RWMODEL II: Computer simulation of the Rescorla-Wagner model of Pavlovian conditioning

RWMODEL II simulates the Rescorla-Wagner model of Pavlovian conditioning. It is written in Delphi and runs under Windows 3.1 and Windows 95. The program was designed for novice and expert users and can be employed in teaching, as well as in research. It is user friendly and requires a minimal level of computer literacy but is sufficiently flexible to permit a wide range of simulations. It allows the display of empirical data, against which predictions from the model can be validated.

Snakes and kittens in the grass: No evidence for preferential processing of fear-relevant animals in visual search

Ohman and colleagues provided evidence for preferential processing of pictures depicting fear-relevant animals by showing that pictures of snakes and spiders are found faster among pictures of fiowers and mushrooms than vice versa and that the speed of detecting fear-relevant animals was not affected by set size whereas the speed of detecting fiowers/mushrooms was. Experiment 1 replicated this finding. Experiment 2, however, found similar search advantages when pictures of cats and horses or of wolves and big cats were to be found among pictures of flowers and mushrooms. Moreover, Experiment 3, in a within subject comparison, failed to find faster identification of snakes and spiders than of cats and horses among flowers and mushrooms. The present findings seem to indicate that previous reports of preferential processing of pictures of snakes and spiders in a visual search task may reflect a processing advantage for animal pictures in general rather than fear-relevance.

Why fear snakes and spiders? Evidence for a learning-based account of fear-relevant stimulus-processing

Fear-relevant stimuli, such as snakes, spiders and heights, preferentially capture attention as compared to nonfear-relevant stimuli. This is said to reflect an encapsulated mechanism whereby attention is captured by the simple perceptual features of stimuli that have evolutionary significance. Research, using pictures of snakes and spiders, has found some support for this account; however, participants may have had prior fear of snakes and spiders that influenced results. The current research compared responses of snake and spider experts who had little fear of snakes and spiders, and control participants across a series of affective priming and visual search tasks. Experts discriminated between dangerous and nondangerous snakes and spiders, and expert responses to pictures of nondangerous snakes and spiders differed from those of control participants. The current results dispute that stimulus fear relevance is based purely on perceptual features, and provides support for the role of learning and experience.

L-Allylglycine dissociates the neural substrates of fear in the periaqueductal gray of rats

The dorsal (dPAG) and ventral (vPAG) regions of the periaqueductal gray are well known to contain the neural substrates of fear and anxiety. Chemical or electrical stimulation of the dPAG induces freezing, followed by a robust behavioral reaction that has been considered an animal model of panic attack. In contrast, the vPAG is part of a neural system, in which immobility is the usual response to its stimulation. The defense reaction induced by the stimulation of either region is accompanied by anti nociception. Although GABAergic mechanisms are known to exert tonic inhibitory control on the neural substrates of fear in the dPAG, the role of these mechanisms in the vPAG is still unclear. The present study examined defensive behaviors and antinociception induced by microinjections of an inhibitor of gamma-aminobutyric acid synthesis, L-allylglycine (L-AG; 1, 3, and 5 mu g/0.2 mu l), into either the dPAG or vPAG of rats subjected to the open field and tail-flick tests. Passive or tense immobility was the predominant behavior after L-AG (1 or 3 mu g) microinjection into the vPAG and dPAG, respectively, which was replaced with intense hyperactivity, including jumps or rearings, after injections of a higher dose (5 mu g/0.2 mu l) into the dPAG or vPAG. Moreover, whereas intra-dPAG injection of 3 mu g L-AG produced intense antinociception, only weak antinociception was induced by intra-vPAG injections of 5 mu g L-AG. These findings suggest that GABA mechanisms are involved in the mediation of antinociception and behavioral inhibition to aversive stimulation of the vPAG and exert powerful control over the neural substrates of fear in the dPAG to prevent a full-blown defense reaction possibly associated with panic disorder. (C) 2009 Elsevier Inc. All rights reserved.

The unconditioned fear produced by morphine withdrawal is regulated by mu- and kappa-opioid receptors in the midbrain tectum

We have recently shown that morphine withdrawal sensitizes the neural substrates of fear in the midbrain tectum structures-the dorsal periaqueductal gray (dPAG) and inferior colliculus (IC). In the present study, we investigated the role of mu- and kappa-opioid receptors in the mediation of these effects. Periadolescent rats chronically treated with morphine (10 mg/kg; s.c.) twice daily for 10 days were implanted with an electrode glued to a guide-cannula into the dPAG or the IC. Forty-eight hours after the interruption of this treatment, the effects of intra-dPAG or intra-IC microinjections of [D-Ala(2) N-Me-Phe(4) Gly(5)-ol]-enkephalin (DAMGO; 0.6 and 1 nmol/0.2 mu l) - a selective mu-receptor agonist - or nor-binaltorphimine (BNI; 2.5 and 5 mu g/0.2 mu l) - a selective K-receptor antagonist with tardive action - on the freezing and escape thresholds determined by electrical stimulation of the dPAG and the IC were examined. For both structures, morphine withdrawal produced pro-aversive effects. DAMGO and BNI had antiaversive effects when injected into the dPAG and IC of non-dependent rats. In morphine-withdrawn rats, only BNI continued to promote antiaversive effects in both structures. Whereas DAMGO lost its antiaversive efficacy when injected into the dPAG, only its highest dose promoted antiaversive effects in the IC of morphine-withdrawn rats, suggesting the development of an apparent tolerance. Thus, the enhanced reactivity of the midbrain tectum in morphine-withdrawn periadolescent rats may be due, at least partially, to an impairment of the inhibitory influence of mechanisms mediated by mu-receptors on the neural substrates of fear in this region. (C) 2009 Elsevier B.V. All rights reserved.

Effects of microinjections of apomorphine and haloperidol into the inferior colliculus on the latent inhibition of the conditioned emotional response

Electrical or chemical stimulation of the inferior colliculus (IC) induces fear-like behaviors. More recently, consistent evidence has shown that electrical stimulation of the central nucleus of the IC supports Pavlovian conditioning and latent inhibition (Li). LI is characterized by retardation in conditioning and also by an impaired ability to ignore irrelevant stimuli, after a non-reinforced pre-exposure to the conditioned stimulus. LI has been proposed as a behavioral model of cognitive abnormalities seen in schizophrenia. The aim of the present study was to determine whether dopaminergic mechanisms in the IC are involved in LI of the conditioned emotional response (CER). To induce LI, a group of rats was pre-exposed (PE) to six tones in two sessions, while rats that were not pre-exposed (NPE) had two sessions without tone presentations. The conditioning consisted of two tone presentations to the animal, followed immediately by a foot shock. PE and NPE rats received IC microinjections of physiological saline, the dopaminergic agonist apomorphine (9.0 mu g/0.5 mu L/side), or the dopaminergic antagonist haloperidol (0.5 mu g/0.5 mu L/side) before both pre-exposure and conditioning. During the test, the PE rats that received saline or haloperidol had a lower suppression of the licking response compared to NPE rats that received vehicle or haloperidol, indicating that latent inhibition was induced. There was no significant difference in the suppression ratio in rats that received apomorphine injections into the IC, indicating reduced latent inhibition. These results suggest that dopamine-mediated mechanisms of the IC are involved in the development of LI. (C) 2008 Elsevier Inc. All rights reserved.

Involvement of the midbrain tectum in the unconditioned fear promoted by morphine withdrawal

The midbrain rectum structures, dorsal periaqueductal gray (dPAG) and inferior colliculus (IC), are involved in the organization of fear and anxiety states during the exposure to dangerous stimuli. Since opiate withdrawal is associated with increased anxiety in both humans and animals, this study aimed to investigate the possible sensitization of the neural substrates of fear in the midbrain tectum and its influence on the morphine withdrawal-induced anxiety. For the production of drug withdrawal, rats received morphine injections (10 mg/kg; s.c.) twice daily during 10 days. Forty-eight hours after the interruption of the chronic treatment, independent groups were probed in the elevated plus-maze and open-field tests. Additional groups of animals were implanted with a bipolar electrode into the dPAG OF the IC and submitted to the electrical stimulation of these structures for the determination of the freezing and escape thresholds after 48 h of withdrawal. Our results showed that the morphine withdrawal promoted clear-cut levels of anxiety without the somatic signs of opiate withdrawal. Moreover, morphine-withdrawn rats had an increase in the reactivity to the electrical stimulation of the dPAG and the IC. These findings suggest that the increased anxiety induced by morphine withdrawal is associated with the sensitization of the neural substrates of fear in the dPAG and the IC. So, the present results give support to the hypothesis that withdrawal from chronic treatment with morphine leads to fear states possibly engendered by activation of the dPAG and IC, regardless of the production of somatic symptoms. (C) 2008 Elsevier B.V. All rights reserved.

Rewarded associative and instrumental conditioning after neonatal ventral hippocampus lesions in rats

Sprague Dawley rats were submitted to bilateral ventral hippocampus lesions 7 days after birth. This corresponds to the Lipska and Weinberger`s procedure for modeling schizophrenia. The aim of the present work was to test the learning capacity of such rats with an associative Pavlovian and an instrumental learning paradigm, both methods using reward outcome (food, sucrose or polycose). The associative paradigm comprised also a second learning test with reversed learning contingencies. The instrumental conditioning comprised an extinction test under outcome devaluation conditions. Neonatally lesioned rats, once adults (over 60 days of age), showed a conditioning deficit in the associative paradigm but not in the instrumental one. Lesioned rats remained able to adapt as readily as controls to the reversed learning contingency and were as sensitive as controls to the devaluation of outcome. Such observations indicate that the active access (instrumental learning) to a reward could have compensated for the deficit observed under the ""passive"" stimulus-reward associative learning condition. This feature is compared to the memory management impairments observed in clinical patients. (c) 2008 Elsevier B.V. All rights reserved.

Contextual politics of service delivery reforms: Lessons from Delhi, Mexico city and Sao Paulo comparison

Little attention has been given to the contextual politics of service delivery reforms. By focusing on cases of reform in the healthcare sector and, to a lesser extent, in the main policies in the social service sector in India, Mexico and Brazil, this article explores two dimensions of analysis which have enormous relevance in understanding the reach and effectiveness of service delivery reforms: (1) the historical timing of reforms and sectorial baselines, and (2) the degree and institutional locus of local discretion in policy. Findings show that depending on both dimensions, there is an extraordinary variation as to the degree, interests involved and meaning of changes which, in theory, correspond to these countries` commitment to the service delivery reforms, However, consideration of the contextual politics is relevant not for the sake of diversity but for the similarities that this diversity reveals, pointing to underlying analytic dimensions that receive attention in this article.

The effect of emotional and attentional processes on blink startle modulation and on electrodermal responses

Emotional accounts of startle modulation predict that startle is facilitated if elicited during aversive foreground stimuli. Attentional accounts hold that startle is enhanced if startle-eliciting stimulus and foreground stimulus are in the same modality. Visual and acoustic foreground stimuli and acoustic startle probes were employed in aversive differential conditioning and in a stimulus discrimination task. Differential conditioning was evident in electrodermal responses and blink latency shortening in both modalities, but effects on magnitude facilitation were found only for visual stimuli. In the discrimination task, skin conductance responses, blink latency shortening, and blink magnitude facilitation were larger during to-be-attended stimuli regardless of stimulus modality. The present results support the notion that attention and emotion can affect blink startle modulation during foreground stimuli.