Denis Mitchell

The psychological vs. the ethological rat: Two views of the poison avoidance behavior of the rat compared

In rebuttal to the above comments on our paper (Mitchell, Scott, & Mitchell, 1977), I would first like to clarify the fundamental differences between my view and that of my adversaries. To do so, I will first outline the pertinent characteristics of each view. I will then briefly compare the two views and finish with specific comments on the present objections to my conclusions raised by my adversaries. As I see them, our theoretical differences are best exemplified by our two views of the rat; the psychological vs. the ethological rat.

Arousal and T-maze choice behavior in mice: A convergent paradigm for neophobia constructs and optimal arousal theory

Abstract Three experiments investigating the effects of arousal on the T-maze choice behavior of inbred mouse strains are reported. In Experiment 1, CBA and NZB mice were administered unrewarded free choice alternation tests on 10 consecutive days under either No Shock, Shock Start (shocked in the start box), or Shock Choice (shocked at the choice point) treatment conditions. Both strain and treatment effects were observed: In the No-Shock condition, the nonreactive CBA strain alternated, but the reactive NZB strain did not. In the Shock Start condition the CBA strain showed only a suppressed alternation, while the NZB strain administered the same treatment perseverated. Both strains perseverated in the Shock Choice condition. In Experiment 2, NZB mice administered identical shocks in the start box and goal arms on both trials of five consecutive tests conducted once a day perseverated to the same goal arm in which they had been shocked on the first trial. In Experiment 3, NZB mice punished for perseverating (with shock continuation) and simultaneously reinforced for alternating (with shock termination) showed a “punishment paradox”; they perseverated despite the reinforcement contingencies. These results, which are congruent with the optimal arousal theory and several characteristics the theory shares with the emergent neophobia construct, support the contention that arousal mediates a symmetrical relationship between approach and avoidance along a novelty-familiarity continuum.

Conditioned taste aversions accompanied by geophagia: evidence for the occurrence of "psychological" factors in the etiology of pica.

&NA; A conditioned taste aversion procedure was used to produce an avoidance of saccharin by rats. In the first experiment, saccharin consumption was paired with cyclophosphamide in two conditioning trials during which the animals were permitted to engage in pica. In the second experiment, saccharin consumption was paired with lithium chloride in four conditioning trials during which the animals were not allowed to engage in pica. Conditioned animals in both experiments subsequently engaged in geophagia when presented with saccharin alone. The absence of geophagia in noncontingently poisoned and “sham” injected control groups indicates that the pica was due to the acquisition of a conditioned illness during the conditioning trials. In addition to providing a demonstration of “psychological” involvement in the etiology of pica, these results indicate that visceral conditioning may accompany the formation of conditioned taste aversions. It is suggested that if there is a relationship between infantile pica and adult drug addiction, a plausible mediational mechanism is that pica‐prone and addiction‐prone individuals are similar in possessing a high susceptibility to visceral conditioning.

Habituation under stress: shocked mice show nonassociative learning in a T-maze.

Conflicting predictions of reinforcement and neophobia-arousal theories were evaluated in a simple choice task. Four groups of C57BL/6J mice were administered daily two-trial tests in a uniform T-maze for 10 consecutive days. For three groups, the contingencies of footshock treatments were manipulated to reinforce alternation, perseveration, or both. A control group that was not administered footshock alternated, but all three groups that were stressed perseverated more and more across tests, despite the differences in reinforcement contingencies. These results are inconsistent with the predictions of reinforcement theory but consistent with the view that stressed or aroused animals are neophobic and use nonassociative learning (habituation) to distinguish between novel and familiar alternatives.

Individual differences in emergence neophobia predict magnitude of perforant-path long-term potentiation (LTP) and plasma corticosterone levels in rats

Emergence neophobia was assessed in an emergence apparatus that provided a choice between novel and familiar alternatives. Two weeks after emergence testing, the threshold to induce perforant-path long-term potentiation (LTP) and the magnitude of perforant-path LTP in the dentate gyrus were assessed under pentobarbital anesthesia. Two measures of emergence behavior, the total duration of time spent in the alley during the 1-h test and the emergence duration per entry into the novel compartment, were significantly correlated with LTP of the extracellular population excitatory postsynaptic potential (EPSP), but not with the population spike. Neophobic animals that spent relatively little time in the novel alley during the 1-h test had a lower threshold to induce LTP and exhibited greater asymptotic EPSP LTP than did neophilic animals that readily entered and explored the novel alley. In a second experiment, plasma corticosterone levels in animals tested in the emergence task were also correlated with emergence duration and were generally lower in neophobic animals. Together, these data suggest that neotic behavior and LTP share a common mechanism, possibly one mediated by an interaction of glucocorticoid hormones and habituation.

Cross-modality contrast: Exteroceptive context habituation enhances taste neophobia and conditioned taste aversions

The relationship between absolute and relative stimulus novelty was examined within the context of the conditioned taste aversion paradigm in which the relative novelty of the conditioned interoceptive stimulus was manipulated by differential exteroceptive context habituation. Rats received similar isolation histories but either 5 or 30 days of habituation to the test environment prior to treatment. One group was administered lithium chloride following saccharin consumption, a second group was administered isotonic saline following saccharin consumption, and a third group was administered saline after water consumption. The animals habituated for 30 days exhibited greater conditioned avoidance and greater neophobic avoidance of saccharin than did animals habituated for only 5 days. The results are interpreted in terms of a cross-modality stimulus contrast effect which implicates context habituation as an important parameter of both taste neophobia and taste aversion learning.

The effects of hippocampal lesions on two neotic choice tasks

We report two experiments in which rats with hippocampal lesions were tested in two neotic choice tasks that provided a clear distinction between novel and familiar alternatives. In the first experiment, rats with either dorsal or complete lesions were tested in an emergence task in which they were permitted to enter and explore a novel alley from a familiar nest box. Hippocampally lesioned animals did not differ from cortical lesioned controls on the latency to enter the novel alley, the duration of time spent in the alley, or the total number of rearings in the alley during the 1-h test. However, animals with complete hippocampal lesions were more active than the controls; they showed a perseverative tendency to return repeatedly to the familiar nest box. In the second experiment, rats with complete hippocampal lesions and cortical lesioned controls were tested in a two-bottle taste neophobia task with their familiar tap water and a novel saccharin solution. There were no differences between the groups in either the initial avoidance of the novel saccharin solution or the subsequent increase in saccharin preference across repeated tests. In both experiments, hippocampally lesioned animals showed the same initial neophobic avoidance followed by the same exploratory habituation as did the controls. We discuss the similarity of the hippocampal perseveration to behavior found in other exploratory tasks and conclude that the hippocampus is not essential for neotic information processing.

Emergence neophobia correlates with hippocampal and cortical glutamate receptor binding in rats

Previous work from our laboratory indicated that emergence neophobia is highly correlated with perforant path long-term potentiation (LTP) in rats. In the present study, we examined the relationship between hippocampal and cortical alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors and emergence behavior in rats. Emergence neophobia was assessed in an exploratory task that provided a choice between a novel alley and a familiar nest box. Quantitative autoradiography using radiolabeled ligands specific for the AMPA subclass of glutamate receptors was performed on frozen brain sections. Both [3H]AMPA and [3H]CNQX (6-cyano-7-nitro-[3H]quinoxaline- 2,3-dione, an AMPA receptor antagonist) binding in the dentate gyrus (stratum moleculare), hippocampal area CA1 (stratum radiatum), and the parietal cortex overlying the hippocampus were significantly correlated with emergence behavior. The correlations indicated that neophobic rats, which had longer latencies to enter the novel alley, made fewer entries into the alley, and spent less time in the novel alley during a 10-min test than their neophilic counterparts, had higher levels of AMPA receptor binding. These results suggest that individual differences in specific hippocampal AMPA receptors reflect variability in a specific class of hippocampal-dependent behaviors.

The neophobia—optimality explanation of contrafreeloading rats: A reassessment

We report a single experiment examining the utility of a neophobia—optimality model in explaining barpressing for earned food in the presence of free food. Rats were trained to barpress and given similar amounts of experience with earned food but different amounts of experience with empty free food containers and/or the contextual cues surrounding the containers. All subjects were subsequently administered four repeated tests for earned food preference. The results support the neophobia—optimality model. Those animals with the most habituation to the free food source, without feeding from it, showed the lowest preference for earned food. Conversely, those animals with the least habituation to the free food source showed the highest earned food preference. The implications of these data for modifying the neophobia—optimality model are discussed.

Rats respond for food in the presence of free food: How free is the “free” food?

Abstract An experiment conducted by A.J. Neuringer ( Science , 1969, 166 , 399–401) in which he reported that rats maintained appreciable levels of bar pressing for earned food in the presence of freely available food was critically examined and replicated. Rats were trained to bar press, then housed in operant chambers and administered a 15-day preference test between free and earned food, followed successively by 10 days of free food only, a second 6-day preference test, and 7 days of earned food only. Throughout the experiment half of the animals were provided with tall free-food containers similar to those used by Neuringer; the other half were provided with short containers similar to those more commonly employed by other researchers. The former animals showed a consistent propensity to bar press for earned food across both preference tests, while the latter animals showed only an initial propensity to bar press which subsequently declined to very low levels. These results indicate that the maintenance of significant amounts of bar pressing by the rats in Neuringers report was due to the relatively more effortful free-food source he employed. The utility of a neophobia-optimality model in explaining the present data is discussed.