J. Bruce Overmier

Pavlovian conditioned stimulus effects upon instrumental choice behavior are reinforcer specific

Abstract In a transfer-of-control experiment with rats, Pavlovian CSs were tested for the specificity of their effects. The instrumental behavior consisted of a discriminative, conditional two-lever choice task in which qualitatively different appetitive reinforcers were contingent upon the two correct choices. In a Pavlovian phase, subjects experienced conditioning to establish either a CS + or CS − for one reinforcer or a CS + or CS − for the other reinforcer. Finally, in a test, these CSs were presented when there was the opportunity to make choice responses. The CS + s evoked choices of the lever which had eventuated in the reinforcer that had served as the Pavlovian US, while the CS − s showed only a slight tendency to evoke the other choice responses. When the CSs were compounded with the original S D s, the CS + s had little effect upon the vigor of responding while the CS − s reduced the vigor of responding to the S D for the reinforcer that was the same as the US used in establishing the CS − . The results are discussed in terms of associative mediational theory and the reinforcer specificity of Pavlovian conditioned excitation and inhibition.

Inflammatory pathogenesis in Alzheimer's disease: biological mechanisms and cognitive sequeli.

Experimental evidence from molecular biology, biochemistry, epidemiology and behavioral research support the conclusion that brain inflammation contributes to the pathogenesis of Alzheimers disease and other types of human dementias. Aspects of neuroimmunology relating to the pathogenesis of Alzheimers disease are briefly reviewed. The effects of brain inflammation, mediated through cytokines and other secretory products of activated glial cells, on neurotransmission (specifically, nitric oxide, glutamate, and acetylcholine), amyloidogenesis, proteolysis, and oxidative stress are discussed within the context of the pathogenesis of learning and memory dysfunction in Alzheimers disease. Alzheimers disease is proposed to be an etiologically heterogeneous syndrome with the common elements of amyloid deposition and inflammatory neuronal damage.

Present Imperfect: A Critical Review of Animal Models of the Mnemonic Impairments in Alzheimer's Disease

This paper reviews the current literature on animal models of the memory impairments of Alzheimers disease (AD). The authors suggest that modeling of the mnemonic deficits in AD be limited to the amnesia observed early in the course of the disease, to eliminate the influence of impairments in non-mnemonic processes. Tasks should be chosen for their specificity and selectivity to the behavioral phenomena observed in early-stage AD and not for their relevance to hypothetical mnemonic processes. Tasks that manipulate the delay between learning and remembering are better able to differentiate Alzheimer patients from persons with other disorders, and better able to differentiate effects of manipulations in animals. The most commonly used manipulations that attempt to model the amnesia of AD are reviewed within these constraints. The authors conclude that of the models examined, lesions of the medial septal nucleus produce behavioral deficits that are most similar to the mnemonic impairments in the earliest stage of AD. However, the parallel is not definitive and more work is needed to clarify the relationship between neurobiology and behavior in AD.

Effects of an exogenous β-amyloid peptide on retention for spatial learning

Three experiments assessed the effects of β-amyloid 1–40 (βA4) on spatial learning in Sprague-Dawley rats. In Experiment 1, rats were trained on a signaled footshock avoidance in a Y-maze. Rats received a single injection of βA4 or vehicle in both sides of the hippocampus immediately after the fifth trial. The βA4 group took significantly longer than the vehicle group to learn to avoid the shock when trained to criterion 1 week later, suggesting a detrimental effect of βA4 on memory consolidation. Experiment 2 used a food reinforcer rather than shock relief under procedures similar to Experiment 1. Again, the βA4 group took longer to learn the maze to criterion. This shows that the effect in Experiment 1 was not specific to shock-maintained learning. In Experiment 3, rats were trained to retrieve a food pellet from each arm of an eight-arm radial maze. After training to criterion, β4 or vehicle was administered intrahippocampally 30 min before the daily session for 26 sessions. There were no acute or chronic effects of βA4 injection on radial maze performance, and no aggregation of βA4 or significant necrosis was observed upon postmortem histological analysis. These experiments suggest that single injections of βA4 impair memory consolidation, but repeated injections of βA4 over an extended period do not affect well-learned behavior.

Inhibition and habituation : Preserved mechanisms of attentional selection in aging and Alzheimer's disease

Are inhibition and habituation, processes that contribute to selective attention, impaired by aging or Alzheimers disease (AD)? Younger adults, older adults, and adults with AD read lists of letters presented either alone or paired with distractor letters. Slower reading times for lists containing distractors relative to lists without distractors indexed concurrent interference (distraction). Slower reading times for lists in which distractors subsequently became targets relative to lists in which distractors and targets were unrelated indexed negative priming (inhibition). Faster reading times when distractors were constant in identity or location rather than random indexed repeated distractor effects (habituation). Distraction increased with aging and AD, whereas inhibition and habituation showed no age- or AD-related decline, suggesting that inhibition and habituation still function to aid attentional selection in older adults and adults with AD.

Teleost telencephalon and learning: an interpretive review of data and hypotheses.

Abstract Normal and telencephalon ablated teleost fish were compared with respect to learning under classical conditioning, instrumental training, and avoidance paradigms. Telencephalic ablation appears not to affect classical conditioning and learning of simple instrumental behaviors (escape and food-getting). However, performances on some complex instrumental tasks and all avoidance tasks are impaired by such ablation. Analysis of the various tasks attempted to isolate those factors which lead to the selective poorer learning by ablated fish. Increased opportunity for response variability and delay of primary reinforcement were implicated. Several hypotheses about teleost telencephalic function were considered: (a) non-specific arousal, (b) dominant response inhibition, (c) short-term memory, and (d) integration of separate learning processes. Support for and shortcomings of each hypothesis were reviewed. A new hypothesis was proposed; it is that the teleost telencephalon mediates utilization of changes in conditioned motivational states that permit reinforcement of behavior. Appropriate tests were suggested. Teleost telencephalic ablation was related to current physiological issues and learning theory questions.

Pavlovian Conditioning and the Mediation of behavior1

Publisher Summary This chapter presents an overview of the two-process approach. It is examined that a Pavlovian conditioning process serves to mediate the behavior observed under the three-term contingency of instrumental training (stimulus–response–reinforcer, S–R–SR). This tenet relies on the observation that imbedded within the instrumental paradigm itself are the necessary and sufficient conditions for Pavlovian conditioning—that is, predictive stimulus–reinforcer pairings. The chapter concludes that a stimulus paired with a UCS gives rise to some “meditational state” or “expectancy.” The focus is on the various properties and functions of these mediators and the mechanism through which they modulate instrumental behavior. One series of the experiments used Pavlovian procedures to manipulate the hypothesized mediational links. These experiments led to the assertion that there are S-M and M-R links in the regulation of behavior and that these are sequential and independent of one another. The two links involved and of a separate, parallel, direct S-R link is not only unnecessary but likely incorrect. Mediational affective properties provide information on the value of the expected event, and this is realized as an energizing function.

A reevaluation of Rescorla's early dictums about pavlovian conditioned inhibition

Rescorlas (1969) recommendations concerning the logical and empirical operations for inferring Pavlovian conditioned inbibition were examined in light of modern comparison theories of Pavlovian conditioning and new data that question whether excitation and inbibition are opposite ends of a single continuum of associative strength

Environmental Contingencies as Sources of Stress in Animals

Control over one’s destiny, knowledge of the “laws of nature”, privilege of choice, and freedom from conflict are among the higher values and goals espoused by individuals. Are these values culturally determined and uniquely human, or are they rooted in the evolutionary biology of the organism? The latter belief is fostered by continued recognition that learning is an evolutionarily derived adaptive mechanism (e.g., Spencer, 1855) the raison d’etre of which is to engage behavioral dependencies (control), environmental contingencies (prediction), and behavioral-environmental alternatives (choices). Averill (1973) and White (1959), recognizing the general adaptive significance of control over the environment, have argued that need for control is a “deep seated” motivational variable of phylogenetic as well as ontogenetic origin. If striving for control, prediction, and choice are emergent properties of basic biological processes, we might well inquire about the pathological consequences for the organism--psychological or physiological--of not having control, of inability to predict, or of the absence of choice. These might be potent sources of stress for man in modern societies which tend toward ever more minute regulation. But how do we assess this within ethical bounds?

Sensitization, conditioning, and learning: Can they help us understand somatization and disability?

This paper reviews those features of non-associative and associative forms of learning, as elaborated in the experimental literature, that might contribute to experienced and reported discomfort in the workplace. Emphasis is given to sensitization, while noting that some models of habituation (e.g. the opponent process model) also produce sensitization-like effects as a by-product that could contribute to persistent complaints. Also noted are ways in which these non-associative processes may enhance associative learning of workplace-avoidance behaviors that are exceptionally persistent - even in the absence of further somatic discomfort.