Rat Serial Pattern Learning Research Articles

Irrelevant relations impact on serial pattern performance after pattern induction

Kundey and Fountain (2011) explored the impact of irrelevant relations on rat serial pattern learning in a circular array. Rats pressed levers according to the same hierarchically-structured serial pattern interleaved with repeating responses on either lever 2, 6, or 8: 122232–223242–324252–425262–526272 (Beginning), 162636–263646–364656–465666–566676 (End), or 182838–283848–384858–485868–586878 (No Irrelevant Relations), where digits indicated the clockwise position of the correct lever. The results indicated that the inclusion of irrelevant relations retarded rats’ learning regardless of their placement within the pattern. Here, we explored the effect of irrelevant relations on performance after a pattern was well learned. In Phase 1, rats learned an interleaved pattern that either did or did not contain irrelevant relations. Subsequently, the interleaved pattern learned in Phase 1 was extended and whether the extension contained irrelevant relations was varied. The results indicated that if the initial pattern was induced in Phase 1 without irrelevant relations, the later inclusion of irrelevant relations when the pattern was extended to double the initial length in Phase 2 was not impairing. However, if irrelevant relations were encountered in Phase 1, performance was disrupted when the pattern was extended. This accords with a similar finding in humans by Hersh (1974), highlighting another similarity of rats’ and humans’ pattern learning and production.

Adolescent exposure to fluoxetine impairs serial pattern learning in the serial multiple choice (SMC) task in adult 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.

Concurrent cognitive processes in rat serial pattern learning: II. Discrimination learning, rule learning, chunk length, and multiple-item memories.

The current experiment examined the factors that determine acquisition for elements of highly structured serial patterns. Three groups of rats were trained on three patterns with parallel rule-based hierarchical structure, but with 3-, 4-, or 5-element chunks, each with a final violation element. Once rats mastered their patterns, probe patterns were introduced to answer several questions. To assess the extent to which the learned response pattern depended on intrachamber location cues for anticipating different element types, Spatial Shift Probes shifted the starting lever of patterns to locations that positioned chunk boundaries where they had never been experienced during training. To assess the extent to which a phrasing cue is necessary for rats to perform a chunk-boundary response, a Cue Removal Probe tested whether rats would produce a chunk-boundary response in the correct serial position if the phrasing cue was omitted. To assess the extent to which cues from multiple trials leading up to the violation element are required to anticipate the violation element, Multiple-Item Memory Probes required rats to make an unexpected response on one of the elements in the last two chunks of the pattern prior to the violation element. The results indicated that rats used multiple concurrent learning and memory processes to master serial patterns, including discrimination learning, rule learning, encoding of chunk length, and multiple-item memories.

Brief massed training reveals epigenetic effects of adolescent nicotine exposure on female rat serial pattern learning

Brief massed training reveals epigenetic effects of adolescent nicotine exposure on female rat serial pattern learning

Phrasing effect with inter-trial cues in serial pattern learning in rats

Phrasing effect with inter-trial cues in serial pattern learning in rats

Irrelevant relations and the active search for pattern structure in rat serial pattern learning

Hersh (Mem Cogn 2:771-774, 1974) investigated the role of irrelevant relations in college students' pattern learning and performance for letter series completion problems. He created irrelevant relations in sequences by inserting items to make pattern structure ambiguous such that it was open to multiple interpretations during initial pattern processing. He reported irrelevant relations impaired humans' performance more when placed at the beginning of patterns than at the end. However, once pattern structure was induced, irrelevant relations were not impairing. Here, we examined the impact on rat serial pattern learning of irrelevant relations positioned at the beginning or end of a serial pattern. Rats pressed levers in a circular array according to the same structured serial pattern, 123 234 345 456 567, where digits indicated the clockwise position of the correct lever. This structured serial pattern was interleaved with repeating responses on lever 2 to produce irrelevant relations at the beginning of the pattern (Beginning: 122232 223242 324252 425262 526272), on lever 6 to produce irrelevant relations at the end of the pattern (End: 162636 263646 364656 465666 566676), or on lever 8 to produce no irrelevant relations (No Irrelevant Relations: 182838 283848 384858 485868 586878. Irrelevant relations significantly retarded learning regardless of their placement within the pattern. However, irrelevant relations retarded learning significantly more when placed at the pattern beginning versus end. The results indicate that rats, like humans, process patterns from beginning to end.

Concurrent cognitive processes in rat serial pattern learning: Item memory, serial position, and pattern structure

Three experiments examined the processes mediating rat serial pattern learning for rule-consistent versus rule-violating pattern elements (“violation elements”). In all three experiments, rats were trained to press retractable levers in a circular array in a specific sequence for brain-stimulation reward (BSR). Experiment 1 examined the role of lever location (L) and element serial position (SP) cues in rats’ ability to learn to anticipate a violation element positioned at the end of a 24-element serial pattern. Rats with L cues either alone or in combination with SP cues learned to anticipate the violation element, whereas those with SP cues alone did not. Rats in groups L and L + SP underwent a series of transfers designed to remove various cues that might have controlled their performance on the violation element. Results indicated that intra-chamber lever location cues mediated performance on the violation element whereas performance on rule-consistent elements within pattern chunks was mediated by an internal mnemonic representation that was insensitive to changes in lever location cues. Experiment 2 examined whether rats could learn to use SP cues alone to anticipate a violation element if it was positioned earlier in a serial pattern. Rats learned to anticipate the violation element based on SP cues alone when it was located in SP6 in a 24-element pattern, but not when it was in SP12. Experiment 3 examined whether or not rats spontaneously encode information about chunk length and the serial position of phrasing cues in serial patterns. Rats were trained to a high criterion on the serial pattern used in Experiment 1, then were challenged with three probe patterns that manipulated both chunk length and overall pattern length. Results indicated that rats spontaneously encoded information regarding the serial position of phrasing cues in relation to chunk length. Thus, rats appear to use at least three cognitive processes concurrently in serial pattern learning tasks, namely, item memory involving external discriminative cues, counting- or timing-like processes for encoding serial position, and rule abstraction for encoding an internal representation of pattern structure.

Blocking in rat serial pattern learning.

Both associative and rule-learning theories have been proposed to account for rat serial pattern learning, but individually they are unable to account for a variety of recent behavioral and psychobiological phenomena. The present study examined the role of rule learning versus discriminative learning in rat pattern learning using a classic associative phenomenon: blocking. Rats learned to press levers in an 8-lever circular array according to a rule-based serial pattern, 123-234-345-456-567-678-781-812, where digits indicate the correct lever in the array for each trial. Each pattern presentation contained a chunk with a final element violation, such as 454 instead of 456. Rats learned in a first phase that a noise signaled the violation chunk; then, a concurrent spatial cue was added in a second phase. A test with spatial cues alone showed that blocking occurred. The results suggest that associative learning mediated cuing of violation elements. Taken together with other behavioral and psychobiological evidence already reported in the literature implicating rule learning when rats learn this pattern in this paradigm, these results implicate multiple concurrent learning processes in rat serial pattern learning.

Adolescent exposure to nicotine impairs adult serial pattern learning in rats

In the present study investigating the effects of adolescent nicotine exposure on adult serial pattern learning, adolescent rats received daily i.p. injections of either 1.0 mg/kg nicotine or saline for 5 days per week for 5 weeks beginning on postnatal day 25 (P25), then were allowed 35 days drug free. Rats then began training on P95 as adults on a 24-element serial pattern composed of eight 3-element chunks. Adolescent exposure to 1.0 mg/kg nicotine produced persistent retardation of learning for the first element of each 3-element chunk of the pattern, that is, for chunk boundary elements, and transient retardation of learning for elements 2 and 3 of each chunk of the pattern, that is, for the within-chunk elements. Deficits at chunk boundaries were interpreted as deficits of phrasing cue discrimination learning whereas deficits for learning responses for elements within-chunks (elements 2 and 3 of chunks) were interpreted as deficits of rule learning. These results indicate that the effects of adolescent nicotine exposure on adult learning and cognitive capacity deserve further scrutiny.

Encoding Structural Ambiguity in Rat Serial Pattern:The Role of Phrasing

Rats, like humans, appear sensitive to the structure of the elements of sequences. In the present study, we examined the effects of phrasing a structurally ambiguous pattern as either a series of “runs” or “trills.” A pattern phrased as runs was easier to learn than when it was phrased as trills, a result that resembles a similar “runs bias” reported in the human sequential learning literature. Whereas rats learning the runs-phrased pattern showed rapid learning and little tendency to make trills errors, rats learning the trills-phrased version of the pattern produced inflated rates of both trills and runs errors. The results show that rats represented the runs- and trills-phrased versions of the pattern differently. These results add to the evidence that, in addition to serving as discriminative cues, phrasing cues can bias pattern perception in rat serial pattern learning resulting in memorial representations characterized by multiple interpretations of the same pattern. The results also fit well with recent behavioral and neurobehavioral studies implicating multiple concurrent psychological and neural processes in rat serial pattern learning.

Determinants of phrasing effects in rat serial pattern learning

Two experiments investigated how brief pauses introduced into serial patterns as phrasing cues would affect pattern learning in rats. In Experiment 1, a 24-element pattern consisted of eight 3-element chunks, whereas a 20-element pattern consisted of four 5-element chunks. In both patterns, 3.0-s temporal pauses placed at chunk boundaries (synchronous phrasing cues) facilitated learning compared to no phrasing. Cues "out of sync" with pattern structure (asynchronous phrasing cues) facilitated learning for the 24-element pattern and retarded learning for the 20-element pattern. Evidence suggested that in the latter case, 3.0-s pauses served as "blank" trials that induced rats to "skip" to the next serial position in sequence. In Experiment 2, shorter 0.5-s pauses served as phrasing cues in the 20-element pattern of Experiment 1. Synchronous short cues facilitated learning, whereas asynchronous phrasing cues had no effect. Furthermore, removal of synchronous cues produced deficits in performance on formerly cued trials, whereas removal of asynchronous cues had no effect. The results of Experiment 2 support the notion that in both experiments phrasing cues served as discriminative cues and indirectly suggest that rats are concurrently sensitive to pattern element cues, extra-sequence cues (such as phrasing cues), and to the relative timing of sequential events.

Are memories for stimulus–stimulus associations or stimulus–response associations responsible for serial-pattern learning in rats?

Previous research has provided convincing evidence that rats can learn to anticipate the individual elements of a stimulus series consisting of differing amounts of food reinforcement. Rats prepared with lesions of the dorsal striatum or hippocampus were initially trained to acquire a three-element series consisting of 21 sucrose pellets, followed by 0- and 7-pellets (Noyes standard), respectively. During the initial 30 days of training, the animals were run in two adjacent runways; the runways included either of a white, rough runway or a black, smooth runway as additional series cues. Thus, training included both floor (S–R) cues and the series (inter-item memory) cues. Anticipation was defined as faster running on the 21- than on the 7-pellet element and 7- than on the 0-pellet element. While anticipation developed more slowly in the lesion groups than in the control group, all animals eventually demonstrated the ability to track the elements of the series. Reversal of the floor cues disrupted tracking in the hippocampus-lesioned and control animals; dorsal striatum-lesioned rats were also affected but did continue tracking. As a final test, shifting the order of the series produced a marked disruption in performance in the dorsal striatum-lesioned rats but not in the hippocampus-lesioned or control rats. The results are consistent with the proposal that integrated neural mediation is required for anticipation, with a system that includes the dorsal striatum necessary for the promotion of a reinforced approach response and a system that includes the hippocampus necessary for associating and temporarily maintaining an internal record of the different elements of the stimulus series.

Differential impairments of rat serial pattern learning and retention induced by MK-801, an NMDA receptor antagonist

Three experiments investigated the role of NMDA receptor dependent systems in sequential learning and memory. Rats tracked serial patterns after systemic administration of MK-801, an NMDA receptor antagonist that blocks plasticity in the hippocampus and other structures. Experiments 1 and 2 sought to describe the effects of MK-801 on acquisition and retention of serial patterns. Patterns were 24 elements long and highly organized, with some groups receiving a “violation” element that did not fit the organization of the rest of the pattern. Experiment 3 evaluated MK-801’s effects on the integration of new information that was either consistent or inconsistent with a previously learned pattern structure. The results of these experiments indicated that MK-801 interfered with serial pattern learning and, to a lesser degree, retention. Learning about structure was relatively spared, whereas learning about interruptions or violations of pattern structure was impaired. The latter differential effects are consistent with the contention in earlier literature that serial pattern learning is subserved by at least two learning/memory systems.

Effects of interrun interval shift in the reward serial learning of the rat on the straight runway

Using runway training procedure, three experiments examined effects of interrun interval (IRI) shift on serial pattern learning in rats. Series consisted of varying number of 0.045 g food pellets given in a goal box of a runway. Groups of rats were trained with 24-10-1-0 or 24-16-10-6-3-1-0 series (Experiment 1), 14-7-3-1-0 series (Experiment 2), and 18-12-6-3-1-0 or 18-7-7-7-1-0 series (Experiment 3), under either short (15-20 s) or long (5-15 min) IRI. In test phases, IRI was shifted from short to long or vice versa. Anticipation of 0 pellet was not disrupted by shortening of IRI, whereas lengthening of IRI eliminated the 0 pellet anticipation of the five- to seven-item monotonic series but did not eliminate that for the four-item series and the nonmonotonic series. These results suggest that rats learn a series with different strategies depending on IRI, pattern length, or structural complexity of a series.

Temporal Phrasing and Overshadowing in Rat Serial-Pattern Learning

Work on experimental manipulations that affect chunking in sequential learning has shown that cues inserted into a sequence, termed “phrasing cues,” can facilitate learning. Two experiments examined how temporal intervals positioned at chunk boundaries facilitate serial-pattern learning. Experiment 1 showed that rat serial-pattern learning can be facilitated when distinct temporal intervals precede chunk boundaries regardless of whether the intervals are longer or shorter than intervals within chunks. Experiment 2 replicated the acquisition results of Experiment 1 with a different serial pattern. In addition, after both 14 and 35 days of acquisition with phrasing cues, cue removal produced severe deficits in tracking Element 1 of chunks, the element directly after the phrasing cues during acquisition. All in all, the results indicate that rats used both short and long temporal phrasing intervals as discriminative cues and that facilitated learning due to phrasing is not the result of additional processing time provided by longer intertrial intervals at chunk boundaries. Furthermore, many of the finer details of the results could be accounted for by the additional assumption that phrasing cues overshadow interitem associations.

Basic evidence and recent developments of serial pattern learning in rats

Basic evidence and recent developments of serial pattern learning in rats

Effects of interrun interval shift and pattern length on serial pattern learning in rats

The present experiment examined effects of interrun interval (IRI) shift and pattern length on serial pattern learning in rats. Rats in a runway received varying number of 45mg food pellets as items of a series. In Phase 1, two groups were given long series (18-10-6-3-1-0 pellets), and the other two groups were given short series (18-1-0 pellets), under short (15-20s) or long (5-7min) IRI. All of the groups were presented their series at one time per day. All the groups developed reliable anticipation of 0 pellet. In Phase 2, each IRI was shifted from short to long or vice versa. The shift in IRI deteriorated the 0 pellet anticipation only in the group which was given 6 item series under short IRI-in Phase 1 and long IRI in Phase 2. No reliable deterioration of 0 pellet anticipation was observed in any other three groups. The interactive effect between direction of shift in IRI and pattern length on pattern tracking performance is explained most appropriately by Hulse's dual theoretical approach which suggests that either associative learning or rule learning mediate serial pattern learning depending on IRI and pattern length.

Sensitivity to violations of "run" and "trill" structures in rat serial-pattern learning.

Rats learned serial patterns composed of either "run" chunks (e.g., 123 234 ...) or "trill" chunks (e.g., 121 232 ...). For each type of pattern, 1 group of rats encountered an element at the end of the pattern that violated the run or trill structure. In both run and trill patterns, violations were unusually difficult for rats to learn, whereas corresponding elements in "perfect" patterns that did not violate pattern structure were easy. Additionally, rats' errors on violation elements conformed to the structure of the patterns in which they were embedded. Thus, rats were sensitive to the run or trill organization of their patterns and mastered the rules governing the pattern before learning "exceptions to the rule."

Sensitivity to violations of "run" and "trill" structures in rat serial-pattern learning.

Sensitivity to violations of "run" and "trill" structures in rat serial-pattern learning.

Effects of Interrun interval and Shift of Reward Sequence on Serial Pattern Learning in Rats

In order to examine the effects of interrun intervals (IRI) on serial pattern learning, two groups of nine albino rats each were trained to achieve five consecutive runs in a straight alley and exposed to a series of reward magnitude varying number of 45mg food pellets at each run. In the first stage of the training, the first group (Group S) was presented with 14-7-3-1-0 monotonic series of food pellets with IRI of 15 to 20 sec between runs. The second group (Group L) was also presented with the same series as the first one but with longer IRI of 5 min between runs. Group S and Group L ran equally slow to 0 pellets in the monotonic series. In the second stage of the experiment, both groups received 14-3-7-1-0 nonmonotonic series with the IRI being same as the first stage. The shift of the series differentially affected the anticipation of the 0 pellets between groups. Anticipation of 0 pellet in Group S was more greatly deteriorated than that in Group L. These results support Hulse's dual theoretical approach to serial pattern learning rather than Capaldi's memory-discrimination theory.