Rapid transfer of training occurs when direct mossy fiber stimulation is used as a conditioned stimulus for classical eyelid conditioning

Fifteen rabbits were classically conditioned using stimulation of the right pontine nuclei as a conditioned stimulus and a corneal airpuff as an unconditioned stimulus. After conditioning criterion was reached, the stimulation conditioned stimulus was transferred to the left pontine nuclei and the rate of conditioned response acquisition observed. Our results indicate that when electrodes were placed symmetrically in the right and left pontine nuclei, extremely rapid transfer of training occurred. Together with previous data, the present data supply further indirect evidence that the site of neural plasticity which underlies acquisition and retention of classically conditioned skeletal muscle responses is located efferent to the pontine nuclei, namely in the cerebellum.     

When pentobarbital is the conditioned stimulus and amphetamine is the unconditioned stimulus, conditioning depends on the type of conditioned response

Injections of drugs into rats were used as conditioned stimuli (CSs) and as unconditioned stimuli (USs). With heart rate (HR) conditioning, the pentobarbital CS produces a higher HR than under control conditions. With avfail (aversion failure) conditioning, the pentobarbital CS loses much of its capacity to induce a conditioned taste aversion. HR conditioning was obtained with forward delays of up to 30 min and backward delays of up to 270 min, where the delays are defined by the interinjection interval. Avfail was obtained with forward delays of up to 270 min but not with backward delays. Neither HR conditioning nor avfail were context specific but could be demonstrated in a test apparatus after pairings that occurred in the home cage. This indicated that the external environment was not an important part of the effective stimulus complex. When HR conditioning was obtained, its latency and duration was not related to the delay between the CS and US injections or whether they were forward or backward.     

Stimulation at a site of auditory-somatosensory convergence in the medial geniculate nucleus is an effective unconditioned stimulus for fear conditioning.

The medial division of the medial geniculate nucleus (MGm) and the posterior intralaminar nucleus (PIN) are necessary for fear conditioning to an auditory conditioned stimulus (CS), receive both auditory and somatosensory input, and project to the amygdala, which is involved in production of fear conditioned responses. If CS-unconditioned stimulus (US) convergence in the MGm-PIN is critical for fear conditioning, then microstimulation of this area should serve as an effective US during classical conditioning, in place of standard footshock. Guinea pigs underwent conditioning (40-60 trials) using a tone as the CS and medial geniculate complex microstimulation as the US. Conditioned bradycardia developed when the US electrodes were in the PIN. However, microstimulation was not an effective US for conditioning in other parts of the medial geniculate or for sensitization training in the PIN or elsewhere. Learning curves were similar to those found previously for footshock US. Thus, the PIN can be a locus of functional CS-US convergence for previously for footshock US. Thus, the PIN can be a locus of functional CS-US convergence for fear conditioning to acoustic stimuli.     

Hippocampal pyramidal cell activity encodes conditioned stimulus predictive value during classical conditioning in alert cats.

We have recorded the firing activities of hippocampal pyramidal cells throughout the classical conditioning of eyelid responses in alert cats. Pyramidal cells (n = 220) were identified by their antidromic activation from the ipsilateral fornix and according to their spike properties. Upper eyelid movements were recorded with the search coil in a magnetic field technique. Latencies and firing profiles of recorded pyramidal cells following the paired presentation of conditioned (CS) and unconditioned (US) stimuli were similar, regardless of the different sensory modalities used as CS (tones, air puffs), the different conditioning paradigms (trace, delay), or the different latency and topography of the evoked eyelid conditioned responses. However, for the three paradigms used here, evoked neuronal firing to CS presentation increased across conditioning, but remained unchanged for US presentation. Contrarily, pyramidal cell firing was not modified when the same stimuli used here as CS and US were presented unpaired, during pseudoconditioning sessions. Pyramidal cell firing did not seem to encode eyelid position, velocity, or acceleration for either reflex or conditioned eyelid responses. Evoked pyramidal cell responses were always in coincidence with a beta oscillatory activity in hippocampal extracellular field potentials. In this regard, the beta rhythm represents a facilitation, or permissive time window, for timed pyramidal cell firing. It is concluded that pyramidal cells encode CS-US associative strength or CS predictive value.     

Eyeblink conditioning using cochlear nucleus stimulation as a conditioned stimulus in developing rats

Previous studies demonstrated that the development of auditory conditioned stimulus (CS) input to the cerebellum may be a neural mechanism underlying the ontogenetic emergence of eyeblink conditioning in rats. The current study investigated the role of developmental changes in the projections of the cochlear nucleus (CN) in the ontogeny of eyeblink conditioning using electrical stimulation of the CN as a CS. Rat pups were implanted with a bipolar stimulating electrode in the CN and given six 100-trial training sessions with a 300 ms stimulation train in the CN paired with a 10 ms periorbital shock unconditioned stimulus (US) on postnatal days (P) 17-18 or 24-25. Control groups were given unpaired presentations of the CS and US. Rats in both age groups that received paired training showed significant increases in eyeblink conditioned responses across training relative to the unpaired groups. The rats trained on P24-25, however, showed stronger conditioning relative to the group trained on P17-18. Rats with missed electrodes in the inferior cerebellar peduncle or in the cerebellar cortex did not show conditioning. The findings suggest that developmental changes in the CN projections to the pons, inferior colliculus, or medial auditory thalamus may be a neural mechanism underlying the ontogeny of auditory eyeblink conditioning.     

Role of the lateral and medial hypothalamus in the reproduction of the motoric reaction which is a signal during the development of classical conditioned reflexes

It has been demonstrated in experiments on three dogs that test electrostimulation of the lateral hypothalamus reproduces the motoric reaction which is the signal stimulus during the development of classical alimentary CR (83%) and does not reproduce it during the development of classical defensive CR (93%). The test electrostimulation of the medial divisions of the hypothalamus, like the electrostimulation of the LH, reproduces the signal motoric reaction, but in a smaller percent of cases (62%), during the development of classical alimentary CR, and does not reproduce it during the development of classical defensive CR. The reproduction of the signal motoric reaction during the electrostimulation of the LH is associated with the activation of a backward conditioned connection from the motivational structures of the hypothalamus to the representation of the signal stimulus in the motor cortex.Translated from Zhurnal Vysshei Nervnoi Deyatel'nosti imeni I. P. Pavlova, Vol. 41, No. 1, pp. 41–50, January–February, 1991.     

Sub-vastus approach is more effective than a medial parapatellar approach in primary total knee arthroplasty: A randomized controlled trial

In a prospective single-centre longitudinal randomized controlled trial 116 patients were allocated to the sub-vastus approach, and 115 to the medial parapatellar approach. At one week follow-up, compared to baseline, range of motion, Knee Society (KS) global, KS knee, and KS pain scores were significantly better in the sub-vastus group. At the one year follow-up, WOMAC global and pain scores, SF36 physical function and role-physical scores, and EuroQol utility and pain score were significantly better in the sub-vastus group. The ease of exposure in the sub-vastus approach was significantly worse. There was no significant difference in length of stay or analgesia intake. The sub-vastus approach to total knee arthroplasty was more effective than a medial parapatellar approach at both one week and one year post-operatively, but surgeons reported a less easy exposure in the sub-vastus group.     

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.     

Autonomic classical conditioning as a function of awareness of stimulus contingencies

Two groups of 32 college students were presented compound CSs (lights and tones presented simultaneously) during a classical conditioning paradigm. By means of a masking task and verbal instructions, a partially informed group was made aware of only the visual CS's contingency with the UCS, while a fully informed group was made aware of both the visual and auditory contingencies. Autonomic indices of conditioning (electrodermal responses, heart rate, and digital pulse volume) were later measured to the individual component CSs and to various compound CSs. It was found that: (1) the partially informed group exhibited conditioning exclusively to the visual CS+ and to compounds which included the visual CS+, while (2) the fully informed group exhibited conditioning to both visual and auditory CS+s. The results confirm the importance of awareness in human autonomic discrimination classical conditioning. It is suggested that human autonomic conditioning may be usefully conceptualized as an information processing task with the autonomic indices of conditioning reflecting central cognitive processes.     

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.     

Disrupted retention of the classically conditioned nictitating membrane response in the aluminum-intoxicated rabbit using electrical stimulation of the brain as a conditioned stimulus

Rabbits were classically conditioned to emit an eyeblink conditioned response (CR) to electrical stimulation (ESB) of the medial geniculate nucleus (MGN) paired with a corneal air puff until they attained a criterion of two consecutive days of greater than 90% CRs. They then received intraventricular injections of 1% AlCl3, HCL, or normal saline. Ten days postinjection, each animal underwent a retention test consisting of 50 ESB alone presentations. Whereas all saline and HCL animals gave at least 90% CRs during retention, no aluminum rabbit emitted more than 30% CRs. Considered with the results of previous work, these data suggest that aluminum-induced neurofibrillary degeneration disrupts retention of the CR by affecting central associative processes.     

Effects of lesions in the central nucleus and lateral nucleus of the amygdala on fear conditioning with a visual conditioned stimulus in rats

Lesions in the central nucleus or lateral nucleus of the amygdala have been known to interfere with the acquisition of fear conditioning when a sound is used as a conditioned stimulus (CS). The present study examined whether or not a similar interference would occur with a visual CS. Seven rats with lesions in the central nucleus (AMY-C group), 8 with lesions in the lateral nucleus (AMY-L group), and 16 unoperated control rats were trained using a visual CS (25 W light, 3.7 s duration) paired with footshock (1.0 mA, 0.5 s). The behavioral index of fear conditioning was a potentiation of startle reflex in the presence of CS. All control rats and AMY-L group showed the potentiation, but AMY-C group did not. These results suggest that the lateral nucleus of the amygdala may not be involved in fear conditioning to a visual CS. It is possible that each modality of CS has a specific pathway to the central nucleus of the amygdala to mediate fear conditioning.     

Amygdaloid unit activity during classical conditioning of the nictitating membrane response in rabbit

Single and multiple unit activity was recorded from the amygdaloid nuclei in awake unanesthestized rabbits during classical conditioning of the nictitating membrane (NM) response. Over half o the unit recordings from the amygdaloid complex demonstrated changes in firing rate following the presentation of the tone conditioned stimulus (CS) or corneal air-puff unconditioned stimulus (US). Of the unit records that were responsive to the training stimuli, 58% showed responses to the CS and 73% showed responses to the US. Amygdaloid responses to either the CS or the US tended to be a long latency (greater than 70 msec), long duration (greater than 250 msec), modest increase (less than 2 fold) in unit firing. There were no statistically significant differences between the spontaneous firing rates, response latencies, response magnitudes, or response type distributions seen during unpaired (control) and paired stimulus presentations. However, four of 18 single and multiple unit groups that were tested during both unpaired and paired training developed new or enhanced responses following the onset of paired training. All four of these records were from the basolateral or lateral amygdaloid nuclei. Although these few records did develop response alterations after CS-US pairing, the majority of the records indicated that essentially the same amygdaloid response patterns occur during unpaired training as during paired training. it is therefore unlikely that the critical neuronal changes that underlying NM conditioning occur within the amygdaloid complex. Other possible roles for the amygdaloid complex during conditioning are considered.     

Movement as a signal during elaboration of classical conditioned reflexes

Translated from Zhurnal Vysshei Nervnoi Deyatel'nosti imeni I. P. Pavlova, Vol. 38, No. 5, pp. 803–811, September–October, 1988.     

Role of the medial and lateral septum in a variable goal spatial problem solving task.

Rats with lesions to the medial (MS) or lateral septal (LS) nuclei were compared to normal controls (CNT) in the acquisition of a spatial working memory task. In this task, animals were first allowed to explore the unbaited three-table apparatus before being fed on one of the two possible goal tables. Animals were then tested on their ability to return to the table where they just had been fed. Only rats with medial septal damage were clearly impaired on this problem, an impairment that dissipated over days. In contrast, the performance of LS rats was not significantly different from controls. During the second phase of the experiment, the same animals received either atropine sulphate (50 mg/kg, IP), atropine methylnitrate (50 mg/kg, IP), or an equivalent volume of saline. Atropine sulphate produced a sharp decrease in performance by all subjects. Meanwhile, atropine methylnitrate produced a mild temporary deficit only in LS rats. Overall, these results confirm that the medial septum plays a crucial role in the acquisition of problem solving. In addition, these results also suggest that the lateral septum may play a possible role in some form of spatial behavior easily disrupted by atropine methylnitrate.     

Environment-specific conditioning produced by electrical stimulation of the lateral hypothalamus

Rats received noncontingent electrical stimulation of the lateral hypothalamus on one side of a place preference apparatus and no stimulation on the other side. Subsequently, when allowed access to both sides, the rats spent more time on the side associated with stimulation. This change in preference was only found in rats receiving stimulation in the side least preferred prior to conditioning trials. It was further shown that the place preference conditioning procedure produces increased locomotor activity. Thus, the place preference obtained was not an artifact produced by a conditioned freezing response. These data suggest that both the reinforcing and activating effects of lateral hypothalamic stimulation may be conditioned to a specific environment. Some methodological problems of the place preference paradigm are discussed.     

An auditory conditioned stimulus modulates unconditioned stimulus-elicited neuronal activity in the cerebellar anterior interpositus and dentate nuclei during nictitating membrane response conditioning in rabbits.

The effects of the presentation of an auditory conditioned stimulus (CS) on unconditioned stimulus (US)-elicited neuronal activity in the anterior interpositus (AIPN) and dentate (DN) nuclei of the cerebellum were investigated during the initial stages of classical conditioning of the nictitating membrane (NM) response in rabbits. In Experiment 1, a 500-ms CS (but not a 30-ms CS) facilitated US-elicited single-unit activity in the AIPN and depressed US-elicited activity in the DN during training. In Experiment 2, lesions of the AIPN but not of the DN prevented acquisition of conditioned NM responses. The results are interpreted within the framework of a model of classical conditioning that proposes that conditioned neuronal activity that underlies behavioral plasticity develops from the modulation of US-elicited neuronal activity by the CS.