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PubMed1992

Increases in excitability of neurons of the motor cortex of cats after rapid acquisition of eye blink conditioning.

Measurements were made of resting potentials, input resistance, and excitability to intracellularly applied, depolarizing current pulses in neurons of the pericruciate cortex of conscious cats before and after acquisition of a rapidly conditioned eye blink reflex (CR). Neuronal excitability increased after conditioning, and an increased input resistance was found to be correlated with the increased level of excitability. No associated changes were found in resting potentials as a consequence of conditioning. When cells were divided into groups according to the latency of spike activity elicited by a click conditioned stimulus (CS) in relation to four separate excitatory EMG components of the compound blink CR, excitability increases were found in cells with increased spike activity at alpha 1 (8-40 msec), alpha 2 (40-72 msec), beta (72-112 msec), and gamma (112-160 msec) latencies after delivery of the CS. Also, the proportion of cells with high excitability (less than 0.7 nA required for spike elicitation) was increased at each latency period after conditioning. Increases in later components of spike discharge could also be found in the cells with increases in earlier components of discharge and increased excitability. The findings suggested that excitability increases facilitated a responsiveness to the CS that supported production of long- as well as short-latency components of the blink CR. Many of the changes in neuronal properties found after rapid eye blink conditioning, such as the increases in excitability and resistance and in the proportion of CS-excitable cells, resembled changes found earlier after acquisition of a slowly developing Pavlovian blink CR, using the same click CS and tap unconditioned stimulus without addition of a hypothalamic stimulus. The possibility should be considered that the (10-100 times) more rapidly acquired form of eye blink conditioning does not represent a different form of conditioning, but instead a change in the rate of conditioning supported by the more rapid production of increases in neural excitability.

Animals↗
PubMed1989

Effect of after-discharge EEG patterns on performance and latency of the conditioned avoidance response in hippocampally kindled cats.

The relation between different EEG after-discharge patterns and memory retrieval of the conditioned avoidance response was studied in 8 hippocampally kindled cats. The after-discharge patterns were classified into 5 basic EEG types. The relation was analyzed in three different situations: A, at the conditioning stimulation onset, B, at the conditioning stimulus termination, and C, when conditioning stimulus onset and termination were studied within the same type of EEG pattern of after-discharge. The moment of presentation of the conditioning stimulus was determined by the type of EEG after-discharge pattern. Significant relation was observed between reflex performance and type II and III EEG AD types. The type II (4.5-12/s spiking activity) was associated with a greater proportion of positive responses if presented on the uniform background of EEG after-discharge patterns. During the type III pattern (EEG dysrhythmia), there were more negative than positive responses in all the three experimental situations, especially if the type III EEG pattern was observed at the time of conditioned stimulus termination. The latency of reflex performance measured in the experimental condition C (the same pattern of EEG during conditioning stimulus onset and termination) was longer during the type II EEG pattern of after-discharges than the latencies found during type III EEG activity and in the control group. During type III pattern associated with greatest proportion of response failures there was, however, no increase of reflex latencies. The results suggest differential effect of different EEG after-discharge patterns on memory retrieval of the well established conditioned avoidance response in cats.

Animals↗
PubMed1989

Operant conditioning of head-waving in Aplysia. I. Identified muscles involved in the operant response.

A basic goal in the neurosciences is to understand the cellular mechanisms underlying associative learning. The 2 major forms of associative learning are classical conditioning and operant conditioning. In recent years considerable progress has been made towards a cellular analysis of classical conditioning in a number of different preparations. In contrast, the cellular mechanisms underlying operant conditioning are poorly understood. Since the marine mollusc Aplysia has proved to be a powerful preparation for studying cellular and molecular mechanisms of a variety of forms of learning, including classical conditioning, we asked whether Aplysia might also be capable of exhibiting operant conditioning. In previous experiments we found that a naturally occurring behavior, the head-waving response of Aplysia, could be operantly conditioned (Cook and Carew, 1986). In the present paper we have carried out a quantitative analysis of the horizontal and vertical components of the head-waving response at the level of individual muscle groups. We have identified a discrete, bilateral band of neck muscles, the lateral columellar muscles (LCMs), whose electromyographic (EMG) activity is significantly correlated with the horizontal component of head-waving, the component modified by operant conditioning. Since head-waving is a complex behavioral response involving a variety of different muscle groups, using a restricted system such as the LCMs as an analog of the head-waving response will greatly facilitate a cellular analysis of operant conditioning in Aplysia.

Animals↗
PubMedDate not supplied

Formation of new cortico-rubral synapses as a possible mechanism for classical conditioning mediated by the red nucleus in cat.

1.) By extracellular and intracellular recordings of the red nucleus (RN) cell activity, we investigated enhancement of signaling effectiveness at the cortico-rubral synapses underlying the establishment of classical conditioning mediated by RN in the cat. The classical conditioning of forelimb flexion was produced by pairing the conditioned stimulus (CS) to the cerebral peduncle (CP) with the unconditioned stimulus (US) to the forelimb skin at an interval of 100 msec for about a week. 2.) The increased responsiveness of RN cells to the CS was correlated with acquisition of the conditioned forelimb flexion, i.e. RN cells responded to the CS with higher firing probability in the animals which received the paired conditioning than those in the animals which received the CS alone or pairing of the CS and the US at random intervals or those in the naive animals which did not receive any training. 3.) Monosynaptic excitation of RN cells in response to the single pulse to CP was most enhanced in the animals which received the paired conditioning. By contrast, response of RN cells, as well as the behavioral response, induced by stimulation of the cerebellar interpositus nucleus (IP) was not enhanced after the paired conditioning. The difference between the responses to the stimulation of CP and IP suggested that the primary site of neuronal change is the cortico-rubral synapses. 4.) In the animals that received the paired conditioning, the excitatory postsynaptic potentials (EPSPs) induced by stimulation of CP had fast-rising components superimposed on the normal slow-rising EPSPs. On the other hand, most of the CP-EPSPs recorded in the naive animals showed a slow time course. The slow time course of the CP-EPSPs has been attributed to the peripheral localization of the cortico-rubral synapses on the dendrites of RN cells. 5.) The electrotonic length of RN cells in the animals which received the paired conditioning was not shorter than that in the naive animals. Therefore, it was suggested that the appearance of the fast-rising component in the CP-EPSPs is cause by formation of the new cortico-rubral synapses on proximal portions of the soma-dendritic membrane of RN cells. 6.) Since it has been established that new synapses formed by collateral sprouting are retained for more than several months, the formation of new synaptic connections could underlie long-lasting behavioral modification.

Animals↗
PubMed1987

Mechanisms underlying retarded emergence of conditioned responding following inhibitory training: evidence for the comparator hypothesis.

The comparator hypothesis posits that conditioned responding is determined by a comparison at the time of testing between the associative strengths of the conditioned stimulus (CS) and stimuli proximal to the CS at the time of conditioning. The hypothesis treats all associations as being excitatory and treats conditioned inhibition as the behavioral consequence of a CS that is less excitatory than its comparator stimuli. Conditioned lick suppression by rats was used to differentiate four possible sources of retarded responding to an inhibitory CS. These include habituation to the unconditioned stimulus (US), latent inhibition to the CS, blocking of the CS-US association by the conditioning context, and enhanced excitatory associations to the comparator stimuli. Prior research has demonstrated the first three phenomena. Therefore, we employed parameters expected to highlight the fourth one--the comparator process. In Experiment 1, our negative contingency training was shown to produce a conditioned inhibitor that passed inhibitory summation and retardation tests. In Experiment 2 we found transfer of retardation from an inhibitory CS to a novel stimulus when the location where retardation-test training occurred was excitatory, which is indicative of contextual blocking and/or comparator effects. In Experiment 3, extinction of the conditioning context was found to attenuate retardation regardless of whether extinction occurred before or after the CS-US pairings of the retardation test. This indicates that much of the present retardation was due to the comparator process rather than to contextual blocking. Experiment 4 demonstrated that habituation to the US did not contribute to retardation in the present case. Collectively, these studies suggest that retardation following inhibitory training can be explained without recourse to any of the traditional mechanisms of conditioned inhibition.

Animals↗
PubMed1986

Forward and backward classical conditioning of the flexion reflex in the spinal cat.

Effects of forward and backward conditioned-unconditioned stimulus (CS-US) intervals on classical conditioning of the flexion reflex were examined in a cat spinal preparation. Interstimulus intervals (ISIs) ranging from +3.0 to -3.0 sec were employed in 9 experimental groups and the results compared with those of an explicitly unpaired control group. Forward conditioning produced an asymmetrical, inverted U-shaped gradient relating magnitude of conditioning to ISI for both acquisition and extinction. The optimum ISI was 1.0 sec. Backward ISIs also produced excitatory conditioning, with optimal conditioning at -0.25 sec. Unlike forward conditioning, backward conditioning produced little sign of retention during extinction trials. The results, which parallel in several ways those of ISI effects in studies of intact animals, support the hypothesis that backward and forward conditioning may be fundamentally different phenomena, under the control of different neural processes.

Animals↗
PubMed1974

Changes in unit postsynaptic responses at sensorimotor cortex with conditioning in rabbits.

A localized, conditioned startle reaction (LCSR) to a click (as conditional stimulus) could be established and recorded electromyographically in rabbits if complex unconditional stimulus was employed. The complex consisted of localized, electrical stimulation applied concurrently to sensorimotor cortex and hypothalamus. The latency of this LCSR was only 12-14 ms. Postsynaptic responses were recorded intracellularly or quasi-intracellularly within the sensorimotor cortex near the placement of the electrodes for the cortical stimulation. The latency distributions of the averaged postsynaptic responses were compared for the naive, conditioned and extinguished dates. Latencies in naive animals were similar to those in the extinguished state, but were significantly (P less than 0.011) different from the Latencies of click-responses in the conditioned state. An increase in the number of responses with 8-17 ms latencies was found after conditioning. Of 30 neurons recorded in conditioned animals six responded with an extremely short latency of 4 to 7 ms. Similar latencies were found in response to much more intense clicks capable of evoking an unconditioned startle reaction in naive animals. Changes in postsynaptic potentials thus occur at the cortex independent of proprioceptive feedback from the conditioned movement. The short latency neuronal responses suggest that a pathway for the LCSR may pass through the sensorimotor cortex. The appearance of responses at less than 7 ms to a previously neutral click in conditioned animals supports the idea that an increase in synaptic effectiveness underlies the neuronal mechanism of conditioning.

Animals↗
PubMedDate not supplied

Conditioned taste aversions accompanied by geophagia: evidence for the occurrence of "psychological" factors in the etiology of pica.

A conditioned taste aversion procedure was used to produce an avoidance of saccharin by rats. In the first experiment, saccharin consumption was paired with cyclophosphamide in two conditioning trials during which the animals were permitted to engage in pica. In the second experiment, saccharin consumption was paired with lithium chloride in four conditioning trials during which the animals were not allowed to engage in pica. Conditioned animals in both experiments subsequently engaged in geophagia when presented with saccharin alone. The absence of geophagia in noncontingently poisoned and "sham" injected control groups indicates that the pica was due to the acquisition of a conditioned illness during the conditioning trials. In addition to providing a demonstration of "psychological" involvement in the etiology of pica, these results indicate that visceral conditioning may accompany the formation of conditioned taste aversions. It is suggested that if there is a relationship between infantile pica and adult drug addiction, a plausible mediational mechanism is that pica-prone and addiction-prone individuals are similar in possessing a high susceptibility to visceral conditioning.

Animals↗
PubMed1984

Some aspects of conditioned reflex activity during sleep.

Acquisition, retrieval and extinction of instrumental alimentary reflexes during various types of sleep was studied in cats with metallic electrodes chronically implanted in different brain structures. The possible acquisition and extinction of a defensive conditioned reflex with the onset of paradoxical sleep (PS) serving as a conditioned signal and painful electrical stimulation of the skin as unconditioned was investigated. Results suggest that: (i) in the presence of a high food motivation the conditioned signals delivered during sleep cause the retrieval of previously acquired instrumental alimentary reflexes, and in PS the brain is capable of discriminating conditioned signals more accurately than during slow wave sleep, (ii) after a conditioned reaction to one of two conditioned signals is extinguished through non- reinforcement, the second signal remains effective, causing an instrumental alimentary reflex, (iii) the extinction of instrumental alimentary reflexes effected during sleep is not retained after the animal's awakening, whereas the extinction of a defensive conditioned reflex is retained, (iv) PS may serve as an endogenous conditioned signal during the acquisition of a defensive conditioned reflex. Thus motivational processes developing during PS are effective endogenous stimuli eliciting past experience dreams.

Animals↗
PubMedDate not supplied

[Dynamics of hippocampal neuronal activity during formation of conditioned avoidance reflexes].

Activity of 72 neurones of the dorsal hippocampus was studied in unrestrained rabbits during avoidance conditioning. In the process of conditioning, associative reorganization of neuronal activity were found, which were of a dynamic nature and depended on the stage of reflex stabilization. The initial stage of elaboration was characterized by a change in background activity between pairings in 87.5% of the hippocampal neurons, recorded in that period. Phasic associative reorganization recorded in 53.1% of neurons in response to a signal stimulus before the appearance of conditioned movements, reflected the orienting component of the conditioned reaction, reaction to time during the period of action of associated stimuli and a change in the level of neurons activity resulting from association of conditioned and unconditioned stimuli. The nature of response was changing in the most of the neurones at the appearance of the conditioned motor reaction. Stabilization of the level of background activity and of phasic responses of neurones to signal stimulus were observed at the stage of stable conditioned reflex. Phasic responses had several modifications which reflected a level of neuronal activity specific for the conditioned reflex, and they were also linked to signal involvement of the system providing for the movement. The data obtained show that participation of regulatory tonic mechanisms is an essential condition of the formation and manifestation of the temporary connection.

Animals↗
PubMedDate not supplied

[Participation of the auditory cortex and emotionogenic subcortical systems in the formation and reproduction of conditioned reactions].

Analysis of the activity of several brain structures in conditioned neurographic response taken as an analog of conditioned motor reaction was performed on a model of short-delay defensive reflex with unavoidable reinforcement (immobilized cats). It has been shown that the conditioned electrographic signs may appear in the central nervous system both in the presence and in the absence of conditioned motor reaction. The probability of their occurance increases in the cortex, Zona incerta and in the preoptic area during achievement of conditioned effector reaction. The probability of their appearance in other formations does not change considerably neither in the absence nor in the occurance of conditioned motor reaction. Combinations of brain structures are singled out in which the appearance of conditioned electrographic signs is accompanied by conditioned effector reaction. The optimal variant for its occurance is simultaneous appearance of the conditioned electrographic signs in Zona incerta, in the cortex and in the preoptic area.

Amygdala↗
PubMed1996

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.

Acoustic Stimulation↗
PubMed1977

[Responses of neurons in the secondary somatosensory zone of the cat cortex during elaboration of a defensive conditioned reflex].

The neuronal responses of the somatosensory secondary cortex during the process of formation and extinction of a conditioned defence reflex to sound stimulus were studied in chronic experimentss on cats. In 21 out of 28 examined neurons a change in activity took place during the formation of a conditioned reflex as a response to the conditional signal. Two types of conditioned reflex responses were observed: excitatory and inhibitory ones. Most of the neurons excited by the conditioned stimulus responded during the first 50 ms, preceding the conditioned movement by 80-100 ms. Significant variability of neuronal responses was observed during formation of the conditioned reflex. After stabilization the neuronal responses to the conditioned stimulus acquired a stable from. During extinction of the neuronal conditioned activity a decrease of the discharge frequency in the excitatory neuronal response and disinhibition of the activity in the inhibitory responses were found.

Animals↗
PubMed1997

Emergence of conditioned cardiac responses to an olfactory CS paired with an acoustic startle UCS during development: form and autonomic origins.

Pairing an olfactory conditioned stimulus (CS) with an acoustic startle unconditioned stimulus (UCS) produced conditioned bradycardia in rats ranging from 12 days of age to adulthood but failed to produce conditioning in 10-day-olds (Experiment 1). The second experiment compared the effects of two different UCSs, acoustic startle and electric shock. The startle UCS produced conditioned bradycardia accompanied by immobility. In contrast, the shock UCS produced conditioned tachycardia accompanied by behavioral activation. Pharmacological analysis revealed that activation of the parasympathetic nervous system (PNS) produced the conditioned bradycardia (Experiment 3) and that activation of the sympathetic nervous system (SNS) produced the conditioned tachycardia (Hunt, Hess, & Campbell, 1994). Further comparisons revealed that the startle UCS established conditioning several days earlier in development than the shock UCS. The ability of the PNS to respond to phasic stimulation earlier in development than the SNS was discussed as a possible mechanism for the early development of conditioned bradycardia.

Acoustic Stimulation↗
PubMed1997

A selective role for corticosterone in contextual-fear conditioning.

The contribution of corticosterone to contextual- and auditory-cue fear conditioning was examined. Adrenalectomized rats showed reduced contextual-fear conditioning when tested 24 hr after conditioning; however, neither immediate contextual- nor auditory-cue fear conditioning was impaired. Contextual-fear conditioning in adrenalectomized rats with corticosterone replacement during the 4-day interval separating surgery and conditioning matched the level of controls. Moreover, rats exposed to the context prior to adrenalectomy showed normal long-term contextual-fear conditioning. Corticosterone replacement administered after the conditioning episode also negated the effects of adrenalectomy. Thus, corticosterone's role in fear conditioning is selective: It appears to contribute to the neural processes that support the consolidation of a long-term memory representation of the context.

Acoustic Stimulation↗
PubMed1998

Amygdalar NMDA receptors are critical for new fear learning in previously fear-conditioned rats.

NMDA receptors in the amygdala seem to be critical for fear conditioning in naive rats. Recent spatial-learning studies suggest that previous learning protected animals from the amnesic effect of NMDA antagonists on new learning (of a similar behavioral task). Therefore, the present study examined whether blocking of NMDA receptors in the basolateral nucleus of the amygdala (BLA) prevents new fear learning in previously fear-conditioned rats, as measured by freezing behavior. Intra-BLA infusions of the NMDA receptor antagonist DL-2-amino-5-phosphonovaleric acid (APV) completely blocked fear conditioning to a tone stimulus in animals that had previously been fear-conditioned to a light stimulus. Similar results were obtained with intra-BLA infusions of APV before contextual fear conditioning in rats that had been fear-conditioned to a different context. Additional experiments showed that intra-BLA APV infusions substantially interfere with the expression and extinction of conditioned fear to tone, light, and context stimuli. Together, these results indicate that NMDA receptors in the BLA are crucial for the encoding of new fear memories (i.e., the formation of specific conditioned stimulus-unconditioned stimulus association), the expression of conditioned fear responses, and the extinction of acquired fear.

Acoustic Stimulation↗
PubMed1999

Cellular traces of behavioral classical conditioning can be recorded at several specific sites in a simple nervous system.

We used a behavioral learning paradigm followed by electrophysiological analysis to find sites in the Lymnaea feeding network in which electrical changes could be recorded after appetitive conditioning. Specifically, we analyzed conditioning-induced changes in cellular responses in the mechanosensory conditioned stimulus (CS) pathway, in the central pattern generator (CPG) network, and in feeding motoneurons. During training, experimental animals received 15 pairings of lip touch (the CS) with sucrose (the unconditioned stimulus, US). Control animals received 15 random CS and US presentations. Electrophysiological tests on semi-intact preparations made from conditioned animals demonstrated a network correlate of the overall feeding conditioned response, a touch-evoked CPG-driven fictive feeding rhythm. At the motoneuronal level, we found significant conditioning-induced increases in the amplitude of an early touch-evoked EPSP and spike activity, recorded from the B3 feeding motoneuron. Increases in EPSP amplitude and motoneuronal spike activity could occur independently of conditioned fictive feeding. These changes in response recorded at the level of CPG interneurons, and motoneurons were preceded by changes recorded in the CS pathway. This was demonstrated by recording a conditioning-induced increase in the number of touch-evoked spikes in the cerebrobuccal connective, which forms part of the CS pathway. The finding that electrophysiological changes after conditioning can be recorded at multiple sites in this simple system provided an important intermediate level of analysis between whole animal behavior and cellular studies on the synaptic sites of plasticity.

Action Potentials↗
PubMed1975

Evolution of average evoked potentials in cats during conditioning before and after tegmental lesions.

Sensory-specific and modality nonspecific average evoked potentials (AEPs) were recorded from the cortical areas and subcortical structures in two groups of cats: (1) normal cats which after conditioning were subjected to brainstem lesions and reconditioning; (2) cats with brainstem lesions and subsequent conditioning. A new waveshape of the visually evoked potenials developed in the visual cortex in the course of conditioning to light flashes (LF) in both groups of cats. In normal cats, a new component, with a peak latency from 80-100 msec and with reversed polarity, was observed in place of the late, longlasting, component of the preconditioning AEP. The latency of the new component is longer in cats with brainstem lesions. The first signs of waveform modification occurred relatively early in the process of learning, well before the animal learned to react consistently to the conditioned stimulus. Also, there seemed to be no clear relationship between the modified waveshapes of the AEPs and performance level during a particular session of conditioning. The modifications did not depend on habituation to the long-lasting exposure to light flashes presented alone. The new waveshape was preserved to a variable degree after brainstem lesions, that is, reconditioning never started with a potential characteristic for a naive animal. AEPs to licks in the auditory cortex, also changed during conditioning, although this modification was not so evident as in visual responses. In contrast to evident modifications of evoked responses in sensory specific structures during the process of conditiong, there were very small if any, changes in modality nonspecific structures, including brainstem reticular formation. Modality nonspecific responses were obtained from the brainstem reticular formation and motor cortex to light flashes and clicks, from the visual cortex to auditory stimuli and from the auditory cortex to light flashes. Only poorly developed evoked responses could be detected in the motor-sensory cortex during conditioning to light flashes although rhythmic EEG activity related to presentation of the conditioned stimulus (CS) was observed from this arena - thus indicating that they were not the same phenomena.

Animals↗