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Biomedical subjects

J M Pearce

Publications and source records attributed to J M Pearce.

At least 37 records · Page 2Linked to original sources
PubMed2001

Theories of associative learning in animals.

Theories of associative learning are concerned with the factors that govern association formation when two stimuli are presented together. In this article we review the relative merits of the currently influential theories of associative learning. Some theories focus on the role of attention in association formation, but differ in the rules they propose for determining whether or not attention is paid to a stimulus. Other theories focus on the nature of the association that is formed, but differ as to whether this association is regarded as elemental, configural, or hierarchical. Recent developments involve modifications to existing theories in order to account for associative learning between two stimuli, A and B, when A is accompanied, not by B, but by a stimulus that has been paired with B. The implications of the theories for understanding how humans derive causal judgments and solve categorization problems is considered.

Animals↗
PubMed2000

Analysis of phospholipid molecular species in brain by (31)P NMR spectroscopy.

Techniques are described for the (31)P NMR analysis of glycerophospholipid (PL) headgroup and molecular species in brain. The (31)P NMR spectrum of PLs from human temporal cortex, solubilized in aqueous Na cholate, typically showed 3 major resonances, assigned to phosphatidylcholine (PC) molecular species containing 0, 1, or 2 fully saturated acyl chains. Less species resolution was obtained for the other PL headgroups under these conditions. Alkylacyl- and alkenylacyl-PC were readily discerned using the CHCl(3)-CH(3)OH-H(2)O solvent method. The chain-length, temperature, and species dependences of the (31)P NMR chemical shifts were explored in model PLs. Assignments of signals from phosphatidylethanolamine (PE) subclasses were confirmed in the sodium-cholate system by lipase-mediated selective hydrolysis of bovine-brain PE. The utility of (31)P NMR to monitor enzymatic PL oxidation was further demonstrated. Possible changes in PL composition with postmortem interval (PMI) in rat brain were examined. No significant changes were seen in PL headgroup or PC species composition with PMI at up to 18 hours. Where comparable, the Na-cholate-solubilization and solvent methods gave similar quantitative results for headgroup analysis on the same samples. The present work demonstrates the feasibility and utility of the dual system for analysis of PLs in brain. Magn Reson Med 44:215-223, 2000.

Aged↗
PubMed2000

Intact negative patterning in rats with fornix or combined perirhinal and postrhinal cortex lesions.

It has been proposed that the hippocampal formation is necessary for the acquisition of tasks that require the use of configural representations for their solution, including spatial learning and negative patterning. Tests of this influential view have, however, yielded conflicting results. For example fornix or hippocampal lesions, which reliably impair spatial learning, do not reliably impair negative patterning. A problem in interpreting these results has been the lack of controls for factors such as over-responding, excitatory effects of reward, and the possibility of non-configural solutions. At the same time, other studies have pointed to a role in configural learning for parahippocampal regions such as the perirhinal cortex. The present experiments controlled for the above factors and revealed that neither lesions of the fornix nor of the perirhinal/postrhinal cortex in the rat had any effect on negative patterning, although subsequent tests of object and spatial memory demonstrated the functional efficacy of the lesions.

Amygdala↗
PubMed2000

The influence of passive preexposure on escape from a Morris pool.

In 3 experiments rats were preexposed to the landmarks that surround a Morris pool by being placed on a submerged platform within the pool. They were then required to escape from the pool by swimming to the platform, which was in a location that had not been used during preexposure. Preexposure facilitated subsequent escape from the pool, provided that the platform was not moved during preexposure and the relative position of the landmarks to each other remained constant throughout preexposure. In contrast, if during preexposure the platform was moved from session to session (Experiment 1), or the array of landmarks was altered unsystematically from trial to trial (Experiments 2 and 3), then subsequent learning to escape from the pool was disrupted. These findings suggest that the effects of preexposure to the landmarks in a Morris pool is determined by whether or not they are of relevance for identifying the location of the platform. When they are relevant, then subsequent learning is facilitated, but when they are irrelevant, then subsequent learning is disrupted.

Animals↗
PubMed2000

Aspects of the failed back syndrome: role of litigation.

OBJECTIVE: A review that attempts to identify the mechanism and causation of persistent or recurring low back pain. DESIGN: A personal assessment of clinical features with a selective review of the literature. RESULTS: Thirty to forty per cent of our population aged 10-65 years report that back trouble occurs on a monthly basis and in 1% to 8% this interferes with work. A definite patho-anatomical cause for the pain is demonstrable in only a minority. It can be deduced that psychosocial factors, including insurance benefits are of importance for this variation. CONCLUSIONS: Neither non-operative nor surgical procedures have a major impact on the capacity for work in this substantial minority of backache sufferers. The main risk factors identified are: Wrong diagnosis, repeated medical certificates for sickness benefits, failed surgery, symptoms incongruous with signs or imaging, multiple spinal procedures, poor social support and poor motivation, psychological illness, clinical depression before or after injury or operation. Pending compensation and delays in settlement are important additional features in claimants for compensation. For patients with unproven diagnostic labels such as 'pain-behaviour', no evidence exists that any type of surgery is cost effective.

Humans↗
PubMed2000

The use of nuclear magnetic resonance spectroscopy in the detection of drug intoxication.

The use of nuclear magnetic resonance (NMR) spectroscopy as a method for drug analysis has the advantages of reduced pre-analytical preparation time and the potential to detect and quantitate drug conjugates and metabolites simultaneously. NMR was investigated as a method to screen for organic substances (and metabolites) in 25 patients who presented to the Emergency Department with clinical indications of a drug overdose. Urine specimens were examined by 1H NMR spectroscopy at 300 MHz and the results compared with gas chromatography-mass spectrometry (GC-MS) results. There was a 56% concordance (14 of 25 samples) between NMR and GC-MS. NMR identified acetaminophen, ibuprofen, aspirin, valproate, carbamazepine, and pseudoephedrine as parent compounds or metabolites. For a patient for whom GC-MS results were negative, NMR strongly suggested the presence of erythromycin. NMR was most successful in identifying analgesics and antiepileptic drugs (sensitivity 83-100%). In 10 patients, signals from 1,2-propanediol, a common vehicle for some pediatric medications, were observed by NMR spectroscopy. NMR had 0% sensitivity in identifying tricyclic antidepressants and antipsychotic drugs. In these samples, GC-MS detected a variety of compounds, including tricyclic antidepressants and their metabolites and chlorpromazine. In addition, other substances that had not been disclosed as having been ingested, such as caffeine, diphenhydramine, and nicotine, were detected by GC-MS. NMR spectroscopy represents an emerging supplementary analytical technique that is applicable to a wide range of possible intoxicants and to the evaluation of the intoxicated patient, particularly when larger amounts of the intoxicant (> 200 mg) are ingested.

Adolescent↗
PubMed2000

Gowers' sign.

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History, 19th Century↗