometimes in young rats. Enrichment tends to accelerate the acquisition of spatial informations in young rats, but it does not succeed to restore the reactivity to spatial change of old rats in the object exploration test. These results, although they do not rule out a persistance of a continued behavioural plasticity during aging, also support the idea that the beneficial effects of environmental stimulations do not succeed to restore high cognitive function, such as the capacity to have a spatial representation, in old animals.

Cognitive and noncognitive processes involved in selective object exploration: comparison between young adult and old rats

The age effects on locomotor activity, object-oriented exploration, habituation, and response to a spatial change were studied in young adult and old rats using an object exploration test. In this test the spatial response was evaluated by the renewal of exploration of a familiar object after its repositioning. The specificity of the spatial response was determined by comparison with control animals not submitted to a spatial change. Male Wistar rats 6 and 24 months old were used. Results showed a significant decrement in locomotor activity, object exploration, and spatial reactivity in old rats. The habituation curve and the reactivity to a new object were preserved. Detail analyses suggest that the spatial deficit of old rats is due to an incapacity to detect the spatial change and not to their poor locomotor or exploratory activity. These results corroborate those obtained in spatial orientation tasks and support the idea that the lack of spatial response observed in old animals is more related to cognitive impairments than to other factors such as sensory, motor, or motivational differences.

Testosterone fails to reverse spatial memory decline in aged rats and impairs retention in young and middle-aged animals

Recently, the vasopressin (AVP) innervation in the rat brain was shown to be restored in senescent rats following long-term testosterone administration. In order to investigate whether this restoration is accompanied by an improvement in learning and memory, both sham- and testosterone-treated young (4.5 months), middle-aged (20 months), and aged (31 months) male Brown-Norway rats were tested in a Morris water maze. All animals learned to localize a cued platform equally well, indicating that the ability to learn this task was not affected by sensory, motoric, or motivational changes with aging or testosterone treatment. There were no significant differences in retention following cue training. Subsequent training with a hidden platform in the opposite quadrant of the pool (place training) revealed impaired spatial learning in middle-aged and aged animals. Retention following place training was significantly impaired in the sham-treated aged rats as compared with sham-treated young rats. Testosterone treatment did not improve spatial learning nor retention of spatial information, but, on the contrary, impaired retention in young and middle-aged animals. The present results confirm earlier reports on an impairment of spatial learning and memory in senescent rats but fail to support a role of decreased plasma testosterone levels and central AVP innervation in this respect.

Age-related changes in the motor response to environmental novelty in the rat

To examine age-related changes in responsiveness to environmental novelty, 3-, 12-, and 24-month-old male Fischer 344 rats were maintained on a restricted diet and exposed to a modified open field for 10 min on each of 10 consecutive days. On the first day of testing, animals of all groups showed equal amounts of rearing. While the 3-month animals continued to show approximately the same levels of rearing until the 8th day, by day 5, the older groups (12- and 24-month) had significantly reduced their rearing. Conversely, grooming was initially highest among the 24-month-old animals. While 3- and 12-month rats showed habituation of grooming, the oldest animals failed to habituate their grooming response by day 5. By day 10, there were no significant differences among the groups in either rearing or grooming. Although food was available in the center of the modified open field, there was little eating and there were no differences among groups. However, all animals did eat quickly when food was made available in their home cages. Thus, all animals displayed a profile of stress-related responses to open field exposure. Plasma corticosterone levels likewise were elevated in the modified open field. Some, but not all, components of this response profile habituated over the 10 days of exposure. Three-month-old animals responded to the novelty predominantly by rearing and 24-month animals predominantly by grooming. This suggests that with aging, locomotor responses to stress are replaced by a more self-directed form of displacement activity.

Measurement of cognitive abilities in senescent animals

The behavioral paradigms used in investigating for differences in the cognitive abilities of young and aged animals are critically reviewed with regard to their power to discriminate between young and aged animals' mental capacity. Irrespective of the kind of task, geronto-behavioral research especially is afflicted with difficulties in controlling motivational and emotional influences on cognitive processes. It is hypothesized-somewhat provocatively-that most of the findings indicating an age-related decline are better attributed to the altered motivational status and/or emotional reactiveness than to impaired cognitive processes of senescent animals. Of the common tasks used in this field, it is concluded that complex mazes and different delayed response tasks seem to represent appropriate paradigms in order to study changed capacities in short- and long-term memory (working- and reference-memory, respectively).

Short term lead exposure, age and food deprivation: interactive effects on wheel running behavior of adult male mice

In three separate experiments, young-adult (75 days old) intermediate-age (220 days old), or older (365 days old) Binghamton Heterogeneous Stock (HET) male mice were maintained on food and either water or a 0.5% lead-acetate drinking solution for only three weeks prior to placement in cages with attached running wheels. Mice were kept on their assigned sources of fluid while in these wheeled cages for six days. On Days 3 and 4 of their 6-day access to the running wheels all mice were deprived of food, but the appropriate drinking fluid remained available continually. Even with this relatively low level of dietary lead exposure, which occurred only during adulthood and immediately prior to (and continued during) the 6-day measurement period, the 48-hour food deprivation challenge differentially altered the wheel running of lead-exposed and control mice; but those effects were apparently altered by the age of the adult mice used in each of the three experiments. These data are discussed in terms of the potency of environmental challenges in revealing behavioral changes related to age and even short-term exposure to environmental/dietary toxicants during adulthood.

Age differences in within-session habituation of exploratory behavior: effects of stimulus complexity

The effects of age on the habituation of exploratory behavior of 8-month- and 28-month-old male C57BL/NNia mice were examined under three different stimulus complexity conditions. Increases in the degree of stimulus complexity resulted in an attenuation of between-session habituation and an initial disruption of within-session habituation by 8-month-old mice. Although increases in stimulus complexity also resulted in an increase in the overall level of exploration by aged mice, stimulus complexity was not found to have a systematic effect on between- or within-session habituation by aged mice. No between-session habituation was observed in aged mice under any of the stimulus complexity conditions. Further, aged mice exhibited significant within-session increases, rather than decreases, in exploration under each stimulus complexity condition. This disruption of within-session habituation in aged mice was found to persist over four daily test sessions. In view of the specific patterns of exploration by aged mice, the disruption of within-session habituation was attributed to age-related differences in reactivity to the arousal-inducing properties of novel stimuli.

Disruption and habituation of stable fixed-interval behavior in younger and older monkeys

Reactivity to novel and irrelevant stimuli has been shown to vary as a function of age. Since differential responsivity to irrelevant events may account for purported age differences on other tasks, the present experiment studied the extent to which these age differences may be reduced with repeated exposure, i.e., habituation. Young (2 to 3 years) and old (15+ years) squirrel monkeys were trained and their performance stabilized over months on a fixed-interval operant task. This behavior was then disrupted by periodic presentations of an auditory stimulus of moderate intensity. Disruption of stable behavior and habituation to the tone stimulus were evaluated across several measures including overall response rates between and within the daily sessions; recovery of baseline response rates during the tone stimulus; and the curvature of the fixed interval "scallop." Old monkeys responded for sweet fruit juice more frequently, but less efficiently, than young monkeys. Their responding was more severely disrupted by intermittent novel auditory stimuli, to which they were slower to habituate.

The effects of age, exposure, preexposure, and noise conditions on variable interval performance

The present study was designed to investigate the differential effects of environmental factors on performance in young and aged rats. Specifically, within- and between-session habituation, environmental preexposure, and noise conditions were examined. Consistent age differences were found in response to environmental change and sensory condition. Variable-interval response rates of the well-habituated old animal were well below those of the young. Stimulus change and increments in noise elevated these behaviors in the aged to levels well above those seen in the young. Aged animals appeared incapable of maintaining higher response rates without corresponding conditions of novelty, contextual change, or increments in ambient sensory conditions. Preexposure to sensory conditions similar to those used in the operant chamber reduced response rates in the old, as did habituation with repeated exposure to the chamber.