Serial Reversal Learning Research Articles

A specific form of cognitive rigidity following excitotoxic lesions of the basal forebrain in marmosets

The effects of N-methyl- d-aspartate-induced lesions of the basal forebrain were studied on performance of a series of visual discrimination tests that examined a range of cognitive functions in the marmoset. These included the ability to attend to the various dimensional properties of stimuli and to use just one of these properties in order to solve a discrimination (intra-dimensional shift); to switch attention from one dimension to another (extra-dimensional shift); to learn the reinforcement value of specific exemplars within a dimension (new learning); and to relearn their reinforcement value following reversal of the reward contingencies (serial reversals). Lesions of the basal forebrain did not impair the ability either to attend selectively to the dimensional properties of the stimuli or to switch attention from one dimension to the other. However, the lesion did affect various aspects of associative learning including a transient impairment of new learning and a marked disruption of serial reversal learning. The reversal deficit could be characterised as a tendency to perseverate on the previously correct stimulus and as a failure to to show the formation of a reversal learning set. In addition, the lesion prevented disruption of performance of a well-learned discrimination when novel exemplars from the irrelevant dimension were introduced (probe test). It is suggested that the functional effects of the basal forebrain lesion reflect impaired learning of stimulus-reward associations and behavioural rigidity. The finding, however, that there was no effect of the lesion on attentional set-shifting suggests that any loss of inhibitory control was specific to the level of stimulus-response or stimulus-reward associations, inhibitory control at the level of attentional selection remaining intact. The similarity of the effects of damage to the basal forebrain to those seen following damage to the orbitofrontal cortex and the amygdala are discussed in the context of the close anatomical and functional relationships that exist among these three structures.

Behavioural rigidity and rule-learning deficits following isolation-rearing in the rat: neurochemical correlates

Isolation-reared rats were compared to those reared in social groups on the acquisition of a conditional visual discrimination (Expt. I), a simultaneous (simple) light/dark discrimination and serial reversal learning (Expt. II). In Expt. I, rats reared in social isolation made more errors during the acquisition of the conditional discrimination but did reach a level of accurate performance which was comparable with that of socially-reared rats. Discrimination performance in isolates was less disruptable by manipulations of the task requirements. Reducing the number of stimulus lights or the introduction of a distracting stimulus increased the number of errors committed by socially-reared rats but did not significantly affect accuracy in isolates. Performance in isolated rats was also remarkably resistant to changes in motivational variables. Isolates responded more frequently during conditions of extinction and were virtually unaffected by pre-feeding prior to testing. In Expt. II, isolation-reared rats were not impaired in the acquisition of a simultaneous discrimination but unlike socially-reared rats isolates failed to show improvement with successive reversals of this discrimination. Isolates exhibited stronger position habits than socially-reared rats following reversal of the contingencies. These results of these two experiments combined have demonstrated a specific impairment in rule learning in isolates. Isolated rats were not impaired on a simultaneous discrimination in which accurate performance can be achieved simply by approaching the stimulus associated with reinforcement, but performed worse than controls on both the conditional discrimination and on serial reversal learning, another form of conditional task. In both of these latter tasks each stimulus becomes equally associated with reward and therefore performance can be improved by learning a rule. Post-mortem neurochemical measurements made at the completion of Expt. II revealed selective alterations in dopaminergic, serotoninergic and cholinergic markers in isolated rats. Correlational analyses indicated specific relationships between neurochemical and behavioural measurements.

Impairment of olfactory, auditory, and spatial serial reversal learning in rats recovered from pyrithiamine-induced thiamine deficiency.

Rats that had recovered from pyrithiamine-induced thiamine deficiency (PTD) were compared with controls for spatial, auditory, and olfactory serial reversal learning (SRL); spatial matching to sample (MTS); auditory go-no-go discrimination; and open-field exploration. PTD rats made more errors reaching criterion for SRL in all modalities but showed normal transfer effects between problems. PTD rats were also impaired in learning the go-no-go and MTS tasks and showed consistent alterations in exploratory activity. It is argued that the PTD rat, like human Korsakoff patients, have impairments of learning and memory (but spared capacity for reference memory) that extend across sensory modalities. Postmortem analyses showed normal indices of cortical cholinergic, noradrenergic, dopaminergic, and serotonergic function and consistent bilateral lesions of the thalamus, which were centered on the internal medullary lamina, and the medial mammillary nucleus.

Impairment of olfactory, auditory, and spatial serial reversal learning in rats recovered from pyrithiamine-induced thiamine deficiency.

Impairment of olfactory, auditory, and spatial serial reversal learning in rats recovered from pyrithiamine-induced thiamine deficiency.

The effects of excitotoxic lesions of the basal forebrain on the acquisition, retention and serial reversal of visual discriminations in marmosets

The effects ofN-methyl- d-aspartate-induced lesions of the basal forebrain (which included the cholinergic cells of the nucleus basalis of Meynert) were studied on three aspects of visual discrimination; learning, retention and reversal performance, in the marmoset. Neurobiological investigations revealed that the lesion produced large reductions in choline acetyltransferase activity within anterior regions of cortex, particularly prefrontal. In Experiment 1 lesioned animals showed impaired retention, one week after surgery, of a visual discrimination learned immediately prior to surgery and subsequently showed impaired performance over a series of reversals. The reversal deficit could be characterized as a tendency to perseverate on the previously correct stimulus on the first reversal and as a failure to show serial reversal learning on subsequent reversals. Acquisition of a novel discrimination was not impaired five weeks after surgery. As time of testing may have been a confounding factor, in Experiment 2 the effects of the same lesion on new learning were examined immediately following surgery and the effects on retention a month later. The lesion was found to disrupt new learning but did not affect retention. From the two experiments it is clear that, whereas disruption of retention and new learning was relatively transient, the impairments in reversal performance were more long lasting. In addition, lesioned animals exhibited behavioural hyperactivity and elevations in consummatory and schedule-controlled licking. The disinhibitory and perseverative effects observed following lesions of the basal forebrain in this study are similar to those following lesions of the orbitofrontal cortex while the disruption of serial reversal learning is commonly seen following damage to the amygdala. Therefore, these results are consistent with the hypothesis that the range of behavioural effects of the lesion result from damage to the cholinergic afferents to orbitofrontal cortex and to the amygdala, two structures intimately connected to one another.

Effects of ibotenic acid lesions of the basal forebrain on serial reversal learning in marmosets.

Five common marmosets (Callithrix jacchus) received unilateral ibotenic acid lesions of the basal forebrain. Seven days post-operatively, choline acetyltransferase activity was reduced by 60% in frontal cortex and 40% in temporal cortex in the ipsilateral side compared with the contralateral side. Four animals receiving bilateral lesions of the same area were impaired on the first post-operative task of serial reversal learning when compared with four animals receiving bilateral saline injections. Although their performance improved with time, the lesioned animals were subequently impaired following administration of a low dose of scopolamine which did not affect the control group. These results show that lesions within the basal forebrain can affect cholinergic function in the cortex and impair learning ability.

Differences in mechanisms of intelligence among vertebrates

Much comparative research aimed at establishing differences in intelligence among vertebrates has failed to convince the sceptic, because it has concentrated on a single experimental paradigm (such as learning sets), while employing a diverse array of species in the hope of establishing a rank ordering of intelligence. The sceptic can insist that such research has not even established that there are any differences in mechanisms of intelligence between any pair of vertebrate species, let alone elucidated the nature of the difference, and even the unsceptical will doubt that such research is ever likely to establish a rank order of intelligence. It is more informative to concentrate on fewer species, but a broader range of experimental paradigms. Thus, studies of serial reversal learning have consistently suggested that goldfish do not show such rapid improvement as do rats. One explanation of this might be that rats learn more effectively than goldfish to use the outcome of one trial to predict the outcome of the next. The suggestion is supported by finding other experimental paradigms, such as alternation learning, which must also tap such a process, and where rats again learn more rapidly than goldfish. Efficient learning-set performance may also depend on this process, but must in addition require the subject to transfer this rule across changes of stimuli. There is reason to believe that not all vertebrates are equally adept at such transfer, and this possibility is explored in a series of experiments studying the transfer of matchingto-sample in pigeons and corvids. The corvids display significantly better transfer and the close similarity in training procedures possible with these subjects makes it unlikely that this is due to differences in these training procedures.

Serial discrimination reversal learning in the pigeon: Potentiation of "pattern" by a conditional cue.

Serial discrimination reversal learning in the pigeon: Potentiation of "pattern" by a conditional cue.

Serial discrimination reversal learning in the pigeon: Potentiation of "pattern" by a conditional cue.

Serial discrimination reversal learning in the pigeon: Potentiation of "pattern" by a conditional cue.

The effect of inferotemporal or foveal prestriate ablation on serial reversal learning in monkeys

Visual discrimination performance during serial reversal learning was studied in monkeys with inferotemporal or foveal prestriate lesions. Both groups were equally impaired in acquisition of the discrimination when compared with normal monkeys. They also learned the reversal series more slowly than control subjects. The reversal deficit of monkeys with inferotemporal lesions was more severe than their acquisition deficit though over successive reversals they achieved normal performance. Monkeys with foveal prestriate lesions were less impaired in reversal learning than in acquisition of the discrimination problem. These results are interpreted in terms of qualitative differences in the effects of the two lesions.

Serial reversal learning in the mallard duck (Anas platyrhynchos)

Serial reversal learning problems have been used primarily with the pigeon to develop theories of learning for the class Aves as a whole. This experiment tested the mallard duck and employed a procedure similar to that used for the pigeon. Five mallard ducks were tested in a visual discrimination task in daily sessions, with the rewarded symbol changed every 20 days. Improvement in the performance of the ducks did not occur to the same degree as that reported for the pigeon, and no evidence was found for a weakening of retention over time.

Reversal of spatial discrimination learning in a water maze by previously undernourished rats

The development of the hippocampus in rats may be vulnerable to undernutrition during the fetal and suckling periods. Hence the behavioral effects of early growth restriction may resemble those of hippocampal lesions. This suggestion was investigated by testing previously undernourished rats for reversal learning, an ability badly affected in hippocampectomized rats. Developing rats were undernourished by feeding their mothers a restricted quantity of a good quality diet during pregnancy and lactation. All rats were fed ad lib from weaning. Reversal of spatial discrimination learning was tested in adult animals using a water T-maze. Previously undernourished rats learned the initial spatial discrimination more quickly than controls. However, there was no effect of early treatment on serial reversal learning in Experiment I or on performance of a single reversal after prolonged initial training in Experiment II.

Short-term retention of response outcome as a determinant of serial reversal learning

The correlation between short-term retention of the outcome of the preceding response and overall learning proficiency was investigated for serial reversal learning. Pigeons were trained to asymptote on a serial reversal problem and then were presented a percentage reinforcement schedule where only some correct trials were rewarded. Nonrewarded correct trials were treated exactly as incorrect trials. The difference in error probability following the two types of correct trials was then used as a measure of short-term retention. When intertrial intervals (ITI) were short (6 sec), substantial differences occurred. When the ITI's were increased, the difference in accuracy declined regularly to no difference at an ITI of 60 sec. This demonstration of a short-term retention gradient, coupled with the finding that overall reversal learning was much better with the shorter ITI's, suggests that a primary mechanism of improvement in serial reversal learning is the acquisition of a conditional discrimination based on the outcome of the preceding response.

Serial reversal learning by monkeys with inferotemporal or foveal prestriate lesions

Monkeys with bilateral lesions of either foveal prestriate cortex or inferotemporal cortex committed many times the errors made by intact monkeys in learning a visual pattern discrimination. This impairment gradually disappeared in the course of learning ten successive reversals of this discrimination. Neither of these lesions then can be characterized as one which produces an inability to form general learning rules.

Cross-modal transfer of serial reversal learning in the monkey

Twelve monkeys were trained on two separate series of 20 reversals. Different stimulus dimensions were relevant in each of the series so that any facilitation between series could not be the result of transfer of response to a dimension. In the experimental group, four animals learned the first series through touch in the dark, and the second through vision in the light; another four were trained in the converse order. Four other animals (the control group) learned both series visually. There was evidence for improvement within each series of reversals in both experimental and control groups, and of transfer between the two visual series in the control group. On the other hand, only slight evidence for transfer between sense-modalities was found, and this is interpreted to be the result of non-specific effects.

Selective attention and response strategies as factors in serial reversal learning.

Selective attention and response strategies as factors in serial reversal learning.

Factors underlying improvement in serial reversal learning.

Factors underlying improvement in serial reversal learning.

Serial reversal learning as a function of the number of trials per reversal.

Serial reversal learning as a function of the number of trials per reversal.

An application of Levine's model for hypothesis behavior to serial reversal learning.

An application of Levine's model for hypothesis behavior to serial reversal learning.