Biomedical subjects

L G Nilsson

Publications and source records attributed to L G Nilsson.

At least 37 records · Page 2Linked to original sources

PubMed1996

Network analysis of positron emission tomography regional cerebral blood flow data: ensemble inhibition during episodic memory retrieval.

Two important objectives in the neuroscience of memory are (1) identification of neural pathways involved in memory processes; and (2) characterization of the pattern of interactions between these pathways. Functional neuroimaging can contribute to both of these goals. Using image subtraction analysis of regional cerebral blood flow data measured with positron emission tomography, we identified brain regions that changed activity during episodic memory retrieval (visual work recognition). Relative to a baseline reading task, decreased activity was observed in bilateral prefrontal, bilateral anterior and posterior temporal, and posterior cingulate cortices. Brain regions showing increased activity were the right prefrontal (different from deactivated regions), left anterior cingulate, and left occipital cortices, and vermis of cerebellum. We then performed a network analysis with structural equation modeling to test the hypothesis that regional decreases came about through active inhibition by regions showing increased activity during retrieval. This analysis demonstrated that the influence of activated regions on deactivated regions was more negative during retrieval than during reading, confirming the inhibition hypothesis. Such confirmation could not have been made from the subtraction analysis alone because decreases can come about, at the very least, through reduction of functional influences as well as by active inhibition. The concepts of ensemble excitation and inhibition, as defined through network analysis, are introduced. We argue that is is critical to examine the combined pattern of excitatory and inhibitory influences to fully appreciate the neural basis of episodic memory.

Analysis of Variance↗

PubMed1996

Activation of medial temporal structures during episodic memory retrieval.

Medial temporal lobe structures have been implicated in human episodic memory. Patients with medial temporal lesions show memory deficits, and functional neuroimaging studies have revealed activation in this region during episodic encoding and retrieval when data are averaged over a sample of subjects. The relevance of such observations for memory performance has remained unclear, however. Here we have used positron emission tomography (PET) to examine cerebral blood flow related to verbal episodic retrieval. We observed strong positive correlations between retrieval and blood flow in left medial temporal structures in individual normal human subjects. In addition, multivariate analysis showed that regions in the left medial temporal lobe were dominant components of a pattern of brain regions that distinguished a high-retrieval condition from conditions of lower retrieval. These results suggest that medial temporal activity is related to retrieval success rather than retrieval attempt, possibly by reflecting reactivation of stored patterns.

Brain Mapping↗

PubMed1996

Genetic markers associated with high versus low performance on episodic memory tasks.

Associations were studied between six serum protein polymorphisms (C3, BF, HP, ORM, TF, and GC) and high versus low scoring on episodic memory tasks in an attempt to identify QTL (quantitative trait loci) contributing to the heritability of this quantitative trait. Since a highly significant sex difference (p = .00002) was found with respect to the distribution of high and low scoring, with men showing a poorer performance, associations were studied separately for males and females. In females significant differences (p < .05) between the high and the low groups were found in four of six marker systems (C3, HP, TF, and CG), whereas in males a significant difference was found only in the HP system. Significant differences from population frequencies were also found more frequently in females than in males. The strongest marker associations were found with complement C3 and the acute-phase reactant HP, which suggests that immune response factors may be of importance in preserving episodic memory function. The overall results appear to indicate that episodic memory is a multifactorial and heritable quantitative trait where sex is an important determinant.

Adult↗

PubMed1996

Oral budesonide as maintenance treatment for Crohn's disease: a placebo-controlled, dose-ranging study. Canadian Inflammatory Bowel Disease Study Group.

BACKGROUND & AIMS: Budesonide is a corticosteroid with high topical anti-inflammatory activity and low systemic activity due to rapid hepatic metabolism. The efficacy and safety of an oral controlled-release preparation of budesonide for maintenance of remission was evaluated in patients with ileal or ileocecal Crohn's disease. METHODS: In a double-blind, multicenter trial, 105 patients were randomly assigned to receive placebo or budesonide at doses of 3 or 6 mg daily for 1 year. The primary outcome measure was relapse defined by a Crohn's Disease Activity Index score of > 150 and a minimum increase of 60 points. RESULTS: Patients receiving 6 mg of budesonide had a median time to relapse or discontinuation of therapy of 178 days compared with 124 days in those receiving 3 mg of budesonide and 39 days in those receiving placebo. However, at 1 year, the rate of relapse in the group receiving 6 mg of budesonide was similar to the rates in the 3-mg and placebo groups. Basal plasma cortisol levels and incidence of corticosteroid-associated effects were similar in the three groups. CONCLUSIONS: Oral controlled-release budesonide (6 mg/day) was well tolerated and prolonged remission in Crohn's disease of the ileum and proximal colon, but this effect was not sustained at 1-year follow-up.

Administration, Oral↗

PubMed1996

Age differences in episodic memory, semantic memory, and priming: relationships to demographic, intellectual, and biological factors.

This study examined age differences in episodic memory, semantic memory, and priming using a random sample of 1,000 men and women from 10 age groups (35, 40, 45, . . . 80 years). The main purpose was to determine whether an age effect existed after differences on various demographic, intellectual, and biological factors had been controlled for. The simple correlations of age with episodic and semantic memory performance were found to be significant, whereas no relationship was found between age and levels of priming. After controlling for differences on the background factors, age predicted episodic but not semantic memory performance. It is proposed that the failure to account for the age effect on episodic memory is because it is caused by age-related neuronal changes.

Adult↗

PubMed1996

Adult age differences in source recall: a population-based study.

Age differences in source recall were investigated in a population-based sample of healthy adults aged 35 to 80 years (N = 1000). Participants, who were screened on a variety of demographic, psychological, and biological variables, studied facts about well-known and unknown persons that were presented in four different ways, depicting four different sources of item information. An age-related deterioration of both item and source recall was observed, with source recall being more impaired than item recall. Source error analyses revealed an increase of source amnesia in subjects aged 75-80 years. Individual differences in background variables, age, gender, and word comprehension were related to source recall of well-known items, whereas age and years of formal education were related to source recall of unknown items. Source amnesia was accentuated in the two oldest cohorts and related to word comprehension. The age-related tendency to forget the source even when the fact is retained is suggested to be a specific feature of cognitive aging.

Adult↗

PubMed1996

Memory dysfunction in mild aphasics.

The effect of mild aphasia (n = 9), as a result of subarachnoid haemorrhage (SAH), was evaluated against one matched (sex, age, and education) control group suffering from SAH of unknown origin without aphasia, and against one matched healthy control group. According to aphasia testing (Reinvang & Engvik, 1980), criteria for a classical diagnosis were not met. Therefore, the patients were characterized as mild aphasics: They generally displayed intact audo-verbal comprehension and repetition abilities, and they demonstrated a fluent, spontaneous speech. However, they showed phonemic and semantic paraphasias, with self-corrections; a few patients displayed alexia and agraphia. Memory performance of these three groups was evaluated by a neuropsychological test battery, designed to tap various components of verbal memory function. From the results it was concluded that: (a) Short-term memory is impaired, as regards the phonological loop and the central executive in working memory, whereas maintenance rehearsal is unaffected, given that the demands on phonological coding is minimized, (b) long-term memory is also generally impaired, whereas long-term learning and forgetting by means of subject-performed tasks proceeds within a normal range. Impairments were hypothesized to reflect less efficient central executive functions of working memory, involving generation of less appropriate semantic codes and phonological representations, (c) mildly aphasic patients are not subjectively aware of their own memory deficits, and (d) aphasia classification by means of standard procedures do not sufficiently characterize the nature of a mildy aphasic patient's memory problems.

Adult↗

PubMed1995

Functional brain maps of retrieval mode and recovery of episodic information.

Positron emission tomography (PET) was used to identify brain regions associated with two component processes of episodic retrieval; those related to thinking back in subjective time (retrieval mode) and those related to actual recovery of stored information (ecphory). Healthy young subjects recognized words that had been encoded with respect to meaning or the speaker's voice. Regardless of how the information had been encoded, recognition was associated with increased activation in regions in right prefrontal cortex, left anterior cingulate, and cerebellum. These activations reflect retrieval mode. Recognition following meaning encoding was specifically associated with increased activation in left temporal cortex, and recognition following voice encoding involved regions in right orbital frontal and parahippocampal cortex. These activations reflect ecphory of differentially encoded information.

Adult↗

PubMed1995

The role of enactment in implicit and explicit memory.

Enactment during the encoding of simple imperatives has been found to improve substantially performance on conceptually driven explicit-memory tests. In two experiments the effect of this manipulation on a conceptually driven implicit test (category association) was studied. A conceptually driven explicit test (free recall) was also included. In Experiment one three different study conditions (enactment with real objects, reading, and generation) were considered. In Experiment two there were two study conditions (enactment with imaginary objects and reading). Compared to reading, generation was found to improve the performance on both free recall and category association, whereas enactment affected free recall only. In a final experiment subjects imagined that they performed the tasks, and this manipulation was found to improve the memory performance on both tests. Taken together, this pattern of results is interpreted as suggesting that free recall and category association have a process in common that is sensitive to semantic processing at study (promoted by generation and imagery, but not by enactment), and that free recall involves a retrieval process in addition that is facilitated by a rich encoding environment (provided by enactment).

Adolescent↗

PubMed1995

Recognition failure of categorised words: further evidence of exceptions.

When subjects study a list of B items paired with A items and are tested for recognition of the B items alone, and then for recall of the B items given the A items as cues, B items that can be recalled frequently go unrecognised. The extent of this recognition failure is predictable from a function discovered by Tulving and Wiseman (1975), which relates the probability of recognising the recallable items to the probability of recognising all items. Two kinds of exceptions to this function have been discovered: encoding exceptions and retrieval exceptions. Very few observations of retrieval exceptions exist. Four experiments described in this article provide further evidence that such exceptions occur when the B items are categorised and the A items are the names of the categories. According to a contextual account of the function and exceptions to it, these retrieval exceptions occur because the information provided by the A-item cues can be largely retrieved from the B items in the recognition test; hence, as cues, the A items do not provide much different contextual information to that provided by the B items. By this account, the function is an empirical law; exceptions fall outside the range of this law and define its boundary conditions.

Adolescent↗

PubMed1995

Dissociative effects of elaboration on memory of enacted and non-enacted events: a case of a negative effect.

One experiment compared the effect of elaboration on enacted and non-enacted events. The commands were either presented in a basic form (e.g., "wave your hands") or in an enriched form. The commands were enriched by adding statements to the commands of how to perform the actions (e.g., "wave your hands as a conductor"). Free- and cued-recall data showed elaboration to have a dissociative effect on enacted and non-enacted events. Memory for the non-enacted events benefited from enrichment, whereas simple enacted events were remembered to a higher extent than complex enacted events. Lack of benefit from elaboration on memory of enacted events is suggested to be due to enactment leading to a sufficient degree of item-specific processing, and a negative effect of elaboration is suggested to occur when the way of manipulating item complexity decreases the familiarity of the actions. Familiarity ratings of the items by two independent groups of subjects supported this interpretation.

Adolescent↗

PubMed1994

Oral budesonide for active Crohn's disease. Canadian Inflammatory Bowel Disease Study Group.

BACKGROUND: Corticosteroids are the most efficacious drugs for inducing remission in active Crohn's disease, but their benefits are frequently offset by serious side effects. Budesonide is a corticosteroid with high topical antiinflammatory activity but low systemic activity because of extensive hepatic metabolism. We investigated the efficacy and safety of an oral controlled-ileal-release preparation of budesonide in patients with active Crohn's disease involving the ileum or ileum and proximal colon. METHODS: In a double-blind, multicenter trial, 258 patients were randomly assigned to receive placebo or one of three doses of budesonide--3, 9, or 15 mg daily. The primary outcome measure was clinical remission, as defined by a score of 150 or less on the Crohn's disease activity index. RESULTS: After eight weeks of treatment, remission occurred in 51 percent of the patients in the group receiving 9 mg of budesonide (95 percent confidence interval, 39 to 63 percent), 43 percent of those receiving 15 mg (95 percent confidence interval, 31 to 55 percent), and 33 percent of those receiving 3 mg (95 percent confidence interval, 21 to 44 percent), as compared with 20 percent of those receiving placebo (P < 0.001, P = 0.009, and P = 0.13, respectively). Improvements in the quality of life, as measured by the patients' responses to the inflammatory bowel disease questionnaire, paralleled these remission rates. Location of disease, prior surgical resection, and previous use of corticosteroids did not affect the outcome. A total of 119 patients (46 percent) were withdrawn from the study before the trial ended, 96 because of insufficient therapeutic effects, 13 because of adverse reactions, and 10 because of noncompliance. Budesonide caused a dose-related reduction in basal and corticotropin-stimulated plasma cortisol concentrations but was not associated with clinically important corticosteroid-related symptoms or other toxic effects. CONCLUSIONS: In an eight-week trial, an oral controlled-release preparation of budesonide at an optimal daily dose of 9 mg was well tolerated and effective against active Crohn's disease of the ileum and proximal colon.

Administration, Oral↗

PubMed1994

Recognition failure and integration.

If a recognition test is followed by a cued recall test then the probability of recognition given recall generally follows the Tulving-Wiseman function. Despite this regularity two types of exceptions have been discovered. Both poor integration and cue overlap causes an observed value of recognition given recall that is higher than predicted. The present study explores the first type of exception by proposing and testing an analytical tool, which emanates from confidence ratings given to recall responses, for relating poor integration directly to variations in the degree of deviation from the function. It is demonstrated that very poor integration produces a deviation above the function, whereas a very good integration produces a deviation below the function. The effect of integration (and cue overlap) is explained by means of a conceptualization cue dependency. Support is also given to the notion that an enhanced variability of goodness of encoding contributes to an enhanced dependence between recall and recognition.

Adolescent↗

PubMed1994

Subarachnoid blood on CT and memory dysfunctions in aneurysmal subarachnoid hemorrhage.

Ninety patients with a previous subarachnoid haemorrhage (SAH) were given a set of memory tests comprising immediate free recall of words (indexing long-term memory, LTM, and short-term memory, STM), final free recall of words (indexing LTM), final cued recall of words (indexing LTM), and a digit span test (indexing working memory, WM). Patients with a large amount of blood on CT, carried out within 72 h of the bleed, showed LTM as well as STM dysfunction, whereas patients with a small amount of subarachnoid blood evidenced only STM dysfunction. Patients with the ruptured aneurysm located on the anterior cerebral artery, however, constituted an exception with dysfunction of both LTM and STM together with intact WM, independent of the amount of subarachnoid blood. Also, patients with internal carotid artery or middle cerebral artery aneurysms and large volume SAH displayed LTM dysfunction, but differed concerning STM, the former showing intact STM and the latter showing STM dysfunction. Thus, it appears, that the combined information from factors such as the amount of subarachnoid blood and the location of the ruptured aneurysm is of vital importance for explaining the different patterns of memory dysfunctions after SAH.

Adult↗

PubMed1994

Angiotensin I is converted to angiotensin II by a serine protease in human detrusor smooth muscle.

The aim of the present study was to investigate whether a pathway for conversion of angiotensin I (ANG I) to angiotensin II (ANG II) other than that via angiotensin-converting enzyme (ACE) is present in the smooth muscle of the human detrusor. Isolated detrusor strips from 11 patients were contracted by ANG I (1 microM) in the absence or presence of enalaprilat (10 microM), soybean trypsin inhibitor (STI, 200 micrograms/ml), or both. The metabolic activity in detrusor membranes from four patients was studied separately using Hip-Gly-Gly or ANG I as a substrate, with or without various protease inhibitors. The contractile response to ANG I (1 microM) was depressed by enalaprilat from 66 +/- 22 (mean +/- SD) to 39 +/- 13% of the K+ (124 mM)-induced response (P < 0.01, n = 11), and the combination of enalaprilat and STI resulted in a further reduction in contractile amplitude to 25 +/- 14% (P < 0.01 vs. K+, and P < 0.05 vs. enalaprilat alone) and a significantly slower developing contraction with a time to peak of 3.7 +/- 1.7 vs. 1.1 +/- 0.3 min for ANG I alone (P < 0.01). In detrusor membranes, a low ACE activity, inhibitable by captopril, was demonstrated by the formation of hippuric acid (0.70 nmol.min-1.mg protein-1) from the synthetic ACE substrate, Hip-Gly-Gly. However, the conversion of ANG I (166 nmol.min-1.mg protein-1) to ANG II was not affected by ACE inhibition, while serine protease inhibitors, e.g., STI and chymostatin, completely prevented ANG II formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1994

The effect of retrieval enactment on recall of subject-performed tasks and verbal tasks.

The effect of retrieval enactment on memory for nouns (objects) or verbal phrases describing simple actions (e.g., "lift the box") was addressed in two experiments. In Experiment 1, the type of object involved in the actions was manipulated, with three different types of object being used (body parts, laboratory-related objects, and external objects). In Experiment 2, the integration between the verb-noun pairs was manipulated (well-integrated vs. poorly integrated). Results from both experiments showed that whereas encoding enactment (motor encoding and verbal test) substantially improved the memory performance compared with a verbal condition (verbal encoding and verbal test), retrieval enactment (verbal encoding and motor test) had no major impact on the number of recalled nouns or phrases. Moreover, there was no additional effect of dual enactment (motor encoding and motor test). The overall pattern of the results suggests that there is a fundamental difference between motor processing at encoding and motor processing at retrieval, and the lack of encoding specificity advantage for the motor modality contradicts the view that encoding enactment of verbal commands results in storage of motor representations.

Adolescent↗

PubMed1993

Mathematical constraints and the Tulving-Wiseman law: a rejoinder.

Hintzman (1991; 1992) has claimed that the reason data points approximate the recognition failure function discovered by Tulving and Wiseman (1975) is that they are mathematically constrained to do so, and the reason that a few data points do not approximate the function, but are exceptions to it, is that these data points are less subject to mathematical constraints. He has additionally argued that such exceptions are more likely with low levels of recall and strong underlying sources of positive covariance. We provide empirical evidence relevant to this mathematical model using 301 observations from a database of all relevant experimental conditions published between 1973 and 1992 (Nilsson & Gardiner, 1993). We conclude that mathematical constraints have only a minor influence on the function, not the causal role assigned to them in Hintzman's (1992) model. By our account, both the function and exceptions to it reflect a single psychological principle, the functional effectiveness of contextual cues.

Cues↗

PubMed1993

Attentional demands and recall of verbal and color information in action events.

Two experiments addressed the influence of secondary task performance at encoding on recall of different features of subject-performed tasks (SPTs) involving objects (e.g., turn the wallet). In Experiment 1, memory for verbs and colors of objects was assessed, with object names serving as cues. In Experiment 2, object and color memory were assessed, with verbs serving as cues. Results from both experiments indicated a greater deterioration of memory performance under divided attention for verbal features than for colors. In addition, intention to remember did not affect performance for any feature in either experiment. The overall pattern of outcome is discussed relative to the view that encoding of verbal features of SPTs is more attention-demanding than encoding of physical task features, such as color.

Adult↗