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)     

Latent inhibition and stimulus generalization of the classically conditioned nictitating membrane response in rabbits (Oryctolagus cuniculus) following hippocampal ablation.

30 male and female New Zealand albino rabbits received 0 to 450 exposures of a tone CS prior to classical defensive conditioning of the nictitating membrane response based on an infraorbital eye shock UCS. Tone preexposure resulted in retarded conditioning in normal Ss, but was not present in Ss with bilateral dorsal hippocampectomy produced by aspiration. Controls with bilateral neocortical and callosal aspiration lesions demonstrated a latent inhibition effect similar to that shown by normal nonoperated Ss. The failure of CS preexposure to retard conditioning in hippocampal Ss was not due to differences in threshold of the conditioned response to the CS or to differences in response mechanisms as determined by tests of habituation and dishabituation of the UCR. A subsequent experiment with 24 Ss used combined-cue summation tests to confirm the fact that preexposure did not endow the tone with conditioned as well as latent inhibitory properties. Finally, tests of stimulus generalization along the auditory frequency dimension indicated flatter relative gradients for hippocampals than for nonoperated controls, with cortical controls in between. (40 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lesions of the middle cerebellar peduncle disrupt acquisition and retention of the rabbit's classically conditioned nictitating membrane response.

Rabbits were classically conditioned to emit a nictitating membrane response (NMR) to either a light or tone conditioned stimulus (CS) paired with an eye shock unconditioned stimulus (UCS). They then received lesions of the middle cerebellar peduncle (MCP) or served as unoperated controls. Following surgery, they were given separate presentations of tone, light, and vibratory CSs, each paired with the eye shock UCS. In this way, conditioned responses (CR) to the previously trained light or tone served as a test of retention, whereas CRs to the remaining two conditioned stimuli (tone and vibratory or light and vibratory) served as a test of acquisition. The results of the study revealed that rabbits with complete lesions of the MCP showed disrupted acquisition and retention of the conditioned NMR to all stimuli, rabbits with partial MCP lesions also showed disrupted acquisition and retention to all CSs, but to a lesser degree, and animals with lesions that missed the MCP and unoperated controls both showed normal acquisition and retention of the conditioned NMR. (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)     

Age-related deficits in retention of the classically conditioned nictitating membrane response in rabbits.

Young and aged rabbits underwent classical conditioning of the nictitating membrane response (NMR) to a tone conditioned stimulus (CS) and a corneal airpuff unconditioned stimulus (UCS) for 18 consecutive days. Rabbits were then returned to their home cages for a 90-day period in which they received no further conditioning, but they were handled daily. On Day 91 they underwent retention testing during which the CS alone was presented 20 times. This was immediately followed by reacquisition in which the CS and UCS were again paired for 100 trials. Reacquisition was repeated on the following day. As in previous studies, aged rabbits acquired the conditioned response (CR) more slowly than young rabbits; however, by the end of acquisition, both groups reached similar asymptotic levels. Retention of the CR was significantly lower for aged than young rabbits. Reacquisition was also retarded in aged vs young rabbits. Nonassociative factors, such as sensitivity to the stimuli or general health, could not account for these differences. Data are discussed in terms of using retention of the conditioned eyeblink response as a model system for studying age-related memory deficits. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acquisition and extinction of a classically conditioned response in hippocampectomized rabbits (Oryctolagus cuniculus).

Compared the responses of 10 male albino rabbits with bilateral hippocampal lesions to those of 15 unoperated and 10 neocortically-lesioned controls. Experimental Ss acquired a classically-conditioned nictitating membrane response faster than the 2 control groups. After initial acquisition, Ss were given extinction training, alternated with reacquisition sessions, and a test of spontaneous recovery. Experimental Ss extinguished normally during initial sessions, but failed to show the significant savings exhibited by controls during subsequent extinction sessions. The test of spontaneous recovery failed to differentiate among the 3 groups. Experimental Ss given preoperative training showed essentially the same extinction deficit as Ss who had not been trained. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential effects of hippocampectomy on classically conditioned rabbit nictitating membrane response related to interstimulus interval.

The effects of hippocampal ablation on acquisition rates and temporal characteristics of classically conditioned nictitating membrane responses were examined in 54 New Zealand albino rabbits trained with a 150-, 300-, or 600-msec interstimulus interval. Acquisition rates were accelerated in the 150- and 600-msec groups. No effect was present in the 300-msec group. Response onset latencies were also affected in the 150-msec group. Results indicate that damage to the hippocampus influences the acquisition of classically conditioned responses only when temporal parameters are relatively complex. Findings also support the notion that the hippocampus modulates learned motor behavior by a neural model of the response to be executed. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Consequences of response-contingent change in unconditioned stimulus intensity upon the rabbit (Oryctolagus cuniculus) nictitating membrane response.

In a between-groups design using a total of 84 naive male and female rabbits, an instrumental contingency was superimposed on classical conditioning of the nictitating membrane response. Ss were exposed to a tonal conditioned stimulus (CS) and, if no conditioned response (CR) occurred, a 5.0-ma paraorbital electric shock unconditioned stimulus (UCS). UCSs of 5.0, 3.3, 1.7, and 0.0 ma, respectively, were contingent on occurrence of a CR in the CS-UCS interval for Ss in the 4 groups of the experiment. The group exposed to contingent UCS omission differed from the other 3 groups in percentage CR, onset latency, amplitude, and 2 indices of CR form, and those 3 groups generally did not differ significantly among themselves on these dependent variables. Results are interpreted to be contrary to "law of effect" formulations of classical conditioning. (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)     

Role of the hippocampus in blocking and conditioned inhibition of the rabbit's nictitating membrane response.

In Exp I, bilateral aspiration of the dorsal hippocampus produced a disruption of blocking of 30 New Zealand rabbits' nictitating membrane response in L. J. Kamin's (1968, 1969) 2-stage paradigm, but had no effect on the formation of a Pavlovian conditioned inhibitor in Exp II (27 Ss). Results of Exp I indicate that normal Ss and those with cortical lesions given conditioning to a light-plus-tone CS gave CRs to both light and tone during nonreinforced presentations of each (test phase). If, however, compound conditioning was preceded by tone acquisition, only the tone elicited a CR during testing; that is, blocking was observed. In Ss with hippocampal lesions, however, CRs were given to both light and tone during testing whether or not compound conditioning was preceded by tone acquisition. Data from Exp II show that Ss with hippocampal lesions could discriminate as well as normal Ss and those with cortical lesions between a light (CS+) and light plus tone (CS-). In addition, when the inhibitory tone was subsequently paired with the UCS in retardation testing, Ss in all 3 lesion conditions acquired the CR at the same rate. Thus, it appears that hippocampal lesions do not disrupt conditioned inhibition. Results are taken as support for the view that the hippocampus is responsible for "tuning out" stimuli that have no adaptive value to the organism. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioning the rabbit's (Oryctolagus cuniculus) jaw-movement response: US magnitude effects on URs, CRs, and pseudo-CRs.

Describes an experiment in which 72 albino rabbits received (a) 45 daily acquisition sessions of single intraoral UCS presentations of 1, 5, or 20 cc. water, paired or unpaired with the CS (an 80 db. tone); and (b) 40 daily extinction sessions of single CS presentations. Results show that sinusoidal jaw movement (UR) rate following UCS offset (reflex afterdischarge) was an increasing function of UCS magnitude and acquisition sessions. Percentage CRs (paired with the CS) and pseudo-CRs (unpaired with the CS) were positively related to UCS magnitude, with paired-group performance consistently superior to that of corresponding unpaired controls. CR amplitude increased over acquisition sessions, while pseudo-CR amplitude remained uniformly low. UCR, CR, and pseudo-CR latencies decreased over acquisition. Frequencies of CRs and UCRs provided partial support for the consummatory response hypothesis, while the pseudo-CR frequencies cannot be completely accounted for by present theoretical formulations. (17 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanisms of efferent neuronal control of the reflex nictitating membrane response in rabbit (Oryctolagus cuniculus).

Analyzed efferent mechanisms controlling the nictitating membrane (NM) reflex response to air puff in the albino rabbit, using stimulation, lesions, and recording techniques with 52 New Zealand male Ss in 6 experiments. In brief, stimulation of the 6th nerve (abducens) yielded short-latency NM extension. Stimulation of the 4th and 7th nerves and the superior cervical ganglion had essentially no effect on the NM. Stimulation of the 3rd nerve caused short-latency retraction of the NM. Lesions and recording data were consistent with this result--the sole efferent neuronal control of NM extension was the 6th cranial nerve and of NM retraction was the 3rd cranial nerve. It is concluded that the NM extension response appears to be mediated by mechanical actions via retraction of the eyeball by the retractor bulbi muscle, and NM retraction appears to result from direct activation of muscle fibers in the NM by the 3rd nerve. The superior cervical ganglion appears to play no role in reflex NM retraction in the rabbit, in contrast to its action in the cat. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioning-specific modification of the rabbit's unconditioned nictitating membrane response.

Robust classical conditioning modifies responding to the unconditioned stimulus (US) in the absence of the conditioned stimulus (CS), a phenomenon the researchers called conditioning-specific reflex modification. Unconditioned responses (URs) to periorbital stimulation varying in intensity and duration were assessed before and after 1, 3, or 6 days of paired, explicitly unpaired, or no presentations of tone and electrical stimulation. After 3 days of pairings, conditioned responding (CRs) reached 94%, and there was an increase in latency to the peak of URs. The peak latency increase was replicated in a 2nd experiment where rabbits reached asymptotic conditioning during 6 days of pairings. There was also a conditioning-specific increase in the amplitude of URs. There were no UR changes as a function of low level of CRs following 1 day of pairings. Data suggest that there are learning-specific changes in pathways mediating the US/UR, as well as in those mediating the CS/CR. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of frontal cortex lesions on differentiation and extinction of the classically conditioned nictitating membrane response in rabbits.

In Exp I 8 male New Zealand rabbits with frontal lesions, compared to 10 Ss with Visual Area II lesions, were impaired in relearning an auditory differentiation involving a classically conditioned defensive response (movement of the nictitating membrane). In Exp II it was shown that frontal lesions in 6 additional Ss also produced perseveration of this response in extinction. Analysis of these findings suggests that frontal lesions impair the ability to suppress conditioned nictitating membrane responses. Results support the view that frontal ablation produces a general impairment in overcoming strong response tendencies independently of the kind of response or reinforcement. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Classical nictitating membrane conditioning in the rabbit (Oryctolagus cuniculus) as a function of unconditioned stimulus locus.

Examined the effects of different placements of electrodes used to present a shock UCS on conditioning the rabbit nictitating membrane response (NMR) in 2 experiments with 32 New Zealand and 24 albino rabbits. Ss were conditioned with shock leads attached either circumorbitally, at the ear base, or at the ear tip. In 1 circumorbital shock group, nictitating membranes of both shocked and unshocked eyes were monitored. Circumorbital, ear base, and ear-tip shock yielded best to poorest performances, respectively, and the shocked membrane yielded better performance than the unshocked one. Analysis of UCR and CR latencies and peak amplitude, as well as slow motion films of responses, suggests that poorer performance resulted from the elicitation of other responses, of which the NMR may have been a secondary or indirect component. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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

Extinguishing a conditioned response (CR) has entailed separating the conditioned stimulus (CS) from the unconditioned stimulus (US). This research reveals that elimination of the rabbit nictitating membrane response occurred during continuous CS-US pairings. Initial training contained a mixture of 2 CS-US interstimulus intervals (ISIs), 150 ms and 500 ms. The CRs showed double peaks, one for each ISI. When the 150-ms ISI was removed, its CR peak showed 2 hallmarks of extinction: a decline across sessions and spontaneous recovery between sessions. When a further stage of training was introduced with a distinctive CS using the 150-ms ISI, occasional tests of the original, extinguished CS revealed another hallmark of extinction, specifically, strong recovery of the 150-ms peak. These results support both abstract and cerebellar models of conditioning that encode the CS into a cascade of microstimuli, while challenging theories of extinction that rely on changes in CS processing, US representations, and contextual control. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Classical nictitating membrane conditioning in the rabbit (Oryctolagus cuniculus): Single alternation with differential intertrial intervals.

Investigated single alternation (SA) patterning behavior in 24 albino New Zealand rabbits by varying in 7 experiments the intertrial intervals (ITIs) following reinforced (R) and nonreinforced (N) trials. When short ITIs followed R trials and long ITIs followed N trials, reliable SA patterning was obtained. Neither (a) the presence of differential ITI cues, (b) the short ITIs prior to the N trials, nor (c) the early position of the N trial within the R-R interval were sufficient in and of themselves to support substantial patterning behavior; instead, each of these features apparently contributed to the patterning effect in a combined fashion. It is concluded that R- and N-trial aftereffects do not play an important role in conditioning the rabbit nictitating membrane. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rapid reacquisition in conditioning of the rabbit's nictitating membrane response.

Reacquisition after extinction often appears faster than original acquisition. However, data from conditioned suppression studies indicate that this effect may arise from spontaneous recovery and reinstatement of unextinguished contextual stimuli related to the unconditioned stimulus/stimuli (UCS). In the present experiments using the rabbit nictitating membrane preparation, spontaneous recovery was eradicated before reacquisition training. UCS contextual stimuli were controlled by retaining the UCS during extinction through explicit unpairings of the conditioned stimulus/stimuli (CS) and UCS. Attempts were also made to drive the associative strength of the CS into the inhibitory region by differential conditioning and conditioned inhibition procedures. In all cases, reacquisition was very rapid in comparison with a rest control. The results are discussed with respect to their implications for CS and UCS processing models of conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Posttraining effects of amphetamine, chlorpromazine, ketamine, and scopolamine on the acquisition and extinction of the rabbit's conditioned nictitating membrane response.

Four experiments examined whether posttraining deliveries of drugs modified the performance of the rabbit's conditioned nictitating membrane response (NMR) during acquisition and extinction. The results show that ketamine accelerated, but that amphetamine, chlorpromazine, and scopolamine retarded, conditioning when the drugs were injected immediately after the completion of daily training sessions. However, all conditioning effects of the drugs were lost when their deliveries were delayed by 2 hrs after the end of training. During extinction, the only drug that altered conditioned performance was ketamine. Specifically, ketamine retarded the rate of extinction when the drug was given immediately after training. However, delaying ketamine by 2 hrs after training neutralized the drug's influence. These findings indicate that the NMR preparation should be useful in examining how the posttraining delivery of drugs influences associative processes in conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Long-term retention of the classically conditioned eyeblink response in rats.

Retention of the classically conditioned eyeblink response in rats was tested with a conditioned stimulus (CS)-alone extinction test and 2 sessions of reacquisition training. Retention of the eyeblink conditioned response (CR) during both tests was highest 24 hrs and 1 mo after initial acquisition. Three months after initial acquisition, responding during the CS-alone test was at baseline, but there was significant savings during reacquisition. By 6 mo after initial acquisition, the memory for the eyeblink CR was not expressed in either test. The group differences in retention, despite initial acquisition of the eyeblink CR to equal levels, suggest that rat eyeblink conditioning may provide a useful behavioral model for studying the neural processes underlying memory retention and loss. (PsycINFO Database Record (c) 2010 APA, all rights reserved)