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PubMedDate not supplied

Effect of prenatal heat stress on brain growth and serial discrimination reversal learning in the guinea pig.

Exposure of pregnant guinea pigs to an environmental temperature of 42 degrees C for 1 hr daily on Days 20-24 of gestation resulted in a significant reduction in the birthweight and brainweight of newborn offspring. These deficits persisted to early maturity and were still evident at 250 days of age following behavioral testing. Although some degree of postnatal neurogenesis and brain growth had occurred, this was not sufficient to compensate for the retarding influence of prenatal hyperthermia. Heat stress was also observed to seriously impair learning performance on the original discrimination task and this tendency persisted over the subsequent 4 reversals for both initial and perseverative errors. Impaired learning performance was related to reduction in brainweight. Animals with lower brainweights made significantly more initial, perseverative and total number of errors over the 5 problems. In addition, 12 of the 14 behaviorally tested stressed progeny had brainweights that were at least 2 standard deviations below the mean of the controls and as a result were classified as micrencephalic. Although heat stressed animals showed a significant reduction in the number of amacrine synapses in the inner plexiform layer of the retina, performance differences were not atrributed to changes in synaptic organisation of the retinal circuitry or to visual or other ophthalmic defects, but brain function. Animals with higher mean maternal poststressing core temperatures gave birth to progeny which had smaller whole and part wet-brainweights. Examination of the effect of poststressing core temperature on brainweight revealed that brain growth, independent of bodyweight, was retarded when this temperature elevated above 41.5 degrees C. This represented a rise of approximately 2.1 degrees C above normal and for each 1 degree C rise above this temperature, brainweight was reduced by 0.4227 g of the control value. Analysis of the atmospheric content of the incubator during stressing sessions ruled out the possibility that changes in level of oxygen and carbon dioxide may have contributed to the retarding influence on fetal development and learning ability in the guinea pig.

Animals↗
PubMed1990

Further evidence of the intricacy of memory span.

Memory span was measured for lists of verbal items constructed such that the items in the first half of the list were of one category and those of the second half were of another. In Experiment 1, the lists consisted of digits and words (e.g., 2, 8, 7, horse, cow, sheep or horse, cow, sheep, 2, 8, 7); in Experiment 2, they consisted of words from the same semantic domain and words from different semantic domains; in Experiments 3 and 4, they consisted of words that rhymed and words that did not rhyme. A category-order effect occurred in each experiment: Span was larger when the digits, same-domain words, or rhyming words occurred in the first half of the list than when they occurred in the second half. These findings suggest that memory span is more complex than is generally assumed.

Adult↗
PubMed1989

Repeated acquisition of behavioral chains: response sequences or conditional discriminations?

The purpose of this study was to determine whether pigeons learn a sequence of positional responses or a series of conditional discriminations under a repeated-acquisition-of-behavioral-chains procedure. Three pigeons were trained under a repeated-acquisition procedure in which three different key colors served as stimuli correlated with the three steps in a chain. The order of presentation of the three stimuli was altered during the latter part of each test session after acquisition had occurred. If the pigeons had acquired a response sequence, the pattern of responding should remain the same as in the initial portion of the test session. However, if the pigeons had acquired a conditional discrimination, the response pattern should change in accordance with the changed order of the key colors. Although the results of this study do not rule out the possibility that the subjects acquired, to some degree, a response sequence, the results suggest that the behavior of pigeons under a repeated-acquisition-of-behavioral-chains procedure is controlled primarily by conditional discriminative stimuli.

Animals↗
PubMed1990

Equivalence classes generated by sequence training.

In Experiment 1, 3, adult females were taught with verbal instructions and contingencies to select, in sequence, three arbitrary visual stimuli from an array of five stimuli. After four different sequences were taught, match-to-sample tests assessed emergent conditional relations among all stimuli that had been selected in the same order in the sequences. Subjects' performances indicated development of four stimulus classes, three based on ordinal position and one based on nonselection. Next, match-to-sample training established conditional relations between each of four novel figures and one member of each of the ordinal stimulus classes. Tests confirmed that the classes were equivalence classes, each expanded by one new member. In subsequent sequence tests, the new stimuli were selected in a sequence that was consistent with ordinal class membership. Experiment 2 replicated Experiment 1 with 2 different adult females, but the verbal instructions were omitted. Results were similar to Experiment 1, except that extensive review and retesting were required before expansion of the ordinal classes with the novel figures was observed.

Adult↗
PubMed1991

Serial processing and the "phonetic route:" lessons learned in the functional reorganization of deep dyslexia.

A patient with chronic agrammatic Broca's aphasia presented with symptoms of deep dyslexia, in which it is presumed that phonologic processing of the written message is disrupted. Functional reorganization of the "nonlexical" or phonetic route of reading was undertaken according to principles of A. R. Luria, whereby the patient must learn consciously to control behaviors that had formerly been unconscious and automatic. This patient's responses in treatment made it clear that the phonetic route encompasses at least two dissociable functions, grapheme-phoneme conversion and sequential analysis. This is discussed in light of Luria's ideas regarding the functions of the precentral and postcentral regions of sensori-motor cortex.

Adult↗
PubMed1991

[Interaction between visual and auditory memories in repetitive learning].

A serial recall experiment under same- and cross-modality conditions was carried out according to Hebb's (1961) paradigm. Subjects memorized strings of nine digits in 18 trials, which were divided into early trials and late ones. Under the same-modality condition the strings used in the 18 trials were presented through the same modality, i.e., visual or auditory, whereas under the cross-modality condition the strings used in the early and late trials were presented through two different modalities. A repeated string and unrepeated strings were presented 3 and 6 times respectively in both early and late trials. The results showed that (1) repetitive learning in the same-modality occurred for both visual and auditory; (2) there was a non-additivity of cross-modal repetitive learning from auditory to visual, whereas there was an additivity of cross-modal repetitive learning from visual to auditory. We inferred that the visual inputs received both visual coding and auditory coding through an audio-transformation so as to be separately memorized in visual and auditory memories, whereas the auditory inputs were memorized in the auditory memory through the auditory coding alone.

Adult↗
PubMed1990

New approaches to the study of comparative cognition.

The rat's memory capacity and performance render it an excellent model of human memory. Rats display serial position, serial anticipation learning, temporal coding, and repetition lag functions as well as utilization of retrospective and prospective codes that are nearly equivalent to that observed for humans. Furthermore, based on the above-mentioned memory performance functions, there are comparable memory-deficit patterns between brain-damaged rats and humans. Thus, the rat can serve as an excellent animal model to evaluate the efficacy of pharmacological treatments or brain damage upon memory.

Animals↗
PubMed1991

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.

Animals↗