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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Scalar timing varies with response magnitude in classical conditioning of the nictitating membrane response of the rabbit (Oryctolagus cuniculus).

The present experiment was aimed at characterizing the timing of conditioned nictitating membrane (NM) movements as function of the interstimulus interval (ISI) in delay conditioning for rabbits (Oryctolagus cuniculus). Onset latency and peak latency were approximately, but not strictly, scalar for all but the smallest movements (.50 mm) were less variable, and their peaks were better aligned with the time of US delivery. These results are discussed with respect to their implications for current models of timing in eyeblink conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Magnitude and timing of conditioned responses in delay and trace classical conditioning of the nictitating membrane response of the rabbit (Oryctolagus cuniculus).

The present experiment characterized conditioned nictitating membrane (NM) movements as a function of CS duration, using the full range of discernible movements (>.06 mm) rather than movements exceeding a conventional criterion (>.50 mm). The CS–US interval was fixed at 500 ms, while across groups, the duration of the CS was 50 ms (trace), 550 ms (delay), or 1050 ms (extended delay). The delay group showed the highest level of acquisition. When tested with the different CS durations, the delay and extended delay groups showed large reductions in their responses when their CS was shortened to 50 ms, but the trace group maintained its response at all durations. Timing of the conditioned movements appeared similar across all manipulations. The results suggest that the CS has both a fine timing function tied to CS onset and a general predictive function tied to CS duration, both of which may be mediated by cerebellar pathways. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Eyeblink conditioning during an interstimulus interval switch in rabbits (Oryctolagus cuniculus) using picrotoxin to disrupt cerebellar cortical input to the interpositus nucleus.

The role of the cerebellar cortex in eyeblink classical conditioning remains unclear. Experimental manipulations that disrupt the normal function impair learning to various degrees, and task parameters may be important factors in determining the severity of impairment. This study examined the role of cerebellar cortex in eyeblink conditioning under conditioned stimulus?unconditioned stimulus intervals known to be optimal or nonoptimal for learning. Using infusions of picrotoxin to the interpositus nucleus of the rabbit cerebellum, the authors pharmacologically disrupted input from the cerebellar cortex while training with an interstimulus interval (ISI)-switch procedure. One group of rabbits (Oryctolagus cuniculus) was 1st trained with a 250-ms ISI (optimal) and then switched to a 750-ms ISI (nonoptimal). A 2nd group was trained in the opposite order. The most striking effect was that picrotoxin-treated rabbits initially trained with a 250-ms ISI learned comparably to controls, but those initially trained with a 750-ms ISI were severely impaired. These results suggest that functional input from cerebellar cortex becomes increasingly important for the interpositus nucleus to learn delay eyeblink conditioning as the ISI departs from an optimal interval. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioning the unconditioned response: Modification of the rabbit's (Oryctolagus cuniculus) unconditioned nictitating membrane response.

Conditioning-specific reflex modification (CRM) occurs when classical conditioning modifies responding to a unconditioned stimulus/stimuli (UCS) in the absence of a conditioned stimulus (CS). Three experiments monitored rabbit (Oryctolagus cuniculus) nictitating membrane unconditioned responses to 5 intensities and 4 durations of periorbital electrical stimulation before and after CS or UCS manipulation. CRM occurred after 12 days of CS-UCS pairings but not following unpaired CS/UCS presentations or restraint. CRM survived CS-alone and CS/UCS-unpaired extinction of the conditioned response (CR) but not presentations of the UCS alone, although CRs remained intact. Thus, CRs could be weakened without eliminating CRM and CRM could be weakened without eliminating CRs. Data indicate CRM is a reliable, associative effect that is more than a generalized CR and may not be explained by habituation, stimulus generalization, contextual conditioning, or bidirectional conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioning-specific reflex modification of the rabbit (Oryctolagus cuniculus) nictitating membrane response: Generality and nature of the phenomenon.

Conditioning-specific reflex modification (CRM) occurs when classical conditioning modifies responding to an unconditioned stimulus in the absence of a conditioned stimulus. This form of reflex modification suggests that learning modifies the unconditioned reflex pathway, Rabbit (Oryctolagus cuniculus) nictitating membrane responses to 5 intensities and 3 durations of airpuff (AP) or periorbital electrical stimulation (ES) were monitored before and after conditioning. AP tests detected strong CRM after conditioning with ES and modest levels of CRM after conditioning with AP. After conditioning with AP, ES tests failed to detect CRM. After conditioning with a stronger AP, CRM was again detected by AP tests. CRM is a general phenomenon but is more readily detected after training with a relatively aversive stimulus; thus, it may be a function of level of arousal. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Inactivation of the central nucleus of the amygdala abolishes conditioning-specific reflex modification of the rabbit (Oryctolagus cuniculus) nictitating membrane response and delays classical conditioning.

The central nucleus (CE) of the amygdala has been gaining attention for its importance in the plasticity underlying conditioned emotional responding. Already known for its role in nictitating membrane response (NMR) reflex facilitation, the CE may also be involved in conditioning-specific reflex modification (CRM)--changes in the NMR to the unconditioned stimulus (US) when tested in the absence of the conditioned stimulus following classical conditioning. To examine the CE's role in acquisition and/or expression of CRM, the authors temporarily inactivated the CE of rabbits (Oryctolagus cuniculus) with muscimol during NMR conditioning and/or during US testing. Results show that CRM was abolished by inactivation during US testing but intact following inactivation during NMR conditioning, suggesting that the CE is involved in CRM expression. Also, inactivation during conditioning delayed the development of conditioned NMRs. These findings show that the CE may act as an output center for expression of emotional responding in one situation (CRM) but is involved in facilitating plasticity in another (NMR conditioning). The authors propose that analysis of CRM may be an important corollary to current models for the treatment of posttraumatic stress disorder. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Studies of binaural detection in the rabbit (Oryctolagus cuniculus) with Pavlovian conditioning.

A Pavlovian conditioned eyeblink response in rabbits (Oryctolagus cuniculus) was used to study psychoacoustical phenomena previously demonstrated in human listeners and other animals. This article contains the results of a tone-in-noise detection study to examine 2 psychoacoustical phenomena in rabbit and in human listeners: (a) the binaural masking level difference (BMLD) and (b) differential performance across reproducible noise masker waveforms. The rabbits demonstrated a BMLD comparable in size to other species. Significant differences in performance across reproducible noise masker waveforms were seen in the rabbits. This performance was compared with the performance of human listeners using the same set of waveforms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Eyeblink conditioning in the rabbit (Oryctolagus cuniculus) with stimulation of the mystacial vibrissae as a conditioned stimulus.

Eyeblink conditioning is a well-understood paradigm for the study of learning and memory and has been successfully employed with the use of auditory and visual conditioned stimuli (CSs). In this study, vibrotactile stimulation of the mystacial vibrissae was examined as an alternative CS in the rabbit ( Oryctolagus cuniculus). The technique is described and acquisition of eyeblink conditioning (EBC) with stimulation of a single row of vibrissae in a delay paradigm is reported. Extinction of EBC with presentation of the CS alone is demonstrated, as well as reacquisition with stimulation of a single whisker. Finally, control experiments ensure that the CS has no auditory components. Ipsilateral presentation of the CS and airpuff is a more effective combination for training than contralateral presentations. Vibrotactile stimulation of the vibrissae as a CS will enable further examination of the neural correlates of learning in a well-characterized sensory system. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A midbrain–brain stem circuit for conditioned inhibition of the nictitating membrane response in the rabbit (Oryctolagus cuniculus).

Conducted 2 experiments with 31 albino rabbits to determine the neural system responsible for the development of conditioned inhibition of the rabbit's nictitating membrane response (NMR). In Exp I, monopolar electrodes were implanted in a variety of midbrain and brain-stem loci. Following acquisition of a conditioned NMR each electrode was tested to determine whether electrical stimulation applied to the electrode inhibited the manifestation of a CR. The most dramatic reduction in the amplitude of the CR was produced by stimulating the nucleus of Darkschewitsch, the interstitial nucleus of Cajal, or the anterior portions of the red nucleus. This disruption of the CR was observed either when the stimulation was aplied prior to the onset of the CS or when the stimulation was applied after the initiation of the CR. In the 2nd experiment, radio-frequency lesions placed in the nucleus of Darkschewitsch, interstitial nucleus of Cajal, anterior portions of the red nucleus, or tegmental reticular formation prevented the development of conditioned inhibition. Lesions placed in the rootlets of the oculomotor nerve, posterior red nucleus, or dorsal tegmental nuclei did not prevent the develoment of conditioned inhibition. It is concluded that a midbrain/brain-stem circuit originating in the nucleus of Darkschewitsch and interstitial nucleus of Cajal is responsible for the development of conditioned inhibition of the rabbit's NMR. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Apparatus Exposure Produces Profound Declines in Conditioned Nictitating-Membrane Responses to Discrete Conditioned Stimuli by the Rabbit (Oryctolagus cuniculus).

The present experiments demonstrated that in the rabbit (Oryctolagus cuniculus) nictitacing-membrane (NM) preparation, exposure to the experimental apparatus produces profound declines in conditioned responding to a discrete conditioned stimulus (CS; Experiments 1, 2A, and 3). Moreover, this decremental effect is at most attenuated in only a minor way when the unconditioned stimulus (US) is presented during exposure to the apparatus (Experiment 2B). Controls for retention loss (Experiments 1 and 3) and for handling and placement in a different context (Experiment 3) did not produce significant declines in responding. These findings challenge theories of extinction that rely primarily on context-US associations but are more consistent with theories that assume context-CS-US associations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Covariation of alternative measures of responding in rabbit (Oryctolagus cuniculus) eyeblink conditioning during acquisition training and tone generalization.

The likelihood, size, and speed of eyelid movements are thought to covary during the acquisition and expression of conditioning in rabbits (Oryctolagus cuniculus) and are generally accepted as interchangeable measures of the associative strength activated by the conditioned stimulus (CS). To test this assumption, the authors examined the patterns of covariation in these eyelid movement measures in acquisition and stimulus generalization in the upper eyelid and nictitating membrane. Rather than the expected covariation among these measures, eyelid movement magnitudes during the CS were distributed in approximately a bimodal manner. That is, eyelid activity consisted largely of a mixture of very small ( 1 mm) movements. The results are discussed with respect to their implications for real-time models of eyelid conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neuronal unit activity in the abducens nucleus during classical conditioning of the nictitating membrane response in the rabbit (Oryctolagus cuniculus).

Recorded neuronal unit activity from the abducens (6th nerve) nucleus during conditioning of the nictitating membrane (NM) response in 16 male New Zealand white rabbits, using a tone CS, an air puff UCS, 250-msec interstimulus interval, and 60-sec intertrial interval. Ss were given 2 days of training (104 trials in 8 blocks/day) and 1 day of extinction. Control Ss were given comparable periods of stimulus presentations, explicitly unpaired. Activity of small clusters of units—multiple unit recording—was compared with the amplitude/time course of NM response. Between-blocks comparisons of neural and behavioral responses indicated almost perfect correlation during acquisition of the CR and a slightly lower correlation during extinction for the conditioning Ss. Within-blocks comparisons indicated close correspondence between histograms of unit activity and the amplitude/time course of the NM response for the conditioning Ss in all phases of training and for controls in the UCS trial blocks. (39 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hippocampus and trace conditioning of the rabbit's classically conditioned nictitating membrane response.

In 2 experiments, 36 New Zealand albino rabbits received classical conditioning of the nictitating membrane response in a trace conditioning paradigm. In this paradigm, a 250-msec tone conditioned stimulus (CS) occurred, after which there was a 500-msec period of time in which no stimuli occurred (the trace interval), followed by a 100-msec air-puff unconditioned stimulus (UCS). In Exp I, lesions of the hippocampus or cingulate/retrosplenial cortex (CRC) disrupted acquisition of the long-latency or adaptive conditioned response (CR) relative to unoperated controls and Ss that received neocortical lesions that spared the CRC. When Ss with hippocampal or CRC lesions were switched to a standard delay paradigm in which the CS and UCS were contiguous in time, they acquired in about the same number of trials as naive Ss. In Exp II, multiple-unit activity in area CA1 of the hippocampus was examined during acquisition of the trace CR. Ss had a 500-msec trace interval (Group T-500), received explicitly unpaired presentations of the CS and UCS, or underwent conditioning with a 2-sec trace interval. Group T-500 acquired the CR in about 500 trials. Early in training, there was a substantial increase in neuronal activity in the hippocampus that began during the CS and persisted through the trace interval. Later in conditioning as CRs emerged, the activity shifted to later in the trace interval and formed a model of the amplitude–time course of the behavioral CR. (65 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spontaneous recovery but not reinstatement of the extinguished conditioned eyeblink response in the rat.

Reinstatement—the return of an extinguished conditioned response (CR) after reexposure to the unconditioned stimulus (US)—and spontaneous recovery—the return of an extinguished CR with the passage of time—are 2 of 4 well-established phenomena that demonstrate that extinction does not erase the conditioned stimulus (CS)–US association. However, reinstatement of extinguished eyeblink CRs has never been demonstrated, and spontaneous recovery of extinguished eyeblink CRs has not been systematically demonstrated in rodent eyeblink conditioning. In Experiment 1, US reexposure was administered 24 hr prior to a reinstatement test. In Experiment 2, US reexposure was administered 5 min prior to a reinstatement test. In Experiment 3, a long, discrete cue (a houselight), present in all phases of training and testing, served as a context within which each trial occurred to maximize context processing, which in other preparations has been shown to be required for reinstatement. In Experiment 4, an additional group was included that received footshock exposure, rather than US reexposure, between extinction and test, and contextual freezing was measured prior to test. Spontaneous recovery was robust in Experiments 3 and 4. In Experiment 4, context freezing was strong in a group given footshock exposure but not in a group given eye shock US reexposure. There was no reinstatement observed in any experiment. With stimulus conditions that produce eyeblink conditioning and research designs that produce reinstatement in other forms of classical conditioning, we observed spontaneous recovery but not reinstatement of extinguished eyeblink CRs. This suggests that reinstatement, but not spontaneous recovery, is a preparation- or substrate-dependent phenomenon. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Delayed extinction attenuates conditioned fear renewal and spontaneous recovery in humans.

This study investigated whether the retention interval after an aversive learning experience influences the return of fear after extinction training. After fear conditioning, participants underwent extinction training either 5 min or 1 day later and in either the same room (same context) or a different room (context shift). The next day, conditioned fear was tested in the original room. When extinction took place immediately, fear renewal was robust and prolonged for context-shift participants, and spontaneous recovery was observed in the same-context participants. Delayed extinction, by contrast, yielded a brief form of fear renewal that reextinguished within the testing session for context-shift participants, and there was no spontaneous recovery in the same-context participants. The authors conclude that the passage of time allows for memory consolidation processes to promote the formation of distinct yet flexible emotional memory traces that confer an ability to recall extinction, even in an alternate context, and minimize the return of fear. Furthermore, immediate extinction can yield spontaneous recovery and prolong fear renewal. These findings have potential implications for ameliorating fear relapse in anxiety disorders. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal dynamics of the rabbit's nictitating membrane response in serial compound conditioned stimuli.

Two experiments, with 88 female albino rabbits, investigated conditioning of the nictitating membrane response to a reinforced serial compound stimulus. The serial compound was composed of a 400-msec CS (CSA), a trace interval of at least 2 sec, and a brief 2nd CS (CSB) prior to the UCS. The CSB duration was either 150, 250, or 400 msec in Exp I, and the CSB duration in Exp II was 400 msec. Exp I compared serial compound training to an "uncoupled" condition, which contained intermixed CSA–UCS trials and CSB–UCS trials. Exp II compared serial compound training with uncoupled training, 2nd-order conditioning (CSA–CSB/CSB–UCS), trace conditioning (CSA–UCS), and generalization testing that entailed CSB–UCS training and unreinforced tests with CSA. The serial compound, uncoupled, and 2nd-order conditioning procedures all produced high levels of responding during CSA, but only the reinforced serial compound procedure yielded an appreciable likelihood of CR initiation during the trace interval between CSA and CSB. The CRs during the trace interval were temporally distinct from the CRs during CSA and did not appear to be belated CRs to CSA itself. Results are discussed in connection with stimulus selection phenomena, for example, overshadowing and potentiation of toxicosis conditioning. (46 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Aluminum-induced neurofibrillary degeneration disrupts acquisition of the rabbit's classically conditioned nictitating membrane response.

Rabbits received intraventricular injections of aluminum chloride, hydrochloric acid, or served as unoperated controls. On the 6th day postsurgery, they underwent 4 days (100 trials per day) of classical conditioning of the nictitating membrane response (NMR) to a tone conditioned stimulus and an air-puff unconditioned stimulus. Unoperated and hydrochloric acid control animals readily acquired the conditioned response. Aluminum intoxicated rabbits, in contrast, did not acquire the conditioned response over the 4 days of testing. This disruption of conditioning in aluminum-treated rabbits could not be attributed to deficits in sensory or motor processes or to illness. Neuropathological analysis revealed widespread neurofibrillary tangle formation in aluminum-treated animals. Furthermore, the degree of neurofibrillary degeneration was significantly negatively correlated with the degree of conditioning. The results are considered in the context of using the rabbit NMR preparation as a model system for studying age-related conditioning disorders. (PsycINFO Database Record (c) 2010 APA, all rights reserved)