Reversible lesions of the cerebellar interpositus nucleus during acquisition and retention of a classically conditioned behavior.

Previous lesion, recording, and stimulation studies have implicated the cerebellum and its associated circuitry as essentially involved in classical conditioning of discrete, somatic muscle responses. In 2 experiments, the interpositus nucleus of the cerebellum as assessed for the plasticity associated with learning and memory of the nictitating membrane (NM) response by using local cooling as a reversible lesion technique. In well-trained animals (Exp 1), NM conditioned responses (CRs) were abolished during cooling of the interpositus but reappeared when the interpositus returned to body temperature. This cooling–warming protocol could be repeated many times. Cooling could be prolonged (1 session, ～1 hr) with recovery of NM CRs as tested on the next day. Multiple-unit recordings related to learning were also absent in the interpositus and red nucleus during cooling. In naive animals (Exp 2), both behavioral and unit CRs did not develop while training with cooling. There was no evidence of savings when training continued without cooling: Behavioral and unit CRs developed as if the animals were still naive. These results support the idea that the interpositus nucleus of the cerebellum is the critical locus for learning and memory of this classical CR. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Transfer of learning but not memory after unilateral cerebellar lesion in rabbits.

Unilateral lesion of the cerebellum in rabbits completely and permanently abolishes previous learning and prevents new learning ipsilateral to the lesion. However, when training continues on the contralateral side, there is substantial savings in that it takes few trials to learn. This observation may imply that the memory survives the lesion. Rabbits were classically conditioned for an eyelid response and then the ipsilateral interpositus nucleus of the cerebellum was lesioned. Then the rabbits were trained on the contralateral side. There is no savings on the contralateral side without first trying to train on the lesioned side. It is concluded that the survival of a memory after the lesion probably does not account for the rapid transfer, but rather that the act of trying to train on the lesioned side in previous studies first induces a new memory on the contralateral side. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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)     

Neural unit activity in the trigeminal complex with interpositus or red nucleus inactivation during classical eyeblink conditioning.

During classical conditioning, many neurons in the trigeminal complex of rabbits exhibit activity that is related to the conditioned stimulus (tone), the unconditioned stimulus (airpuff), or to the conditioned response (eyeblink). For these reasons the trigeminal complex has been hypothesized to be a brainstem locus for the neuronal plasticity associated with conditioning. In this experiment, the learning-related activity (unit activity associated with the conditioned response) in the trigeminal is abolished when either the red nucleus or interpositus nucleus of the cerebellum is temporarily inactivated by cooling, but the stimulus-evoked activity is unaffected by cooling. This study and previous results support the suggestion that the learning-related activity seen in the trigeminal is driven by the interpositus by way of the red nucleus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Classical conditioning of the rabbit eyelid response with a mossy-fiber stimulation CS: II. Lateral reticular nucleus stimulation.

Stimulation of mossy fibers arising from the pontine nuclei can be used as a conditioned stimulus (CS) during classical conditioning of the eyelid/nictitating membrane response (NM). In the present experiment we stimulated another source of mossy fibers, the lateral reticular nucleus (LRN), as a CS for NM conditioning. LRN stimulation was an effective CS, resulting in learning, and the conditioned response to LRN stimulation showed normal extinction. Unpaired presentation of CS and US did not result in pseudo-conditioning. Lesions of the cerebellar dentate-interpositus region abolished the conditioned response but left the unconditioned reflex response intact. We suggest that mossy fibers may normally carry CS information to the cerebellum. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cooling the area postrema induces conditioned taste aversions in male rats and blocks acquisition of LiCl-induced aversions

The experiments presented in this article were designed to examine whether area postrema (AP) lesions attenuate LiCl-induced conditioned taste aversions (CTAs) by disruption of information about the illness-producing properties of LiCl or by a lesion-induced malaise. Reversible lesioning of the AP caused by cooling induced a CTA in male rats. The cooling-induced CTA could be blocked if males were exposed to cooling for several days before acquisition day. Acquisition of a LiCl-induced CTA was blocked in males if they were exposed to cooling before acquisition day and during LiCl administration on acquisition day was attenuated but not blocked in males if they were exposed to cooling only before acquisition day, and was unchanged in males if they were exposed to cooling only during LiCl administration. Taken together these results indicate that the AP is important for acquisition of LiCl-induced CTAs but that inactivation of this area is so aversive it will induce CTAs that can obscure the attenuation of LiCl-induced aversions.     

Classical conditioning of the rabbit eyelid response with a mossy-fiber stimulation CS: I. Pontine nuclei and middle cerebellar peduncle stimulation.

The nictitating membrane/eyelid responses of 18 rabbits were classically conditioned using cerebellar mossy-fiber stimulation as a conditioned stimulus (CS) and air puff as an unconditioned stimulus (US). The dorsolateral, lateral, and medial pontine nuclei and the middle cerebellar penduncle were effective stimulation-CS sites for training. In one group of rabbits, robust conditioned eyelid responses were produced with paired trials and subsequently extinguished with CS-alone and explicitly unpaired presentation of the CS and US. In a second group of rabbits, no conditioned responses were evident for 4 days of unpaired CS and US presentations. Conditioned responses did develop, however, after paired training was begun. Lesions of the interpositus nucleus of the cerebellum completely abolished the conditioned responses of a third group of rabbits overtrained with the mossy-fiber CS and air-puff US. Results support studies that have demonstrated that the cerebellum is critically involved in acquisition and retention of simple learned responses and theories of cerebellar function which have proposed that mossy fibers supply critical "learning" input to the cerebellum for acquisition and retention of motor skills. (PsycINFO Database Record (c) 2010 APA, all rights reserved)