Classical conditioning of the nictitating membrane response of the rabbit

Summary The nictitating membrane response (NMR) of 15 rabbits was conditioned to light and white noise conditional stimuli (CSs) using a periorbital shock unconditional stimulus (US). Unilateral lesions of the inferior olive were then made. Lesions restricted to the medial parts of rostral dorsal accessory olive (DAO) and principal olive (PO) abolished conditioning and prevented subsequent acquisition on either side. Unconditional responses to the US were intact. Lesions in all other parts of the olive did not impair conditioning. The effective lesions were located in that part of the olive which supplies somatosensory information from the face to cerebellar lobule HVI. Lobule HVI is also essential for NMR conditioning. We suggest that this region of the inferior olive is part of a circuit which provides US information to the cerebellar cortex during NMR conditioning.     

Single-unit activity in red nucleus during the classically conditioned rabbit nictitating membrane response

Previous investigations have suggested that the cerebellum and associated brainstem structures, including the red nucleus, are essential for the expression of the classically conditioned nictitating membrane (NM) response. The present study examined the firing patterns of extracellularly-recorded single units in the red nucleus of the awake rabbit during differential conditioning. Tones were used as conditioned stimulus (CS+ and CS−) and periocular electrostimulation was used as the unconditioned stimulus (US). Most units exhibited one or more changes in firing rate during the presentation of the CS, and increases in firing were much more common than decreases. The onset of some of these changes appeared to be time-locked to the onset of the CS (‘CS-locked’ responses), while other changes were time-locked to the onset of the CR (‘CR-locked’ responses). About one-third of all CS-locked changes were CR-dependent, meaning that the neuronal response was reduced when the CR did not occur. About two-thirds of all CR-locked responses preceded the onset of the CR, and lead times varied considerably across units. Many CR-locked units were located in what has been described as a dorsal face region of the red nucleus. Most units responded to the US, and some of the US responses were CR-dependent: i.e., a smaller US response was evoked when a CR preceded the US than when the CR was absent. Our results support the notion that cerebellum-brainstem circuits are involved in generating NM CRs.     

Cholesterol modifies classical conditioning of the rabbit (Oryctolagus cuniculus) nictitating membrane response

Cholesterol plays an important role in synapse formation, receptor function, and synaptic plasticity, and animal studies show that modifying cholesterol may improve learning and memory. Other data show that feeding animals cholesterol can induce beta amyloid accumulation. Rabbits (Oryctolagus cuniculus) fed 2% cholesterol for 8 weeks were given trace conditioning of the nictitating membrane response using a 100-ms tone, a 700-ms trace, and periorbital electrical stimulation or airpuff. Rabbits fed cholesterol showed significant facilitation of trace conditioning to airpuff and conditioning-specific reflex modification to periorbital electrical stimulation and airpuff. The cholesterol-fed rabbits had beta amyloid accumulation in the cortex, but little in the hippocampus. The data suggest cholesterol had facilitative effects that outweighed potential amnesic effects of cortical beta amyloid.     

Neuronal activity in rabbit neostriatum during classical eyelid conditioning

Extracellular multiple- and single-unit recordings were made from the neostriatum of rabbits during classical eyelid conditioning. Neostriatal neurons processed information regarding the conditioned auditory stimulus (CS) and conditioned eyelid response (CR) as well as the unconditioned stimulus/response (US/UR). These data are consistent with previous reports that neostriatal neurons respond to movement and movement-related sensory stimuli. In most cases, neostriatal neurons increased activity to the US during the early phase of training, but to the CR as training progressed. A close temporal correlation was found between neuronal activity and CR onset with unit discharges typically preceding CR onset by 10–50 ms. The activity of some multiple and single units was monitored after injection of haloperidol, a neuroleptic and dopamine antagonist known to disrupt neostriatal function. Interestingly, haloperidol caused a greater disruption of CRs at low-intensity than at high-intensity CSs, but conditioning-related neuronal activity was disrupted equally at both intensities. These data are discussed in terms of a possible role for the neostriatum in eyelid conditioning.     

Classical conditioning of the nictitating membrane response of the rabbit

Summary We report the connections of cerebellar cortical lobule HVI in the rabbit. We have studied the anterograde and retrograde transport of wheatgerm-agglutinated horseradish peroxidase (WGA-HRP) following its injection into HVI to reveal efferent and afferent connections. All of the cases showed strong anterograde transport to the anterior interpositus nucleus (AIP) — indicating that this is the major efferent target of HVI. Retrogradely labelled cells were found in the inferior olivary, spinal trigeminal, lateral reticular, inferior vestibular and pontine nuclei. Within the olive, the medial part of the rostral dorsal accessory olive (DAO) and the adjacent medial part of the principal olive (PO) were consistently labelled in all cases. This area is known to receive somatosensory information from the face and neck. There was no projection to the hemispheral part of lobule VI from visual parts of the olive within the dorsal cap and medial parts of the medial accessory olive. Likely sources of visual and auditory information to HVI are the dorsolateral basilar pontine nuclei and nucleus reticularis tegmenti pontis, which were densely labelled in all cases. These anatomical findings are consistent whith the suggestion that, during NMR conditioning, information related to the periorbital shock unconditional stimulus (US) may be provided by climbing fibres to HVI and light and white noise conditional stimulus (CS) information may be supplied by pontine mossy fibres.     

Activity of deep cerebellar nuclear cells during classical conditioning of nictitating membrane extension in rabbits

Summary The activity of neurons in the interposed and dentate nuclei of the cerebellum was investigated during differential classical conditioning of the rabbit eye blink/ nictitating membrane response. Forty-seven percent of the 165 cells in the study responded to the orbital stimulation used as the unconditioned stimulus (US). The latency distribution of US-elicited responses was bimodal with peaks at 7 and 19 ms. Twenty-one percent of the cells responded with short latencies to the tones used as conditioned stimuli (CSs). These cells typically responded to both the reinforced and nonreinforced CSs. Forty-one percent of the cells responded on conditioned response (CR) trials but not on trials without CRs. The average lead of the neural response to the CR was 71.4 ms. Cells that responded on CR trials were more likely to respond to the CSs, or to the CSs and the US, than cells that did not respond on CR trials. For about half of the cells that responded on CR trials the latency of response followed trial-by-trial variations of CR latency. For the remainder, the response was time-locked to CS-onset. Cells whose responses paralleled the CR may be involved in the initiation or modulation of the CR, while those whose responses were time-locked to the CS may be involved in sensory processing underlying the initiation of the movement. The pathways that may underlie the US- and CS-elicited responses are also discussed.     

Classical conditioning of the nictitating membrane response of the rabbit

The nictitating membrane response (NMR) of 20 rabbits was conditioned to light and white noise conditional stimuli (CSs) using a periorbital shock unconditional stimulus (US). Unilateral lesions of the cerebellar cortex, sparing the underlying deep nuclei, were then made. Small lesions of cerebellar cortical lobule HVI abolished conditioning on the side of the lesion to both CSs leaving unconditional responses to the US intact. Larger lesions of the posterior lobe which spared HVI did not impair NMR conditioning. We conclude that cerebellar lobule HVI is essential for NMR conditioning in the rabbit. Degeneration following critical lesions of HVI was seen in a restricted region of the inferior olive - the medial part of the dorsal accessory olive and the adjoining medial part of the dorsal leaf of the principal olive. This region of the olive provides somatosensory information from the face to HVI. We suggest that HVI receives information related to the US via climbing fibres from the olive and CS information via mossy fibres from the pontine nuclei. The critical changes underlying NMR conditioning may be the association of these two inputs at the Purkinje cells of cortical lobule HVI.     

Classical conditioning of the nictitating membrane response of the rabbit

The classically conditioned nictitating membrane response (NMR) of the rabbit, a simple form of associative motor learning, is crucially dependent upon the cerebellum. Discrete unilateral lesions of the cerebellar nuclei were made in 20 rabbits. Lesions of the anterior interpositus nucleus (IA) abolished NMR conditioning to light and white noise stimuli on the side of the lesion without affecting unconditional responses. Lesions of the posterior interpositus nucleus, fastigial and dentate nuclei were without effect upon NMR conditioning.     

Effects of morphine, ethylketocyclazocine, and N-allylnormetazocine on classical conditioning of the rabbit nictitating membrane response

The rabbit's nictitating membrane response was classically conditioned to tone and light conditioned stimuli presented for 800 ms before delivery of a 100-ms unconditioned shock stimulus. Both the mu receptor agonist morphine (5 mg/kg) and the kappa receptor agonist ethylketocyclazocine (1 mg/kg) significantly retarded the acquisition of conditioned responses (CRs). The retardant effects of both morphine and ethylketocyclazocine on CR acquisition could still be detected when the rabbits were tested 5 days after cessation of drug injections. At the dose employed in this study (5 mg/kg), the sigma receptor agonist N-allylnormetazocine had no effect on acquisition. The retardant effects of morphine and ethylketocyclazocine on acquisition were significantly antagonized by both naloxone (1 mg/kg) and N-allylnormetazocine (5 mg/kg). It was suggested that mu and possibly kappa receptors are involved in the retardant effects of opiates on the acquisition of classically conditioned responses.     

Heart rate and somatomotor activity in rats during signalled escape and yoked classical conditioning

In the first of three studies, heart rate, movement, and EMG activity during signalled escape and regular classical conditioning were examined in unrestrained and restrained groups of rats. The direction of the HR CR was accelerative in the unrestrained groups and decelerative in the restrained groups, regardless of the presence or absence of the escape contingency. Both CRs were enhanced by the presence of directionally similar changes in movement to the CS. The decelerations of the restrained groups were correlated with decreases in movement and increases in EMG activity. Increasing the somatomotor activity associated with the US failed to modify the decelerative direction of the HR CRs of restrained rats in the second and third studies. It was suggested that HR CRs in rats may be accompaniments of naturally occurring defense behaviors such as freezing in restrained rats and aggression in unrestrained rats.     

Magnitude and timing of nictitating membrane movements during classical conditioning of the rabbit (Oryctolagus cuniculus)

A trial-by-trial, subject-by-subject analysis was conducted to determine whether generation of the conditioned response (CR) occurs on a continuous or all-or-none basis. Three groups of rabbits were trained on different partial reinforcement schedules with the conditioned stimulus presented alone on 10%, 30%, or 50%, respectively, of all trials. Plots of each rabbit's nictitating membrane movements revealed that their magnitude rose in a continuous fashion. Response growth during acquisition followed a sigmoidal curve, and the timing of CR-sized movements was largely stable throughout the experiment. The results are discussed with respect to alternative models of CR generation.     

Bilateral nictitating membrane conditioning in rabbits under asymmetrical levels of cutaneous afferent activity

The effect of asymmetrical levels of cutaneous afferent activity (CAA) on the performance of a bilaterally conditioned nictitating membrane response in New Zealand albino rabbits was investigated. Afferent activity levels were controlled by varying US locus, corneal applications of a local anesthetic (0.5% tetracaine hydrochloride) and by exerting mechanical tension on the eyelids. Performance of the response in each eye was controlled independently of the response levels concurrently attained by the contralateral eye. Appropriate tests suggested that the two eyes do not function independently in learning, regardless of the disparity in CAA level between them, due to central transfer.     

Identity and expression processing during classical conditioning with faces

In classical conditioning, conditioned responses (CRs) to aversively paired (CS+) relative to unpaired (CS‐) face images are often interpreted in terms of the specific individual displayed in the CS + face image having adopted an aversive emotional connotation. This interpretation requires conditioning to rely on an association between CS + face identity and the occurrence of the aversive event (UCS). Here, we tested this requirement assuming that if an association between CS + face identity and UCS occurrence is established, CRs to originally conditioned face images should transfer to novel images of same‐identity faces. Forty‐eight participants underwent MultiCS conditioning with eight neutral faces as CSs and electric shock as UCS. Central, peripheral, evaluative, and behavioral CRs signaled successful emotional learning (as reported in Pastor et al., 2015). Behavioral and EEG responses of consecutive passive viewing showed enhanced reactions to novel angry and happy expressions of previously shocked CS + versus nonshocked CS‐ identities, indicating successful CR transfer within the dimension of face identity. Investigating the nature of CR transfer, EEG revealed an interaction of identity and expression information during face processing that followed emotional congruency (i.e., stronger reactions to congruent angry CS + and happy CS‐ vs. incongruent angry CS‐ and happy CS + compounds). While correlates of transfer appeared in late and midlatency time intervals, the congruency interaction became significant within the first 100 ms of face processing. Our results suggest conditioning to rely on an association of UCS occurrence with CS + identity and point to fast dynamic interrelations between identity and expression processing.     

Retardation of rabbit nictitating membrane conditioning by subseizure electrical stimulation of hippocampus.

The experiment involved classical conditioning of the nictitating membrane response of rabbits with subseizure, posttrial electrical stimulation of hippocampus. Hippocampal electrical activity was recorded before, during and after each trial to assure that no seizure activity was present. Stimulated animals, in comparison with unstimulated controls, showed a marked retardation of CR onset which paralleled that of previous research employing seizure producing stimulation. This implies that brain seizures are not the critical element in the disruption effect, but rather the anatomical locus of stimulation. Results are discussed in the context of recent lesion, recording and stimulation research employing the conditioned nictitating membrane response of rabbits as a model system.     

Stimulation of the spinal trigeminal nucleus supports classical conditioning of the rabbit's nictitating membrane response

Acquisition, extinction, and differential conditioning of the rabbit's nictitating membrane response to a tone conditioned stimulus were supported by electrical stimulation of the spinal trigeminal nucleus. Stimulation of the accessory abducens nucleus, the abducens nucleus, and the reticular formation at the level of the spinal trigeminal nucleus supported lower, transient levels of conditioning. The results are discussed in terms of stimulation of sensory inputs to the brainstem and cerebellum.     

Age-related disruption of trace but not delay classical conditioning of the rabbit's nictitating membrane response

Young (6 months of age) and old (36-60 months) New Zealand albino rabbits underwent classical conditioning of the nictitating membrane response in either a delay conditioning (Experiment 1) or a trace conditioning (Experiment 2) paradigm. There was no difference between old and young animals in acquisition of the conditioned response in the delay paradigm, nor were there any age-related differences in generalization to the tone conditioned stimulus (CS) or in sensitivity to the tone CS or eye shock unconditioned stimulus. In the trace conditioning paradigm, however, old animals acquired the conditioned response significantly more slowly than young rabbits. Because the same stimulus parameters and the same response were used in both experiments, it is unlikely that age-related differences in trace conditioning were due to stimulus sensitivity, motivation, or fatigue. The results are discussed in terms of how brain changes that accompany aging could differentially affect these two types of classical conditioning.     

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.     

Thermosensitivity and instrumental conditioning in newborn rats

Infant rats (20 minutes to 8 days old) display reliable locomotor responses to some thermal stimuli. They can be trained to escape from a cold (10–13°), surface to a warm (28–30°) one or to a warm (30–35°) air stream. Using this method, we found a significant (p<0.01) decrease in the mean latency of a locomotor escape response during a 10 trial session (intertrial interval=20 sec) in 4-to-8-day old Wistar rats. In the same situation, more than 60% of the rats of this age span reached a criterion of five consecutive correct responses in a spatial discrimination test during a 25 trial session (inter-trial interval=40 sec).     

Amygdala central nucleus lesions: effect on heart rate conditioning in the rabbit

The present study was designed as an initial step in determining the specific anatomical systems of the amygdala which may contribute to the expression of conditioned heart rate responding during aversive Pavlovian conditioning in the New Zealand rabbit. Animals receiving either small or large radio-frequency lesions of the central nucleus of the amygdala demonstrated a significant attenuation of the conditioned bradycardia response to the conditioned stimulus when compared to that demonstrated by control animals. No significant effects of the lesions on baseline heart rate or on the heart rate orienting response to the conditioned stimulus were observed. Central nucleus lesions also produced a significant effect on the unconditioned heart rate response to the unconditioned stimulus manifested in an increased duration and prolonged habituation of the unconditioned response. The results are consistent with anatomical and physiological evidence suggesting the involvement of the central nucleus in the expression of emotional responses including accompanying cardiovascular alterations.     

Cerebellar Purkinje cell activity related to the classically conditioned nictitating membrane response

Summary Because of the purported critical role of cerebellar lobule HVI in classical conditioning of the nictitating membrane response of the rabbit, we recorded extracellularly from HVI Purkinje cells (PCs) during differential conditioning. Rabbits were trained using tonal conditioned stimuli (CSs) and stimulation of the periocular region as the unconditioned stimulus (US). Many PCs responded to the US, the most frequently observed response being a burst of simple spikes. PCs in HVI showed a variety of responses to CSs that were related to conditioned responses (CRs). The most frequently observed response was an increase in simple spikes correlated with CRs. The activity of many of these cells antedated CRs by 20–200 ms. A smaller proportion of cells exhibited inhibition of simple spike activity that antedated CRs. The existence of PCs that alter their firing before CRs suggests that they may be causally involved in this behavior, and in this respect they reinforce reports that lesions of HVI or its connections disrupt nictitating membrane CRs. Although complex spike activity was not generally related to the US or to CRs, a few PCs responded in relation to CRs with only complex spikes. In demonstrating CR-related activity in cerebellar PCs, this study supports theories of cerebellar learning such as those of Marr and Albus.