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Results for “fear conditioning”

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At least 811 records · Page 45Linked to original sources
PubMed2006

A short intertrial interval facilitates acquisition of context-conditioned fear and a short retention interval facilitates its expression.

Rats were shocked in a context on two occasions and then tested for fear reactions as indexed by freezing. Rats spent the interval between conditioning trials and between conditioning and test in their home cages. A short interval between context-conditioning trials or between trials involving a discrete conditioned stimulus (CS) produced better learning than longer intervals. A short retention interval between conditioning and test produced better performance than longer intervals. The effects of the intertrial interval on learning are the opposite of those reported previously and are opposite to those predicted by contemporary learning theories. The effects of the training to test interval on performance are predicted by Wagner's sometimes opponent process (SOP) theory (Wagner, 1981).

Animals↗
PubMed2005

Neural activation during cat odor-induced conditioned fear and 'trial 2' fear in rats.

Exposure to cat odor, an innate threat stimulus for rats, engages a conditioning process whereby the environment in which the odor was experienced comes to elicit fear. Additionally, response to cat odor appears to change with repeated exposure, with benzodiazepines having an anxiolytic effect upon first, but not second, cat odor exposure. We explored the neural correlates of these two phenomena using Fos immunohistochemistry. Rats were exposed to cat odor (a worn cat collar) and were allowed to hide from this stimulus. A 'trial 1' group was perfused after a single exposure, and a 'trial 2' group after two exposures. A 'context' group was exposed to cat odor once, then perfused after re-exposure to the odor-paired context. Trial 1, trial 2 and context groups showed similar defensive responses including avoidance and hiding. The trial 1 group showed Fos expression in limbic, hypothalamic and brainstem regions associated with defensive behavior. The trial 2 group showed a similar pattern although with less activation in the lateral septum, anterior and ventromedial hypothalamus, and dorsolateral periaqueductal gray. The context-exposed group showed Fos expression in a subset of the regions activated by cat odor itself: the dorsal premammillary nucleus, ventrolateral periaqueductal grey, cuneiform nucleus and locus ceruleus. Little activation was seen in the amygdala or hippocampus. These results show that stimuli associated with predatory threat come to activate similar brain regions to the threat stimulus itself.

Adaptation, Psychological↗
PubMed1998

Destruction of the auditory thalamus disrupts the production of fear but not the inhibition of fear conditioned to an auditory stimulus.

The auditory thalamus is part of a neural circuit that mediates the expression of fear to auditory stimuli. Bilateral lesions of the auditory thalamus prevent the expression of fear to an auditory stimulus paired with shock. The present study assessed whether bilateral lesions of the auditory thalamus would also disrupt the inhibition of fear to an auditory stimulus paired with the absence of shock. Rats were given bilateral lesions of the auditory thalamus followed by Pavlovian conditioned inhibition training in which a light was paired with shock and a noise and light compound was presented in the absence of shock. Fear and the inhibition of fear were measured with the fear-potentiated startle effect. Lesions of the auditory thalamus did not disrupt the ability of the noise to inhibit the expression of fear to the light. However, these lesions did disrupt the ability of the noise to produce fear-potentiated startle after it had been subsequently paired with shock. These results suggest that although the auditory thalamus is an essential part of a neural circuit that mediates the expression of fear to auditory stimuli, it is not an essential part of the circuit that mediates the inhibition of fear to auditory stimuli.

Acoustic Stimulation↗
PubMed2000

Protection from extinction in human fear conditioning.

Two experiments examined the ability of an added stimulus to interfere with extinction of a target excitatory fear stimulus (a predictor of shock) in human autonomic conditioning. Both experiments demonstrated disruption of extinction when the added stimulus was inhibitory (a predictor of no shock, or safety signal). Subjects showed a return of fear when the target stimulus was tested alone, on both self-reported shock expectancy and skin conductance measures. The second experiment also demonstrated disruption of extinction when the added stimulus was excitatory. This results suggests that protection from extinction may occur even when the added stimulus is not inhibitory. Additional factors that may contribute to protection from extinction include context-specificity, occasion-setting and external inhibition. The results highlight the role that concurrent stimuli play in extinction, and emphasise the need to keep concurrent stimuli as similar as possible to the desired transfer context in practical applications of extinction such as exposure therapy for anxiety.

Adolescent↗
PubMedDate not supplied

Conditional fear, anxiety, and morphine-seeking behavior.

Two Cebus albifrons monkeys were given discriminative operant conditioning with visual stimuli, with Sidman avoidance and punishment as the components. The instrumental response was an unelicited increase in skin conductance. Both animals had surgically implanted catheters for automatic injection of morphine into the heart. After autonomic conditioning, the animals were given the opportunity to self-administer the morphine by touching the primate press panel that displayed the visual stimuli. One contingency-free segment per session was used for morphine injection, while the contingencies remained in force during the other segments. One of the monkeys made significantly more skin conductance responses during avoidance than during punishment, and this monkey received ten times as many shocks in punishment. This monkey also made more responses overall and had a much higher heart rate than the other animal. The other monkey did not differentiate significantly autonomically and received equal numbers of shocks in avoidance and punishment. The monkey that showed autonomic differentiation made significantly (and increasingly) more panel-presses during punishment than during avoidance. The other animal showed hardly any tendency at all to panel-press.

Animals↗
PubMed2001

Parallel neural responses in amygdala subregions and sensory cortex during implicit fear conditioning.

We used event-related fMRI to measure neural activity in volunteer subjects during acquisition of an implicit association between a visual conditioned stimulus (CS+) (angry face) and an auditory unconditioned stimulus (UCS) (aversive, loud noise). Three distinct functional regions were identified within left amygdala: a UCS (noise)-related lateral region, a CS+-related ventral region, and a dorsal region where CS+-related responses changed progressively across the learning session. Differential neural responses to the visual CS+ were also evoked in extrastriate and auditory cortices. Our results indicate that learning an association between biologically salient stimuli of different sensory modalities involves parallel changes of neural activity in segregated amygdala subregions and unimodal sensory cortices.

Adult↗
PubMed2002

No sex difference in contextual control over the expression of latent inhibition and extinction in Pavlovian fear conditioning in rats.

Three experiments with Wistar rats searched for a sex difference in contextual control over the expression of latent inhibition and extinction. Experiment 1 used a latent inhibition procedure; Experiments 2 and 3 employed an extinction preparation. All experiments used a shock as the unconditioned stimulus, a tone as the conditioned stimulus, and suppression of food magazine visits as the measure of conditioned responding to the tone. Each experiment revealed a reliable context effect on conditioned responding to the tone; after conditioning in a separate context, conditioned responding in the former latent inhibition or extinction context was attenuated relative to conditioned responding in a control context. There was no sex difference in the magnitude of this effect. These results are discussed in the framework of sex differences in the hippocampus and of the putative role of this structure in various instances of contextual learning.

Acoustic Stimulation↗
PubMed1994

A deficit in one-trial context fear conditioning is not due to opioid analgesia.

Rats given a foot shock immediately after placement in a box subsequently freeze (immobility) much less in that box than rats given the same shock 2 min after placement. A possible explanation of this result is that these two procedures might induce different levels of opioid analgesia at the time of shock. Opioids might be present immediately after handling, transporting, and exposure to a new situation, but absent 2 min later. Two experiments examined this possibility by giving the opioid antagonist naloxone before conditioning (Experiment 1) or before conditioning and testing (Experiment 2). There was no effect of naloxone relative to saline controls. The results do not support the analgesia hypothesis. Experiment 2 precludes a stage-dependent learning account of the results.

Analgesia↗
PubMed1991

Telencephalic but not diencephalic noradrenaline depletion enhances behavioural but not endocrine measures of fear conditioning to contextual stimuli.

Three experiments investigated the effects of primarily cortical or hypothalamic noradrenaline depletion on aversive conditioning of explicit and contextual stimuli in rats. In Expt. 1, two groups of rats were trained to respond under a variable interval schedule for food reward. One group of rats subsequently received injections of 6-hydroxydopamine into the dorsal noradrenergic bundle, resulting in profound depletion of cortical noradrenaline; the second group received vehicle injections. All rats were exposed to 5 pairings of an auditory stimulus (CS) and footshock (UCS) in a distinctive environment (the dark chamber of a place preference apparatus). During testing in a separate, neutral environment, DNAB-lesioned rats suppressed responding for food reward, in the presence of the aversive CS, to a greater degree than controls. Lesioned rats also showed a greater aversion to the distinctive environment in which they were shocked. In contrast, plasma corticosterone concentrations, measured immediately following each of these behavioural tests, revealed no differences between DNAB-lesioned and control rats. Expt. 2 showed that the DNAB lesion did not affect habituation to the light chamber of the place preference apparatus used in Expt. 1. Expt. 3 showed that 6-OHDA injection into the ventral noradrenergic bundle component of the central tegmental tract, which damages primarily the noradrenergic innervation of hypothalamus, had no effect on either behavioural or endocrine responses to conditioned aversive, explicit or contextual cues. The results are discussed in relation to other reports of the effects of DNAB lesions on simple associative learning in an aversive context.

Animals↗
PubMed1999

An electrophysiological characterization of ventral tegmental area dopaminergic neurons during differential pavlovian fear conditioning in the awake rabbit.

Recent research has suggested that the mesencephalic dopaminergic (DA) system is activated by stress. For example, alterations in DA metabolites have been found in the ventral tegmental area (VTA) following footshock and immobilization in the rat [15,37]. Furthermore, this activation appears selective to DA neurons within the VTA since no changes were observed within the substantia nigra [15,16]. While this research suggests that DA neurons in the VTA are activated by aversive events, there has been a paucity of electrophysiological research designed to examine the sensory response characteristics of these DA neurons, and in particular their response to stimuli which predict aversive events. The present study was conducted to investigate the response characteristics of DA neurons within the VTA of the awake rabbit to acoustic stimuli which, via Pavlovian aversive conditioning procedures, came to predict the occurrence of a mild shock to the pinna. 45%, of the neurons meeting pre-established criteria for DA neurons demonstrated either significant excitation or inhibition to conditioned aversive stimuli. These neurons responded differentially to CS+ and CS- presentations. Some of these neurons (65%) demonstrated a greater increase in activity during the CS+ compared to the CS-, some (22%,) demonstrated a greater decrease in activity during the CS+ compared to the CS- and some (13%) demonstrated a greater increase in activity during the CS- compared to the CS+. Further, conditioned heart rate responses in the rabbits occurred during the recording of a majority of these neurons. These overall results suggest that conditioned aversive stimuli can affect the firing of VTA DA neurons and that these neurons comprise a heterogenous population with respect to their response profiles.

Acoustic Stimulation↗
PubMed2003

Development of reorganization of the auditory cortex caused by fear conditioning: effect of atropine.

Reorganization of the frequency map in the central auditory system is based on shifts in the best frequencies (BFs; hereafter, BF shifts), together with the frequency-response curves, of auditory neurons. In the big brown bat, conditioning with acoustic stimulation followed by electric leg-stimulation causes BF shifts of collicular and cortical neurons. The collicular BF shift develops quickly and is short term, whereas the cortical BF shift develops slowly and is long term. The acetycholine level in the auditory cortex must be high during conditioning to develop these BF shifts. We studied the effect of atropine (an antagonist of muscarinic acetylcholine receptors) applied to the auditory cortex on the development of the long-term cortical BF shift in the awake bat caused by a 30-min conditioning session. We found 1) the cortical BF shift starts to develop approximately 15 min after the onset of the conditioning, gradually increases over 60 min, and reaches a plateau, 2) the cortical BF shift changes from short to long term approximately 45 min after the onset of the conditioning, 3) the cortical BF shift can plateau at different frequencies between the BF of a given neuron in the control condition and the frequency of the conditioning tone, 4) the maximum BF shift is determined approximately 70 min after the onset of the conditioning, and 5) acetylcholine plays an important role in the development of the cortical BF shift. Its role ends approximately 180 min after the onset of the conditioning.

Acoustic Stimulation↗
PubMed1990

The lateral amygdaloid nucleus: sensory interface of the amygdala in fear conditioning.

Previous work has implicated projections from the acoustic thalamus to the amygdala in the classical conditioning of emotional responses to auditory stimuli. The purpose of the present studies was to determine whether the lateral amygdaloid nucleus (AL), which is a major subcortical target of projections from the acoustic thalamus, might be the sensory interface of the amygdala in emotional conditioning. Lesions were placed in AL of rats and the effects on emotional conditioning were examined. Lesions of AL, but not lesions of the striatum above or the cortex adjacent to the AL, interfered with emotional conditioning. Lesions that only partially destroyed AL or lesions placed too ventrally that completely missed AL had no effect. AL lesions did not affect the responses elicited following nonassociative (random) training. AL is thus an essential link in the circuitry through which auditory stimuli are endowed with affective properties and may function as the sensory interface of the amygdala during emotional learning.

Acoustic Stimulation↗