Katherine Dyer

Scientists have been interested in the mechanisms which allow organisms to perform complex behaviors, such as behavioral sequences, for decades. One such type of complex sequential behavior which is of interest to scientists is serial pattern learning. Serial pattern learning, the performance of patterned sequences of responses, has been investigated in many species including rats and humans (Fountain & Rowan, 1995b). Both past and current research of this phenomenon seeks to better understand the mechanisms underlying this form of complex behavior. For example, rats can recruit multiple cognitive mechanisms during serial pattern learning (Muller & Fountain, 2010, 2016; Stempowski, Carman, & Fountain, 1999). Furthermore, prior researchers attributed differences in the learning and performance of serial patterns to these different cognitive mechanisms (Muller & Fountain, 2010, 2016). However, simpler explanations of these findings, such as differences in learning experience, remained unexplored in the research. Thus, the current study investigated the influence of these simpler mechanisms on serial pattern learning processes. To determine how amount of learning experience affects pattern performance, rats were trained on one of two patterns of varying structures. One pattern equated amount of learning experience amongst element types in the pattern, while another pattern contained unequal amounts of learning experience amongst element types in the pattern. Effects of amount of learning experience were measured during acquisition, on pattern performance during a muscarinic cholinergic drug challenge, and on pattern performance during a retention test. Results showed that the amount of learning experience rats had with element types per pattern completion affected the rate at which those various pattern element types were learned. However, amount of learning experience did not affect subsequent learned-pattern performance in later challenges. In a second experiment, the effects of serial pattern mastery on pattern performance during drug challenges were examined. One group of rats received three drug challenges to challenge three separate pattern element types at the same levels of mastery. Another group of rats received one drug challenge at the end of acquisition to challenge three separate pattern element types at different levels of mastery. Results showed that the level of mastery at which pattern elements were challenged did not affect pattern performance during drug challenges. Therefore, though differences in pattern learning are not wholly due to the separate cognitive mechanisms recruited during serial pattern learning, as previously theorized, findings continue to support that differences in learned-pattern performance are likely a result of these separate cognitive mechanisms. Thus, the serial pattern learning process involves both simple and complex mechanisms which contribute to how sequences of behaviors are learned and performed by animals.

•Rats received 1.0, 2.0, or 4.0 mg/kg/day of fluoxetine (FLX) during adolescence.•Rats were trained on a serial multiple choice (SMC) task in adulthood.•Adolescent FLX differentially impaired acquisition of serial pattern element types.•FLX impaired stimulus-response and multiple-cue learning but not rule-learning.•Adolescent exposure to FLX impaired some aspects of adult cognition in rats.
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.

There is a growing body of research on matching- and non-matching-to-sample (MTS, NMTS) relations with rats using olfactory stimuli; however, the specific characteristics of this relational control are unclear. In the current study we examine MTS and NMTS in rats with an automated olfactometer using a successive (go, no-go) procedure. Ten rats were trained to either match- or non-match-to-sample with common scents (apple, cinnamon, etc.) as olfactory stimuli. After matching or non-matching training with four odorants, rats were tested for transfer twice with four new odorants on each test. Most rats trained on MTS showed immediate transfer to new stimuli, and most rats trained on NMTS showed full transfer by the second set of new odors. After meeting criterion on the second transfer test, the contingencies were reversed with four new odor stimuli such that subjects trained on matching were shifted to non-matching and vice versa. Following these reversed contingencies, the effects of the original training persisted for many trials with new odorants. These data extend previous studies on same-different concept formation in rats, showing strong generalization requiring few exemplars. The critical role of olfactory stimuli is discussed.