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Biomedical subjects

B J Knowlton

Publications and source records attributed to B J Knowlton.

28 records · Page 2Linked to original sources
PubMed1993

Dissociation of kainic acid lesion effects on the asymmetry of rotation and lateral head movements.

The present study tested the relationship between horizontal head movement asymmetry and rotation behavior after unilateral kainic acid (KA) lesions of the pontine reticular formation (PRF). In line with previous studies, the lesions decreased the rate of ipsilateral spontaneous head movements and spared contralateral spontaneous head movements. In contrast to previous studies, however, these lesions facilitated ipsilateral rather than contralateral rotation. Histological analysis revealed that the ipsilateral rotation may be accounted for by distant effects of the KA injection in the PRF on the ipsilateral substantia nigra (SN). We conclude that unilateral lesions consisting solely of the PRF lead to a preference for contralateral horizontal head movements which then channel rotated away from the lesioned side. KA injections in the PRF, however, are also associated with distant lesions within the ipsilateral extrapyramidal system which override the channeling effect of the contralateral head movements and induce instead ipsilateral rotation.

Animals↗
PubMed1992

Conditioning using a cerebral cortical conditioned stimulus is dependent on the cerebellum and brain stem circuitry.

Electrical stimulation of the auditory cortex (AC) was used as a conditioned stimulus (CS) in the rabbit conditioned eyeblink preparation to trace the functional anatomical connections between the AC and the circuitry underlying this conditioned response. Conditioning was shown to be dependent on the cerebellar interpositus nucleus and the pontine nuclei (PN), structures that are essential for conditioning using a peripheral CS. The results suggest that the cerebellum and associated brain stem circuitry are a necessary part of the memory trace circuit for the conditioned eyeblink response, even when the cerebral cortex is artifically engaged as a CS by electrical stimulation. The results also suggest that the PN are a site of convergence between the CS circuit subserving classical conditioning for peripheral stimuli and the AC, and may therefore be a site where the AC can modulate more elaborate forms of conditioning.

Animals↗
PubMed1989

Stimulation of the lateral septum is a more effective conditioned stimulus than stimulation of the medial septum during classical conditioning of the eye-blink response.

Eight rabbits were trained in the classically conditioned eye-blink response procedure using stimulation of the septal nuclei as the conditioned stimulus (CS). Each rabbit was trained with both medial septal stimulation and lateral septal stimulation. Stimulation of the medial septum was a far less effective CS than stimulation of the lateral septum. This effect may be due to the different roles of these two nuclei in classical conditioning. Conditioning using lateral septal stimulation as a CS is dependent on the cerebellar interpositus nucleus as is conditioning using peripheral and other brain stimulation CSs.

Animals↗
PubMed1989

Hippocampal seizures disrupt working memory performance but not reference memory acquisition.

The effect of hippocampal seizures in rats was assessed in two spatial memory tasks: The reference memory task was a simultaneous two-choice discrimination in a T-maze. The working memory task was a delayed conditional discrimination in a radial arm maze. In each task the hippocampus of each rat was stimulated to seizure after the presentation of the information to be remembered. In the reference memory task, hippocampal seizures did not impair acquisition, whether the stimulation was given immediately after or 4 hr after the presentation of the stimuli to be remembered. In the working memory task, hippocampal seizures did impair performance in a group of the same rats. These results support the distinction between a trial-dependent working memory system that requires hippocampal function and a trial-independent memory system that does not depend on hippocampal function.

Animals↗
PubMed1988

Microinjections of local anesthetic into the pontine nuclei reduce the amplitude of the classically conditioned eyelid response.

Seventeen rabbits were implanted bilaterally with cannulae into the pontine nuclei, and were then trained in the classically conditioned eyeblink procedure. Nine of the rabbits were trained with a tone as a conditioned stimulus (CS), and eight were trained with both tone and a light CS. After each rabbit had learned the conditioned response (CR) well, testing began. One microliter of 5% lidocaine injected bilaterally significantly impaired the CR amplitude for both tone and light as a CS, although unconditioned response amplitude was not affected. Injection of 1 microliter of isotonic saline did not impair CR amplitude, suggesting that the impairment seen after lidocaine injection was due to the anesthetic action of lidocaine in the pons, and not to nonspecific effects distal to the site of injection. These results support and extend the lesion data which shows that the pontine nuclei and their mossy fiber projection to the cerebellum are necessary for eyeblink conditioning using a peripheral CS.

Animals↗
PubMed1988

The effect of lesions of cerebellar cortex on retention of the classically conditioned eyeblink response when stimulation of the lateral reticular nucleus is used as the conditioned stimulus.

Ten male albino rabbits were implanted with stimulating electrodes in the lateral reticular nucleus (LRN). These rabbits were given paired classical conditioning training of the nictitating membrane response with stimulation of the LRN as the conditioned stimulus (CS) Each rabbit was given daily training sessions until it consistently made conditioned responses (CRs). Each rabbit then received an aspiration lesion of cerebellar cortex; the ipsilateral anso-paramedian lobule (n = 6), the anterior or central vermis (n = 2), the central vermis and ansiform lobule (n = 1), or the central vermis and paramedian lobule (n = 1). After recovery, these rabbits were again given paired classical conditioning training with LRN stimulation as the CS. The rabbits with anso-paramedian lesions did not retain the CR after the lesion, but were able to relearn it. The rabbits with lesions of the vermis, the vermis and ansiform, or the vermis and paramedian retained the CR after the lesion. These results are contrasted with previous results, which show that after aspiration of the anso-paramedian lobule, the conditioned response is not retained or relearned when stimulation of the dorsolateral pontine nucleus (DLPN) is used as a CS. The differences between the mossy fiber outputs of the LRN and DLPN may account for this discrepancy. Different regions of the cerebellum are apparently involved in retention of classically conditioned responses depending on the population of mossy fibers carrying the CS information.

Animals↗
PubMed1987

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 UCS 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.

Afferent Pathways↗
PubMed1985

Basal forebrain lesions produce a dissociation of trial-dependent and trial-independent memory performance.

The behavioral effects of lesions in the basal forebrain (BF) of rats were evaluated using two tasks. The BF lesions included both the nucleus basalis magnocellularis (NBM) and the medial septal area (MSA). The first task was a Stone maze, which has 14 consecutive choice points and is a task of complex, trial-independent memory. BF lesions did not impair choice accuracy in this task. The second task was a win-shift spatial discrimination in a radial arm maze, which requires trial-dependent memory. BF lesions produced a significant decrease in choice accuracy in this task. These results demonstrate that BF lesions impair trial-dependent (working) memory but not trial-independent reference memory, and that task difficulty is not the sole factor determining whether BF lesions produce behavioral impairments.

Animals↗
PubMedDate not supplied

Probabilistic classification learning in amnesia.

Amnesic patients and control subjects participated in a study of probabilistic classification learning. In each of three tasks, four different cues were each probabilistically associated with one of two outcomes. On each trial, the cues could appear alone or in combination with other cues and subjects selected the outcome they thought was correct. Feedback was provided after each trial. In each task, the amnesic patients learned gradually to associate the cues with the appropriate outcome at the same rate as control subjects, improving from 50% correct to approximately 65% correct. Presumably because the cue-outcome associations were probabilistic, declarative memory for the outcomes of specific trials was not as useful for performance as the information gradually accrued across trials. Nevertheless, declarative memory does appear to make a contribution to performance when training is extended beyond approximately 50 trials, because with further training control subjects eventually outperformed the amnesic patients. It was also demonstrated that performance on the probabilistic classification task was not the result of holding knowledge of cue-outcome associations in short-term memory, because both control subjects and amnesic patients demonstrated significant savings when testing was interrupted by a 5-min delay (experiment 2). Probabilistic classification learning appears to provide an analog in human subjects for the habit learning tasks that can be acquired normally by animals with hippocampal lesions.

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