Induction of receptive field plasticity in the auditory cortex of the guinea pig during instrumental avoidance conditioning.

Classical tone conditioning shifts frequency tuning in the auditory cortex to favor processing of the conditioned stimulus (CS) frequency versus other frequencies. This receptive field (RF) plasticity is associative, highly specific, rapidly acquired, and indefinitely retained—all important characteristics of memory. The investigators determined whether RF plasticity also develops during instrumental learning. RFs were obtained before and up to 24 hr after 1 session of successful 1-tone avoidance conditioning in guinea pigs. Long-term RF plasticity developed in all subjects (N?=?6). Two-tone discrimination training also produced RF plasticity, like classical conditioning. Because avoidance responses prevent full elicitation of fear by the CS, long-term RF plasticity does not require the continual evocation of fear, suggesting that neural substrates of fear expression are not essential to RF plasticity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential effects of forward or simultaneous conditioned stimulus-unconditioned stimulus intervals on the defensive behavior system of the Norway rat (Rattus norvegicus).

To test several predictions derived from a behavior-systems approach, the authors assessed Pavlovian fear conditioning in rats after 30 trials of forward, simultaneous, or unpaired training. Direct evidence of conditioned fear was collected through observation of flight and freezing reactions during presentations of the conditioned stimulus (CS) alone. The authors also tested the CS's potential to reinforce an instrumental escape response in an escape-from-fear paradigm. On the one hand, rats that received forward training showed conditioned freezing, but no conditioned flight was observed. On the other hand, rats that received simultaneous training showed conditioned flight, but no conditioned freezing was observed. Rats that received either forward or simultaneous pairings showed instrumental learning of the escape-from-fear response. Implications for several theories of Pavlovian conditioning are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Persistence of fear-reducing behavior: Relevance for the conditioning theory of neurosis.

Provided experimental support for O. H. Mowrer's (1939) conditioning theory of neurosis. 16 female naive hooded rats were given conditioned stimulus/stimuli (CS) shock trials (fear conditioning) in one side of a 2-compartment apparatus. Then, in the absence of shock, Ss were allowed to escape fear by jumping a hurdle to a safe compartment. The hurdle-jumping response was considered to be analogous to anxiety-based symptomatic behavior indicative of psychopathology in that the performance of the response was unrelated to the receipt of further shock. All Ss learned the hurdle-jumping response, and then performance gradually declined until an extinction criterion was reached. Thus, a response instrumental in reducing fear was learned and was maintained over many trials. A subsequent single fear-conditioning trial led immediately to a high level of performance followed by gradual extinction. Findings imply that, when fear is extinguished, instrumental responding can cease even though some response strength remains; the importance for therapy of focusing on the extinction of both instrumental (symptomatic) behavior and fear is suggested. Evidence for the spontaneous recovery of fear is also provided. (41 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of pretraining compatible and incompatible responses on subsequent one-way and shuttle-avoidance performance in rats.

Conducted 6 experiments with male Holtzman rats. A single noncontingent footshock was found to facilitate subsequent one-way and shuttle avoidance if the CS in preshock and avoidance training was the same. If the to-be-established instrumental response was punished during preshock, or if Ss were required to run toward the CS paired with shock during pretraining, the facilitative effects of preshock were eliminated. Facilitation by a single preshock was not enhanced if shock was escapable, regardless of the CSs, task, or whether escape was immediate or delayed. If Ss received 10 one-way escape trials, the beneficial effects of preshock on one-way and shuttle avoidance were enhanced. In contrast, shuttle-escape training produced no such beneficial effects on avoidance performance. (19 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of response-produced and exteroceptive feedback in the attenuation of fear over the course of avoidance learning.

Possible mechanisms mediating fear attenuation over prolonged avoidance learning were examined. In Replication 1, two groups of rats (masters) received 50 or 200 trials of signaled avoidance training. Six groups were yoked to each master group: Three were strictly yoked, and three were yoked only for reinforced conditioned stimulus (CS) presentations (yoked fear conditioning). Of the six groups, two (one strictly yoked and one yoked fear conditioning) received exteroceptive feedback contingent upon the reponses of the masters, two received random/noncontingent feedback, and two received no feedback. Fear of the conditioned stimulus (CS), indexed by freezing during the CS, was lowest in the 200-trial masters and in the two 200-trial groups receiving contingent feedback. In Replication 2, which was procedurally identical to Replication 1 except that the master groups received contingent exteroceptive feedback, fear was lowest in the same three groups. These results support the conclusion that the response-produced feedback that an avoidance response provides is responsible for the fear attenuation seen in well-trained avoidance responders. Several hypotheses concerning the effects of feedback in mediating fear attenuation are examined. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intertrial interval effects in classically conditioned fear to a discrete conditioned stimulus and to situational cues.

In Exp I fear was classically conditioned in a total of 240 female hooded and Sprague-Dawley rats with a discrete conditioned stimulus (CS) at intertrial intervals (ITIs) of 15, 45, 75, 105, 165, or 225 sec and in Exp II, with an additional 144 Ss, with or without a discrete CS at ITIs of 165, 225, or 285 sec. The amount of fear conditioned to situational cues and to the discrete CS plus situational cues was then measured by the learning of a hurdle-jumping response which allowed escape from the fear-eliciting stimuli. Results suggest that as ITI was lengthened fear conditioned to situational cues alone and to the discrete CS increased. However, following conditioning with a discrete CS, fear elicited by situational cues increased with ITI but then decreased, presumably because a discrimination had been formed between the situational cues and the compound of CS plus situational cues. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pavlovian analysis of avoidance conditioning in the goldfish (Carassius auratus).

Conducted 2 experiments in which 144 and 54 goldfish, respectively, were trained in a shuttlebox with light as CS and brief shock as UCS. Performance was measured in terms of "initial response" to the CS (at least 1 crossing of the hurdle on any trial) and-where the CS was not terminated by the initial response-in terms of "multiple response" to the CS (more than 1 crossing on any trial). The level of initial responding was as high in classically conditioned Ss (shocked on every trial) as in avoidance Ss, whether or not the CS was terminated by response, but lower in control Ss, yoked with the avoidance Ss, and lower also in punished Ss (shocked only if they responded). Multiple responding was negligible in avoidance Ss, but common in classically conditioned and in punished Ss. Results can be accounted for in purely Pavlovian terms, no reference to instrumental learning being required. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differentiation of escape and avoidance responding in rats.

Examined escape and avoidance performance in 144 female Holtzman albino rats by factorially arranging immediate or postponed CS and UCS termination with shuttle or bar-press escape and avoidance responses. High levels of avoidance responding occurred only when the shuttle response (running) was both the escape and avoidance response, perhaps reflecting that rats are prepared to run but contraprepared to bar press when threatened by aversive stimulation. In addition, postponed UCS termination reduced avoidance performance drastically while CS termination conditions were without effect. Measures of UCS duration and clock terminations also indicated that immediate UCS termination was superior to postponed termination but additionally showed that this was so because postponed termination seriously impaired escape behavior. Results have particular relevance for how escape responses become anticipatory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hippocampal lesions alter conditioning to conditional and contextual stimuli

The control of conditioned fear behaviour by a conditional stimulus (CS) and contextual stimuli (CXT) was compared in rats with lesions to the hippocampus (HPC) or neocortex (CO), and operated controls (OC). After classical fear conditioning in a distinctive context, rats were subsequently tested in the presence of the CS and CXT (CS + CXT), the CS alone (CS-only), or context alone (CXT-only). Two experiments were conducted in which conditioned fear was measured by an active avoidance response (experiment 1) or by response suppression (experiment 2). Groups did not differ in acquiring the conditioned fear response, as measured in the CS + CON test but, in both experiments, hippocampal (HPC) groups exhibited more conditioned fear behaviour than controls in the CXT-Only and CS-Only conditions. It was suggested that control rats conditioned the fear response to a stimulus complex that incorporated the CS and CTX. Rats with HPC lesions did not form this association between the stimulus elements; instead they segregated the CS and CXT and formed independent associations between the conditioned response (CR) and each component. In showing that HPC damage disrupts the process of forming associations between environmental stimuli and that the effect is not restricted to contextual cues, the results help to resolve apparently contradictory findings regarding the role of HPC in contextual information processing.     

The role of fear in theories of avoidance learning, flooding, and extinction.

Summarizes the major lines of evidence that demonstrate a dissociation or desynchrony between measures of fear and avoidance responding. The evidence bearing on the role of fear in theories of avoidance learning and extinction is reviewed and critically evaluated. In addition, research is discussed regarding the determinants of fear over the course of avoidance acquisition, flooding, and extinction. Particular emphasis is placed on discussing the extent to which fear extinction is necessary and/or sufficient for avoidance response extinction with conventional extinction procedures and with response prevention techniques. (3? p ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role and mechanisms of action of glucocorticoid involvement in memory storage

Adrenal steroid hormones modulate learning and memory processes by interacting with specific glucocorticoid receptors at different brain areas. In this article, certain components of the physiological response to stress elicited by learning situations are proposed to form an integral aspect of the neurobiological mechanism underlying memory formation. By reviewing the work carried out in different learning models in chicks (passive avoidance learning) and rats (spatial orientation in the Morris water maze and contextual fear conditioning), a role for brain corticosterone action through the glucocorticoid receptor type on the mechanisms of memory consolidation is hypothesized. Evidence is also presented to relate post-training corticosterone levels to the strength of memory storage. Finally, the possible molecular mechanisms that might mediate the influences of glucocorticoids in synaptic plasticity subserving long-term memory formation are considered, mainly by focusing on studies implicating a steroid action through (i) glutamatergic transmission and (ii) cell adhesion molecules.     

The effects of chronic morphine administration upon a modified Sidman avoidance schedule that utilizes response-independent shock

Six male squirrel monkeys were subjected to a Sidman nondiscriminated avoidance schedule (R-S, S-S-20 sec) that superimposed 3-min conditioned stimuli (CS) unavoidable shock pairings upon the ongoing avoidance behavior. Five of the 6 animals demonstrated facilitated avoidance response rates during the CS, while one animal demonstrated suppressed rates during the CS. Morphine sulfate (0.5, 1.0, 2.0, 3.0, 4.0 mg/kg) altered these patterns, causing the suppressor to facilitate, while the facilitators demonstrated reduced levels of response elevation during the aversive CS. Morphine also led to a reliable reduction in overall response rate and an increase in the number of shocks received. No consistent drug effects were noted with regard to general motor activity. These results were interpreted to suggest that a potent analgesic agent, such as morphine, was able to reduce the level of fear motivation normally generated by the aversive CS. Since changes in relative rate during the aversive CS were quite reliable both within and between animals, it was suggested that this behavioral schedule might prove useful in assaying the fear-reducing qualities of a variety of drugs. A cautionary note, however, indicated that other explanations, most notably, a rate dependent hypothesis, could account for the data without assuming the level of fear was altered.     

Role of facial expression in "cooperative-avoidance conditioning" in monkeys.

This experiment was performed to determine whether a monkey would perform an avoidance response to affective expression in another monkey, 6 monkeys were individually trained to perform an instrumental avoidance response and were then tested in pairs in a "cooperative-conditioning" situation. The "stimulus animal" received the CS but lacked the response mechanism while the "responder" had the response lever but no CS. The responder could, however, observe the face of the stimulus monkey via television. The data revealed that emotional expressions of the stimulus monkey upon CS presentation elicited discriminated avoidance behavior by the responder. The results suggest that the cooperative-conditioning paradigm may permit identification of the specific facial expressions associated with various affects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Corticosterone levels during avoidance learning in rats with cingulate lesions suggest an instrumental reinforcement deficit.

Studied changes in fear or arousal during 2-way avoidance learning in male Moll-Wistar rats with cingulate lesions. The 12 Ss with lesions restricted to the cingulum bundle and rostral one-third to one-half of the cingulate cortex exhibited no deficit compared with the 15 operated control Ss in the acquisition of 2-way active avoidance. However, the cingulate-lesioned Ss did not exhibit the increase in intertrial sniffing and grooming or the decline in plasma corticosterone levels to the degree observed in control Ss in the course of acquisition and stabilization of the avoidance response. The primary effect of this lesion may therefore be less effective reinforcement of the instrumental response. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behavioral expression of learned fear: Updating of early memories.

The expression of learned fear emerges in a response-specific sequence where freezing occurs before fear potentiated startle (FPS) to an odor conditioned stimulus (CS; Postnatal Day [PN] 16 vs. PN 23; e.g., Hunt, 1997; Richardson, Paxinos, & Lee, 2000). Studies have shown that learned fear is expressed in a manner appropriate to the animal's age at training and not its age at test (Richardson & Fan, 2002; Richardson et al., 2000). Specifically, animals trained with an odor CS at PN 16 exhibit avoidance but not FPS when tested at PN 23. The present study shows that subsequent training with a different CS can "update" an early memory, allowing it to be expressed in a manner appropriate to the animal's age at test. This updating effect appears to be modality specific, whereby the subsequent training must involve a CS of the same sensory modality as the original training. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Simple determination of urinary aldosterone without chromatography]

Previously acquired continuous avoidance performance of pigs in a shuttle-box was modified by a Pavlovian fear-conditioning procedure. Diazepam (1 mg/kg) given before the Pavlovian conditioning session prevented the increase in corticosteroids and the impairment of performance in the subsequent test session before the presentation of the fear signal. Diazepam given before the Pavlovian conditioning session and/or the test session did not prevent the increase of response to the CS presentation; however, the temporal pattern of increase differed according to the drug condition: the diazepam treatment on the day of the test significantly delayed the peak of responding to the CS; in pigs treated with diazepam on the day of Pavlovian conditioning and with saline on the day of test, the increase of response was diffuse instead of being localized to the CS presentation period. Pigs treated with diazepam both during learning and performance of fear conditioning showed some evidence of performance facilitation. Usual unitary interpretations cannot account for such results which would appear to be the net result of several intermingled effects among which state-dependent learning, acquisition deficit, and performance facilitation seem to be of importance.     

Learning-induced physiological memory in adult primary auditory cortex: receptive fields plasticity, model, and mechanisms

It is well established that the functional organization of adult sensory cortices, including the auditory cortex, can be modified by deafferentation, sensory deprivation, or selective sensory stimulation. This paper reviews evidence establishing that the adult primary auditory cortex develops physiological plasticity during learning. Determination of frequency receptive fields before and at various times following aversive classical conditioning and instrumental avoidance learning in the guinea pig reveals increased neuronal responses to the pure tone frequency used as a conditioned stimulus (CS). In contrast, responses to the pretraining best frequency and other non-CS frequencies are decreased. These opposite changes are often sufficient to shift cellular tuning toward or even to the frequency of the CS. Learning-induced receptive field (RF) plasticity (i) is associative (requires pairing tone and shock), (ii) highly specific to the CS frequency (e.g., limited to this frequency +/- a small fraction of an octave), (iii) discriminative (specific increased response to a reinforced CS+ frequency but decreased response to a nonreinforced CS- frequency), (iv) develops extremely rapidly (within 5 trials, the fewest trials tested), and (v) is retained indefinitely (tested to 8 weeks). Moreover, RF plasticity is robust and not due to arousal, but can be expressed in the deeply anesthetized subject. Because learning- induced RF plasticity has the major characteristics of associative memory, it is therefore referred to as "physiological memory". We developed a model of RF plasticity based on convergence in the auditory cortex of nucleus basalis cholinergic effects acting at muscarinic receptors, with lemniscal and nonlemniscal frequency information from the ventral and magnocellular divisions of the medial geniculate nucleus, respectively. In the model, the specificity of RF plasticity is dependent on Hebbian rules of covariance. This aspect was confirmed in vivo using microstimulation techniques. Further, the model predicts that pairing a tone with activation of the nucleus basalis is sufficient to induce RF plasticity similar to that obtained in behavioral learning. This prediction has been confirmed. Additional tests of the model are described. RF plasticity is thought to translate the acquired significance of sound into an increased frequency representation of behaviorally important stimuli.     

Effects of signaling inescapable shock on subsequent escape learning: Implications for theories of coping and "learned helplessness."

The present experiments reveal that shuttle-escape performance deficits are eliminated when exteroceptive cues are paired with inescapable shock. Experiment 1 indicated that, as in instrumental control, a signal following inescapable shock eliminated later escape performance deficits. Subsequent experiments revealed that both forward and backward pairings between signals and inescapable shock attenuated performance deficits. However, the data also suggest that the impact of these temporal relations may be modulated by qualitative aspects of the cues because the effects of these relations depended upon whether an increase or decrease in illumination (Experiment 2) or a compound auditory cue (Experiment 4) was used. Preliminary evidence suggests that the ability of illumination cues to block escape learning deficits may be related to their ability to reduce contextual fear (Experiment 3). The implications of these data for conceptions of instrumental control and the role of fear in the etiology of effects of inescapable shock exposure are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Strain differences in avoidance conditioning as a function of the classical CS-US contingency.

Examined rates of shuttle box avoidance responding in 3 strains of rats as a function of classical and instrumental contingencies in 2 experiments. Ss were a total of 126 female albino Fischer, Lewis, and Long-Evans rats. In Exp I, during classical conditioned-stimulus-unconditioned-stimulus (CS-UCS) pairings in the absence of an avoidance contingency, there were large differences between the 3 strains in rates of anticipatory responding to the CS. The same pattern of differences was observed in Exp II when the avoidance contingency was added. None of the instrumental contingencies of CS termination, UCS termination, or the avoidance contingency differentially affected the strains. Classically elicited anticipatory responses and their compatibility with the required avoidance response were viewed as central factors in both the acquisition and maintenance of skeletal avoidance responses. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cognitive and affective aspects of thigmotaxis strategy in humans.

The present article describes the cognitive and emotional aspects of human thigmotaxis (a wall-following spatial strategy) during exploration of virtual and physical spaces. The authors assessed 106 participants with spatial and nonspatial performance-based learning-memory tasks and with fear and anxiety questionnaires. The results demonstrate that thigmotaxis plays a distinct role at different phases of spatial learning. The 1st phase shows a positive correlation between thigmotaxis and general phobic avoidance, whereas there is no association between thigmotaxis and general phobic avoidance during later phases of learning. Furthermore, participants who underperformed in working memory tests and in a spatial construction task exhibited greater thigmotaxis and a higher potential for fear response. Findings are interpreted in the framework of interactions among emotion-, action-, and knowledge-controlled spatial learning theories. (PsycINFO Database Record (c) 2010 APA, all rights reserved)