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)     

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)     

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)     

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)     

Trial distribution effects on postasymptotic performance and retention of the rabbit's (Oryctolagus cuniculus) classically conditioned nictitating membrane response.

Conditioned the nictitating membrane response to asymptote under identical experimental parameters in 3 groups of albino rabbits (N = 36). Subsequently, the 1st group was shifted to a longer modal intertrial interval (ITI) for further training, the 2nd group was switched to a shorter modal ITI, and the 3rd group was continued with intermediate ITI values. Results reveal (a) immediate incremental and decremental performance adjustments following the shift to longer and shorter modal ITIs, respectively, which were maintained over 10 postasymptotic sessions; (b) evidence of within-session performance decrements during postasymptotic conditioning; and (c) no evidence of retention losses in a retention test conducted 72 hr following the final conditioning session. (16 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)     

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)     

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)     

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)     

Phenytoin blocks the reversal of a classically conditioned discriminative eyeblink response in rabbits

The aim of the present study was to assess the role of vascular alpha 1D-adrenoceptors in the sympathetic vasopressor response in vivo. Specifically, we evaluated the effect of a selective alpha 1D-adrenoceptor antagonist, BMY 7378 (8-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-8-azaspiro(4,5)dec ane-7,9- dione 2HCl), on the vasopressor response induced by preganglionic (T7-T9) sympathetic stimulation in the pithed rat. The vasopressor response was dose-dependently sensitive to inhibition by intravenous BMY 7378 (0.1, 0.31, 1 and 3.1 mg/kg), doses of 1 and 3.1 mg/kg being equally effective. Like BMY 7378, 5-methylurapidil (0.1, 0.31, 1 and 3.1 mg/kg) antagonized the vasopressor response to spinal stimulation; doses of 1 and 3.1 mg/kg were also equally effective. In combination experiments, BMY 7378 (1 mg/kg, i.v.) and the alpha 1A-adrenoceptor antagonist, 5-methylurapidil (1 mg/kg, i.v.), showed an additive effect. The present results demonstrate that the alpha 1D-adrenoceptor subtype plays an important role in the pressor response to sympathetic nerve stimulation in the pithed rat, and confirm the participation of the alpha 1A-adrenoceptor subtype in the same response.     

Reversible lesions of the red nucleus during acquisition and retention of a classically conditioned behavior in rabbits.

Previous lesion, recording, and stimulation studies implicated the cerebellum and its associated brain-stem circuitry as essentially involved in classical conditioning of discrete, somatic muscle responses. A prior study of interpositus cooling showed that the formation of memory was prevented. The present study assesses the red nucleus (RN) for its role in the plasticity associated with learning and memory by using local cooling as a reversible lesion technique. A cooling probe was implanted lateral to the RN. Recording electrodes were implanted in the right RN and the left interpositus nucleus (IPN). Animals were trained for 6 days with the cooling probe activated. No behavioral CRs developed, and multiple unit recordings related to learning did not develop in the RN. However, a learning related model did develop in the IPN. After 5 days of training while cooling, animals were given 5 days of normal training (cooling probe inactive) to assess retention. Substantial savings were evident when normal training was given. CRs appeared quickly on the 1st day of normal training, and multiple unit models were present in both RN and IPN. Results support the idea that the red nucleus is a necessary efferent for the memory trace formed in the cerebellum. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Extinction and retention of a classically conditioned flexor nerve response in acute spinal cat.

Conditioned adult male and female cats by pairing a mild electrical stimulus to the superficial peroneal sensory nerve (CS) with a stronger electrical stimulus to the ankle skin (UCS) of the same leg. Subsequent extinction was produced by presenting CS-alone trials. In Exp I (42 Ss), Ss given massed extinction trials showed response decrements to base levels, but Ss that received distributed extinction trials showed no decrements. In Exp II, .5-, 1-, 2-, 3-, or 4-hr intervals between acquisition and extinction produced no significant differences in the extinction data. In Exp III (20 Ss), Ss received extinction trials immediately or 30 min after acquisition trials, followed by 20 additional extinction trials 30 min later. Data indicated significant acquisition and extinction in the 10- and 20-acquisition trial groups. As in Exp II (35 Ss), varying the interval between acquisition and extinction did not produce any group differences in the extinction data. These results demonstrate that response increases produced by paired trials in the spinal preparation do not decay spontaneously over time and are not caused by sensitization effects. (23 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acquisition of a second-order classically conditioned response.

Following alleyway food-training on a 50% random partial reinforcement schedule and 10 forward 1st-order (CS1-UCS) conditioning trials elsewhere, forward 2nd-order (CS2-CS1) classical conditioning trials were initiated for 40 female albino rats (Group 1) and equivalent but backward (CS1-CS2) training was started for 20 additional Ss (Group 2). After each set of 2 CS1-UCS and 3 CS2-CS1 trials (or 3 CS1-CS2 trials for Group 2) were given, the CS2 was presented in the goal area of the alley on nonreinforced trials to assess its suppressing effect on total running times. While the performance of Group 2 to the CS2 was unchanged as a function of conditioning trials, Group 1 evinced both increasing suppression and skin conductance levels as 2nd-order training progressed. Maximum suppression was obtained by the 12th CS2-CS1 trial. (French summary) (16 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)     

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

16 6-mo-old and 15 36–60 mo old New Zealand albino rabbits underwent classical conditioning of the nictitating membrane response in either a delay conditioning (Exp I) or a trace conditioning (Exp II) paradigm. There was no difference between old and young Ss in the acquisition of the CR in the delay paradigm, nor were there any age-related differences in generalization to the tone CS or in sensitivity to the tone CS or eyeshock UCS. However, in the trace conditioning paradigm, old Ss acquired the CR significantly more slowly than young Ss. 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. Results are discussed in terms of how brain changes that accompany aging could differentially affect these 2 types of classical conditioning. (32 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lateral subthalamic area as mediator of classically conditioned bradycardia in rabbits.

Examined whether a central efferent pathway passing through the lateral zona incerta (LZI) of the subthalamus would selectively mediate the bradycardia conditioned response (CR) in 22 New Zealand albino rabbits. Electrodes were implanted bilaterally in LZI or in control sites just dorsal or ventral to LZI. Two days following surgery, Ss were subjected to Pavlovian conditioning or to pseudoconditioning. Subsequent bilateral electrolytic lesions did not infuence the heart rate (HR) orienting response, unconditioned response (UCR), baseline, or lack of response to pseudoconditioning. Bilateral LZI lesions alone abolished the HR CR. In a follow-up experiment, the corneoretinal potential (CP) CR and HR were recorded in 4 Ss. Bilateral LZI lesions following conditioning to a criterion of 65% CP CRs abolished the HR CR without affecting CP CRs. Findings indicate that LZI is part of an efferent pathway that selectively mediates the HR CR in rabbits. (24 ref) (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)     

Five-year retention of the classically conditioned eyeblink response in young adult, middle-aged, and older humans

OBJECTIVE: To describe the clinical profile of demyelinating optic neuritis in African Americans. METHODS: The medical records of all patients with a diagnosis of optic neuritis examined at the Neuro-Ophthalmology Unit at the Emory University Eye Center (Emory) and at the Grady Memorial Hospital Eye Clinic (Grady), Atlanta, Ga, between 1989 and 1996 were retrospectively reviewed. PATIENTS: African American and white patients, aged 15 through 55 years, with a single initial episode of acute optic neuritis of unknown or demyelinative origin were included in the study. Study patients included 23 African American patients and 56 white patients examined at Emory as well as 10 African American patients examined at Grady. RESULTS: There were no significant differences among the African American study patients, the white study patients, and patients from the Optic Neuritis Treatment Trial (ONTT) regarding sex (P=.36), age (P=.73), or the presence of disc edema (P=.40), lesions found on magnetic resonance imaging (P=.43), or multiple sclerosis (P=.54) at the onset of an initial episode of optic neuritis. The Emory African American patients presented with more frequent severe visual loss (13 [93%] of 14 patients with a visual acuity < or =20/200) compared with Emory white patients (12 [39%] of 31 patients; P=.002) and with ONTT patients (161 [36%] of 448 patients; P<.001). At follow-up examination of at least 1 year, Emory African American patients had worse vision (9 [39%] of 23 patients <20/40, and 4 [17%] of 23 patients < or =20/200) compared with Emory white patients (5 [8%] of 63 patients <20/40, P=.001; 3 [5%] of 63 patients < or =20/200, P=.08), and with ONTT patients (29 [7%] of 409 patients <20/ 40, P=.0001; 12 [3%] of 409 patients < or =20/200, P=.01). Compared with ONTT patients, the Emory African American patients combined with the Grady African American patients had more frequent severe visual loss (visual acuity < or =20/200) at presentation (18 [90%] of 20 patients vs 161 [36%] of 448 patients; P<.001) and at follow-up examination of at least 1 year (6 [18%] of 33 patients vs 12 [3%] of 409 patients; P=.002). Seven (58%) of 12 African American patients with multiple sclerosis had a "neuromyelitis optica" presentation defined by the presence of neurological deficits limited to the optic nerves and spinal cord. CONCLUSIONS: The African American study patients with a single episode of demyelinating optic neuritis had visual acuities more severely affected at onset and after 1 year of follow-up compared with the white study patients and with patients in the ONTT. In the African American patients, multiple sclerosis occurred most frequently in a "neuromyelitis optica" form.     

Effects of attenuating cutaneous afferent activity on a preestablished nictitating membrane response in rabbits.

Conducted 3 experiments with a total of 27 New Zealand albino rabbits. Ss' nictitating membrane response conditioned during high levels of cutaneous afferent activity from the cornea and paraorbital region. Afferent activity levels were controlled by varying UCS locus, corneal applications of a local anesthetic (.5% tetracaine hydrochloride), and exerting mechanical tension on the eyelids. After attainment of criterion levels of responding, levels of afferent activity were varied. Results indicate that subsequent response levels were a direct function of cutaneous afferent activity. Latency and amplitude measurements of the UCR under procedures used to manipulate cutaneous afferent activity did not support the possibility of a mechanical impedence of the response. Stimulus change did not appear to be critically important. (24 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of amygdala lesions on reflex facilitation and conditioned response acquisition during nictitating membrane response conditioning in rabbit.

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 rabbits. Before behavioral training, the central nucleus of the amygdala and adjacent areas were lesioned electrolytically. In Exp 1, the lesioned animals exhibited no reflex facilitation of the unconditioned NM response at conditioned stimulus (CS)–unconditioned stimulus (UCS) intervals of 125–8,000 ms. In Exps 2 and 3, in which 1 CS–UCS 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 1,000-Hz tone CS intensity was 65 dB, but not when the intensity was 85 dB. (PsycINFO Database Record (c) 2010 APA, all rights reserved)