Cortical spreading depression: A case of state dependent learning

Transfer between learning with the cortex normal (N) and with the cortex under bilateral spreading depression (D) was investigated in 3 phases: (1) escape pretraining (EPT), (2) original learning (OL), (3) relearning (RL). Twenty-eight male hooded rats were randomly assigned to the following conditions: (a) normal EPT, normal OL, depressed RL (nnd): (b) normal EPT, depressed OL, depressed RL (ndd); (c) depressed EPT, depressed OL, normal RL (ddn); (d) depressed EPT, normal OL, normal RL (dnn); (e) no EPT, depressed OL, depressed RL (xdd); (f) no EPT, normal OL, normal RL (xnn). The results indicated that (1) D-EPT facilitated D-OL but not N-OL, (2) N-EPT had no effect on D-OL or N-OL, (3) there was no appreciable transfer from D-OL to N-RL although N-OL and D-OL transferred readily to D-RL, (4) no negative transfer was found from either EPT to OL or from OL to RL. The data were interpreted to support state dependent learning theory presenting a case of asymmetrical dissociation. A cortical inhibition model was applied to explain the results. The results suggest that either subcortical and/or extracortical structures are sufficient for the forming, retaining and retrieving of a complex response pattern.     

Impaired heat discrimination learning after capsaicin treatment

A heat discrimination experiment has been designed with the intention of deciding whether rats treated with capsaicin are insensitive to heat or their thermolytic reactions are impaired. The animals were trained in a T-maze on an 11°C discrimination. The capsaicin-treated rats were slow in learning the task, and their running time was significantly longer than that of the controls even when they had mastered the problem. No such differences were found in the visual discrimination experiment in the same T-maze. It is suggested that the deficiency of the thermolytic reactions in the capsaicin treated rats may be due to an impaired heat sensitivity.     

Enhancement of discrimination learning following unilateral lesions of posterior neocortex in guinea pigs

Monocular acquisition and interocular transfer of a horizontal-vertical discrimination were measured in 16 male albino guinea pigs which were restricted to using either the contralateral or ipsilateral primary visual fibers; restriction was accomplished by introduction of a unilateral striate lesion coupled with monocular occlusion. Eight sham-operated animals served as controls. The animals restricted to use of the contralateral fibers showed reliably enhanced rates of acquisition as compared to the controls, while the animals restricted to the ipsilateral fibers were unable to master the discrimination. The control animals learned readily, but demonstrated fairly low levels of interocular transfer. The data suggest that there is some form of interhemispheric interference which is eliminated by the introduction of unilateral ablations of the posterior neocortex.     

Effect of bilateral olfactory bulbectomy on discrimination avoidance conditioning in rats

Studies were made with the two-way shuttle box method on the acquisition of discrimination avoidance learning by olfactory bulbectomized rats in relation to changes in emotional behavior. Bulbectomized rats showed a marked increase in locomotor activity, with accompanying augmentation of the reactivity and the appearance of muricidal behavior. Initially, the bulbectomized rats showed elevated conditioned avoidance responses to both the CS+ and the CS-. In later stages, there was a continued slow increase in responses to the CS+ accompanied by a decrease in responses to the CS-, until responses to both stimuli were only slightly elevated above the levels shown by control rats. This result suggests that olfactory bulbectomy does not affect discrimination ability itself, but the impairment of discrimination during the initial stages is resulted from hyperemotionality induced by olfactory bulbectomy.     

Effects of chronic manipulations of dietary choline on locomotor activity,discrimination learning and cortical acetylcholine release in aging adult fisher 344 rats

Dietary levels of choline have been shown to influence central cholinergic neurotransmission. To further examine the behavioral and neurochemical effects of dietary choline, adult Fisher 344 rats were maintained on choline deficient (n=6), enriched (n=6) or usual lab chow (n=6) diets for 38 weeks. During 14 weeks of free access to these diets, controls gained little weight whereas the deficient group increased and the enriched group decreased. For the remaining 24 weeks the weights of all groups were maintained at 90% of their original level. Locomotor activity did not differ significantly in a 90 min session but during a 20 hr session controls were most active, deficient rats least with the enriched group in between. The groups showed no significant differences in the acquisition or reversal of a discrimination. Spontaneous and evoked cortical release of acetylcholine was enhanced in the enriched group and decreased in the deficient group relative to controls. These data suggest that chronic manipulations of dietary choline may significantly influence Locomotor and neurochemical activity but not discrimination learning.     

Variability and discrimination reversal learning in the open field following septal lesions in rats.

Response variability on a 10 position horizontal response task and a position-habit discrimination followed by 2 reversals was examined in groups of rats with septal damage and operated control rats in the open field. As revealed by the number of positions with responses and the one position with the most responses, the rats with septal damage were reliably less variable in responding than the controls. In addition, the rats with septal damage made a reliably greater number of responses during extinction of the response. In the second experiment, groups of animals were tested for discrimination learning in a 2 part experiment using both a free-ranging and restricted open field. In both parts of the experiment, the rats with septal lesions learned the discrimination and both reversals faster than the controls. Animals tested in the restricted field learned the discrimination slightly faster than those tested in the free-ranging field. The superior discrimination learning for the rats with septal lesions was discussed as a lesion-induced increase in the incentive value of positive reward, producing shorter observed response latencies, resulting in a shorter delay of reinforcement.     

A comparison of state dependent learning induced by electroconvulsive shock and pentobarbital

Two experiments compared the efficacy of electroconvulsive shock (ECS) and ECS preceded by footshock (FS-ECS) to produce state dependent learning relative to pentobarbital (12 and 25 mg/kg). In Experiment 1, rats were trained in a water T-maze and retrained 72 hr later. Comparison with controls indicated: (a) FS-ECS administered 24 hr prior to training but not retraining (Agent-O order) produced state dependency but did not when animals were trained in the normal state and received FS-ECS 24 hr prior to retraining (O-Agent order) as in most retrograde amnesia experiments; (b) pentobarbital, 12 or 25 mg/kg, injected just prior to either training or retraining produced state dependency in the O-Agent order but not the Agent-O order; and, (c) ECS alone was not effective in either treatment order. Experiment 2 used reversal training to determine the state dependency effect of the agents. Conclusions were the same as in Experiment 1 except that FS-ECS produced state dependency in both treatment orders. These data indicate that FS and ECS interact to produce a dissociation effect 24 hr later that is as complete as that produced shortly after pentobarbital injections. The results of Experiment 2 but not of Experiment 1 support the notion that amnesia observed 24 hr after a training trial FS followed 0.5 sec later by ECS may be due to a state dependency effect rather than the failure of memory fixation.     

Genetic analysis of water maze discrimination learning for Mus musculus: polygenes and albinism.

Recombinant inbred strains, their progenitor strains and reciprocal F1 hybrids were given thirty spatial discrimination learning trials in the water maze. The pattern of RI strains in relation to the reciprocal F1 hybrids and the progenitor strains, and differences among strains, suggested that different sets of genes affect the various components of water maze discrimination learning. There was no evidence that the albino gene influenced either inferior or superior performance. Pigmented strains performed as well as, or better than, some albino strains, and albino strain BALB/cBy differed significantly from albino strains CXBG and CXBI. The two reciprocal F1 hybrids differed from blocks 2 and 3 of discrimination trials when swimming time was used a dependent variable. Thus, it appears that performance of the F1 hybrids was influenced by paternal effects, maternal effects, or paternal maternal interactions.     

Y-Chromosomal effects on discrimination learning and hippocampal asymmetry in mice

From a four-way cross between unrelated inbred strains of mice, a random-breeding line was developed that segregated at two coat-color loci and carried Y chromosomes from different sources. Adult males were used for measurements of black-white discrimination learning and 7-day response retention in a water maze, body weight, brain weight, and left- and right-side hippocampus weight. Clear evidence was obtained of Y-linked influences on response acquisition, body weight, right-side hippocampus weight, and hippocampal asymmetry, whereas direct effects of autosome 9 were indicated with regard to right-side hippocampus weight only. However, epistatic interactions of the Y chromosome with autosome 9 were found for response acquisition and body weight and with autosome 4 for hippocampal asymmetry.     

Effects of actinomycin D on brain RNA synthesis and discrimination learning in the goldfish (Carassius auratus)

Intracranial injection of actinomycin D 2 microgram inhibited about 70% of the brain RNA synthesis from 3 hr to 4 days after injection in the goldfish. Under these conditions, fish were given 4-day-training of visual discrimination between a card with vertical stripes and one with horizontal stripes. Fish injected intracranially with actinomycin D showed deficits in between-day retention (long-term memory) but not interruption of within-day acquisition (short-term memory). It is suggested that brain RNA synthesis is necessary only for the formation of long-term memory but not short-term memory.     

l-DOPA improves odor discrimination learning in rats

Using a forced-choice odor discrimination task in rats, we show here that intraperitoneal injections of l-DOPA improve rats' odor discrimination performance in comparison to control rats injected with saline. Although the exact mechanism of l-DOPA and potential action on dopamine receptors remains unclear, the present results indicate that rats injected with the 20-50 mg/kg of l-DOPA performed significantly better in an odor discrimination task than did control rats. In addition, we observed a significant correlation between the concentration of l-DOPA and odor discrimination performance.     

Inheritance of discrimination learning ability and retention in BA and DBA mice

Male house mice from two inbred strains, DBA/2 and BA, and their F₁ and F₂ crosses and backcrosses, B₁ and B₂, were tested for black-white discrimination learning and 24-hr response retention in a water maze. The BA strain exhibited an inferior learning performance. Nonparametric and biometrical genetic analyses provided only weak evidence of unifactorial inheritance of acquisition, but somewhat stronger evidence in the case of retention.     

Probability discrimination learning in hippocampectomized rats

Rats with hippocampal lesions or neocortical lesions and normal rats were trained on a spatial probability discrimination task where one side of a T maze was reinforced on 70% of the trials and the other side on the remaining 30% of the trials. Training was to a criterion of 39 correct trials out of 40 using a noncorrection procedure. There was no difference between the learning rates of normal rats and with neocortical lesions, but the rats with hippocampal lesions learned the discriminiation more rapidly than the other two groups. These results indicated that the hippocampus does not function as a stimulus gating system, but is probably concerned in the selection and rejection of hypothese (central-sets).     

Discrimination learning and stimulus generalization in rats with hippocampal lesions

Rats with hippocampal lesions and sham operated control animals were trained on a go-no-go tone discrimination. For half of the animals of each group the tone was the positive stimulus while for the other half the tone was negative. The hippocampal tone negative group took the greatest number of days to learn the task. Tone generalization tests administered the day after the learning criterion was reached did not yield any differences in either excitatory or inhibitory stimulus control between the hippocampal and sham animals.     

Deep hypothermia in mice: Effect of the interval between learning and treatment

Mice received deep hypothermia at different intervals after the partial acquisition in a Skinner box and were tested 24 hr later. The deficit of performances was related to the time interval between acquisition and minimum temperature and no deficit was found when this interval reaches 3 hr. Consolidation duration and memory processes are discussed.     

Gustatory stimulus control and reversal learning in rats

Behavioral indices of taste discrimination have been used to study gustatory physiology and psychophysics though they are often biased by taste and position preferences and offer limited stimulus control. In the present experiment five rats were trained to discriminate distilled water from 0.9% NaCl using a discretetrials go-no go procedure. When two rats were further trained on a series of 0.1% saccharin/NaCl discrimination reversals, correct responding occurred more rapidly following saccharin presentations independent of its stimulus property (S^D or S^Δ). The results are discussed in the context of experimental methods and the usefulness of the present technique for studies of gustatory physiology.     

The effect of medial thalamic lesions on emotionality,activity, and discrimination learning in the rat

Three experiments were conducted to examine the effects of medial thalamic lesions on emotionality, open-field activity, and discrimination learning. The first study revealed that rats with large medial thalamic lesions are significantly less responsive to capture and to handling than are sham-operated rats. The second study failed to produce any significant differences in open-field activity. A third study revealed that rats with large medial thalamic lesions, and with both small anterior and posterior medial thalamic lesions are impaired on the acquistion of an appetitive visual-tactile discrimination task, with the deficit being greatest in the large lesion group. It was concluded that the medial thalamus plays a role in the neural mediation of certain emotional responses and is critical in the acquisition of complex appetitive tasks.     

Serial reversal learning of position discrimination in developing rats

The current study established a procedure to evaluate the capability of rats on postnatal days (PND) 21, 26, and 30 to perform a spatial serial reversal task using a T-maze. Training consisted of an acquisition session followed by a series of six reversal sessions. To examine the role of proactive interference in the serial reversal effect, the point of reversal was manipulated so that it occurred at the start of each session (between-sessions) or the midpoint of each session (within-sessions). Performance was initially impaired during the first reversal but improved dramatically across the series. Reversal between-sessions enhanced this serial reversal effect in comparison to reversal within-sessions. Experiment 1 showed that rats of all ages learned the between-sessions serial reversal task at a comparable rate. However, on the within-sessions task, PND21 rats were impaired relative to the PND26 and 30 rats, which did not differ. Experiment 2 revealed that the addition of a tactile cue that is correlated with each phase of reversal eliminated age and task differences in serial reversal performance. These findings suggest that higher-order cognitive processes underlying serial reversal are present during the weanling period, but there is some improvement with age under conditions involving high memory interference and/or difficulty in detecting the transition between reversal phases.     

Effects of posttrial vasopressin injections on appetitively motivated learning in rats

Sixty male rats, maintained on 23-hr food deprivation were trained on two types of appetitive tasks: bar press responding under a CRF schedule, and under a differentially reinforced (light+, dark?) schedule. Performance of rats treated with lysine vasopressin, injected immediately after each training session, was compared to that of control animals injected with saline. In the CRF stage, treated animals reached learning criterion significantly later than did control rats, and made significantly fewer bar presses. During acquisition and extinction of a light-dark discrimination, learning and retention were not altered by vasopressin, though the number of bar presses was significantly decreased, and a differential effect was found according to previous CRF performance. The results are discussed considering the hypothesis of a facilitatory effect of vasopressin on memory processes.     

Evidence for effector independent and dependent representations and their differential time course of acquisition during motor sequence learning

To investigate the representation of motor sequence, we tested transfer effects in a motor sequence learning paradigm. We hypothesize that there are two sequence representations, effector independent and dependent. Further, we postulate that the effector independent representation is in visual/spatial coordinates, that the effector dependent representation is in motor coordinates, and that their time courses of acquisition during learning are different. Twelve subjects were tested in a modified 2x10 task. Subjects learned to press two keys (called a set) successively on a keypad in response to two lighted squares on a 3x3 display. The complete sequence to be learned was composed of ten such sets, called a hyperset. Training was given in the normal condition and sequence recall was assessed in the early, intermediate, and late stages in three conditions, normal, visual, and motor. In the visual condition, finger-keypad mapping was rotated 90 degrees while the keypad-display mapping was kept identical to normal. In the motor condition, the keypad-display mapping was also rotated 90 degrees, resulting in an identical finger-display mapping as in normal. Subjects formed two groups with each group using a different normal condition. One group learned the sequence in a standard keypad-hand setting and subsequently recalled the sequence using a rotated keypad-hand setting in the test conditions. The second group learned the sequence with a rotated keypad-hand setting and subsequently recalled the sequence with a standard keypad-hand setting in the test conditions. Response time (RT) and sequencing errors during recall were recorded. Although subjects committed more sequencing errors in both testing conditions, visual and motor, as compared to the normal condition, the errors were below chance level. Sequencing errors did not differ significantly between visual and motor conditions. Further, the sequence recall accuracy was over 70% even by the early stage when the subjects performed the sequence for the first time with the altered conditions, visual and motor. There were parallel improvements thereafter in all the conditions. These results of positive transfer of sequence knowledge across conditions that use dissimilar finger movements point to an effector independent sequence representation, possibly in visual/spatial coordinates. Initially the RTs were similar in the visual and the motor conditions, but with training RTs in the motor condition became significantly shorter than in the visual condition, as revealed by significant interaction for the testing stage and condition term in the repeated measures ANOVA. Moreover, using RTs for single key pressing in the three conditions as baseline indices, it was again observed that RTs in the visual and motor conditions were not significantly different in the early stage, but motor RTs became significantly shorter by the late testing stage. These results support the hypothesis that the motor condition benefits more than the visual because it uses identical effector movements to the normal condition. Further, these results argue for the existence of effector dependent sequence representation, in motor coordinates, which is acquired relatively slowly. The difference in the time course of learning of these two representations may account for the differential involvement of brain areas in early and late learning phases found in lesion and imaging studies.