Conditioned suppression of the proboscis-extension response in young, middle-aged, and old Drosophila melanogaster flies: Acquisition and extinction.

Young (7 days old), middle-aged (30 days old), and old (50 days old) Drosophila melanogaster males were used in an inhibitory conditioning of the proboscis-extension response. Two reinforcement schedules were applied, constant vs. partial. Partial reinforcement increased the number of trials needed to reach the learning criterion to the same extent in all age groups. Young flies needed fewer trials to reach the criterion than both middle-aged and old flies, which did not differ from each other. Extinction was delayed in the partial reinforcement groups by the same amount in all age groups. The slowest rate of extinction was observed in the old group and the fastest for the middle-aged flies. The results are discussed in connection with hypotheses that consider extinction an index either of behavioral rigidity or of strength of the initial learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evaluation of the relation between Pavlovian occasion-setting and instrumental discriminative stimuli: A blocking analysis.

Retracted October 1990. (See record 1991-03475-001.) Conducted 2 experiments with 72 male Sprague-Dawley rats, using a blocking design (A+, then AB+) to assess the relation between Pavlovian occasion-setting and instrumental discriminative stimuli. Prior conditioning of both associative and occasion-setting functions of A in a serial feature-positive procedure blocked acquisition of an instrumental discriminative function by a novel stimulus (B) trained in compound with A. Neither prior conditioning of only an A/unconditioned stimulus/stimuli (UCS) association nor prior conditioning of Stimulus A using a Pavlovian simultaneous feature-positive procedure, which does not endow A with an occasion-setting function, blocked acquisition of an instrumental discriminative function by B. Prior acquisition of an instrumental discriminative function by A blocked acquisition of a Pavlovian occasion-setting function by a novel stimulus (B) trained in compound with A but did not block acquisition of an association between B and the UCS. (39 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Measurement of stimulus control during discriminative operant conditioning.

Procedures in common use in discriminative operant conditioning are examined. It is concluded that they do not provide useful measures of stimulus control during acquisition because they confound the discriminative stimuli with antecedent reinforcement-nonreinforcement. Procedures which avoid confounding and provide measures of stimulus control during an uninterrupted acquisition process are described. 1 such procedure is applied in an experiment on sequential effects in discrimination learning. Substantial effects of antecedent reinforcement-nonreinforcement on generalized response probability and on the difference in probability of response to the discriminative stimuli are shown. The existence of effects of this type indicates that confounding can introduce serious biases into the measures of stimulus control in discriminative operant conditioning. (19 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ontogeny of passive avoidance learning in domestic chicks: Punishment of key-peck and running responses.

Determined the effect of the number of prepunishment acquisition trials on the age dependency of passive avoidance (PA) learning of the chick in keypeck and runway tests. In 9 experiments, 1- and 4-day-old Ss were first trained to respond for heat reward. After a variable number of reinforced acquisition trials (ATs), Ss' responses were punished with aversive wing shocks. Results show that the age dependency of PA learning of the young S is related specifically to the number of reinforced training trials given prior to PA testing. When several prepunishment ATs were given, 1-day-old Ss learned as quickly as 4-day-old Ss to withhold responding when punished. However, when only a few ATs preceded PA testing, 1-day-old Ss showed significantly less response suppression than 4-day-old Ss. Rather, results suggest that the 1-day-old chick, compared with the 4-day-old chick, is deficient in learning or detecting changes in stimulus– and/or response–reinforcement contingencies. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of primary motivation in stimulus preexposure effects.

It is currently a matter of debate whether the deficit in conditioning observed after stimulus preexposure is one of acquisition or one of performance. The major criticism of performance-based theories is their inability to specify what is learned during nonreinforced preexposure that may influence subsequent acquisition of conditioned responding. Experiments 1 and 2 used an excitatory appetitive conditioning procedure and Experiment 3 used an inhibitory appetitive conditioning procedure, with rats as subjects, and consistently found that the effects of preexposure to a stimulus transferred to conditioning only when the reinforcer was relevant to the motivational state in which that preexposure was conducted. This finding suggests that during preexposure, rats learn that a stimulus is unrelated to events of relevance to their current motivational state. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ontogeny of conditioned inhibition in domestic chicks.

Used the combined-cue test to measure age-dependent changes in learned stimulus inhibitory control in 40 young Vantress * Arbor Acre chicks trained to key peck for heat reinforcement. Both 1- and 4-day-old chicks were given either 96 or 384 discrete trials in a successive discrimination test, and then their response latencies to the novel combined cue (S+, S-) and the prior S+ cue were compared with those of age-matched controls during extinction. Major findings are as follows: (a) One-day-old chicks showed significant response suppression to the combined cue only after receiving 384 discrete trials, whereas 4-day-old chicks showed significant response suppression after both 96 and 384 trials. (b) While control chicks (S+ training only) of both age groups pecked more quickly at the novel cue than at the prior S+ cue during extinction, only the younger chicks pecked more quickly at the novel cue as the number of their prior S+ responses increased. The main conclusion from these experiments is that even the 1-day-old chick has the capacity to acquire learned inhibitory stimulus control but does so at a slower rate than the 4-day-old chick. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perirhinal cortex lesions impair simultaneous but not serial feature-positive discrimination learning.

The role of the perirhinal cortex in discriminative eyeblink conditioning was examined by means of feature-positive discrimination procedures with simultaneous (A-/XA+) and serial (A-/X→A+) stimulus compounds. Lesions of the perirhinal cortex severely impaired acquisition of simultaneous feature-positive discrimination but produced no impairment in serial feature-positive discrimination. The results suggest that the perirhinal cortex plays a role in discriminative eyeblink conditioning by resolving ambiguity in discriminations with overlapping stimulus elements. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Awareness in classical differential eyeblink conditioning in young and aging humans.

The role of awareness and its impact on learning the conditioned eyeblink response was investigated in both trace and delay discrimination eyeblink conditioning in young and aging participants, in 4 paradigms: delay 750, delay 1250, trace 500, and trace 1000. Participants concurrently watched a silent movie about which they were questioned afterward. Acquisition in both the trace and delay discrimination task was correlated with awareness of conditioning stimulus contingencies, regardless of age. Age-dependent deficits were observed in trace discrimination but not in delay discrimination, with more severe deficits appearing at the longer trace interval. The percentage of aware participants was also found to be greater in the young population than in the aging population. These results indicate that awareness or knowledge of stimulus contingencies may be an important contributor to successful acquisition in higher order discrimination tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Selective hippocampal lesions in rats disrupt acquisition and retention of a positive patterning discrimination

To determine the contribution of the hippocampus in the processing of a configural positive patterning discrimination (PPD) task, discrimination between reinforced presentations of a tone plus light compound stimulus and nonreinforced presentations of each of its components (TL+/T-,L-) was examined using a conditioned-suppression paradigm. In the first experiment, rats demonstrated a rapid acquisition of the PPD with an appropriate discriminative responding. Rats submitted to posttraining hippocampal lesions (using multiple injections of ibotenic acid) were no longer able to master correctly the previously solved discrimination, demonstrating significant differences in their response rates during the 2 never-reinforced elemental stimulus presentations. In Experiment II, lesioned rats were not able to correctly learn the PPD, demonstrating the same pattern of responding as in Experiment I. These rats were also severely disrupted in a radial maze elimination task. Experiment IIIa indicated that, in a simple conditioning task (T+, L+), normal rats acquired a rapid conditioned suppression for both stimuli, with the tone being slightly more susceptible to conditioning than the light stimulus. In Experiment IIIb, conditioning to the compound tone plus light stimulus led to a clear conditioning to the tone and almost no conditioning to the light, suggesting an overshadowing from the tone to the light. Similar results were obtained in rats with hippocampal lesions. These results strongly suggest that the disruption showed by rats with hippocampal lesions in the PPD task cannot be due to an alteration of the relative salience of the stimulus. The inability of rats with hippocampal lesions to solve correctly the PPD is due to difficulties in eliminating responding to some unimportant events of the situation, reflecting a deficit in selective attention processes rather than in an ability to process configural stimuli. In the discussion, the putative role of the hippocampus in selective attentional processes is more fully discussed.     

Lesions of the cerebellar vermis and cerebellar hemispheres: Effects on heart rate conditioning in rats.

The effects of lesions of the cerebellum on the acquisition of heart rate (HR) conditioned responses (CRs) were examined in rats. Large lesions of the cerebellar vermis severely attenuated the acquisition of differentially conditioned bradycardic responses in restrained rats without affecting unconditioned HR responses to the tone conditioned stimuli (CSs) or the shock unconditioned stimulus/stimuli (UCS). In Exp 2, Ss were trained unrestrained, and under these conditions the CR was tachycardia in control Ss. Lesions of the vermis again severely attenuated acquisition of this CR without affecting unconditioned response (UCR) to the CSs or UCS. Bilateral lesions of the cerebellar hemispheres did not affect HR conditioning in either test procedure. The vermis of the cerebellum is an essential component of an HR conditioning circuit in the rat. The cerebellar hemispheres, which are involved in some discrete somatomotor CRs, have no essential functional contribution to HR conditioning. Results are discussed in relation to contributions from a forebrain system involved in HR conditioning and in relation to lateral cerebellar contributions to discrete somatomotor CRs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulus configuration, classical conditioning, and hippocampal function.

Hippocampal participation in classical conditioning (CC) is described in terms of a multilayer network that portrays stimulus configuration. The network (1) describes behavior in real time, (2) incorporates a layer of "hidden" units positioned between input and output units, (3) includes inputs that are connected to the output directly as well as indirectly through the hidden-unit layer, and (4) uses a biologically plausible backpropagation procedure to train the hidden-unit layer. Nodes and connections in the neural network are mapped onto regional cerebellar, cortical, and hippocampal circuits, and the effect of lesions of different brain regions is formally studied. Computer simulations of the following CC paradigms are presented: acquisition of delay and trace conditioning, extinction, acquisition–extinction series of delay conditioning, blocking, overshadowing, discrimination acquisition, discrimination reversal, feature-positive discrimination, conditioned inhibition, negative patterning, positive patterning, and generalization. The model correctly describes the effect of hippocampal and cortical lesions in many of these paradigms, as well as neural activity in hippocampus and medial septum during CC… (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hazardous materials and work safety in veterinary practice. 1: Hazardous material definition and characterization, practice documentation and general rules for handling

The role of the nicotinic acetylcholine receptor (nAChR) in the discriminative and aversive stimulus effects of ethanol was studied in rats. In the operant drug discrimination procedure the rats were trained to discriminate between 1.0 g/kg ethanol and saline under the FR10 schedule of sweetened milk reinforcement. Neither the nAChR agonist, nicotine (0.1-0.6 mg/kg) nor the nAChR antagonist, mecamylamine (3.0-6.0 mg/kg) substituted for the ethanol stimulus. Moreover, mecamylamine (0.5-6.0 mg/kg) did not antagonise the ethanol stimulus. The cross-familiarisation conditioned taste aversion procedure was used as an alternative method to study stimulus resemblance between ethanol and nicotine. Six daily injections of nicotine (0.6 mg/kg) significantly decreased a subsequent ethanol-induced taste aversion conditioning. The aversive stimulus effects of ethanol were investigated with the conditioned taste aversion (CTA) paradigm. Mecamylamine (1.0-3.0 mg/kg) did not attenuate an ethanol-induced CTA. These results suggest that: (1) nAChRs are not primarily involved in the discriminative stimulus effects of ethanol when studied with the operant drug discrimination test; (2) nAChRs are not critically involved in the ethanol-induced CTA.     

Effect of naloxone on conditioned suppression in rats.

Painful stimuli are known to engage an endorphin analgesic system that can be reversed by the opiate antagonist, naloxone. Naloxone, then, should increase the effectiveness of aversive unconditioned stimulus/stimuli (UCS) in Pavlovian fear conditioning. Consistent with this hypothesis, naloxone administered during the acquisition of conditioned suppression in rats enhanced posttrial suppression and preconditioned stimulus (pre-CS; context-controlled) suppression. Furthermore, it enhanced CS-elicited suppression during extinction when administered during acquisition but not when administered only during extinction. Thus naloxone does not enhance an already existing fear nor enhance the memory of previous conditioning; instead, it enhances the conditioning of fear presumably by making the aversive UCS more painful. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Malleability of conditioned associations: Path dependence.

Using conditioned suppression of barpressing to investigate the stability of a conditioned stimulus–unconditioned stimulus (CS–UCS) association, the present authors gave 151 water-deprived rats either a few pairings of the CS with a strong footshock UCS or many pairings with a weak footshock UCS so that barpress suppression in response to CS was equated. Exp I established training parameters that yielded this equivalence. Specifically, rapid acquisition to a preasymptotic level of responding with strong shock produced suppression comparable to the asymptotic level reached more slowly with weak shock. Exp II showed that although equivalent performance was obtained from extensive conditioning with a weak shock or limited conditioning with a strong shock, only extensive conditioning with weak shock resulted in retarded acquisition of an association between that same CS and a footshock level perceived as midway between the 2 initial training shock intensities as implied by asymptotic performance in Exp I. Exp III demonstrated that the observed retardation in Ss given many conditioning trials with weak shock was CS-specific. It is concluded that the malleability of learned behavior is not simply a function of initial associative strength but is dependent on the path during initial acquisition. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contributions of postrhinal and perirhinal cortex to contextual information processing.

The role of the postrhinal cortex (POR) and the perirhinal cortex (PER) in processing relational or contextual information was examined with Pavlovian fear conditioning. Rats with electrolytic or neurotoxic lesions of the POR or PER were tested in 2 contextual fear conditioning paradigms. In Experiment 1, electrolytic lesions of the POR or PER produced impairments in contextual fear conditioning but not in conditioning to a phasic auditory conditioned stimulus. Neurotoxic lesions of the POR or PER likewise resulted in anterograde (Experiment 2) and retrograde (Experiment 3) deficits in fear conditioning to the training context in an unsignaled shock paradigm. The results suggest that operations performed on sensory information by the POR and PER are necessary to support contextual learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

What starts an internal clock?

Five experiments with 52 male Charles River CD rats investigated under what conditions a stimulus is timed by the internal clock used in time-discrimination procedures. In Exps I–IV, Ss were trained to time one stimulus (e.g., light) and then tested as to whether they timed a stimulus from another modality (e.g., sound). The 2nd stimulus was treated in 3 ways: exposed (presented alone), paired with food, and extinguished. Exps I and II used the peak procedure, similar to a discrete-trial FI schedule, and paired the treated stimulus with food using instrumental training; Exps III and IV used a psychophysical choice procedure and paired the treated stimulus with food using classical conditioning. All 4 experiments found that there was cross-modal transfer of the time discrimination after pairing but not after exposure or extinction. This suggests that Ss' internal clock timed the treated stimulus after pairing but not after exposure or extinction. Exp V suggested that the decline of responding observed in extinction was not due to changes in timing. Thus, the internal clock apparently times stimuli with signal value (associative strength) and does not time stimuli without signal value. (46 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Response–reinforcer versus stimulus–reinforcer pretraining influences S+ versus S– discriminative control.

In 2 experiments, 60 male Long-Evans rats trained on a visual discrimination task (leverpresses reinforced) received stimulus–reinforcer (noise–food) trials, no training, or response–reinforcer (reinforcement of keypressing) training. Ss then learned an auditory discrimination (keypresses reinforced), in which the positive stimulus (S+) was a noise (N) and the negative stimulus (S–) was a tone (T). Noise–food training resulted in the greatest enhancement of leverpressing on N trials and the least suppression on T trials during a summation test. Prior training of keypress responses produced the opposite pattern of results. Findings are interpreted as reflecting the operation of the combination laws that R. A. Rescorla and A. R. Wagner (1972) proposed to account for intracompound dynamics in classical conditioning. (36 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Blocking during serial feature-positive discriminations: Associative versus occasion-setting functions.

Previous work indicates that during serial feature-positive discriminations (i.e., feature–trace interval/common element/food presentations and separate nonreinforced common element presentations) the feature (A) acquires an association with food (unconditioned stimulus [UCS]) and also a capacity to modulate the common element (X)–UCS relation, which has been termed occasion setting (OS). In the present 2 experiments with 32 male Sprague-Dawley rats, a blocking design, serial feature-positive discrimination procedures, and a behavioral observation technique were used to assess the relation between associative and OS functions acquired by stimuli. In Exp I, prior conditioning of associative and OS functions to A blocked acquisition of both stimulus functions by a novel stimulus (B) trained in compound with A. In Exp II, prior acquisition of an A–UCS association blocked acquisition of a B–UCS association but had no effect on acquisition of B's OS function. These outcomes are discussed (a) as indicating that associative and OS functions are independent and may be based on separate learning processes, (b) as extending the known conditions for acquisitions of OS, and (c) with regard to the theoretical implications of assuming independence of associative OS functions acquired by stimuli. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Determination of operating characteristics of cats using conditioned suppression.

Reports a method for assessing frequency discrimination in cats by analyzing conditioned suppression as a decision-making process. After establishing a steady baseline of responding (lick rate), 3 cats were trained to discriminate between tone bursts that differed in frequency. Suppression ratios were treated as a confidence rating response from which receiver operating characteristics and sensitivities were determined. Results indicate that conditioned suppression is a viable procedure to use in auditory frequency discrimination and that the suppression ratio does conform with the detection of auditory signals. (10 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)