Classical conditioning of a flexor nerve response in spinal cats: Effects of tibial nerve CS and a differential conditioning paradigm.

Examined, in 4 experiments using 59 cats, the effects of a differential conditioning paradigm on the deep peroneal motor nerve response. Results show that flexor nerve response increases were produced when the conditioned stimulus/stimuli (CS) was delivered to the whole tibial nerve or to the medial plantar branch. The responses to CS/unconditioned stimuli presentations on the superficial peroneal nerve increased, whereas responses to CS presentations on the tibial nerve remained unchanged. However, lack of extinction effects in the superficial peroneal data suggests that stimulation of the tibial nerve potentiated superficial peroneal evoked responses. Furthermore, responses evoked by stimulation of either nerve increased when paired trials were given on the tibial nerve. These data demonstrate that stimulation of the tibial nerve potentiates responses to superficial peroneal nerve stimulation but that superficial peroneal nerve stimulation has no effect on responses to CS presentations to the tibial nerve. (7 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Aversive second-order conditioning in the pigeon: Elimination of conditioning to CS1 and effects on established second-order conditioning.

After aversive 2nd-order conditioning was established in groups of female White Carneaux pigeons, conditioning to the 1st-order CS was eliminated by either nonreinforced presentations of CS or truly random presentations CS 1 and UCS. Subsequent testing of CS 2 revealed that nonreinforced CS presentations significantly reduced previously established 2nd-order conditioning, but truly random presentations of CS 1 and UCS did not. Data suggest that an association between the CS 2 memory and UCS memory was formed during 2nd-order conditioning. Results do not support conclusions drawn from previous research that indicated that rats form a direct association between CS 2 memory and CR in both appetitive and aversive 2nd-order conditioning preparations and that pigeons form an association between CS 2 and CS 1 memories in a 2nd-order autoshaping preparation. (French abstract) (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A simplified preparation for relating cellular events to behavior: contribution of LE and unidentified siphon sensory neurons to mediation and habituation of the Aplysia gill- and siphon-withdrawal reflex

We have begun to analyze several elementary forms of learning in a simple preparation consisting of the isolated mantle organs and abdominal ganglion of Aplysia. Previous studies suggested that plasticity at siphon sensory neuron synapses contributes to habituation and dishabituation of the gill- and siphon-withdrawal reflex in this preparation. We next wished to identify the sensory neurons that participate in the reflex and examine their plasticity more directly. To investigate the contribution of the LE siphon mechanosensory cells, we recorded from them and gill or siphon motor neurons during the same siphon stimulation that has been used in behavioral experiments in this preparation. Our results indicate that the LE cells make a substantial contribution to the evoked response in the motor neurons under these conditions, but they suggest that other as yet unidentified siphon sensory neurons with lower thresholds and shorter latencies also contribute. In addition, we find that homosynaptic depression of monosynaptic postsynaptic potentials (PSPs) from LE sensory cells makes an important contribution to habituation of the response in the motor neurons. To investigate plasticity of PSPs from the unidentified sensory neurons, we recorded the PSP that was produced in a motor neuron by water-movement stimulation of the siphon, which does not cause firing of LE cells. Our results suggest that PSPs from the unidentified sensory neurons and the LE neurons undergo similar plasticity during habituation and dishabituation training. These results support the idea that plasticity at synapses of both LE and unidentified sensory neurons contributes to habituation and dishabituation of the reflex response in this preparation.     

Classical conditioning and conditioning-specific reflex modification of rabbit heart rate as a function of unconditioned stimulus location.

Heart rate conditioning is used as an index of conditioned fear and is important for understanding disorders of anxiety and stress, including post traumatic stress disorder (PTSD). One important feature of PTSD is that patients generalize conditioned fear from danger signals to safety signals especially when the two signals have overlapping features. What has not been determined is whether generalization occurs between unconditioned stimuli with overlapping features. In the current experiment, heart rate conditioning and conditioning-specific reflex modification of rabbit heart rate were examined as a function of two different unconditioned stimulus locations. Heart rate conditioning occurred at identical terminal levels whether electrical stimulation was presented near the eye or on the back. Despite different heart rate response topographies to electrical stimulation at the two locations, conditioning-specific reflex modification was detected near the eye and on the back and appeared to generalize between the locations. Interestingly, only conditioning-specific reflex modification detected on the back persisted for a week after heart rate conditioning. This persistence may be a model for some features of post traumatic stress disorder. Overgeneralization of unconditioned responses to unconditioned stimuli similar to the trauma may also be an important aspect of PTSD modeled here. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Classical differential and operant conditioning in rabbits (Oryctolagus cuniculus) with septal lesions.

12 normal New Zealand white rabbits and 12 with septal lesions received classical differential conditioning of the nictitating membrane response (NMR), followed by auditory generalization tests run in extinction. Although rate of acquisition and asymptotic responding to positive conditioned stimuli did not differ, septals responded more than normals to nonreinforced stimuli. Resultant decrements in differential conditioning could not be attributed to changes in auditory or shock thresholds or to increased spontaneous NMRs. Septals also responded at higher rates in both operant conditioning (barpresses reinforced with food pellets on a variable interval schedule) and extinction sessions. No difference in suppression in a passive avoidance task was found. Results are discussed in relation to R. A. McCleary's (1966) response disinhibition analysis of septal function, and an habituation hypothesis is considered. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Classical conditioning of hippocampal theta patterns in the rat.

Electrical stimulation (88 Hz) of the lateral hypothalamus elicited a sustained theta response at hippocampal recording sites in 11 male Sprague-Dawley rats immobilized with succinylcholine. By pairing this UCS with a 10-sec presentation of a light, conditioned theta responses were demonstrated in as few as 40 trials. Spectral analysis of hippocampal bioelectric patterns during acquisition, extinction, and reconditioning indicated that the earliest change as a result of conditioning was a loss of power in EEG frequency below 8 Hz, followed by the development of a peak at 8 Hz with further conditioning. Extinction was associated with an increase in power of the frequencies below 8 Hz. When the conditioned Ss were tested in the absence of the neuromuscular blocking agent, the CS elicited a theta response that was associated with slow motor activity on 70% of the trials. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Classical nictitating membrane conditioning in the rabbit (Oryctolagus cuniculus): Single alternation with differential intertrial intervals.

Investigated single alternation (SA) patterning behavior in 24 albino New Zealand rabbits by varying in 7 experiments the intertrial intervals (ITIs) following reinforced (R) and nonreinforced (N) trials. When short ITIs followed R trials and long ITIs followed N trials, reliable SA patterning was obtained. Neither (a) the presence of differential ITI cues, (b) the short ITIs prior to the N trials, nor (c) the early position of the N trial within the R-R interval were sufficient in and of themselves to support substantial patterning behavior; instead, each of these features apparently contributed to the patterning effect in a combined fashion. It is concluded that R- and N-trial aftereffects do not play an important role in conditioning the rabbit nictitating membrane. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Classical conditioning and brain systems: the role of awareness

Classical conditioning of the eye-blink response, perhaps the best studied example of associative learning in vertebrates, is relatively automatic and reflexive, and with the standard procedure (simple delay conditioning), it is intact in animals with hippocampal lesions. In delay conditioning, a tone [the conditioned stimulus (CS)] is presented just before an air puff to the eye [the unconditioned stimulus (US)]. The US is then presented, and the two stimuli coterminate. In trace conditioning, a variant of the standard paradigm, a short interval (500 to 1000 ms) is interposed between the offset of the CS and the onset of the US. Animals with hippocampal lesions fail to acquire trace conditioning. Amnesic patients with damage to the hippocampal formation and normal volunteers were tested on two versions of delay conditioning and two versions of trace conditioning and then assessed for the extent to which they became aware of the temporal relationship between the CS and the US. Amnesic patients acquired delay conditioning at a normal rate but failed to acquire trace conditioning. For normal volunteers, awareness was unrelated to successful delay conditioning but was a prerequisite for successful trace conditioning. Trace conditioning is hippocampus dependent because, as in other tasks of declarative memory, conscious knowledge must be acquired across the training session. Trace conditioning may provide a means for studying awareness in nonhuman animals, in the context of current ideas about multiple memory systems and the function of the hippocampus.     

Classical conditioning of opioid activity in the fetal rat.

Milk promotes activity in the kappa opioid system of the rat fetus that reduces responsiveness to cutaneous stimulation. In this study, fetuses on Gestational Day 20 were presented with an artificial nipple (conditioned stimulus [CS]) paired with an intraoral infusion of milk (unconditioned stimulus [UCS]). One paired presentation of the CS and UCS reduced fetal responsiveness after reexposure to the CS. Selective antagonism of opioid receptors after conditioning indicated that reduced responsiveness was due to mu opioid activity. Mu and kappa opioid activity was evident after 3 paired presentations of CS and UCS and reexposure to milk. Kappa opioid activity during conditioning was necessary for mu involvement after reexposure to the CS or UCS. These experiments, which were conducted with fetal Ss that lacked suckling experience, suggest that neurochemical systems engaged during suckling may change rapidly after the newborn's initial experiences at the nipple. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Habituation, prepulse inhibition, fear conditioning, and drug modulation of the acoustically elicited pinna reflex in rats.

A reliable component of the acoustic startle response in animals is a flexion of the ears, the pinna reflex (PR). The present investigation attempted to develop a preparation and apparatus suitable for analyzing the PR in the awake rat. A 2nd goal was to examine the PR under behavioral and pharmacological conditions known to affect other response systems, such as whole-body startle, and determine whether the PR is a valid model for analyzing behavioral plasticity. The amplitude of the PR in 17 spinally transected male Sprague-Dawley rats was directly related to stimulus intensity and exhibited short-term habituation, prepulse inhibition, and enhancement by prior fear conditioning. PR amplitude increased following intraperitoneal administration of strychnine HCl (0.75 mg/kg) and was decreased following clonidine HCl (40 μg/kg). It is concluded that this preparation and response system are valid for studying various forms of behavioral modification. Findings are discussed in terms of the potential utility of this response system in investigating the cellular correlates of behavioral plasticity in mammals. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Classical eyeblink conditioning in two strains of mice: Conditioned responses, sensitization, and spontaneous eyeblinks.

Conditioned eyeblink responses (CRs), sensitization, and spontaneous eyeblinks were studied in C57BL/6J and BALB/c mice. Both strains of mice acquired CRs during 10 days of classical delay eyeblink conditioning. The BALB/c mice reached a higher asymptotic CR level than the C57BL/6J mice. The CRs were extinguished and recovered in both strains following conditioned stimulus-alone and paired conditioned stimulus-unconditioned stimulus training. During 10 days of explicitly unpaired training, the control groups showed no signs of sensitization and low incidence of spontaneous eyeblinks. When switched to paired training, the unpaired groups exhibited significant conditioned inhibition. These results suggest that strain differences must be considered in experimental design and data interpretation for these basic aspects of associative learning and memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neurotoxic lesions of basolateral, but not central, amygdala interfere with Pavlovian second-order conditioning and reinforcer devaluation effects

Considerable evidence suggests that various discrete nuclei within the amygdala complex are critically involved in the assignment of emotional significance or value to events through associative learning. Much of this evidence comes from aversive conditioning procedures. For example, lesions of either basolateral amygdala (ABL) or the central nucleus (CN) interfere with the acquisition or expression of conditioned fear. The present study examined the effects of selective neurotoxic lesions of either ABL or CN on the acquisition of positive incentive value by a conditioned stimulus (CS) with two appetitive Pavlovian conditioning procedures. In second-order conditioning experiments, rats first received light-food pairings intended to endow the light with reinforcing power. The acquired reinforcing power of the light was then measured by examining its ability to serve as a reinforcer for second-order conditioning of a tone when tone-light pairings were given in the absence of food. Acquisition of second-order conditioning was impaired in rats with ABL lesions but not in rats with CN lesions. In reinforcer devaluation procedures, conditioned responding of rats with ABL lesions was insensitive to postconditioning changes in the value of the reinforcer, whereas rats with CN lesions, like normal rats, were able to spontaneously adjust their CRs to the current value of the reinforcer. The results of both test procedures indicate that ABL, but not CN, is part of a system involved in CSs' acquisition of positive incentive value. Together with evidence that identifies a role for CN in certain changes in attentional processing of CSs in conditioning, these results suggest that separate amygdala subsystems contribute to a variety of processes inherent in associative learning.     

Studies in early infant learning: Classical conditioning of the neonatal heart rate.

Three experiments demonstrated that human newborn heart rate level can be reliably modified through classical conditioning procedures. The theory of sensitization served as a frame of reference for Exps I and II, and drive reduction served for Exp III. In Exp I the delay, delay-trace, and control groups, with 10 2-day-old newborns in each, received 5 preconditioning trials of the CS alone, 16 conditioning trials with CS–UCS pairings differing for each group, and 5 extinction trials. Exp II was a replication of the 1st study and involved only the delay and delay-trace groups with 10 infants each. In both studies the delay group curves showed significant monophasic acceleratory responses during extinction. Results support the sensitization hypothesis (i.e., the CR occurring in the interstimulus interval was fashioned out of the response to the CS). In Exp III, the measure of conditioning was the response to the probe technique. 10 experimental Ss received preconditioning trials of nitrogen puff (UCS?) administered to the abdomen, followed by 10 CS–UCS? (500-Hz tone acetic acid) pairings with an interstimulus interval of 3 sec. 10 controls received the same design with a CS–UCS? interval of 40 sec. Analyses of the probe stimulus trials showed significant changes for the control group and none for the experimental group. The CS–UCS? pairings in the experimental group are interpreted as producing increased drive and adaptive damping of the heart rate response. Findings show that early learning may occur under a variety of conditions and that the results can be incorporated by different theories. (79 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The capacity of motor reflex and vocalization thresholds to support avoidance conditioning in the rat.

Unconditioned responses (UCRs) of the rat that predict 1-trial, step-through passive avoidance conditioning were identified. The UCRs examined were spinal motor reflexes (SMRs) and vocalization aftercharges (VADs) generated by tailshock. In Exp 1, SMR and VAD thresholds were determined following systemic administration of saline or morphine sulfate. Exp 2 revealed that the capacity of these tailshocks to support conditioning covaried with the probability that VADs were elicited and were independent of the proportion of SMRs that were generated. This pattern of conditioning was not a consequence of either morphine-induced memory deficits or its induction of state-dependent learning (Exp 3). The results are consistent with the 2-process theories of J. Konorski (1967) and A. R. Wagner and S. E. Brandon (1989) in which the unconditional stimulus is viewed as being composed of separate but interrelated epicritic–sensory and protopathic–emotive attributes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Classical nictitating membrane conditioning in the rabbit (Oryctolagus cuniculus) as a function of unconditioned stimulus locus.

Examined the effects of different placements of electrodes used to present a shock UCS on conditioning the rabbit nictitating membrane response (NMR) in 2 experiments with 32 New Zealand and 24 albino rabbits. Ss were conditioned with shock leads attached either circumorbitally, at the ear base, or at the ear tip. In 1 circumorbital shock group, nictitating membranes of both shocked and unshocked eyes were monitored. Circumorbital, ear base, and ear-tip shock yielded best to poorest performances, respectively, and the shocked membrane yielded better performance than the unshocked one. Analysis of UCR and CR latencies and peak amplitude, as well as slow motion films of responses, suggests that poorer performance resulted from the elicitation of other responses, of which the NMR may have been a secondary or indirect component. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Classical conditioning of the eyeblink response in the delay paradigm in adults aged 18–83 years.

To determine if age differences in classical conditioning of the eyelid response begin to appear in middle age in humans as they do in animals, adult subjects aged 18–83 years were trained in the delay conditioning paradigm. Large age effects occurred. Statistically significant differences first appeared in the decade of the 40s. Within-age-group variability was large. To reduce variability, subjects were classified by the magnitude of their unconditioned response (UR). Regardless of age, subjects with low amplitude URs conditioned poorly. In the normal UR amplitude group, the correlation between age and total percentage conditioned responses (CRs) was –.58. Eyeblink rate and voluntary responding did not account for age differences in conditioning, and it was unlikely that hearing acuity or corneal sensitivity caused the differences. Parallels between human and animal eyelid conditioning are considered, and it is suggested that age changes in the cerebellum may affect conditioning in aging mammals, including humans. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Unit activity in cingulate cortex and anteroventral thalamus of the rabbit during differential conditioning and reversal

Multiple-unit activity was recorded from the rabbit anterior cingulate cortical area (AC) and from the anteroventral nucleus of the thalamus (AV) during differential avoidance conditioning and reversal. The positive and negative conditioned stimuli were tones of different frequency, and the unconditioned stimulus (UCS) was shock delivered through the grid floor of a rotating-wheel conditioning apparatus. Conditioning was preceded by pretraining with tones and noncontingent presentations of the shock UCS. The results showed associative (differential) neuronal activity in both AC and AV during differential conditioning. The effect in AC occurred in the intermediate and final sessions of conditioning. A very large differential effect appropriate to original conditioning occurred in AC in the first two sessions of reversal training. The differential effect in AV occurred in the final session of conditioning when the behavioral response was well learned. There was no clear neuronal reversal in AC or AV.     

Activity of units in the hippocampal circuit of the rat during differential classical conditioning.

Recorded unit activity from electrodes chronically implanted in various hippocampal areas of 17 male Holtzman albino rats during differential classical conditioning. 1 auditory frequency signaled food, another signaled electric shock. Unit activity was recorded during 1 sec. prior to applications of the tones and during the 1-sec CS-UCS intervals. Response latencies and changes in frequency of unit activity throughout the recording period were determined. Units in the dentate had longer latencies than units in the hippocampus, some of which responded within 16 msec. of the application of the CS. The dentate was the only area to show excitation in response to a positive signal and inhibition in response to a negative signal. (18 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)