Megan E. Miller-Cahill’s research while affiliated with Kent State University and other places

The neural, behavioral, and cognitive processes that convert experiences into neural and cognitive representations of experiences in sensation, perception, conditioning, memory, anticipation, problem solving, language, and related cognitive systems.

The effects of chronic adolescent fluoxetine (FLX, Prozac®) exposure on adult cognition are largely unknown. We used a serial multiple choice (SMC) task to characterize the effects of adolescent FLX exposure on rat serial pattern learning in adulthood. Male rats were exposed to either 1.0, 2.0, or 4.0 mg/kg/day FLX for five consecutive days each week for five weeks during adolescence, followed by a 35-day drug-free period. As adults, the rats were trained in a task that required them to learn a highly structured sequential pattern of responses in an octagonal chamber for water reinforcement. In a transfer phase, the terminal element of the pattern was replaced by a violation element that was inconsistent with previously learned pattern structure. Results indicated that adolescent FLX exposure caused differential learning deficits for different types of elements in the serial pattern. Adolescent exposure to 1.0 or 4.0 mg/kg/day FLX, but not 2.0 mg/kg/day FLX, impaired chunk-boundary element learning, which is known to be mediated by stimulus-response (S-R) learning. All three doses of FLX impaired violation element learning, which is known to be mediated by multiple-cue learning. FLX did not impair within-chunk element learning, which is known to be mediated by rule-learning mechanisms. The results indicate that adolescent FLX exposure produced multiple cognitive impairments that were detectable in adulthood long after drug exposure ended.

Serial pattern learning is a model paradigm for studying parallel-processing in complex learning in rats. The current experiment extends the paradigm to the study of sequential memory by examining forgetting curves for the component element types that make up a serial pattern. Adult male and female rats were trained in a serial multiple choice (SMC) task in which rats learned a serial pattern of nose-poke responses in a circular array of 8 receptacles mounted on the walls of an octagonal operant chamber. The pattern was 123-234-345-456-567-678-781-818, where digits represent the clockwise positions of successive correct receptacles. Previous work has shown that chunk-boundary elements (the first element of each 3-element chunk), within-chunk elements (the second and third elements in all but the last chunk), and the "violation element" (the last element of the pattern) are learned via different cognitive mechanisms. After each rat was trained to an 85% correct performance criterion on the violation element, we then assessed serial pattern retention at 24-hour, 2-week, and 4-week retention intervals. For chunk-boundary and within-chunk elements, forgetting was observed only at the 4-week retention interval. Sex differences were observed; females performed better than males on within-chunk elements at 24-hour and 4-week retention intervals. For the violation element, significant forgetting was observed earlier at the 2-week retention interval as well as at the 4-week retention interval. Thus, pattern elements that were learned slower were forgotten faster. The experiment provides a proof of concept for evaluating forgetting curves separately for the multiple memory systems rats appear to employ concurrently in this paradigm, a method that may prove useful in characterizing the impact of relevant neurobiological manipulations on forgetting in multiple sequential memory systems.