Effects of habituation and classical conditioning on reflex modification

Reflex modification is the inhibition or facilitation of a reflex by a stimulus (S1) occurring prior to a reflex-eliciting stimulus (S2). Two experiments were conducted that investigated the effects of habituation of the orienting response (OR) and classical conditioning on reflex modification of skin conductance responses (SCRs). During the first phase of Expt. 1 two groups (Group S1 and the Control group) received pre-presentations of S1 (200 Hz). Another group (Group S3) received pre-presentations of a different tone (S3, 3000 Hz). During the second phase, Groups S1 and S3 received pairings of S1 with S2 (white noise), whereas the Control group received pairings of S2 with S1. The predictions were: if the OR to S1 produces reflex modification of the response to S2, then Group S1 and the Control group will display larger SCRs on the first trial of the second phase of the experiment compared to Group S3, in which the OR to S1 will produce reflex modification. However, if conditioned diminution of the unconditioned response (UR) elicited by S1 produces reflex modification of the response to S2, then there should be no initial differences between the groups in the second phase of the experiment. The results showed that SCRs in Group S1 were significantly larger in the second phase compared to Group S3. This result favors an OR explanation of reflex modification. In Expt. 2, the effect of conditioned diminution of the UR on reflex modification was further investigated.(ABSTRACT TRUNCATED AT 250 WORDS)     

Capacity of visual classical conditioning in Drosophila larvae

Vision is an ancient sense essential for various aspects of animal behavior. Visual information not only leads to immediate, temporary, and rapid behavioral responses but also has lasting effects. Na?ve behavioral responses to light are not always identical but can be altered based on positive or negative experience-a process defined as visual learning. In this study, Drosophila larvae were used as a simple model to study visual classical conditioning. We show that larvae are able to associate positive or negative cues with either light or darkness, thus changing their native light-preference. This effect can be robustly provoked through gustatory stimuli and electric shock. We further show that light can not only be used as a conditioned stimulus but also as an unconditioned stimulus, as punishment in the olfactory classical conditioning procedure, possibly forming two different kinds of memories. Our findings show that even though larvae show a strong na?ve response when exposed to light, the animals display a comparably large repertoire of visual memories that can be formed. Therefore, our study provides an impacting entry point into the genetic dissection of the neuronal circuit that underlies different types of visual learning.     

Startle reflex facilitation as a function of classical eyeblink conditioning in humans

I investigated whether classical eyeblink conditioning increases the activating effect of the conditional stimulus (CS) on the relevant alpha motoneuron pool in the facial nucleus. The activating effect was measured by the reflex modification method, where startle reflexes, sharing the facial nerve motor pathway with conditional and unconditional eyeblink reflexes, were elicited in the presence of reinforced and nonreinforced CSs (CS+ and CS?). To reduce influences of conditional arousal on startle, a weak airpuff to the eye was used as unconditional stimulus and relatively short stimulus onset asynchronies (SOAs) of 300 and 600 ms were used in three startle tests presented while conditioning was in progress. Two groups (N= 72) received 100% or 0% reinforcement (Groups 100 and 0) of a tone CS+. The CS? was not reinforced. Three startle tests, consisting of acoustic startle probes presented alone and after CS+ and CS? onset, were conducted early, middle, and late in conditioning. Results showed increased startle reflex facilitation after CS+ onset in the late startle test in Group 100, indicating that startle increased as a function of classical conditioning. Although reflex facilitation at the 300-ms SOA in Group 100 is consistent with the hypothesis that CS presentations activated motoneurons in the facial nucleus, the present study cannot itself definitively support this hypothesis. Reflex facilitation at the 600-ms SOA in Group 100 could be influenced by conditional arousal.     

Conditioned facilitation of the unconditioned reflex after classical eyeblink conditioning.

The present study (N=40) investigated the time-course of conditioned facilitation of the unconditioned eyeblink reflex (UR). In a single-cue delay classical conditioning procedure, a tone conditioned stimulus (CS) signaled an airpuff unconditioned stimulus (airpuff US) to the eye. A paired group received 40 trials of CS/US presentations with an interstimulus interval (ISI) of 200 ms. An unpaired group received an equal number of explicitly unpaired presentations of the CS and US. Thereafter, eyeblink reflex facilitation was assessed by presenting 94 dB white noise (noise US) 10, 30, 50, 100, 150, and 1000 ms after CS onset. In the paired group, URs were significantly increased as early as 100 ms after CS onset compared to the unpaired group. This reflex facilitation was correlated with CR magnitude, indicating that conditioned facilitation of eyeblink URs indexes an early, automatic, preattentive stage in CR formation.     

Effects of mutant Drosophila K+ channel subunits on habituation of the olfactory jump response

The olfactory-jump response assay was used to analyze habituation in Drosophila mutants of potassium (K(+)) channel subunits. As with physiological assays of the giant fiber-mediated escape reflex, mutations at loci that encode K(+) channel subunits have distinct effects on habituating the olfactory-jump response. The data for slowpoke and ether à go-go indicate similar effects on habituation of the olfactory-jump response and the giant fiber-mediated escape. Habituation in the olfactory jump assay in Hyperkinetic and Shaker mutants was drastically different from the degree of defect in the giant fiber-mediated escape reflex, indicating differential control mechanisms underlying the two forms of non-associative conditioning.     

Modulation of trigeminal reflex excitability in migraine: effects of attention and habituation on the blink reflex.

The modulation of trigeminal reflex excitability in migraine patients was evaluated during the asymptomatic phase by studying the effects of attention, habituation and preconditioning stimulus on the R2 and R3 components of the blink reflex (BR). Fifty patients suffering from migraine without aura, 20 affected by migraine with aura and 35 sex- and age-matched controls were selected. In subgroups of migraine with-aura and without-aura patients, and normal controls, the blink reflex was elicited during different cognitive situations: (a) spontaneous mental activity; (b) stimulus anticipation; (c) recognition of target numbers. In the remaining subjects, R2 and R3 habituation was evaluated by repetitive stimulation at 1, 5, 10, 15, 20, 25 and 30 s intervals. The R2 and R3 recovery curves were also computed. A reduced R3 threshold with a normal pain threshold was found in migraine with-aura and without-aura patients; the R3 component was not significantly correlated with the pain thresholds in patients and controls. The R2 and R3 components were less influenced by the warning of the stimulus in migraine without-aura and migraine with-aura patients, in comparison with the control group. A slight increase of both R2 and R3 recovery after preconditioning stimulus was also observed in migraine patients, probably caused by a phenomenon of trigeminal hyperexcitability persisting after the last attack. The abnormal BR modulation by alerting expresses in migraine a dysfunction of adaptation capacity to environmental conditions, probably predisposing to migraine.     

Olfactory Adaptation in Drosophila Larvae

To accommodate both high sensitivity as well as the ability to respond to a broad range of stimulus concentrations, an organism must possess some means of modulating the gain of its sensory systems. This phenomenon is known as adaptation. Here, we demonstrate that Drosophila larvae can adapt to three odorants in a behavioral paradigm. Larval olfactory adaptation is concentration- and dose-dependent. Olfactory and visual adaptation in Drosophila melanogaster adults is dependent on the transient receptor potential (trp) calcium channel. Recovery from olfactory adaptation, which is TRP-dependent in adults, is shown to be unaffected by a loss-of-function trp mutation in larvae. Moreover, the TRP gene product is not expressed in the larval olfactory organs. These observations suggest a role for trp in mediating sensory function that is conserved between sensory modalities in adults but is not conserved between developmental stages.     

Olfactory adaptation in Drosophila larvae

To accommodate both high sensitivity as well as the ability to respond to a broad range of stimulus concentrations, an organism must possess some means of modulating the gain of its sensory systems. This phenomenon is known as adaptation. Here, we demonstrate that Drosophila larvae can adapt to three odorants in a behavioral paradigm. Larval olfactory adaptation is concentration- and dose-dependent. Olfactory and visual adaptation in Drosophila melanogaster adults is dependent on the transient receptor potential (trp) calcium channel. Recovery from olfactory adaptation, which is TRP-dependent in adults, is shown to be unaffected by a loss-of-function trp mutation in larvae. Moreover, the TRP gene product is not expressed in the larval olfactory organs. These observations suggest a role for trp in mediating sensory function that is conserved between sensory modalities in adults but is not conserved between developmental stages.     

Contralateral and long latency effects of human biceps brachii stretch reflex conditioning

Results from previous studies on monkeys and human subjects have demonstrated that the biceps brachii spinal stretch reflex (SSR) can be operantly conditioned. The extent to which conditioning paradigms influence contralateral SSRs or longer latency responses in the same limb has not been examined. Nine subjects were given 10 training sessions to either increase or decrease the size of their biceps brachii SSR. Group changes were compared to the mean of six baseline (control) sessions. Both groups showed progressive SSR changes over the training sessions. Up-trained subjects increased their SSR responses by an average of 135.3% above baseline, with the last three sessions showing a 237.5% increase, while down-trained subjects reduced their average SSR responses by 43.4%, with a 52.7% reduction over the last three sessions. Ipsilateral longer latency responses showed average changes of 68.9% and-68.7% for up- and down-trainers, respectively. As in the case of SSRs, these responses changed progressively over sessions, with a 131.5% increase seen in the last three up-training sessions and an 82.4% reduction over the same period for down-trainers. Correlation coefficients between SSR and longer latency responses were high (R=0.90, up-trainers; R=0.87, down-trainers). Contralateral SSR and longer latency responses, measured in the absence of feedback and at least 10 min after ipsilateral conditioning, showed directional changes that were similar to the trained side, but their magnitudes were not as profound. Collectively, these data suggest that unilateral SSR conditioning affects spinal circuits controlling contralateral SSRs and influences longer latency responses.     

Voltage-clamp analysis of the effects of classical conditioning on the hippocampus

1. Effects of nictitating membrane conditioning on K+ currents of CA1 pyramidal cells of rabbit hippocampus were studied by the use of the single-electrode voltage-clamp (SEVC) technique. 2. IQ, IM, IC, and IAHP were recorded in slices from control animals, showing behavior similar to that previously described for other preparations. IQ developed as an inward current during hyperpolarizing steps to potentials more negative than the K+ equilibrium potential. IM appeared as an inward inactivating relaxation during hyperpolarizing pulses, from potentials slightly more positive than the resting potential (approximately -40 mV). Such depolarization is thought to activate the IM, IC was recorded during long depolarizing pulses as a slow outward current. IAHP appeared during short depolarizing pulses as an outward current peaking at approximately 200 ms after the pulse. Progressively more positive pulses were accompanied by a linear increase of the peak IAHP value. The slope of the IAHP-voltage relation was used for comparison of cells between groups of animals that had different training experience. 3. Responses of control cells to cholinergic agents were similar to those previously characterized in other preparations. Specifically, cholinergic agonists blocked IM and IAHP, partially reduced IC, and did not affect IQ. 4. Conditioning did not affect IQ, IM, and IC but reduced the slope values of the IAHP-voltage relation. This change is consistent with the conditioning-specific afterhyperpolarization (AHP) reduction previously reported. 5. The effect of conditioning on the IAHP but not on the IC, both Ca(2+)-dependent K+ currents, suggests a direct effect on the former, rather than a reduction of ICa2+ or a change in the levels of Cai2+.     

Context conditioning in habituation in the nematode Caenorhabditis elegans

Habituation has traditionally been considered a nonassociative form of learning. However, recent research suggests that retention of this nonassociative form of learning may be aided by associations formed during training. An example of this is context conditioning, in which animals that are trained and tested in the presence of a contextual cue show greater retention than animals trained and tested in different environments. This article reports context conditioning in habituation in the nematode Caenorhabditis elegans. The results showed that retention of habituation to tap at both 10- and 60-s interstimulus intervals was significantly greater if training and testing occurred in the presence of the same chemosensory cue (NaCH3COO). This context conditioning showed both extinction and latent inhibition, demonstrating that these simple worms with only 302 neurons are capable of associative context conditioning.     

Classical conditioning,sensitization and habituation in the spinal cat

Changes in the flexion reflex of the tibialis anterior muscle of acute spinal cats were examined during conditioning, sensitization and habituation paradigms. Experimental animals were classically conditioned by pairing electrical stimulation of the saphenous nerve (CS) with stimulation of the superficial peroneal nerve (US). Recordings from these nerves assured known and constant stimulus inputs. The response observed was an increase in the magnitude of the reflex response to the CS over training. Habituation (CS only) and sensitization (CS and US presentations, unpaired) control animals exhibited no such reflex facilitation. The results of post-tetanic potentiation studies indicated that the intertrial intervals used were not a factor in the differences observed between experimental and control groups. The results give positive support to the concept of spinal conditioning and emphasize the potential of this model system for the study of neural correlates of learning.     

小脑皮层与经典眨眼条件反射

损毁、药物失活和电生理记录等领域研究的结果提示,小脑皮层是参与经典眨眼条件反射建立、保留和任务执行过程的关键脑区.在此,本文综述了近年来关于小脑皮层在经典眨眼条件反射过程中作用和机制的研究进展.     

Olfactory discrimination conditioning in the moth Spodoptera littoralis

We used a proboscis extension reflex (PER) to study the olfactory discrimination capability in the moth Spodoptera littoralis. Already after a single experience, moths were capable to discriminate a rewarded from an unrewarded odor. In the first experiment, when rewarded and unrewarded odors were substituted for each other, moths were able to undergo reversal conditioning already after two experiences. Both shorter and longer inter-trial intervals (ITIs) supported high degrees of learning. In a second experiment, moths could solve both feature-positive and -negative discrimination tasks. Two hypotheses for the way in which these associations exert their discrimination performance are considered. The moth's olfactory physiology has been extensively studied. This animal thus provides a powerful system in which to study the neurobiology of olfactory discrimination and odor recognition.     

Olfactory conditioning facilitates diet transition in human infants

We evaluated whether Pavlovian conditioning methods could be used to increase the ingestion of non-preferred solutions by formula-fed human infants. In baseline measures, 5-7 month old infants sucked less frequently and consumed less water than regular formula. During a 3-day olfactory conditioning period, parents placed a small scented disk, the conditioned stimulus, on the rim of their infants' formula bottle at every feeding. Following this training, infants' responses to water were tested when their water bottles had a disk scented with the training odor, a novel odor, or no odor. Infants tested with the training odor sucked more frequently and consumed significantly more water than they had at baseline. Infants tested with no odor or a novel odor consumed water at or below baseline levels. These data demonstrate that olfactory conditioning can be used to enhance ingestion in infants and suggest that such methods may be useful for infants experiencing difficulty when making transitions from one diet to another.     

Effects of stimulus frequency on habituation: patellar reflex

Habituation and recovery of the patellar reflex were studied in an adult human as a function of stimulus frequency, ranging from 10 to 60 per min. Habituation occurred more rapidly and response decrement was greatest for higher frequencies with decline in amplitude linear over much of its course. The decline in response amplitude was more pronounced for measures of force than for EMG.     

Retention of habituation of vestibulo-ocular reflex and sensation of rotation in humans

In humans, habituation of vestibulo-ocular reflex (VOR) by repeated caloric or rotational stimulation has been well documented. However, less attention has been directed to the effect of habituation on the sensation of self-rotation and little is known about the retention duration of vestibular habituation. To investigate these characteristics, subjects were exposed to ten sessions of angular velocity steps in yaw, with a chair rotating either alternatively in both CW and CCW directions (bidirectional protocol) or always in the same direction (unidirectional protocol), i.e., CW or CCW. The retention of habituation of VOR and sensation of rotation induced by both protocols was studied for a period up to 8 months following the end of the habituation protocols. There was a progressive decline in the VOR peak slow phase velocity and time constant throughout the sessions during both protocols. These parameters then followed an exponential recovery with a time constant of about 1 month. The duration of the sensation of rotation also habituated during repeated angular velocity steps, but it was shorter for both directions of stimulation, including after the unidirectional protocol. Sinusoidal VOR gain was not affected by vestibular habituation to velocity steps, but sinusoidal VOR phase showed an increase in phase lead at 0.02 and 0.04 Hz, which also returned to baseline values within about 1 month. We conclude that vestibular habituation is a long-lasting phenomenon. These results may be helpful for designing and scheduling the protocols for drug studies using crossover design, rehabilitation of balance disorder patients, and for the application of intermittent artificial gravity during space missions.