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Rats with lesions of the hippocampus or mammillary bodies were impaired in learning reversal problems in a T-maze. Test trials given after learning each reversal disclosed little forgetting in the mammillary body group but rapid forgetting in the hippocampal group. These findings resemble those recently reported in patients with amnestic syndromes.
Previous studies with mice lacking 5-HT(1A) (1AKO) and 5-HT(1B) (1BKO) receptors in hippocampus-dependent learning and memory paradigms, suggest that these receptors play an important role in learning and memory, although their precise role is unclear. In the present study, 1AKO and 1BKO mice were studied in operant behavioural paradigms of decision making and response inhibition, to further study the putative involvement of these receptors in prefrontal cortex-dependent learning and memory. Moreover, because 1AKO mice have been shown to exhibit an antidepressant-like phenotype and 1BKO mice to be more impulsive in ethological studies, mice were trained in a differential-reinforcement-of-low-rates (DRL) procedure. Overall, results indicate that 1AKO and 1BKO mice display subtle differences in operant paradigms of decision making and response inhibition compared to wild type (WT) mice. In addition, when responding under a DRL 36-s schedule had stabilised, 1BKO mice showed a phenotype indicative of increased impulsivity, whereas 1AKO mice did not differ from WT mice. In conclusion, 5-HT(1B) receptors appear to play an important role in impulsivity and a minor role in prefrontal cortex-dependent learning and memory as shown by the results obtained in serial reversal learning and extinction. In contrast, 5-HT(1A) receptors appear to be involved in facilitation of autoshaping, but their role in impulsivity and prefrontal cortex-dependent learning and memory appears to be limited.
Nine marmosets (Callithrix jacchus) were tested on a variety of visual discrimination learning tasks in a Wisconsin General Test Apparatus with or without alpha-noradrenergic receptor blockade achieved by the administration of aceperone. After aceperone, animals were found to be severely and consistently impaired at learning the first task of each test session and to be impaired on new and repeated reversal learning. They were, however, unimpaired on learning another similar task in each test session and on performance of a well-learnt task. Results were interpreted as evidence for defective association formation which can be compensated for by suitable priming or practice.
This study investigated the role of the hippocampus in pigeons learning of a food-related choice task. The effects of lesions induced by ibotenic acid were analyzed in two experiments. Experiment 1 investigated the effects of hippocampal damage on postoperative memory retrieval and in reversal learning. Experiment 2 investigated the effects of hippocampal lesions on the acquisition and reversal of learning. In both experiments probe tests were used to assess the behavioral strategies underlying the choice. In Experiment 1 hippocampal lesions impaired the preoperative learned performance in terms of choice latency but not choice accuracy. Experiment 2 data showed that, in postoperative learning sessions, latency as well as choice accuracy were impaired by hippocampal damage. The probe tests, in which a curtain was placed around the chamber, revealed behavioral patterns of a non-mapping strategy. This was true in both experiments and groups (experimental and controls). Immediately after training, during the probe tests of both experiments, in which food cups were omitted, the three groups spent more time in the target quadrant. However, immediately after the reversal condition, neither hippocampal damaged nor control pigeons showed a preference for the target quadrant. This may be interpreted as evidence for a hippocampal role in stimulus location learning involving non-mapping strategies.
Light-dark discrimination learning in rat offspring born to mothers treated with chlorpromazine was studied. Daily doses of 16 mg/kg, administered from gestation day 17 to day 21, had no effect on the acquisition of lever press responses and on the original discrimination learning. However, acquisition of the reversal learning was retarded. The same dose administered during the nursing period did not produce such behavioral changes. The results indicate that high doses of chlorpromazine administered during the peripartum period might cause learning impairment in the offspring.
Rats with bilateral 192 IgG-saporin lesions to the nucleus basalis magnocellularis (nBM) were tested on olfactory discrimination learning set (ODLS), olfactory discrimination reversal learning set (DRLS), and open field activity. Control animals demonstrated learning set in both the ODLS and DRLS tasks. The nBM-lesioned animals showed initial acquisition impairment in learning set in the ODLS task but eventually demonstrated learning set in both ODLS and DRLS tasks. There were no group differences in open-field activity. Results suggest that removal of the nBM cholinergic system through 192 IgG-saporin lesions impairs early acquisition of learning set compared to control animals, but does not prevent later use of learning set formation. Implications for the non-cholinergic basal forebrain cells in learning set are discussed.
The effects of thyroid hormone depletion and enhancement on litter size, survival, body mass, ambulation, quadrant crossing, home orientation, day of eye opening, and free serum T3 and T4 levels were examined in Study 1. In Study 2, the effects of the timing of prenatal insult and the level of thyroid hormone depletion on litter size, survival, body mass, and free serum T3 and T4 levels were examined. Upon the completion of Study 1, randomly selected pups were maintained on ad-libitum water and food for 2 years, and performance was evaluated on fixed and variable ratio schedules, fixed and variable interval schedules, and probability and reversal learning tasks (Study 3). In Study 4, human subjects diagnosed with and treated for either congenital hypothyroidism or congenital hyperthyroidism were tested on the operant procedures used in Study 3, as well as on a series of simple reaction time, serial timing, and conjunctive and disjunctive search tasks. Dose-dependent decreases in survival and delays in the presentation of early motor and exploratory skills were observed following thyroid hormone depletion; dose-dependent accelerations in the presentation of early motor and exploratory skills were observed following thyroid hormone enhancement. Pups that had been prenatally exposed to propylthiouracil (PTU) 1-2 years after the return of thyroid hormones to baseline levels were significantly less accurate at timing on fixed and variable interval schedules, demonstrated an inability to allocate responding on probability tasks, and committed more errors during original learning (OL) and on each reversal problem. Similar deficits were observed in follow-up tests with humans diagnosed with congenital hypothyroidism, as were deficits in serial timing and visual searching. Collectively, the present results demonstrate that the pervasive and negative effects of prenatal thyroid deficiency on early behavior are also expressed during adult operant performance.
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.
Sixteen rats, eight with bipolar electrodes implanted bilaterally in the anterodorsal head of the caudate-putamen and eight with similar electrodes in the posteroventral caudate-putamen, learned a spatial and a form discrimination task and their reversals while receiving "continuous" stimulation. Rats receiving stimulation to the anterodorsal caudate-putamen were imparied on spatial reversal learning compared with the posteroventral group. On form discrimination reversal the posteroventral group were impaired compared with the anterodorsal group. This dissociation is related to the particular cortical neostriatal projection system for the region stimulated and demonstrates a behavioral differentiation in rat neostriatum comparable with that observed in the monkey.
Rats with quisqualic acid lesions of the nucleus basalis magnocellularis (nBM) and control rats were compared in discrimination reversal learning set (DRLS) and olfactory discrimination learning set (ODLS) tasks, a delayed matching-to-sample task (DMTS), and open-field activity. Evidence of learning set formation was seen in control rats but not in nBM-lesioned rats in both the DRLS and ODLS tasks. Better-than-chance performances were seen for both groups in DMTS, indicating no impairment after nBM lesions. There were no group differences in open-field activity. These findings suggest that the nBM is important for higher cognitive processing such as "learning to learn" and thus is important for a complex form of reference memory. In addition, perseverational, working memory, and attentional deficits could not explain learning set impairment after nBM lesions.
Using the proboscis extension response we conditioned pollen and nectar foragers of the honey bee (Apis mellifera L.) to tactile patterns under laboratory conditions. Pollen foragers demonstrated better acquisition, extinction, and reversal learning than nectar foragers. We tested whether the known differences in response thresholds to sucrose between pollen and nectar foragers could explain the observed differences in learning and found that nectar foragers with low response thresholds performed better during acquisition and extinction than ones with higher thresholds. Conditioning pollen and nectar foragers with similar response thresholds did not yield differences in their learning performance. These results suggest that differences in the learning performance of pollen and nectar foragers are a consequence of differences in their perception of sucrose. Furthermore, we analysed the effect which the perception of sucrose reward has on associative learning. Nectar foragers with uniform low response thresholds were conditioned using varying concentrations of sucrose. We found significant positive correlations between the concentrations of the sucrose rewards and the performance during acquisition and extinction. The results are summarised in a model which describes the relationships between learning performance, response threshold to sucrose, concentration of sucrose and the number of rewards.
Experiments were carried out to investigate the effects of post-trial reinforcing stimulation of the lateral hypothalamus on learning in rats. The reinforcing stimulation was always presented for a duration of 20--30 sec (0.2 sec on/0.8 sec off), and was administered either immediately, 30 sec delayed or 300 sec delayed after exposure to the learning situation. In experiment 1 post-trial stimulation led to improved passive avoidance learning of an alcove-avoidance task when presented 30 sec compared to immediately after the footshock. In Experiment 2 reversal learning of a one-way shuttle-box avoidance task was facilitated by 30 sec delayed, but not 300 sec delayed post-trial reinforcing stimulation. In Experiment 3 appetitive left-right discrimination was investigated using a T-maze task. Thirty sec delayed post-trial reinforcing stimulation presented contingent on errors facilitated learning of this task. Together, the 3 studies provide further support for the hypothesis that reinforcers directly influence labile memory processes (such as short-term memory) and thereby improve learning.
30 subjects volunteered from three sources: community adults (M age = 32.8, SD = 13.4), college adults (M age = 23.8, SD = 8.3), and children (M age = 9.5, SD = 1.7) and were categorized as 'left-' and 'right-dominant' by scores on Your Style of Thinking and Learning. They reported the number of Necker cube reversals perceived in 90 sec., attempted to locate four embedded figures, and blindly traversed a 16-choice point finger maze in that order. 'Right-dominant' subjects located more embedded figures and made fewer errors on the finger maze than did 'left-dominant' subjects. College adults reported more Necker cube reversals than did community adults and children, and community adults reported more reversals than did children. Confounds of performance measures with fatigue and/or practice require further research.
Four experiments examined effects of quinolinic acid-induced lesions of the anterior cingulate, posterior cingulate, and medial frontal cortices on tests of visual discrimination learning, using a new "touchscreen" testing method for rats. Anterior cingulate cortex lesions impaired acquisition of an 8-pair concurrent discrimination task, whereas posterior cingulate cortex lesions facilitated learning but selectively impaired the late stages of acquisition of a visuospatial conditional discrimination. Medial frontal cortex lesions selectively impaired reversal learning when stimuli were difficult to discriminate; lesions of anterior and posterior cingulate cortex had no effect. These results suggest roles for the anterior cingulate, posterior cingulate, and medial frontal cortex in stimulus-reward learning, stimulus-response learning or response generation, and attention during learning, respectively.
The influence of 33 days of combined dietary sodium and water deprivation on the taste sensitivity and responsivity of the rat to a wide range of NaCl solutions and discrimination tasks was examined using double-blind procedures, high-precision gustometry, and an automated operant go/no-go task. Sodium concentration in urine and saliva but not plasma decreased significantly only in the sodium-deficient rats. The same measures remained unchanged in control animals. Nonparametric measures of taste sensitivity and responsivity to NaCl did not differ between sodium-deficient and control animals and performance on taste discrimination, reversal learning, and lick-rate tasks remained the same between the groups as well. The present results support and extend previous findings that dietary-induced sodium deficiency increases NaCl and water consumption, but alters neither the sodium-deficient rat's taste sensitivity and responsivity nor performance on simple and complex tasks in which tastants serve as cues for discriminative responding.
The effects of cytotoxic lesions in either the anterior cingulate cortex or the retrosplenial cortex were compared with those of fornix lesions on three tests of spatial memory. Two of the tasks, delayed nonmatching-to-position and spatial reversal learning, were tested in an automated apparatus. The third task, forced alternation, was tested in a T-maze. Neither anterior cingulate nor retrosplenial cortex damage produced any significant impairment on the three tasks. In contrast, rats with fornix lesions (hippocampal system damage) were markedly impaired on all three tasks. The results, which were considered in the light of proposals for a hippocampal--anterior thalamic--cingulate system that is important for spatial memory, suggest that neither of the cingulate regions involved in this study form a critical subcomponent of this proposed system. It is therefore assumed that the cingulate cortices are only critical for certain classes of spatial problem. It is also suggested that in some previous studies the effects of inadvertent damage to the cingulum bundle may have contributed to the apparent effects of cingulate lesions.
In two experiments, pigeons with bilateral lesions of the hyperstriatum were compared with unoperated control birds on tasks designed to test an attentional account of hyperstriatal function. In both experiments, hyperstriatal lesions disrupted reversal learning but did not influence the retardation of learning associated with either nonreinforced preexposure to the to-be-conditioned stimulus (Experiment 1) or prior nondifferential reinforcement to the to-be-discriminated stimuli (Experiment 2). There was, however, evidence of an impairment in both the acquisition and maintenance of autoshaped responding in lesioned birds, an impairment which may reflect a disruption of classical associations in hyperstriatal pigeons.
The concentration of the major polyunsaturated fatty acid (PUFA) in brain, docosahexaenoate, may be markedly reduced by two or more generations of dietary restriction of sources of n-3 fatty acids in the diet. Such a deficiency was induced through the feeding of safflower oil as the principal source of essential fatty acids. The reference point for this diet was an n-3 adequate diet to which alpha-linoleate and docosahexaenoate were added through the addition of a small quantity of flax seed or algael oils, respectively. The loss of brain DHA was associated with poorer performance in spatial tasks and an olfactory-cued reversal learning task. No difference could be observed in the hippocampal gross morphology. This study demonstrates the importance of providing a source of n-3 fatty acids during mammalian growth and development.