Merrill F. Elias

Differences in reversal learning between two inbred mouse strains

DBA/2J and C56BL/6J mice were given original learning and 11 reversals of a spatial discrimination habit. The former strain required fewer trials to shift from incorrect to correct responding after a reversal and made fewer errors on reversals. These data suggest that (1) genetic characteristics contribute to differences in reversal learning, and (2) generalizations concerning phyletic differences in reversal learning may be premature prior to testing of diverse strains within species.

Spatial Discrimination Reversal Learning for Mice Genetically Selected for Differing Brain Size: A Supplementary Report

Spatial discrimination reversal learning was explored for mice genetically selected for high brain weight and unselected controls with lower brain weights. Control-line Ss escaped from a water maze more rapidly, but high-line Ss made fewer errors and took less trials to reach criterion on the first reversal. Control-line Ss were unable to complete more than 1 reversal, while high-line Ss all completed at least 7 reversals. This positive relation between reversal learning and brain size is consistent with comparisons among species and experiments manipulating brain size by means of drugs or surgery.

Reversal learning and RNA labeling in neurological mutant mice and normal littermates.

Abstract Incorporation of radioactive uridine into five brain areas, following reversal learning, was explored for neurological mutant mice with a deficit of myelin in the brain and spinal cord (quaking, qk qk ) and normal littermates (?/+) from strain C57BL/6- qk (Jackson Laboratory). Both groups mastered the reversal task, although the mutants performed at a lower level. There was a Genotype × Test Conditions × Brain Area interaction with littermates exhibiting increased labeling of RNA in the amygdala and the hippocampus, and the quaking mice exhibiting no significant changes in these two areas following learning. Findings suggest that a genetic defect in the integrity of the CNS, a deficiency of myelin, affects reversal learning, and that this effect may be reflected in changes in RNA synthesis, or specific activity, for structures which are critical to reversal learning ability.

Effects of amygdaloid lesions on reversal learning in the deermouse.

Abstract Electrolytic lesions were placed in the basolateral, cortical or medial amygdaloid nuclear groups in male deeermice using the stereotaxic atlas for this species. Sham-operated and intact control groups were also included in the study. After allowing the animals a two-week recuperative period, they were tested in a black sheet metal T-shaped water maze especially constructed for mice. Following habituation to the water maze, all animals were run through original learning and four reversal learning stages. Results indicate that a decrement of learning occurred in animals with lesions in the cortical or basolateral amygdaloid nuclear groups while those animals with lesions in the medial amygdaloid area did not exhibit any significant changes when compared to either the sham-operated or intact control groups.

Strain differences in memory and incentive as a function of external stimulation

Inbred mouse strains DBA/2J and C57BL/6J were subjected to either air blast or control handling immediately after each of 30 spatial discrimination trials given 22 to 26 h apart. Errors were more frequent and swimming times were longer for the air-blast group of the C57BL/6J strain. Data were interpreted in terms of interference with memory consolidation and incentive to respond by means of aversive external stimulation.

Proactive and retroactive effects of diethyl ether on spatial discrimination learning in inbred mouse strains DBA/2J and C57BL/6J

Diethyl ether was given before or after a single daily spatial discrimination trial in a water maze. Both C57BL/6J and DBA/2J mice made more errors than controls of these same strains when they were etherized after a trial, although the decremental effect on performance was more notable in the former strain. Pretrial etherization had no effect on errors, but mice etherized prior to each trial showend faster swimming times than control Ss. These data were discussed in terms of strain differences in ether-stimulated arousal or activity level.

Effect of Pattern Configuration on the Relation between Pattern Area and Pattern Discrimination

To explore the possibility that brightness-area disparity in sub-portions of correct and incorrect patterns contributes to improved learning with increasing pattern area, hooded rats were tested with two discrimination problems: high disparity (triangle apex-up versus triangle apex-down) and low disparity (triangle apex-left versus triangle apex-right). Increasing pattern area resulted in improved learning for the high-disparity but not for the low-disparity condition. It was concluded that brightness-area disparity does contribute to improved learning with larger patterns and might provide a useful dimension for classification of patterns in experiments designed to explore the interaction of pattern size and pattern configuration.

Administration of inhalation anesthetics to small animals: Some problems and solutions

Some problems inherent in administering inhalation anesthetics to small laboratory animals in studies of memory consolidation are discussed. A simple and inexpensive apparatus which has been designed to eliminate some of these problems is described.

Relation of mental ability to preference for varying rates of auditory stimulation

Preferences for varying rates of auditory stimulation were compared for three groups: (a) older Ss of average IQ, (b) younger Ss of average IQ, and (c) older retarded Ss. All possible pairs of eight different auditory rates, consisting of differing numbers of tones per 10-sec period, were presented. Younger Ss of average IQ showed a greater preference for the highest rates of stimulation than the older Ss. Preferences of older retardates were more similar to younger Ss.