Enhanced performance of aged rats in contingency degradation and instrumental extinction tasks.

Abstract

Normal aging in rats affects behavioral performance on a variety of associative learning tasks under Pavlovian conditions. There is little information, however, on whether aging also impacts performance of instrumental tasks. Young (9–12 mo) and aged (24–27 mo) Fisher 344 rats were trained to press distinct levers associated with either maltodextrin or sucrose. The rats in both age groups increased their lever press frequency at a similar rate, suggesting that the initial acquisition of this instrumental task is not affected by aging. Using a contingency degradation procedure, we then addressed whether aged rats could adapt their behavior to changes in action-outcome contingencies. We found that young and aged rats do adapt, but that a different schedule of reinforcement is necessary to optimize performance in each age group. Finally, we also addressed whether aged rats can extinguish a lever press action as well as young rats, using two forty minute extinction sessions on consecutive days. While extinction profiles were similar in young and aged rats on the first day of training, aged rats were faster to extinguish their lever presses on the second day, in spite of their performance levels being similar at the beginning of the session. Together these data support the finding that acquisition of instrumental lever press behaviors is preserved in aged rats, and suggest that they have a different threshold for switching strategies in response to changes in action-outcome associations. This pattern of result implies that age-related changes in the brain are heterogeneous and widespread across structures.

Age differences in strategy selection and risk preference during risk-based decision making.

“…A novel finding that emerged from this study is that aged rats are slower to acquire lever-reward representations when two rewarding options are available simultaneously. This finding is in contrast with the initial acquisition of instrumental lever press, which is preserved in aged rats (Samson et al, 2014). The age difference in acquisition rate found in the current study appears to be specific to the initial acquisition of a decision making paradigm involving differently valued rewards.…”

“…This finding is in contrast with the initial acquisition of instrumental lever press, which is preserved in aged rats (Samson, Venkatesh, Patel, Lipa, & Barnes, 2014). The age difference in acquisition rate found in the current study appears to be specific to the initial acquisition of a decision making paradigm involving differently valued rewards.…”

Emergence of β-Band Oscillations in the Aged Rat Amygdala during Discrimination Learning and Decision Making Tasks

“…After the Morris swim task, rats were food deprived to 85% body weight and trained to press two levers for food reinforcement (vanilla-flavored Ensure). The shaping and training procedure is described in Samson et al (2014, 2015 ). Briefly, once rats were able to press levers, they were trained for seven consecutive days, at a predefined probability schedule to reinforce their lever press performance.…”

Metabolic switching is impaired by aging and facilitated by ketosis independent of glycogen

“…Many tests of cognitive function require animals to be restricted to <85% of their body weight to motivate participation by feeding once daily, making a large portion of investigations on the neurobiology of cognitive aging into incidental experiments of caloric restriction with TRF. While incentive motivation for food rewards does not change with age [60], robust agerelated deficits are observed on working memory [61][62][63], other executive functions [64][65][66], as well as behaviors that require the prefrontal cortex and medial temporal lobe [14,[67][68][69].…”