Relationships among age, conditioned stimulus-unconditioned stimulus interval, and neuropsychological test performance

To evaluate the effect of age at various conditioned stimulus (CS)-unconditioned stimulus (US) intervals, 144 young, middle-aged, and older adults were tested on eyeblink classical conditioning at CS-US intervals of 500, 1,000, or 1,500 ms. Reaction time, response timing, motor learning, declarative memory, and attention were assessed to identify correlates of conditioning at various CS-US intervals. Previously reported middle-aged and older adults were impaired at a 400-ms CS-US interval, but the addition of 100 ms to the CS-US interval in this study enabled equal conditioning in middle-aged and young adults. At a 1,000-ms CS-US interval, older adults remained significantly impaired. It was only at the 1,500-ms CS-US interval that conditioning was equal for the 3 age groups. Measures of reaction time, timing, and motor learning were not correlated systematically with conditioning. Whereas the results of age differences at various CS-US intervals were clear and striking, patterns of relationships among neuropsychological and conditioning variables were not consistent in indicating sources of age differences.     

An associative process maintains reflex facilitation of the unconditioned nictitating membrane response during the early stages of training

The presentation of a neutral or conditioned stimulus (CS) at an appropriate interval prior to the presentation of a corneal airpuff, or a paraorbital shock (unconditioned stimulus, US) can facilitate the amplitude of the unconditioned nictitating membrane (NM) response in rabbit. In two experiments, it was demonstrated that an associative process mediates the maintenance of that facilitation during repeated CS-US pairings. Although CS-alone presentations produced a substantial decrease in the amount of reflex facilitation in animals not pretrained with the CS, pretraining that consisted of paired CS-US presentations prevented that decrease when CS-alone presentations were subsequently given. Conditioned facilitation of the unconditioned response occurred very rapidly (within 5-12 trials in these experiments) and long before the appearance of overt conditioned responses to the CS. In addition, it was demonstrated that conditioned facilitation can be relatively specific to the tonal frequency of the CS. These results indicate the first sign of conditioning of the NM response is exhibited in the amplitude of the unconditioned response.     

Avoidance learning under delayed shock termination in prenatally x-irradiated rats

Groups of MP1 male albino rats were exposed to x-irradiation of 200 rad on Day 17 of gestation. Irradiated and control rats were trained in a shuttlebox with either immediate or .5-sec delayed termination of both the electric shock (US) and the conditioned stimulus (CS) on escape trials. An avoidance response always produced prompt CS termination. Irradiated rats showed a higher degree of avoidance behavior than controls and, under the delay condition, tended to run rapidly in the CS-US interval.     

Hypothermia modifies the effective CS-US interval in conditioned taste aversion in rats

Conditioned taste aversion can be acquired when rats experience an unconditioned stimulus (US) while anesthetized. In contrast to anesthetics, a hypothermia-induced comatose state immediately after presentation of a taste conditioned stimulus (CS) prevented a taste-illness association at relatively short CS-US intervals and potentiated the aversion at longer intervals. Results at shorter CS-US intervals were explained on the basis of hypothermia's temporally graded amnesitc properties. Evidence for conditioning at the longer intervals was discussed in relation to slowing down metabolism allowing for associations to be formed at CS-US intervals that normally do not result in evidence of conditioning. Manipulating body temperature during the CS-US interval was demonstrated to alter rats' ability to bridge temporal gaps in associative learning.     

Temporally specific extinction of conditioned responses in the rabbit (Oryctolagus cuniculus) nictitating membrane preparation

Extinguishing a conditioned response (CR) has entailed separating the conditioned stimulus (CS) from the unconditioned stimulus (US). This research reveals that elimination of the rabbit (Oryctolagus cuniculus) nictitating membrane response occurred during continuous CS-US pairings. Initial training contained a mixture of 2 CS-US interstimulus intervals (ISIs): 200 ms and 1,200 ms. The CRs showed double peaks, one for each ISI. When 1 ISI was removed, its CR peak showed the hallmarks of extinction: a decline across sessions, spontaneous recovery between sessions, and rapid reacquisition when the absent ISI was reintroduced. These results support real-time models of conditioning that segment the CS into microstimuli while challenging theories that rely on contextual control, US representations, CS processing, and response inhibition.     

Time-specific extinction and recovery of the rabbit's (Oryctolagus cuniculus) conditioned nictitating membrane response using mixed interstimulus intervals

Extinguishing a conditioned response (CR) has entailed separating the conditioned stimulus (CS) from the unconditioned stimulus (US). This research reveals that elimination of the rabbit nictitating membrane response occurred during continuous CS-US pairings. Initial training contained a mixture of 2 CS-US interstimulus intervals (ISIs), 150 ms and 500 ms. The CRs showed double peaks, one for each ISI. When the 150-ms ISI was removed, its CR peak showed 2 hallmarks of extinction: a decline across sessions and spontaneous recovery between sessions. When a further stage of training was introduced with a distinctive CS using the 150-ms ISI, occasional tests of the original, extinguished CS revealed another hallmark of extinction, specifically, strong recovery of the 150-ms peak. These results support both abstract and cerebellar models of conditioning that encode the CS into a cascade of microstimuli, while challenging theories of extinction that rely on changes in CS processing, US representations, and contextual control.     

A Comparison of Two Model Systems of Associative Learning: Heart Rate and Eyeblink Conditioning in the Rabbit

In four classical conditioning experiments heart period and eyeblink responses were assessed concomitantly. The conditioned stimuli (CSs) were tones and the unconditioned stimulus (UCS) was a brief paraorbital electric shock. Using a 0.5-s duration CS, bradycardiac conditioned responses that consisted of a 4–5 ms change from pre-CS baseline occurred within 10–20 CS-UCS presentations. However, eyeblink conditioned responses began to occur only after 100–150 CS–UCS presentations. A 1.0-s CS duration resulted in bradycardiac conditioned responses of 15–30 ms change from pre-CS baseline, which again reached asymptote within 10–20 trials. Using a 4-s CS duration, in a differential classical conditioning paradigm, heart period discrimination between a reinforced CS+ and a nonreinforced CS? occurred within 10 trials; asymptotic performance of the heart period conditioned response occurred within 15 CS-UCS presentations and consisted of a bradycardiac response of 40–50 ms for the 12th interbeat interval following tone onset. These data thus indicate that these two model systems of mammalian learning (based on heart period and eyeblink responses) show quite different acquisition functions. It is also significant that heart rate slowing always accompanied the eyeblink conditioned responses, even though increases in general electromyographic activity as well as eyeblink conditioned responses were simultaneously observed during CS presentation.     

Ketaset-Rompun extends the temporal gradient for hypothermia-induced retrograde amnesia.

In studies of experimentally induced retrograde amnesia (RA), as the interval between training and the amnestic treatment is lengthened, amnesia decreases (4). This temporal gradient for RA has been reported with a wide variety of amnestic agents, including RA produced by thermoregulatory disturbances (8). This temporal gradient for RA is not unlike certain characteristics of classical conditioning, where weaker conditioned responding occurs when the interval between the conditioned stimulus (CS) and unconditioned stimulus (US) is lengthened. Furthermore, there is evidence that administration of anesthetics can lengthen the "effective conditioning" interval between the CS and US, as demonstrated in a conditioned taste-aversion (CTA) procedure (10). In that study, little conditioning was observed when a 3-h delay (or more) was incorporated between presentations of the CS (flavor) and the US (toxin). However, if subjects were anesthetized immediately after the CS was delivered and remained anesthetized during the CS-US interval, strong conditioning was observed with CS-US intervals of up to 9 h. The aim of the present experiment was to determine if the temporal gradient for hypothermia-induced RA could also be lengthened. That is, we tested whether the interval between training and hypothermia treatment could be lengthened by anesthetizing subjects with Ketaset-Rompun. The results indicate that the training-to-amnestic agent interval could be lengthened within moderate limits. The implications for hypothermia-induced RA is further discussed.     

Effects of amygdala lesions on reflex facilitation and conditioned response acquisition during nictitating membrane response conditioning in rabbit.

The present study demonstrated that large lesions of the amygdala disrupt the maintenance of reflex facilitation of the unconditioned nictitating membrane (NM) response and slow the acquisition of conditioned NM responses in rabbit. Before behavioral training, the central nucleus of the amygdala and adjacent areas were lesioned electrolytically. In the 1st experiment, the lesioned animals exhibited no reflex facilitation of the unconditioned NM response at conditioned stimulus (CS)-unconditioned stimulus (US) intervals of 125-8,000 ms. In the 2nd and 3rd experiments in which one CS-US interval (500 ms) was used, the lesions disrupted the maintenance of reflex facilitation but did not alter the facilitation exhibited in the 1st block of training. The lesions retarded the acquisition of conditioned NM responses when the 1000-Hz tone CS intensity was 65 dB but not when the intensity was 85 dB.     

Conditioned hippocampal cellular response to a behaviorally silent conditioned stimulus.

Multiunit activity (MUA) was chronically recorded in the hippocampal CA3 field of rats using a blocking paradigm with conditioned suppression of lever pressing for food as the measure of conditioning. In Experiment 1, a classical blocking paradigm demonstrated the good conditionability of 2 stimuli (a light and a tone) and their respective ability to block each other. In Experiment 2, MUA was recorded in CA3 cells in rats submitted to a similar paradigm. Four groups received either tone (groups B and B1) or click (groups BC and B1C) conditioned stimulus (CS) presentations that were followed immediately by an electrical footshock (unconditioned stimulus, US). The rats were then given either 40 (groups B and BC) or 1 (groups B1 and B1C) tone + light-footshock presentations. During test sessions, the animals showed MUA responses to the added CS (light), with no conditioned suppression of lever presses occurring during CS presentations. The results of Experiment 3 strongly suggest that hippocampal increase in cellular activity to the light appeared at the first compound trial presentation. Conditioning to the light obtained by increasing the US intensity after the single compound trial suggests that the hippocampal response reflects a redundant CS-US association (light-shock). Long-term retention tests given 45 days after the end of conditioning revealed that behavioral and hippocampal responses could still be detected but only in response to the stimulus that had elicited a behavioral response during learning.     

Learning to fear suffocation: a new paradigm for interoceptive fear conditioning

The present study aimed to establish a new interoceptive fear conditioning paradigm. The conditioned stimulus (CS) was a flow resistor that slightly obstructs breathing; the unconditional stimulus (US) was a breathing occlusion. The paired group (N = 21) received 6 acquisition trials with paired CS–US presentations. The unpaired group (N = 19) received 6 trials of unpaired CS–US presentations. In the extinction phase, both groups were administered 6 CS‐only trials. Measurements included startle eyeblink response, electrodermal responses, and self‐reported US expectancy. In the paired group, startle blink responses were larger during CS compared to intertrial interval during acquisition and extinction. Electrodermal and US expectancies were larger for the paired than for the unpaired group during acquisition, but not during extinction. The present paradigm successfully established interoceptive fear conditioning with panic‐relevant stimuli.     

Time and stimulus specificity in extinction of the conditioned nictitating membrane response in the rabbit (Oryctolagus cuniculus)

The present experiments demonstrated that, in the rabbit nictitating membrane preparation, a conditioned response (CR) can be selectively eliminated in one portion of a conditioned stimulus (CS) while it is still paired with the unconditioned stimulus (US). Rabbits were initially trained with two stimuli (tone, light). Each was paired with the US by using a mixture of two CS-US interstimulus intervals (ISIs): 200 ms and 1,200 ms in Experiment 1; 150 ms and 500 ms in Experiment 2. The CRs showed double peaks, one for each ISI. Subsequently, one CS (A) was trained with only the longer ISI, whereas the other CS (B) continued to be trained with both ISIs. Consequently, the CR peak based on the shorter ISI disappeared for CSA but not for CSB. The later CR peaks during both CSA and CSB were maintained. These results support time-based models of conditioning. Implications for proposed mechanisms of extinction are discussed.     

Cell analog of the conditioned reflex to cortical electrical stimulation

Conclusion The possibility of obtaining a cellular analog of a CR was investigated on the sensory motor cortex of the unanesthetized rabbit. Single unit activity was analyzed. Stimulation through surface cortical electrodes 2.5–12mm away from the recording microelectrode was used as the conditional stimulus (CS). The unconditional stimulus (US) was stimulation through two closely situated electrodes.With short (1–5 sec) inter-trial intervals, and with a US of sufficient strength and duration, a well-marked augmentation of the excitatory response to CS was obtained in most neurons. However, it was short (less than 30 sec) and, as a rule, it was the analog not of a CR but of a pseudo conditioned reflex, for it did not require pairing of the CS and US, but appeared after one or a few presentations of the US alone.In 9 of the 21 neurons tested with longer intervals between trials (7–120 sec) conditioned-reflex changes were observed. These changes consisted of the appearance (or modification) of a response to the CS during conditioning trials and disappearance during extinction trials, or of the appearance of a response at the time corresponding to the missing US when the US was intermittently omitted. The character of the conditioned-reflex changes (activation or inhibition) was the same as that of the cell's response to the US. Changes appeared after the first 10–20 conditioning trials and recovery after extinction took place more rapidly than initial conditioning, i.e., in 5–10 combinations.     

CLASSICAL CONDITIONING OF THE ELECTRODERMAL RESPONSE WITH NOVEL STIMULI

Most attempts to classically condition the electrodermal response (GSR) have used aversive stimuli. A series of 20 novel slides were used as unconditional stimuli in a delayed differential conditioning paradigm involving reinforced and unreinforced conditional stimuli. Thirty female Ss were given 10 habituation trials, 40 conditioning trials of which half were reinforced, and 10 extinction trials. Orienting response, anticipatory response, and post-conditional stimulus response components were analyzed separately for the different series. Differential conditioning was obtained for two of the responses during the conditioning and extinction series. The results indicate that a relatively mild novel stimulus can also effectively condition the GSR.     

A retrograde gradient for disruption of a conditioned aversion to drinking cold water by ECS administered during the CS-US interval

Rats were used to examine the effects, upon a conditioned aversion to cold drinking water, of electroconvulsive shock (ECS) delivered during the delay between cue and unconditioned stimulus. An injection of LiCl (US) 30 min after ingestion of novel cold water (CS) produced a reliable aversion to the cold water. ECS given immediately following the ingestion of cold water substantially attenuated this aversion. An orderly decrease in the attenuation of the aversion was observed when ECS was delayed 5, 10 or 20 min after offset of the cold water cue. The results indicate that ingestive cue aversions can be formed without electrochemical neural-transmission-based representation of the cue being maintained during the CS-US interval. The differential effectiveness of ECS suggests that this agent retroactively interferes with processing of the ingestive cue.     

PERCEPTUAL MODE AND CARDIAC CONDITIONING

Conditional heart rate responses were measured for field-dependent and field-independent subjects. The conditional stimulus (CS) was a colored light and the unconditional stimulus (US) was an electric shock delivered to the finger. The CS-US interval was 10 sec. The field-independent subjects demonstrated an initial cardiac acceleration followed by a cardiac deceleration, whereas the field-dependent subjects showed only the cardiac deceleration. When these data are compared with the previously reported galvanic skin response (GSR) data, a model of sympathetic-parasympathetic reactivity is evolved wherein the field-independent group shows both conditioned sympathetic and parasympathetic autonomic activity, while the field-dependent group shows only parasympathetic activity.     

Temporal patterns of the rabbit's nictitating membrane response to compound and component stimuli under mixed CS-US intervals

The acquisition of the rabbit's nictitating membrane response to a tone and light compound and to its components was examined when compound presentations were reinforced at one conditioned stimulus-unconditioned stimulus (CS-US) interval and individual component presentations were reinforced at another CS-US interval. Examination of the time course of the CRs revealed that (a) despite the mixture of CS-US intervals, conditioned response (CR) timing remained accurate, that is, CRs reached their peaks at the alternative points of US delivery; (b) the momentary magnitude of the CR to the compound was predominantly an additive function of the CR magnitude to the individual components; but (c) there was modest evidence of differentiation between the compound as a unit and the individual components. The results are discussed in terms of their implications for the study of the neural substrates of temporal and sensory integration as they modulate CR acquisition.     

Elicitation of Subjective Uncertainty during Vasomotor and Electrodermal Discrimination Classical Conditioning

Subjective uncertainty was introduced during discrimination classical conditioning of the skin conductance and vasomotor responses. All 48 college student subjects were informed that one 7-sec colored light would always be followed by a shock (CS+) while a 7-sec light of another color would never be followed by a shock (CS?). After half of the conditioning trials, a novel stimulus (NS) was illuminated (a third color) and remained on. One group was previously informed about the NS while the other group was noninformed. Results of between trial verbal reports and postsession interviews indicated that noninformed subjects experienced more general uncertainty and more uncertainty regarding the CS-US contingency on the postNS trials than did the informed group. On the trial pair following the NS onset, the short latency electrodermal response (1 to 4.5 sec) of the noninformed subjects increased while the informed subjects maintained a stable level of responding. Evaluation of later postNS trials revealed that the long latency response (4.6 to 7.9 sec) of the noninformed subjects decreased more than for the informed subjects. The decrease for the noninformed subjects was greatest to CS+. No group differences in vasomotor activity were elicited by NS onset. It was concluded that momentary increases in orienting and more sustained decreases in preparatory activity may accompany increases in subjective uncertainty.     

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

Previous studies have shown flexor nerve response increases produced by classical conditioning procedures in spinal cats when the conditioned stimulus (CS) was delivered to the superficial peroneal nerve and the unconditioned stimulus (US) was delivered to the ankle skin. In this study, these effects were produced when the CS was delivered to the whole tibial nerve or to the medial plantar branch. The finding that response increases followed by extinction effects could be obtained when either the superficial peroneal or the tibial nerve was utilized allowed the assessment of the effects of a differential conditioning paradigm. The responses to CS-US 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 suggested 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.     

Imagery and Pavlovian Heart Rate Decelerative Conditioning

The present experiment was designed to investigate the role of US-imagery in Pavlovian heart rate(HR) decelerative conditioning with a head-up to head-down body tilt as the unconditional stimulus (US). From imagery theories of Pavlovian conditioning (e.g., King, 1973), it was hypothesized that the nature (content) of the imagery instructions would affect the conditional response (CR). Two groups of 20 subjects were employed: an Experimental (CS-US) group and a Control (US-CS) group. Half the subjects in each group were instructed to imagine the tilt-US whenever the CS was presented (Relevant Imagery condition); the remaining subjects were instructed to imagine a car-ride whenever the CS was presented (Irrelevant Imagery condition). The HR CR was assessed on a second-by-second basis during CS-alone lest trials. The results of the experiment supported the hypothesis: despite an identical CS-US contingency, only the Experimental/Relevant Imagery group (as opposed to the Experimental/Irrelevant Imagery group) demonstrated a marked, monophasic decelerative CR to the CS relative to control groups. Differences in imagery ability, instructed-imagery vividness ratings, and US-awareness ratings could not account for the data. The significance and implications of these findings are discussed in relation to stimulus substitution (S-R) and cognitive (S-S) theories of conditioning.