The relative difficulty of reversal learning (reversal index) as a basis of behavioural comparisons.
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Animals↗
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Aging in the rhesus monkey: effects on visual discrimination learning and reversal learning.
The behavior of aged rhesus monkeys (18 years and older) was compared to that of young monkeys (3 to 6 years old) to evaluate their relative abilities to learn a series of visual discrimination and discrimination reversal problems. Using a subject-paced, automated experimental procedure designed to optimize stimulus control and facilitate execution of choice responses, no consistent age-related differences were observed in the ability to learn new color and pattern discrimination problems of varying difficulty. However, a severe and consistent deficity on reversal learning did occur. A detailed analysis of this deficit revealed that not only did the aged monkeys take longer to extinguish the old habit and return to chance performance, but they continued to display a deficit in establishing accurate performance at above-chance levels as well. Since no reliable age differences were observed on the original discrimination learning problems, these data suggest that aging impairs mechanisms involved with response rigidity and/or susceptibility to intertrial proactive interference, more severely than those involved with the simple formation of new associations.
Aging↗
Reversal learning of an avoidance response in detelencephalated rats.
Avoidance learning followed by reversal learning was tested in rats after removal of all telencephalic brain structures. In phase I, 24 h after ablation of the telencephalon, rats were given a learning trial in the up-hill avoidance task and tested for retention 2 h later. The animals receiving a tail-shock contingent on the up-hill response showed significant increases in step-up latencies in comparison with control animals that had received noncontingent shock. In phase II, rats of the "reversal learning" group received a tail-shock if they did not perform the up-hill response within 5 s. Control animals received either another up-hill contingent shock or no shock. Two hours later the "reversal" group animals showed a decrement in step-up latencies in comparison with control animals, suggesting that reversal learning of the up-hill avoidance task is possible in rats devoid of the telencephalon.
Animals↗
Normal learning set and facilitation of reversal learning in rats with combined fornix-amygdala lesions: implications for preserved learning abilities in amnesia.
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Amygdala↗
Discrimination reversal learning in the crayfish.
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Animals↗
Reversal learning and forgetting.
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Animals↗
Normal olfactory discrimination learning set and facilitation of reversal learning after medial-temporal damage in rats: implications for an account of preserved learning abilities in amnesia.
Recent evidence of preserved skill learning in patients with "global" amnesia has led to the postulation of a qualitative distinction between functionally separate memory systems, one of which may remain preserved when the other is profoundly impaired. On one account, the separate memory systems support either the learning of declarative knowledge, i.e., facts and associations, or the learning of procedural knowledge, i.e., knowledge that permits the expression of skilled performance without reference to specific facts or associations. In an effort to develop a rodent model of amnesia that illustrates the same distinction between memory systems, rats were trained in a series of discrimination and reversal problems using olfaction, a sensory modality in which they rapidly learn new associations. Rats with bilateral fornix, amygdala, or combined fornix and amygdala damage learned successive two-odor discriminations as quickly as normal and sham-operated control subjects. Furthermore, all groups rapidly acquired the skills of discrimination as revealed in the development of a learning set. Subsequent presentation of a reversal of one discrimination elicited a marked dissociation among groups: Normal rats and rats with amygdala lesions required many more trials to acquire the reversal than to acquire a new discrimination problem, whereas rats with fornix lesions learned the reversal rather easily. A detailed analysis of response strategies suggested that normal rats and rats with amygdala lesions first extinguished the prior response tendencies and then abandoned the learning set skills and treated the reversal much as they did the initial discrimination problem.(ABSTRACT TRUNCATED AT 250 WORDS)
Amnesia↗
Serial spatial reversal learning in rats: comparison of instrumental and automaintenance procedures.
Serial reversals of a spatial discrimination were trained in rats under automaintenance conditions, in which food reward occurred regardless of responding. This automaintained reversal learning was compared to instrumental reversal learning in other rats trained under a similar procedure which required responding for reward. In the automaintenance (AU) procedure, rats received food after every retraction of a "positive" response lever (S+); retraction of a second, "neutral" lever (So) was not paired with food delivery. Responses to the S+ were elicited at fairly constant rates during daily 100-trial conditioning sessions. Responses to the So occurred early in each session but rapidly diminished across trials. When the valences of the levers were reversed, responding shifted to the new S+ and diminished on the new So. Criterion for reversal was defined as a discrimination ratio (DR) of at least 90% responding to the S+ in two consecutive 10-trial blocks. With repeated reversals, acquisition of criterion performance occurred with increasing rapidity, reaching an asymptote below that required for the original discrimination. A second group of rats was trained on a similar instrumental schedule, in which at least one response to the S+ was required for food delivery. Response rates in this instrumental (IN) group were approximately double those of the AU group. However, ratios of S+ to So response rates were similar to those of the AU group, and the serial reversal curves generated were qualitatively similar. Thus rats can show improvement across serial reversals of a spatial discrimination based entirely on pairings of stimulus events (automaintenance), in a manner similar to that observed in instrumental procedures, in which reward is contingent upon correct responding.
Animals↗
Reversal learning deficits in young monkeys exposed to lead.
The reversal learning capacity of young rhesus monkeys in visual discrimination tasks was examined during daily exposure to dietary lead acetate throughout the first year of life. While not affected in physical development, all lead-treated monkeys showed performance deficits on reversal learning tasks. These deficits were independent of lead-induced changes in motivation. Over a series of problems, the overall learning rate of monkeys with blood lead concentrations in the range of 70-90 microgram/dl was retarded, which resulted partly from a pronounced difficulty in attaining criterion on the first of a series of reversals within a given problem. This latter deficit resulted from an increase in errors, balks, and total trials to criterion on the first reversal. Monkeys exposed to blood lead concentrations of 40-60 microgram/dl required significantly more trials to finish all problems, but did not show the first-reversal deficit. Theoretical implications of these data were discussed.
Aging↗
Delay-dependent impairment of reversal learning in rats treated with trimethyltin.
Recent theories of hippocampal function focus on its role in the formation of associations in the temporal domain. A reversal learning paradigm based on leverpress automaintenance was developed to vary the CS-US relationship along two independent dimensions, one temporal and one not: CS(+)-US delay and the probability of reinforcement [P(RFT)] following the CS+. Eight male hooded Long-Evans rats were trained to reverse these automaintained discriminations repeatedly, until stable performance was achieved. The neurotoxicant trimethyltin (TMT) was used to induce lesions in the CNS, including the CA3-4 region of Ammon's Horn in dorsal hippocampus. Following iv injection of 7 mg/kg TMT to half the rats, reversal learning was assessed under varying conditions of delay and P(RFT). After recovery from the acute effects of TMT (1-2 weeks), treated rats reversed normally when no delay separated the CS+ and US; with delays of 2 to 4 s, they reversed less completely within a session than did controls. Changing P(RFT) did not affect reversal learning in either group, but reduced response rates similarly in both groups. Morphological damage was quantified by measuring the length of the remaining pyramidal cell line in sections of dorsal hippocampus. The degree of behavioral impairment correlated significantly with hippocampal damage only at nonzero CS(+)-US delays. These results indicate that TMT impaired ability of rats to integrate temporal relationships between stimulus events, and are consistent with theories of hippocampal mediation of temporal associations.
Animals↗
T-maze discrimination and reversal learning after unilateral temporal or frontal lobe lesions in man.
The interpretation of conditional discrimination and reversal learning as acquisition of declarative knowledge suggests that subjects with temporal lobe/hippocampal lesions are likely to be impaired on such tasks. Patients with unilateral left or right temporal lobectomy (and small hippocampal excisions) and patients with unilateral frontal lobe resections were compared with healthy controls on a discrimination reversal task, embedded in a computer game modelled on T-maze tasks traditionally used in animal experiments. The right temporal group showed a deficit in acquiring an initial conditional discrimination, and the frontal group tended to display a marginal impairment in discrimination reversal. These findings are compared with results from animal studies in terms of the mechanisms underlying reversal learning.
Adult↗
Quality of stimuli and prefrontal lesions effects on reversal learning in go-no go avoidance reflex differentiation in cats.
Go no go avoidance reflex differentiation of two acoustic stimuli has been previously established in cats. Then the signalling properties of the conditioned stimuli were reversed and the course of acquisition of a new go-no go differentiation was studied in normal cats and in cats with prefrontal lesions. The hypothesis based on stimulus intensity dynamism theory was: (i) in normal cats acquisition of the new differentiation would be easier if the more effective stimulus of the pair were used as the positive stimulus, and (ii) in prefrontal cats this effect of stimulus quality would be l a or absent. Results confirmed both predictions. The differences in rapidity of reversal learning were almost exclusively due to differences in responding to the new positive stimulus. Prefrontal cats were not deficient in comparison with normal cabs in their inhibitory abilities in spite of the fact that extinction of bar-pressing to the new negative conditioned stimulus was much slower than trader of the avoidance response to the new positive stimulus. At the beginning of reversal learning two opposite changes in responding on no-go trials were observed: (i) a decrease in the number of long-latency responses, which reflected the changed signalling value of the previously positive stimulus, and (ii) an increase in the number of short-latency responses, which was positively correlated with the increase in rate of intertrial responding. The increases in number of short-latency responses to the new negative stimulus and in rate of intertrial responding observed at the beginning of reversal learning were smaller in prefrontal than in normal cabs. Results of the experiment indicate that the "drive disinhibition hypothesis" does not account for the effects of prefrontal lesions on avoidance behavior.
Animals↗
Beneficial effect of chronic treatment with Org 2766 and alpha-MSH on impaired reversal learning of rats with bilateral lesions of the parafascicular area.
The effects of chronic treatment with the ACTH-(4-9) analogue Org 2766, alpha-MSH, and gamma 2-MSH were studied on T-maze reversal learning and on behavior assessed on the basis of open-field and other gross behavioral activities, grasping responses, inspection of various reflexes and electrical footshock sensitivity of rats with parafascicular lesions or sham-lesions. Repeated administration of Org 2766 and alpha-MSH to parafascicular area-lesioned rats resulted in functional recovery of impaired T-maze reversal learning. The structurally related neuropeptide gamma 2-MSH was without any effect. The alpha-MSH effect did not depend on time after lesioning as treatments during the first or second post-operative week were equally effective. Chronic peptide treatments did not change disturbed motor functions of parafascicular-lesioned rats, as measured by open-field activity, other gross behavioral activities and grasping responses. Since acute peptide treatments did not affect the impaired reversal learning performance of lesioned rats, the beneficial effect of Org 2766 and alpha-MSH could not be explained as a short-term effect on attention and motivation. It was more likely to be an accelerated recovery of cognitive function as a result of long-term neurotropic influences.
Adrenocorticotropic Hormone↗
Tactile-visual acquisition and reversal learning deficits in rats with prefrontal cortical lesions.
Rats with prefrontal cortex (PFC) lesions or sham operations were tested for acquisition and reversal learning with tactile-visual stimuli. PFC rats performed extremely poorly during acquisition and also differed from control rats in reversal learning. Both higher-order processing and subtle motoric dysfunctions may have combined to account for the marked effects of these cortex lesions.
Animals↗
Human temporal behavior and discrimination-reversal learning.
The present study demonstrates that a relationship exists between individual differences in temporal behavior and individual differences in human discrimination-reversal learning behavior. When the results of performance on a time-estimation task employing the method of reproduction are compared with the results of acquisition performance on a complex form of discrimination-reversal learning task is can be demonstrated that underestimation of time is associated with faster learning and overestimation of time is associated with slower learning of the discrimination task. The experimental design was based on the historical fact that the Sechenov-Pavlov and Spence-Hull formulations assigned a primary role in learning to excitation and inhibition as intervening variables between the input of stimulation and output of response. The present study also used the tasks of time estimation and discrimination learning as dependent variables; and the concept that underestimation of time is associated with and underlying predominance of excitatory processes as a hypothetical construct. The conclusion was reached that one of the many theoretical processes which may be used to explain discrimination learning is the concept that acquisition of the correct response may be viewed as a function of the individual rates at which excitatory processes come to be conditioned to a predominance over existing inhibitory processes.
Adult↗
Facilitated reversal learning of a spatial-memory task by medial septal injections of 6-hydroxydopamine.
To assess the role of hippocampal norepinephrine in learning and memory, rats were treated with medial septal injections of 6-hydroxydopamine either prior to or after acquisition of a spatial-memory task. No effect on acquisition learning or retention was observed. However, reversal learning was significantly enhanced in all treated animals regardless of whether treatment was prior to or after acquisition. Our results do not support a role of hippocampal norepinephrine in selective attention, but rather indicate a direct involvement in memory processes.
Animals↗
Persistence of impaired reversal learning in young monkeys exposed to low levels of dietary lead.
Lead acetate in milk was fed daily to infant rhesus monkeys at doses averaging 0 (control), 0.287 (low-Pb), or 0.880 (high-Pb) mg/kgd for the first year of life. Pb concentrations in whole blood (PbB) averaged 4.15, 31.71, and 65.17 microgram/dl for the control, low-Pb, and high-Pb groups, respectively, during the year of treatment and declined toward control levels when Pb dosing was stopped. Behavioral observations during the year of treatment had shown that both experimental groups were retarded in their acquisition of object-cue discrimination reversal learning sets. At 4 yr of age, when PbB levels in all animals were normal, the ability of the same monkeys to acquire a series of 3 spatial-cue reversal learning sets was examined; these data form the basis for this report. In the first problem, the high-Pb group was significantly retarded in acquisition of the original discrimination and of most reversals, and the low-Pb group was retarded on reversal 1 only. These deficits declined in severity across the three problems administered, in a manner similar to that seen in the tests given during the first year of life. These data demonstrate that reversal learning retardation, observed early in life, can recur in postadolescent primates with a history of chronic, low-level Pb intoxication during infancy.
Animals↗
Visual discrimination and reversal learning in the aged monkey (Macaca mulatta).
Visual discrimination and reversal learning were assessed in young adult (10-12 years old, n = 4) and aged (23-27 years old, n = 5) female rhesus monkeys. Performance was comparable across age groups in many tasks, suggesting that the acquisition of stimulus-reward associations remains largely intact in the aged monkey. Most older subjects, however, required more training than any young animal to learn an initial pattern discrimination. In combination with previous findings from the same groups of monkeys, these data suggest that deficits in attending to the relevant stimulus features in novel testing procedures may contribute to poor performance in aged subjects across a variety of learning and memory tasks. In addition, preliminary findings from a discrimination probe procedure raise the possibility that aged subjects may adopt alternate testing strategies that compensate for some aspects of age-dependent cognitive dysfunction.
Aging↗