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Biomedical subjects

Mikael Johansson

Publications and source records attributed to Mikael Johansson.

At least 19 recordsLinked to original sources
PubMed2006

When remembering causes forgetting: electrophysiological correlates of retrieval-induced forgetting.

People tend to forget information that is related to memories they are actively trying to retrieve. On the basis of results from behavioral studies, such retrieval-induced forgetting is held to result from inhibitory control processes that are recruited to attenuate interference caused by competing memory traces. Employing electrophysiological measures of brain activity, the present study examined the neural correlates of these inhibitory processes as they operate. The results demonstrate that sustained prefrontal event-related potentials were 1) related to whether or not selective memory retrieval was required during reprocessing of previously studied words and 2) predictive of individual differences in the amount of forgetting observed in an ensuing recall test. The present findings give support to an inhibitory control account of retrieval-induced forgetting and are in accord with the view that prefrontal regions play an important role in the selection and maintenance of relevant memory representations at the expense of those currently irrelevant.

Adult↗
PubMed2006

Efficient and selective sulfoxidation by hydrogen peroxide, using a recyclable flavin--[BMIm]PF6 catalytic system.

A new flavin catalyst 2 immobilized in an ionic liquid ([BMIm]PF6) was used for the highly selective oxidation of sulfides to sulfoxides by hydrogen peroxide. The sulfoxides were obtained in good to high yields and high selectivity without any detectable overoxidation to sulfone. The catalyst in the ionic liquid was recycled up to seven times without loss of activity or selectivity.

Catalysis↗
PubMed2006

Conceptual and perceptual memory: retrieval orientations reflected in event-related potentials.

In memory retrieval, search can be guided by mental sets towards different subsets of the available evidence. Such retrieval orientations have been suggested to leave an imprint on event-related potentials (ERPs). The present study aimed at characterizing orientations towards perceptual and conceptual evidence in a recognition task, where pictures and words were studied. In the recognition test, items were presented in either the same format as at study or in the opposite format. A between-subjects manipulation modified the task, instructing an Exclusion group to endorse only items that preserved their format from study, and an Inclusion group to endorse both formats of a studied item. It was hypothesized that exclusion instructions would instill a perceptual and inclusion instructions a conceptual orientation. As a corollary, instructions were expected to dissociate the high end from the low end of the picture-word mirror effect. This expectation was confirmed in a behavioural experiment. In an ERP experiment, retrieval orientations were examined in their effects on correct rejections of new pictures and words. Confirming earlier findings [Hornberger, M., Morcom, A. M., & Rugg, M. D. (2004). Neural correlates of retrieval orientation: effects of study-test similarity. Journal of Cognitive Neuroscience, 16(7), 1196-1210], a perceptual orientation was accompanied by more positive-going amplitudes over widespread areas. The difference was larger for pictures than for words, supporting behavioural evidence that new pictures are more easily rejected on perceptual grounds than are new words. The Exclusion group showed no ERP evidence of cross-format old-new effects, despite reaction times indicative of involuntary conceptual recognition. The results indicate that perceptual and conceptual retrieval orientations imprint distinct signatures on ERPs. They further suggest that the examined old-new effects in ERPs are mainly linked to voluntary aspects of memory, even in a task where involuntary memory exerts effects on reaction times.

Adult↗
PubMed2006

Cross-platform classification in microarray-based leukemia diagnostics.

Gene expression profiling is a powerful technique for classifying hematologic malignancies. Its clinical use is, however, currently hindered by the need to collect large sets of expression profiles at each diagnostic facility. To overcome this limitation, we introduced cross-platform classification, allowing classifier construction using pre-existing microarray datasets. As proof-of-principle, we performed cross-platform classification of acute myeloid leukemia and childhood acute lymphoblastic leukemia using expression data from four different facilities. We show that cross-platform classification of these disorders is achievable, and, strikingly, that the diagnostic accuracy can be retained. We conclude that cross-platform classification constitutes an effective and convenient way to implement microarray diagnostics.

Humans↗
PubMed2005

Addition of palladium and platinum tri-tert-butylphosphine groups to Re-Sn and Re-Ge bonds.

The reaction of Re2(CO)8[mu-eta2-C(H)=C(H)Bu(n)](mu-H) with Ph3SnH at 68 degrees C yielded the new compound Re2(CO)8(mu-SnPh2)2 (10) which contains two SnPh2 ligands bridging two Re(CO)(4) groups, joined by an unusually long Re-Re bond. Fenske-Hall molecular orbital calculations indicate that the bonding in the Re2Sn2 cluster is dominated by strong Re-Sn interactions and that the Re-Re interactions are weak. The 119Sn Mössbauer spectrum of 10 exhibits a doublet with an isomer shift (IS) of 1.674(12) mm s(-1) and a quadrupole splitting (QS) of 2.080(12) mm s(-1) at 90 K,characteristic of Sn(IV) in a SnA2B2 environment. The IS is temperature dependent, -1.99(14) x 10(-4) mm s(-1) K(-1); the QS is temperature independent. The temperature-dependent properties are consistent with the known Gol'danskii-Kariagin effect. The germanium compound Re2(CO)8(mu-GePh2)2 (11) was obtained from the reaction of Re2(CO)8[mu-eta2-C(H)=C(H)Bu(n)](mu-H) with Ph3GeH. Compound 11 has a structure similar to that of 10. The reaction of 10 with Pd(PBu(t)3)2 at 25 degrees C yielded the bis-Pd(PBu(t)3) adduct, Re2(CO)8(mu-SnPh2)2[Pd(PBu(t)3)]2 (12); it has two Pd(PBu(t)3) groups bridging two of the four Re-Sn bonds in 10. Fenske-Hall molecular orbital calculations show that the Pd(PBu(t)3) groups form three-center two-electron bonds with the neighboring rhenium and tin atoms. The mono- and bis-Pt(PBu(t)3) adducts, Re2(CO)8(mu-SnPh2(2)[Pt(PBu(t)3)] (13) and Re2(CO)8(mu-SnPh2)2[Pt(PBu(t)3)]2 (14), were formed when 10 was treated with Pt(PBu(t)3)2. A mono adduct of 11, Re2(CO)8(mu-GePh2)2[Pt(PBu(t)3)] (15), was obtained similarly from the reaction of 11 with Pt(PBu(t)3)2.

Journal Article↗
PubMed2005

New rhenium-tin cluster adds palladium phosphine groups across Re-Sn bonds.

The new rhenium-tin complex Re2(CO)8(mu-SnPh2)2, 1 was obtained in 52% yield from the reaction of Re2(CO)8(mu-H)[mu-C(H)C(H)Bu] with Ph3SnH. Compound 1 contains two SnPh2 groups bridging a long Re-Re single bond, Re-Re = 3.1971(4) A [3.1902(4) A], Re-Sn = 2.7429(4) A [2.7445(4) A], and 2.7675(4) [2.7682(5) A]. A bis-Pd(PBut3) adduct of 1, Pd2Re2(CO)8(mu-SnPh2)2(PBut3)2, 2 was obtained from the reaction of 1 with Pd(PBut3)2. Compound 2 contains Pd(PBut3) groups bridging two of its four Re-Sn bonds. The Re-Re bond and the unbridged Re-Sn bonds in 2 are significantly longer than those in 1, 3.245(1) A and 2.8167(14) A, respectively. Fenske-Hall molecular orbital calculations on 1 and 2 have been performed to explain the metal-metal bonding in these unusual mixed-metal polynuclear metal complexes.

Journal Article↗
PubMed2005

Age-related differences in familiarity and recollection: ERP evidence from a recognition memory study in children and young adults.

Using event-related potentials (ERPs), we examined the relative contributions of familiarity and recollection to recognition memory for items and their study contexts in school-aged children and adults. Whereas adults were able to selectively accept target items and to reject familiar nontarget items in an exclusion task, this discrimination was more difficult for children, as was evident in the high false alarm rates to nontargets even when item memory was controlled for. The analysis of the adults' ERPs revealed more flexible and task-appropriate retrieval mechanisms, as was evident in the correlates of familiarity, recollection, and nontarget retrieval, as well as in postretrieval evaluation. In contrast, children's ERPs revealed a parietal old/new effect for targets taken as a putative correlate of recollection. These findings suggest that children rely predominantly on recollection during recognition judgments, even in the absence of efficient memory control processes. The latter processes enable adults to monitor and verify the retrieved information and to control nontarget retrieval in the service of adequate source memory performance.

Adolescent↗
PubMed2004

Impact of choice of therapeutic strategy for acute cholecystitis on patient's health-related quality of life. Results of a randomized, controlled clinical trial.

BACKGROUND: The aim of this prospective, randomized study was to determine if health related quality of life is affected by the choice of surgical strategy in the management of acute cholecystitis. MATERIAL AND METHODS: After diagnostic workup, patients were randomized to one of two groups: (1) early laparoscopic cholecystectomy (i.e. within 7 days after onset of symptoms) or (2) initial conservative treatment followed by delayed laparoscopic cholecystectomy. Seventy-four patients entered the early operation group and 71 patients were assigned to the delayed operation strategy. Assessments of quality of life were made at 1, 3 and 6 months after surgery, and in the delayed operation group also one month after the initial conservative treatment. RESULTS: The gastrointestinal symptom scores were significantly better in three dimensions (diarrhea, indigestion, abdominal pain) one month after surgery for the acute operation group (p < 0.01). Three and 6 months after the operation we were unable to detect any significant differences between the groups. The patients in the delayed operation group did not appear to suffer from more symptoms in the period of time waiting for their elective operation. Psychological general well-being showed no major differences between the groups. CONCLUSION: Cholecystectomy in the acute phase of acute cholecystitis offers a significant reduction of gastrointestinal symptoms during the first postoperative month and to that associated improved quality of life in this group of patients.

Acute Disease↗
PubMed2004

The direct catalytic asymmetric alpha-aminooxylation reaction: development of stereoselective routes to 1,2-diols and 1,2-amino alcohols and density functional calculations.

Proline-catalyzed direct asymmetric alpha-aminooxylation of ketones and aldehydes is described. The proline-catalyzed reactions between unmodified ketones or aldehydes and nitrosobenzene proceeded with excellent diastereo- and enantioselectivities. In all cases tested, the corresponding products were isolated with >95 % ees. Methyl alkyl ketones were regiospecifically oxidized at the methylene carbon atom to afford enantiomerically pure alpha-aminooxylated ketones. In addition, cyclic ketones could be alpha,alpha'-dioxidized with remarkably high selectivity, furnishing the corresponding diaminooxylated ketones with >99 % ees. The reaction mechanism of the proline-catalyzed direct asymmetric alpha-aminooxylation was investigated, and we performed density functional theory (DFT) calculations in order to investigate the nature of the plausible transition states further. We also screened other organocatalysts for the asymmetric alpha-oxidation reaction and found that several proline derivatives were also able to catalyze the transformation with excellent enantioselectivities. Moreover, stereoselective routes for the synthesis of monoprotected vicinal diols and hydroxyketones were found. In addition, short routes for the direct preparation of enantiomerically pure epoxides and 1,2-amino alcohols are presented. The direct catalytic alpha-oxidation is also a novel route for the stereoselective preparation of beta-adrenoreceptor antagonists.

Alcohols↗
PubMed2004

Anaerobicity prepares Saccharomyces cerevisiae cells for faster adaptation to osmotic shock.

Yeast cells adapt to hyperosmotic shock by accumulating glycerol and altering expression of hundreds of genes. This transcriptional response of Saccharomyces cerevisiae to osmotic shock encompasses genes whose products are implicated in protection from oxidative damage. We addressed the question of whether osmotic shock caused oxidative stress. Osmotic shock did not result in the generation of detectable levels of reactive oxygen species (ROS). To preclude any generation of ROS, osmotic shock treatments were performed in anaerobic cultures. Global gene expression response profiles were compared by employing a novel two-dimensional cluster analysis. The transcriptional profiles following osmotic shock under anaerobic and aerobic conditions were qualitatively very similar. In particular, it appeared that expression of the oxidative stress genes was stimulated upon osmotic shock even if there was no apparent need for their function. Interestingly, cells adapted to osmotic shock much more rapidly under anaerobiosis, and the signaling as well as the transcriptional response was clearly attenuated under these conditions. This more rapid adaptation is due to an enhanced glycerol production capacity in anaerobic cells, which is caused by the need for glycerol production in redox balancing. Artificially enhanced glycerol production led to an attenuated response even under aerobic conditions. These observations demonstrate the crucial role of glycerol accumulation and turgor recovery in determining the period of osmotic shock-induced signaling and the profile of cellular adaptation to osmotic shock.

Anaerobiosis↗
PubMed2004

Recognition memory for emotional and neutral faces: an event-related potential study.

This study examined emotional influences on the hypothesized event-related potential (ERP) correlates of familiarity and recollection (Experiment 1) and the states of awareness (Experiment 2) accompanying recognition memory for faces differing in facial affect. Participants made gender judgments to positive, negative, and neutral faces at study and were in the test phase instructed to discriminate between studied and nonstudied faces. Whereas old-new discrimination was unaffected by facial expression, negative faces were recollected to a greater extent than both positive and neutral faces as reflected in the parietal ERP old-new effect and in the proportion of remember judgments. Moreover, emotion-specific modulations were observed in frontally recorded ERPs elicited by correctly rejected new faces that concurred with a more liberal response criterion for emotional as compared to neutral faces. Taken together, the results are consistent with the view that processes promoting recollection are facilitated for negative events and that emotion may affect recognition performance by influencing criterion setting mediated by the prefrontal cortex.

Adult↗
PubMed2003

Isolating the retrieval of imagined pictures during episodic memory: activation of the left precuneus and left prefrontal cortex.

The posterior medial parietal cortex and the left prefrontal cortex have both been implicated in the recollection of past episodes. In order to clarify their functional significance, we performed this functional magnetic resonance imaging study, which employed event-related source memory and item recognition retrieval of words paired with corresponding imagined or viewed pictures. Our results suggest that episodic source memory is related to a functional network including the posterior precuneus and the left lateral prefrontal cortex. This network is activated during explicit retrieval of imagined pictures and results from the retrieval of item-context associations. This suggests that previously imagined pictures provide a context with which encoded words can be more strongly associated.

Adult↗
PubMed2003

The late posterior negativity in ERP studies of episodic memory: action monitoring and retrieval of attribute conjunctions.

The focus of the present paper is a late posterior negative slow wave (LPN) that has frequently been reported in event-related potential (ERP) studies of memory. An overview of these studies suggests that two broad classes of experimental conditions tend to elicit this component: (a) item recognition tasks associated with enhanced action monitoring demands arising from response conflict and (b) memory tasks that require the binding of items with contextual information specifying the study episode. A combined stimulus- and response-locked analysis of data from two studies mapping onto these classes allowed a temporal and functional decomposition of the LPN. While only the LPN observed in the item recognition task could be attributed to the involvement of a posteriorly distributed response-locked error-related negativity (or error negativity; ERN/Ne) occurring immediately after the response, the source-memory task was associated with a stimulus-locked negative slow wave occurring prior and during response execution that was evident when data were matched for response latencies. We argue that the presence of the former reflects action monitoring due to high levels of response conflict, whereas the latter reflects retrieval processes that may act to reconstruct the prior study episode when task-relevant attribute conjunctions are not readily recovered or need continued evaluation.

Association Learning↗
PubMed2003

Are covert verbal responses mediating false implicit memory?

In the DRM paradigm, illusory memories of a nonpresented word can be induced by the presentation of strong associates to this word. In two experiments, we explored previous findings of false implicit memory of the nonpresented words (McDermott, 1997; McKone & Murphy, 2000). Experiment 1 extended the finding of false priming to the anagram task. Furthermore, participants attributed this "false" influence on performance to the difficulty of the anagrams and judged them as easier to solve for other students. In Experiment 2, articulatory suppression during the study of the associates resulted in nonsignificant levels of false priming, whereas the normal priming effect was in the same range as that observed in Experiment 1. The study replicates and extends findings of false implicit memory to the anagram task and suggests that future studies should examine the role of covert verbal responses in producing false implicit memory.

Adult↗
PubMed2002

Memory for perceived and imagined pictures--an event-related potential study.

Event-related potentials (ERPs) and behavioural measures were used to investigate recognition memory and source-monitoring judgements about previously perceived and imagined pictures. At study, word labels of common objects were presented. Half of these were followed by a corresponding picture and the other half by an empty frame, signalling to the participants to mentally visualise an image. At test, participants in a source-monitoring task made a three-way discrimination between new words and words corresponding to previously perceived and imagined pictures. Participants in an old/new-recognition task indicated whether test words were previously presented or not. In both tasks, correctly identified old items elicited more positive-going ERPs than correctly judged new items. This widely distributed old/new effect was found to have an earlier onset and to be of a greater magnitude for imagined than for perceived items. Task (source versus item-memory) affected the old/new effects over prefrontal areas and the reaction times to remembered old items. The present findings are consistent with the view that a greater amount, or a different type, of information is necessary for accurate source-memory judgements than for correct recognition, and moreover, that different types of source-specifying information revive at different rates. In addition, the results add weight to the view that the late widespread ERP-old/new effect is sensitive to the quality or the amount of information retrieved from memory.

Adult↗
PubMed2002

Spatial expression of VEGF-A in human glioma.

Astrocytoma, especially of high grade, is dependent on neovascularization for its growth and progression. The expression of vascular endothelial growth factor (VEGF-A), an important angiogenesis factor, has been demonstrated in perinecrotic cells in glioblastoma. In order to achieve more knowledge regarding the process of astrocytoma angiogenesis and growth we have investigated the expression of VEGF-A immunohistochemically in different areas of tumors. In 21 patients with astrocytomas of varying grade serial stereotactic biopsies were performed. Biopsies were taken from brain adjacent to tumor (BAT), tumor periphery, and tumor center. In the BAT region of high-grade astrocytomas, we found a frequent expression of VEGF-A in tumor cells and less frequent in blood vessels. In the periphery, there was an expression mainly in tumor cells while in the center of grade IV tumors VEGF-A was also frequently expressed in cells adjacent to necrosis. VEGF-A in astrocytoma grade II was demonstrated in viable tumor cells preferentially in the periphery but also in peripheral vessels and in centrally located tumor cells. The findings indicate that, in addition to hypoxia in necrotic areas there may be other factors that stimulate the expression of VEGF-A. It is suggested that VEGF-A may be a prerequisite for the aggressive and infiltrative growth of astrocytomas. Therefore, when operating high-grade astrocytomas it may be of importance to resect this aggressive peripheral part of the tumor and also to take this finding into account when planning radiotherapy.

Brain Neoplasms↗
PubMed2002

Inducing and reducing false memories: a Swedish version of the Deese-Roediger-McDermott paradigm.

Participants tend to falsely remember a nonpresented critical word after having studied a list of the word's primary associates. We present here a Swedish version of the Deese-Roediger-McDermott paradigm, which provides a tractable method of experimentally inducing and investigating such illusory memories. In Experiment 1 it was demonstrated that the constructed stimulus material induced highly reliable false-recall and false-recognition effects, and, moreover, that veridical and false memories were associated with a similar phenomenological experience of remembering. The results from Experiment 2 indicated that the susceptibility to false recognition can be substantially reduced when participants are explicitly required to monitor the sources of their memories. These findings are consistent with predictions derived from the source-monitoring framework.

Adult↗