Active role of the shock-avoidance contingency in shuttlebox-avoidance learning in Fischer344 rats

Different groups of Fischer344 rats acquired and maintained shuttlebox-avoidance responses under one, two, all three, or none of the shock-avoidance, warning-signal (WS) termination, and shock-escape contingencies. The intertrial interval was fixed at either 30 or 60 s. Removal of the shock-avoidance contingency led to a marked disruption of avoidance behavior at both intervals. This result was not produced by a selective punishment effect of the avoidance response by an inevitable shock. Thus, the shock-avoidance contigency provided particularly effective control over the avoidance learning. The WS termination contingency appeared to have little overall effect at the 60-s intertrial interval. It is suggested that response-contingent stimulus change served only as a discriminative cue for the absence of a shock.     

Partial avoidance contingencies: Absolute omission and punishment probabilities

Avoidance contingencies were defined by the absolute probability of the conjunction of responding or not responding with shock or no shock. The “omission” probability (ρ₀₀) is the probability of no response and no shock. The “punishment” probability (ρ₁₁) is the probability of both a response and a shock. The traditional avoidance contingency never omits shock on nonresponse trials (ρ₀₀=0) and never presents shock on response trials (ρ₁₁=0). Rats were trained on a discrete-trial paradigm with no intertrial interval. The first lever response changed an auditory stimulus for the remainder of the trial. Shocks were delivered only at the end of each trial cycle. After initial training under the traditional avoidance contingency, one group of rats experienced changes in omission probability (ρ₀₀>0), holding punishment probability at zero. The second group of rats were studied under different punishment probability values (ρ₁₁>0), holding omission probability at zero. Data from subjects in the omission group looked similar, showing graded decrements in responding with increasing probability of omission. These subjects approximately “matched” their nonresponse frequencies to the programmed probability of shock omission on nonresponse trials, producing a very low and approximately constant conditional probability of shock given no response. Subjects in the punishment group showed different sensitivity to increasing absolute punishment probability. Some subjects decreased responding to low values as punishment probability increased, while others continued to respond at substantial levels even when shock was inevitable on all trials (noncontingent shock schedule). These results confirm an asymmetry between two dimensions of partial avoidance contingencies. When the consequences of not responding included occasional omission of shock, all subjects showed graded sensitivity to changes in omission frequency. When the consequences of responding included occasional shock delivery, some subjects showed graded sensitivity to punishment frequency while others showed control by overall shock frequency as well.     

Effects of US-Presentation and CS-termination contingencies on avoidance extinction following partial and continuous reinforcement

The present study assessed the role of both the US-presentation (punishment) and CS-termination contingencies on the maintenance of the shuttlebox avoidance responding in gerbils following acquisition under either partial reinforcement (PR) or continuous reinforcement (AV). Following PR, a stronger relationship obtained between delay of CS termination CR frequency than was found between delay of punishment and extinction performance. Following AV training, however, delay of CS termination and delay of punishment were equally effective determinants of avoidance extinction. These results were interpreted in terms of both the enhanced efficacy of the CS-termination contingency, possibly due to its increased informational value, and the attenuation of punishment suppression in PR-trained Ss.     

Running-wheel avoidance learning in rats (Rattus norvegicus): effects of contingencies and comparisons of different strains

In Experiment 1, we showed that active- and passive-avoidance responding in a running wheel was learned because of the avoidance contingency. In Experiment 2, strain differences among four commercially bred rats were assessed in an active-avoidance paradigm. Wistar, Donryu, and Fischer rats learned faster than Sprague-Dawleys. In Experiment 3, learning in a multiple active/passive avoidance schedule was examined, and both components of this task were learned. This multiple schedule was used to investigate strain differences in selectively bred rats in Experiments 4 and 5. Tsukuba low-emotional (TLE) rats responded more than Tsukuba high-emotional (THE) rats in both components. However, discrimination of passive components was better in THE than in TLE rats. Syracuse high-avoidance rats were superior in the active component, whereas Syracuse low-avoidance rats showed superior performance in the passive component.     

Molecular contingencies in schedules of intermittent punishment

In two experiments, key pecking of pigeons was maintained by a variable-interval 180-s schedule of food presentation. Conjointly, a second schedule delivered response-dependent electric shock. In the first experiment, shocks were presented according to either a variable-interval or a nondifferential interval-percentile schedule. The variable-interval shock schedule differentially delivered shocks following long interresponse times. Although the nondifferential shock schedules delivered shocks less differentially with respect to interresponse times, the two shock schedules equally reduced the relative frequency of long interresponse times. The second experiment differentially shocked long or short interresponse times in different conditions, with resulting decreases in the relative frequency of the targeted interresponse times. These experiments highlight the importance of selecting the appropriate level of analysis for the interaction of behavior and environment. Orderly relations present at one level of analysis (e.g., interresponse times) may not be revealed at other levels of analysis (e.g., overall response rate).     

Reaction to punishment, reflectivity, and passive avoidance learning in extraverts

Passive avoidance learning occupies a central role in accounts of disinhibited behavior, ranging from psychopaths' persistent criminality (Hare 1970) to extraverts' gregariousness (Gray, 1972). To explore the mechanism underlying passive avoidance deficits, we assessed the relation of extraversion, neuroticism, and response latency after punishment to passive avoidance learning by using two successive go/no go discrimination tasks. The tasks were designed to examine two aspects of subjects' reactions to punishment: response speed on trials immediately following punishment (Experiment 1) and time to terminate punishment feedback between successive trials (i.e., reflectivity; Experiment 2). Consistent with previous findings, the results of Experiment 1 showed that extraverts commit more passive avoidance errors than introverts do (Newman, Widom, & Nathan, 1985) and fail to pause following punished errors (Nichols & Newman, 1986). In Experiment 2, only neurotic extraverts displayed this pattern of performance differences. In both experiments, longer pausing following punishment predicted better learning from punishment for both introverts and extraverts. These results suggest that, in the presence of salient cues for reward, extraverts' characteristic reaction to punishment interferes with processing punished errors and may contribute to their more general propensity for impulsive, nonreflective action.     

The effectiveness of reward and punishment contingencies on response inhibition

The relative effectiveness of reward and punishment on the development of response inhibition was evaluated developmentally. Forty kindergarten and forty second-graders received response inhibition training with half of each group rewarded for inhibiting and half punished for not inhibiting. Reward involved the presentation of positive reinforcers, whereas punishment involved their removal. Punishment produced more inhibition at both age levels than did reward. Transfer of inhibition training was evaluated in two tasks. Transfer effects were observed only on one of the two tasks. Reinforcement contingencies and age did not differentially influence the magnitude of transfer.     

Delay discounting in Lewis and Fischer 344 rats: steady-state and rapid-determination adjusting-amount procedures

Lewis rats have been shown to make more impulsive choices than Fischer 344 rats in discrete-trial choice procedures that arrange fixed (i.e., nontitrating) reinforcement parameters. However, nontitrating procedures yield only gross estimates of preference, as choice measures in animal subjects are rarely graded at the level of the individual subject. The present study was designed to examine potential strain differences in delay discounting using an adjusting-amount procedure, in which distributed (rather than exclusive) choice is observed due to dynamic titration of reinforcer magnitude across trials. Using a steady-state version of the adjusting-amount procedure in which delay was manipulated between experimental conditions, steeper delay discounting was observed in Lewis rats compared to Fischer 344 rats; further, delay discounting in both strains was well described by the traditional hyperbolic discounting model. However, upon partial completion of the present study, a study published elsewhere (Wilhelm & Mitchell, 2009) demonstrated no difference in delay discounting between these strains with the use of a more rapid version of the adjusting-amount procedure (i.e., in which delay is manipulated daily). Thus, following completion of the steady-state assessment in the present study, all surviving Lewis and Fischer 344 rats completed an approximation of this rapid-determination procedure in which no strain difference in delay discounting was observed.     

Fischer 344 and wistar rats differ in anxiety and habituation but not in water maze performance

The fact that various neuropharmacological substances have anxiolytic as well as amnesic effects suggests that neuronal mechanisms of anxiety and learning/memory closely interact. Hence, we hypothesized that differences in anxiety-related behavior could be accompanied with differences in cognition or habituation. Two rat strains with different levels of anxiety, more anxious Fischer 344 rats by Charles River (FC) and less anxious Wistar rats by Winkelmann (WW), were tested in the Morris water maze task and an open field test for habituation learning. Additionally, we investigated the effect of different light intensities on the performance in the Morris water maze and the elevated plus maze. The results of the water maze task indicate that differences in anxiety-related behavior do not go along with differences in this performance of learning/memory. Moreover, the test was not affected by different light intensities. In contrast, illumination did affect performance in the elevated plus maze test, wherein dim light provoked an anxiolytic effect in both rat strains. The findings that neither different baseline levels of anxiety nor fear modulating light conditions were accompanied by changes in the performance of rats in the Morris water maze led us to the suggestion that there is no connection between anxiety and learning/memory in this task. Contrarily, anxiety might be associated with habituation learning in the open field test, shown by the superior habituation of the anxious FC rats in comparison to the less anxious WW rats. In sum, these results indicate that anxiety and learning/memory seem to be independently regulated behaviors, whereas habituation might be more closely correlated with anxiety. Nevertheless, a general statement about the relation between emotionality and learning/memory mechanisms would be premature and the link between behaviors remains to be clarified.     

The effects of estradiol on avoidance learning in ovariectomized adult rats

The present study examined the effects of ovariectomy and subsequent estradiol replacement on learning in young adult rats using a set of instrumental avoidance paradigms differing in the nature and extent of prior experience in the learning context. Thus, one group of animals was placed directly into avoidance learning (AV). A second group was trained on an appetitive task first, and then transferred into the aversive context (AP-AV). The third group was exposed to the training context without any specific appetitive response requirement, and then required to learn an active avoidance response (Context-AV). We found that estradiol (OVX+E) impaired avoidance acquisition in all cases relative ovariectomized controls (OVX). In contrast, while avoidance learning is improved following appetitive training or context exposure in both OVX+E and OVX animals, the OVX+E animals profit to a greater extent from the appetitive or context experience than do the OVX controls. We suggest that this difference may be due to enhanced attentional processes or improved hippocampal processing of contextual factors. Thus, estradiol negatively influences simple associative avoidance learning in ovariectomized rats, but appears to promote positive transfer.     

Effects of combined treatment with vitamins C and E on passive avoidance learning and memory in diabetic rats

Learning and memory deficits occur in diabetes mellitus. Although the pathogenesis of cognitive impairment in diabetes has not been fully elucidated, factors such as metabolic impairments, vascular complications and oxidative stress are thought to play possible roles. Here we investigated the effect of chronic treatment with vitamin C (50 mg/kg, p.o), vitamin E (100 mg/kg, p.o) and both together on passive avoidance learning (PAL) and memory in male Wistar control and diabetic rats. Treatments were begun at the onset of hyperglycemia. Passive avoidance learning was assessed 30 days later. Retention was tested 24 h after training. At the end, animals were weighed and blood samples were drawn for plasma glucose measurement. Diabetes caused impairment in acquisition and retrieval processes of PAL and memory. The combination of vitamin C and E improved learning and memory in controls and reversed learning and memory deficits in diabetic rats. Combined treatment also affected the body weight and plasma glucose level of diabetic treated animals compared to untreated diabetic animals. Hypoglycemic effects and antioxidant properties of the vitamins may be involved in the nootropic effect of such treatment. These results show that combined treatment with vitamins C and E improved PAL and memory of control rats. In addition, combined vitamins administration to rats for 30 days from onset of diabetes alleviated the negative influence of diabetes on learning and memory. Therefore, combined vitamins treatment may provide a new potential alternative for prevention of impaired cognitive functions associated with diabetes and may warrant further clinical study.