Unconditioned Response Amplitude Research Articles

Conditioned diminution of the unconditioned skin conductance response.

During Pavlovian conditioning the expression of a conditioned response typically serves as evidence that an association between a conditioned stimulus (CS) and an unconditioned stimulus (UCS) has been learned. However, learning-related changes in the unconditioned response (UCR) produced by a predictable UCS can also develop. In the present study, we investigated learning-related reductions in the magnitude of the unconditioned skin conductance response (SCR). Healthy volunteers participated in a differential conditioning study in which one tone (CS+) was paired with a loud white-noise UCS and a second tone (CS-) was presented alone. In addition, probe trials that consisted of UCS presentations paired with the CS+ (CS + UCS) and CS- (CS - UCS), as well as presentations of the UCS alone were included to assess UCR diminution. SCR and participants' expectations of UCS presentation were monitored during conditioning. Greater diminution of the UCR was observed to the UCS when it followed the CS+ compared to when it followed the CS- or was presented alone. Further, UCR amplitude showed an inverse relationship with the participants' ratings of UCS expectancy. However, conditioned UCR diminution was also observed independent of differential UCS expectancies. Our findings demonstrate conditioned diminution of the unconditioned SCR. Further, these findings suggest that although UCR amplitude is modified by conscious expectations of the UCS, conditioned diminution of the UCR can be expressed independent of learning-related changes in these expectations.

Acute stress impairs trace eyeblink conditioning in females without altering the unconditioned response

Exposure to an acute stressor of inescapable swimming or intermittent tailshocks impairs classical eyeblink conditioning 24 h later in female rats ( Wood, Beylin, & Shors, 2001). This effect is often attributed to a deficit in “learning,” but since stress has been shown to induce analgesia ( Jackson, Maier, & Coon, 1979), an alternative explanation is that stressor exposure reduces conditioning by lessening the perceived intensity of the unconditioned stimulus (US). To address this possibility we examined the amplitude of the unconditioned response (UR) during training and found that although exposure to the stressor impaired trace conditioning, there was no difference in the UR amplitude. We also found that eyeblink responses to different US intensities (4–12 V) in the absence of training were unaffected by stressor exposure. Taken together, these experiments indicate that the stress-induced impairment of conditioning in females is not due to a decreased perception of US strength.

Effects of CS-US Interval on Unconditioned Response Diminution in Human Heart Rate Classical Conditioning

Abstract This experiment studies the role of the conditioned response (CR) in explaining the unconditioned response (UR) diminution phenomenon in heart rate (HR) classical conditioning. In order to analyze the implication of the different CR components on UR diminution, the interstimulus interval (ISI) was varied. Sixty volunteer subjects received discrimination training with an interval between conditioned stimulus (CS) and unconditioned stimulus (US; aversive white noise) of 8 s. After the discrimination training phase, subjects were randomized into three different groups according to an ISI of 1, 5, or 8 s. The subjects of each group were then tested with five presentations of CS+/US. The results showed that UR amplitude as well as the deceleration immediately before this response (pre-UR deceleration) were significantly lower in the 5 s and 8 s ISI groups than in the 1 s ISI group. In addition, UR amplitude and pre-UR deceleration were statistically the same in the 5 s and 8 s ISI groups. These findings are discussed in terms of the adaptative role of the CR in classical conditioning.

Interpositus nucleus inactivation reduces unconditioned response amplitude after paired but not explicitly unpaired treatment in rabbit eyeblink conditioning

The amplitude of unconditioned responses (URs) in unconditioned stimulus (US) alone presentations were measured in six rabbits during explicitly unpaired and classical conditioning treatments. After both phases of the experiment, the interpositus nucleus (IPN) was reversibly inactivated by a cold probe. URs after unpaired treatment were unaffected by inactivation but after acquisition of a robust level of conditioned responses (CRs), URs in US-alone test trials were reduced in amplitude compared with URs immediately before and after inactivation. The results suggest that the IPN has a role in CR-related reflex modification.

Eyeblink conditioning in the freely moving rat: square-wave stimulation as the unconditioned stimulus

The freely-moving rat model of eyeblink conditioning has been gaining popularity as a model of associative learning. The most commonly used preparation uses subcutaneous electrodes to deliver the unconditioned stimulus (US), which has usually been a 60-Hz electrical shock. However, measurement of the unconditioned response (UR) has been controversial, because the US (SHOCK) interferes with electromyograph (EMG) activity if measured shortly after US delivery. Here, we present a modification of eyeblink conditioning in the freely-moving rat that uses a square-wave stimulation as the US. Videographic evidence demonstrated that use of stimulation allowed eyelid opening to be evaluated in EMG activity. A parametric study demonstrated that: (1) the stimulation US supported acquisition of the eyeblink conditioned response (CR); (2) stimulation intensity was reflected in UR amplitude; and; (3) UR amplitude decreased with acquisition of the eyeblink CR. The stimulation US fulfils the basic criteria for a US, while allowing delivery of the US through subcutaneous electrodes. Thus, the stimulation US is a viable alternative for eyeblink conditioning in the freely-moving rat preparation.

Conditioning in Identical Twins with Ataxia-Telangiectasia

Abstract Evidence has accumulated to indicate an essential role for the cerebellum in eyeblink classical conditioning, with normal acquisition impaired by lesions in the cerebellar cortex. For this reason, eyeblink conditioning was studied in a pair of 16-year-old identical twin females with ataxia-telangiectasia (AT), a disorder with onset in early childhood characterized by diffuse, almost selective, degeneration of the cerebellar cortex with extensive loss of Purkinje cells. We also tested a pair of 16-year-old identical twin female normal control subjects. Twins with AT produced significantly fewer conditioned responses (CRs). The mean percentages of CRs over 144 trials for each eye were 23.0% (left eye) and 10.2% (right eye) in patients with AT, and 45.9% (left eye) and 45.3% (right eye) in normal control subjects. The magnitude of the eyeblink reflex, assessed as unconditioned response amplitude, was not different between patients with AT and control subjects. The results indicate that patients with...

Conditioning in identical twins with ataxia-telangiectasia

Evidence has accumulated to indicate an essential role for the cerebellum in eyeblink classical conditioning, with normal acquisition impaired by lesions in the cerebellar cortex. For this reason, eyeblink conditioning was studied in a pair of 16-year-old identical twin females with ataxia-telangiectasia (AT), a disorder with onset in early childhood characterized by diffuse, almost selective, degeneration of the cerebellar cortex with extensive loss of Purkinje cells. We also tested a pair of 16-year-old identical twin female normal control subjects. Twins with AT produced significantly fewer conditioned responses (CRs). The mean percentages of CRs over 144 trials for each eye were 23.0% (left eye) and 10.2% (right eye) in patients with AT, and 45.9% (left eye) and 45.3% (right eye) in normal control subjects. The magnitude of the eyeblink reflex, assessed as unconditioned response amplitude, was not different between patients with AT and control subjects. The results indicate that patients with AT are impaired in the acquisition of CRs and provide further evidence for the role of the cerebellum in eyeblink classical conditioning in humans.

Nitrous oxide: Sensory, motor, associative, and behavioral tolerance effects in classical conditioning of the rabbit nictitating membrane response

Experiment 1, of a series of six experiments with the rabbit nictitating memebrane response (NMR) preparation, revealed that nitrous oxide (0%, 33%, 67%) impaired acquisition of conditioned responses (CRs). Subsequent experiments indicated that nitrous oxide (N 2O) had no reliable effects upon nonassociative processes (Experiment 2); impaired unconditioned response (UR) amplitude (Experiment 3); attenuated tone-conditioned stimulus (CS) intensity (Experiment 4); decremented tone-induced reflex modification of the unconditioned NMR (Experiment 5); and demonstrated no reliable evidence of behavioral tolerance (Experiment 6). It was concluded that N 2O's impairment of CR acquisition was attributable to its attenuation of the intensity of tone CSs and shock USs and/or UR amplitude. These findings are consistent with the behavioral laws of conditioning: the attenuation of the intensive sensory properties of the CS and US and/or UR components of conditioning affect their ability to enter into the establishment of CS-CR connections and, therefore, the development of associative learning.

Acquisition of classically conditioned eyeblink response following bilateral lesions of flocculus and paraflocculus

Stimulation of regions of the cerebellar flocculus can elicit eyeblinks, but the relationship of this floccular eyeblink zone to eyeblink classical conditioning is unknown. In this experiment, New Zealand white rabbits received bilateral lesions of the flocculus and paraflocculus and were subsequently classically conditioned with tone and corneal airpuff on the left and then the right eye. All animals reached training criterion on both eyes, with the exception of one animal whose lesion included the superior cerebellar peduncle and who was unable to learn on the ipsilateral eye. The lesioned group was not significantly different from unlesioned controls in rate of acquisition or conditioned or unconditioned response amplitude. These results indicate that the flocculus and paraflocculus are not by themselves the essential site of plasticity for classical conditioning of the rabbit eyeblink response.

The temporary inactivation of the red nucleus affects performance of both conditioned and unconditioned nictitating membrane responses in the rabbit.

These experiments are part of a series of studies examining the role of the red nucleus in the performance of the conditioned and unconditioned nictitating membrane reflexes in the rabbit. Specifically, the experiments test the hypothesis that the temporary inactivation of the red nucleus selectively affects the performance of the conditioned reflex. The experiments were designed to assess the effects of lidocaine and control saline microinjections on conditioned as well as unconditioned responses in both paired and unpaired trials. Rabbits were chronically implanted with cannulae through which small injecting tubes were passed stereotaxically to the red nucleus. The animals were conditioned using a delay paradigm in which a 1 kHz tone and an air puff applied to the cornea were used as the unconditioned and conditioned stimulus, respectively. Once conditioned, the effects of either lidocaine or saline injection were evaluated while alternating paired trials with unpaired trials in which only the air puff was applied. The principal finding of this study was that the amplitudes of both the conditioned and unconditioned responses were reduced following lidocaine injection into the red nucleus. The effect on the unconditioned response amplitude could not be ascribed to any interaction between the conditioned and unconditioned responses, since it also was present in the unpaired trials. The reduction in amplitude of the conditioned and unconditioned responses was shown to be correlated with changes in other characteristics of the same responses. The data suggest that the red nucleus contributes to the performance of both the conditioned and unconditioned nictitating membrane reflexes and consequently is not likely to be involved only in pathways responsible for mediating and/or storing the engram for the conditioned reflex.

Delay classical conditioning in young and older rabbits: initial acquisition and retention at 12 and 18 months.

Classical conditioning of the nictitating membrane-eyeblink response in young (7 months old) and older (36 months old) New Zealand white rabbits in a delay paradigm with a 400-ms conditioned stimulus-unconditioned stimulus interval was examined for initial acquisition and retention. Older animals required significantly more acquisition trials to reach learning criterion. Age differences in acquisition were temporary. Older rabbits responded at a level comparable to that of young rabbits such that total performance over the 630 trials of acquisition was not different. Rabbits in the explicitly unpaired control groups exhibited no age differences in unconditioned response amplitude or latency measures. Twelve- and 18-month retests demonstrated no significant age effects on retention. Patterns of retention differed between the age groups. Older rabbits required fewer trials to obtain the learning criterion at each phase of testing. Younger rabbits maintained a stable performance throughout training.

Disruption of classical eyelid conditioning after cerebellar lesions: damage to a memory trace system or a simple performance deficit?

Over the past 10 years, a number of laboratories have reported that classically conditioned skeletal muscle responses, such as conditioned nictitating membrane/eyelid responses, are critically dependent on activity in the cerebellum. For example, unilateral lesions of the cerebellar interpositus nucleus have been shown to prevent acquisition and abolish retention of the conditioned eyelid response on the side ipsilateral to the lesions without affecting conditioned responding (CR) on the contralateral side. Also, recording studies involving the interpositus nucleus have consistently revealed patterns of neuronal discharge that predict execution of the CR. The lesion and recording studies have generally been cited as evidence that plasticity in the cerebellum is critically involved in the learning and memory of classically conditioned responses. This interpretation was recently challenged by Welsh and Harvey (1989a), who claimed that cerebellar lesions simply produced a performance deficit and speculated that the role of the cerebellum was not in learning and memory processes associated with the CR but only in performance of the eye blink response. Presented here are three experiments that provide additional strong evidence for a critical role of the cerebellum in the learning and memory of the Pavlovian CR. These experiments include (1) demonstrations of complete and permanent CR abolition after appropriate interpositus lesions, (2) a failure to find systematic or persisting decrements in the unconditioned response amplitude (i.e., the eye blink reflex) after appropriate interpositus lesion, and (3) observations of differential effects on the CR and unconditioned response after lesions were placed in populations of motoneurons responsible for executing the eye blink response. These data are discussed in the context of performance versus learning issues; evidence presented here rules out the possibility that interpositus lesion abolition of the eye blink CR is simply due to lesion effects on performance.

Laws of the unconditioned reflex in the rabbit nictitating membrane preparation

The unconditioned response (UR) of the rabbit’s nictitating membrane (NM) was examined as a function of the intensity and duration of electrotactile and airpuff unconditioned stimuli (USs). For both USs, increases in US intensity produced increases in UR likelihood and amplitude, and decreases in onset latency. Increases in US duration had similar but smaller effects on the UR. The peak latency of the UR was also examined, but it proved to be highly variable. The data were analyzed by using progressively larger NM movements to define a UR. The lower criteria of 0.125, 0.250, and 0.500 mm produced virtually identical results. The more stringent criteria of 0.750, 1, and 2 mm produced decreases in the observed UR likelihood, increases in apparent UR amplitude, and increases in apparent peak latency.

Potentiation or diminution of discrete motor unconditioned responses (rabbit eyeblink) to an aversive pavlovian unconditioned stimulus by two associative processes: conditioned fear and a conditioned diminution of unconditioned stimulus processing.

In two experiments using the rabbit conditioned eyeblink preparation, the conditions under which a Pavlovian conditioned stimulus (CS) potentiates or diminishes the unconditioned response (UR) were examined. The results indicated that, after discrimination training (CS+ vs. CS-), the CS+ diminished UR amplitude at the training interstimulus interval (ISI). When CS+ trials were segregated into trials on which a conditioned response (CR) did or did not occur, the CS+ diminished the UR when it elicited a CR, but not when a CR failed to occur. When the CS-unconditioned stimulus (US) interval was lengthened to 10 s, the CS+ reliably potentiated the eyeblink UR on CR trials but did not potentiate responding on trials on which a CR was absent. The results are discussed in terms of the modulatory effects and temporal properties of conditioned fear and an associatively produced decrement in US processing.

Are eyeblink responses to tone in the decerebrate, decerebellate rabbit conditioned responses?

Bloedel and associates recently claimed to have established conditioned eyeblink responses in the acute decerebrate, decerebellate rabbit. Their training procedure was extreme massed practice (mean intertrial interval of 9 s) and they used an idiosyncratic definition of the conditioned response (10% or more of the unconditioned response amplitude). They did not measure or control the excitability of their preparations and did not run any separate control groups for alpha responses, alpha conditioning or pseudoconditioning. Using normal animals we compared their training procedure with procedures standard in the field and analyzed the consequences of their scoring procedure. Our group trained at a 30-s intertrial interval (ITI) showed clear learning in the training session. In marked contrast, 3 groups trained at a 9-s ITI developed no conditioned responses. We also found that the method of scoring used by Bloedel and associates counts many spontaneous responses as conditioned responses (CRs) if unconditioned response (UR) amplitudes are low, excludes genuine CRs if UR amplitudes are high and does not control for the occurrence of spontaneous responses. It must therefore be concluded that the eyeblink responses to tone reported by Bloedel and associates to occur in the decerebrate, decerebellate rabbit are not associative CRs as they develop in the normal animal.

Microinjections of local anesthetic into the pontine nuclei reduce the amplitude of the classically conditioned eyelid response

Seventeen rabbits were implanted bilaterally with cannulae into the pontine nuclei, and were then trained in the classically conditioned eyeblink procedure. Nine of the rabbits were trained with a tone as a conditioned stimulus (Cs), and eight were trained with both tone and a light Cs. After each rabbit had learned the conditioned response (CR) well, testing began. One μ.l of 5% lidocaine injected bilaterally significantly impaired the CR amplitude for both tone and light as a Cs, although unconditioned response amplitude was not affected. Injection of 1 μl of isotonic saline did not impair CR amplitude, suggesting that the impairment seen after lidocaine injection was due to the anesthetic action of lidocaine in the pons, and not to nonspecific effects distal to the site of injection. These results support and extend the lesion data which shows that the pontine nuclei and their mossy fiber projection to the cerebellum are necessary for eyeblink conditioning using a peripheral CS.

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.

Red nucleus lesions impair acquisition of the classically conditioned nictitating membrane response but not eye-to-eye savings or unconditioned response amplitude

Following a single electrocoagulating RF lesion aimed at left red nucleus, rabbits received classical conditioning of the nictitating membrane (NM) response. A tone was the conditioned stimulus (CS) and electrostimulation of the eye was the unconditioned stimulus (US). The US was applied to the right eye during the initial phase of training. It was then switched to the left eye to assess transfer of learning and ultimately switched back to the right eye. NM responses were recorded simultaneously from both eyes during each phase of training. Consistent with reports implicating a cerebellar-rubro circuit in this behavior, RN lesions disrupted acquisition of CRs in the eye contralateral to the lesion. Animals with disrupted NM CRs of the right eye resembled controls in showing transfer of conditioning to the left eye. CR-disrupting lesions did not affect UR amplitude.

Sensory and associative effects of LSD (Oryctolagus cuniculus) nictitating membrane response.

Three experiments were conducted to determine the effects of LSD (30 nmol/kg) on the acquisition of the rabbit's classically conditioned nictitating membrane response. Experiment 1 revealed that LSD significantly enhanced the acquisition of conditioned responses [CRs], and control groups receiving unpaired conditioned stimulus/unconditioned stimulus (CS/UCS) presentations served to identify LSD's effect to be on learning. Accordingly, subsequent efforts were directed at determining whether LSD's enhancing effects could have arisen from its altering the sensory processing of the CS and/or the UCS. In Experiment 1, unconditioned response (UCR) amplitude to a 30mA UCS was not significantly affected by LSD. Moreover, Experiment 2 revealed that LSD had no significant effect on the psychophysical functions relating UCS intensity to the frequency or amplitude of UCRs and that the drug did not affect the UCS-intensity threshold for evoking UCRs. On the other hadn, Experiment 3 revealed that LSD significantly enhanced the frequency of CRs to an extended range of CS intensities in the psychophysical function relating CS intensity to CR frequency. Furthermore, LSD lowered the CS-intensity threshold. The drug's enhancement of the sensory processing of the CS was postulated to facilitate conditioning through both learning and preformance mechanisms.