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P Berg

Publications and source records attributed to P Berg.

At least 73 records · Page 4Linked to original sources
PubMed1997

Mapping EEG-potentials on the surface of the brain: a strategy for uncovering cortical sources.

This paper describes a uniform method for calculating the interpolation of scalp EEG potential distribution, the current source density (CSD), the cortical potential distribution (cortical mapping) and the CSD of the cortical potential distribution. It will be shown that interpolation and deblurring methods such as CSD or cortical mapping are not independent of the inverse problem in potential theory. Not only the resolution but also the accuracy of these techniques, especially those of deblurring, depend greatly on the spatial sampling rate (i.e., the number of electrodes). Using examples from simulated and real (64 channels) data it can be shown that the application of more than 100 EEG channels is not only favourable but necessary to guarantee a reasonable accuracy in the calculations of CSD or cortical mapping. Likewise, it can be shown that using more than 250 electrodes does not improve the resolution.

Brain↗
PubMed1997

Identification of motor and sensory brain activities during unilateral finger movement: spatiotemporal source analysis of movement-associated magnetic fields.

We investigated the movement-related cortical fields (MRCFs) recorded by magnetoencephalography (MEG) to identify the motor and sensory brain activities at the instant of the unilateral finger movement using six normal subjects. We focused our investigation on the source analysis of the events tightly linked to movement onset, and we used brain electric source analysis (BESA) to model the sources generating MRCFs during the interval from 200 ms before to 150 ms after the movement onset. Four sources provided satisfactory solutions for MRCF activities in this interval. Sources 1 and 2, which were located in the pre-central regions in the hemisphere contralateral and ipsilateral to the moved finger, respectively, generated the readiness fields (RF), but source 1 was predominant just before movement onset. The motor field (MF), the peak of which was just after movement onset, was mainly generated by source 1. Sources 3 and 4 were located in the post-central regions in the hemisphere contralateral and ipsilateral to the moved finger, respectively. The first motor evoked field (MEF-I), the peak of which was about 80 ms after the movement, was mainly generated by source 3, but with the participation of sources 1, 2 and 4. The results indicated that the activities of both pre -and post-central regions in bilateral hemispheres were related to voluntary movements, although the predominant areas varied over time. This is the first noninvasive study to clarify the complex spatiotemporal activities relating movements in humans using a multi-channel MEG system.

Adult↗
PubMed1997

The postimperative negative variation following ambiguous matching of auditory stimuli.

Previous studies using the delayed-matching-to-sample paradigm with visual stimuli reliably induced a postimperative negative variation (PINV) in both schizophrenic patients and healthy controls. The PINV was found to be: (a) larger in schizophrenic patients than controls; (b) larger under conditions of ambiguous as compared to clear matching conditions; and (c) larger over right-hemispheric, fronto-temporal regions in controls, while a less asymmetrical distribution with a tendency for left-frontal predominance occurred in schizophrenic patients. The present study examined to what extent the development and scalp distribution of the PINV were modality-specific by applying the delayed-matching-to-sample design using auditory stimuli. Furthermore, the neurophysiological state during anticipatory negativity (CNV) and PINV was examined by presenting acoustic probe stimuli (one per trial on 50% of the trials) during baseline, CNV or PINV interval. Event-related slow and probe-evoked potentials were recorded in 13 patients with a chronic schizophrenic disorder (DSM-III-R) and 13 healthy control Ss from 15 electrode sites including midline and two sagittal rows over each hemisphere. Comparable group differences and effects of ambiguity on PINV amplitudes were found for both modalities, visual and auditory. The auditory stimuli produced a fronto-central distribution of the PINV in both groups. The probe-evoked vertexpotential was smaller in patients compared to controls, but exhibited comparable modulation with the largest amplitude during the CNV in both groups. Results suggest modality-non-specific cognitive determinants of the PINV. However, stimulus modality did affect the scalp distribution of the PINV. Probe-evoked responses point to different functional meaning of negativities prior to (CNV) and following (PINV) task-relevant stimuli.

Acoustic Stimulation↗
PubMed1997

Characterization of strand exchange activity of yeast Rad51 protein.

The Saccharomyces cerevisiae RAD51 gene product takes part in genetic recombination and repair of DNA double strand breaks. Rad51, like Escherichia coli RecA, catalyzes strand exchange between homologous circular single-stranded DNA (ssDNA) and linear double-stranded DNA (dsDNA) in the presence of ATP and ssDNA-binding protein. The formation of joint molecules between circular ssDNA and linear dsDNA is initiated at either the 5' or the 3' overhanging end of the complementary strand; joint molecules are formed only if the length of the overhanging end is more than 1 nucleotide. Linear dsDNAs with recessed complementary or blunt ends are not utilized. The polarity of strand exchange depends upon which end is used to initiate the formation of joint molecules. Joint molecules formed via the 5' end are processed by branch migration in the 3'-to-5' direction with respect to ssDNA, and joint molecules formed with a 3' end are processed in the opposite direction.

Adenosine Triphosphate↗
PubMed1997

Differences in malignant melanoma between children and adolescents. A 35-year epidemiological study.

OBJECTIVE: To investigate whether there was an increase of malignant melanoma in children. Malignant melanomas are rare in people younger than 20 years. Although melanoma represents one of the most rapidly increasing neoplasm in adults, it is rarely studied in children. DESIGN: Retrospective study from 1958 through 1992. SETTING: The compulsory Swedish Cancer Registry in Stockholm, Sweden. PATIENTS: We present 287 cases of malignant melanoma in patients younger than 20 years during 35 years in Sweden. INTERVENTION: None. MAIN OUTCOME MEASURES: Data from cancer reports and death certificates in Sweden. RESULTS: The study shows a strong increase in malignant melanomas in puberty after a presumably constant prevalence before the age of 14 years. The melanomas are more common in females (162) than males (125). The distribution was the same as in adults. Of 287 cases, 44 patients died as a result of their tumors (15.3%), with a median survival time of 3 years after diagnosis. CONCLUSIONS: The incidence of malignant melanoma during adolescence has doubled in 10 years. This is not the case for the incidence of melanomas in children younger than 14 years, which seems to be unchanged. It is necessary to be aware of the risk of malignant melanomas in children after puberty.

Adolescent↗
PubMed1996

Saccharomyces cerevisiae mutants defective in plasmid-chromosome recombination.

We have studied the recombinational repair of a double-strand break (DSB) in a plasmid-borne ade2::HO-site by an intact ade2 allele following the induction of a galactose-inducible GAL-HO gene. If GAL-HO expression is not attenuated by the presence of a low level of glucose in the galactose medium, deleterious effects are observed. Our comparison of the effects of several rad mutations on the relative efficiencies of DSB repair at both the ade2::HO-site and at the chromosomal MAT locus indicate that the two processes share common functions. Not surprisingly, most of the recombination-defective mutants found using our assay are alleles of genes in the RAD52 epistasis group. The recombination and repair deficiencies vary among the different mutant groups and also among mutants within a group. In general, there is a correlation between the extents of the recombination and repair defects. Our screen also turned up a novel rfa1 allele with a pronounced deficiency in DSB repair and recombination and a srs2 mutation which causes only a mild defect.

Alleles↗
PubMed1996

Contingent negative variation (CNV) and determinants of the post-imperative negative variation (PINV) in schizophrenic patients and healthy controls.

A slowly rising cortical potential shift with negative polarity following the imperative stimulus of a forewarned reaction time task, the 'post-imperative negative variation' (PINV), is regularly observed in schizophrenic patients but not in controls. The topography of the PINV suggests that it may originate in frontal cortical regions. We used a task designed to test two putative prefrontal cortical functions: working memory and processing of ambiguity. Nineteen patients with a chronic schizophrenic disorder and 19 control subjects matched for age, sex, and education participated in two experimental sessions. The EEG was recorded from frontal, central, temporal, and parietal leads over both hemispheres using a DC amplifier. PINV amplitudes were generally larger in patients than in controls. If the result of comparing physical features of the two successively presented stimuli (warning and imperative stimulus) was ambiguous rather than clear, an augmentation of the PINV amplitudes was seen in both groups. If this comparison required high rather than low involvement of working memory functions, PINV amplitudes were augmented in schizophrenic patients only. Scalp distribution of the PINV indicated a left-hemisphere fronto-central PINV maximum in patients, and a right-hemisphere predominance in controls, which was larger following ambiguous stimulus comparisons. These results suggest that ambiguity during the comparison of physical features of successively presented stimuli may be a general factor of the PINV in schizophrenic patients and healthy controls. Augmented involvement of working memory functions, presumably subserved by the prefrontal cortex, specifically affected the fronto-centrally predominant PINV in schizophrenic patients. This result is compatible with the hypothesis of prefrontal cortical dysfunctions in schizophrenia.

Adult↗
PubMed1996

The HIV nef protein associates with protein kinase C theta.

Expression of the human immunodeficiency virus (HIV) Nef protein has been linked to both decreased cell surface expression of CD4 and an impairment of signal transduction. The recently reported association of Nef with an unidentified serine kinase provides a clue as to how Nef might exert its effects. Considering the key role of protein kinase C (PKC) in T cell activation, we investigated the possibility that Nef interacts with PKC. Our results, using two approaches for detecting interactions between Nef and PKC isozymes in Jurkat cells, show that Nef interacts preferentially with thetaPKC. The interaction of Nef and thetaPKC is independent of calcium, enhanced by phospholipid activators of PKC and not affected by a PKC pseudosubstrate peptide. Phorbol 12-myristate 13-acetate and phytohemagglutinin stimulation of Jurkat cells expressing Nef fails to produce the usual translocation of thetaPKC from the cytosol to the particulate fraction; translocation of betaPKC and epsilonPKC was unaffected. Indeed, there appears to be a net loss of thetaPKC in Nef-expressing cells following stimulation. The loss of thetaPKC, which may be a result of inhibition of its binding to RACKs due to Nef binding, could contribute to the various impairments of T cell function associated with HIV infection and Nef expression.

Biological Transport↗
PubMed1996

Modulation of auditory responses during oddball tasks.

The modulation of auditory input processing in relation to slow event-related potentials was examined in two studies. A steady-state response (SSR) was evoked by a stimulus train delivered at 40 Hz. Slow potentials were elicited by an oddball task implemented as changes in the pitch of single stimuli within this 40-Hz train. In study 1, subjects responded to rare targets by means of a button press. In study 2, subjects responded to targets by means of a motor response in one session and by silent counting in another session. In both studies, the oddball task elicited a P300 to targets. SSR amplitude was reduced 100 ms following each stimulus, while a second amplitude reduction around 350-400 ms was discovered following targets, in particular, following a button press. Parallel to SSR amplitude reductions, the latencies between stimulus and subsequent SSR peak were reduced. Results indicate that processing of oddball stimuli and motor responding alters 'automatic' auditory processing at the level of the primary auditory cortex; the second SSR amplitude reduction which develops in parallel to P300 might support the hypothesis that slow positive potentials indicate widespread (disfacilitation) inhibition of cortical neural excitability.

Adult↗
PubMed1996

The impact of performance uncertainty on the postimperative negative variation.

In a delayed matching-to-sample task, the impact of clear or ambiguous go versus clear no-go signals on the post-imperative negative variation (PINV) was examined in 11 patients with a chronic schizophrenic disorder (DSM-III-R) and in a control group of 13 healthy subjects matched to the patient sample by age, sex, and education. Size and spatial position of a visual S2 had to be matched to one of two visual patterns in the S1 presented 4 s earlier. In 96 trials, the S2 was identical in size with one of the two patterns of S1 (clear matching). These trials varied pseudorandomly, with 60 trials in which the S2 was of intermediate size. On a randomly interspersed additional 48 trials, an S2 differing in color and shape signaled no-go. The electroencephalogram was recorded from Fz, Cz, Pz, F3, F4, C3, C4, P3, and P4. Although groups did not differ in contingent negative variation amplitude, the PINV was generally more pronounced in patients than in controls. In both groups, ambiguity of the to-be-matched S2 produced larger PINV amplitudes; the no-go signal elicited only a small PINV. Differential effects of ambiguity and no-go on PINV amplitude and its scalp distribution suggest that "performance" and "action" uncertainty contribute to PINV generation and that thresholds for both effects are reduced in schizophrenics.

Acoustic Stimulation↗
PubMed1995

Complex formation in yeast double-strand break repair: participation of Rad51, Rad52, Rad55, and Rad57 proteins.

The repair of DNA double-strand breaks in Saccharomyces cerevisiae requires genes of the RAD52 epistasis group, of which RAD55 and RAD57 are members. Here, we show that the x-ray sensitivity of rad55 and rad57 mutant strains is suppressible by overexpression of RAD51 or RAD52. Virtually complete suppression is provided by the simultaneous overexpression of RAD51 and RAD52. This suppression occurs at 23 degrees C, where these mutants are more sensitive to x-rays, as well as at 30 degrees C and 36 degrees C. In addition, a recombination defect of rad55 and rad57 mutants is similarly suppressed. Direct in vivo interactions between the Rad51 and Rad55 proteins, and between Rad55 and Rad57, have also been identified by using the two-hybrid system. These results indicate that these four proteins constitute part of a complex, a "recombinosome," to effect the recombinational repair of double-strand breaks.

Adenosine Triphosphatases↗
PubMed1995

Maintenance of an extrachromosomal plasmid vector in mouse embryonic stem cells.

We have constructed and characterized a polyoma virus-based plasmid that is maintained as an autonomously replicating extrachromosomal element (episome) in mouse embryonic stem (ES) cells. Plasmid pMGD20neo contains the polyoma origin of replication harboring a mutated enhancer (PyF101), a modified polyoma early region that encodes the large tumor (T) antigen only, and a gene that confers resistance to G418 (neo). After transfection, the plasmid replicates in ES cells and is maintained as an extrachromosomal element in 15% of G418-resistant clones. Integration of the plasmid DNA is undetectable for at least 28 cell generations. In one clone, the transfected DNA persists unaltered as an episome at 10-30 copies per cell for at least 74 cell generations in the presence of G418. Cells that maintain the autonomously replicating plasmid can efficiently replicate and maintain a second plasmid that carries the polyoma origin of replication. Independent vector-containing ES cell lines showed no significant alteration of the karyotype, and two cell lines yielded several chimeric animals when introduced into blastocysts, suggesting that the presence of an episomal element and expression of polyoma large T do not eliminate the ES cells' ability to populate an embryo. This system offers an efficient means for manipulating and analyzing various aspects of gene expression in ES cells.

Animals↗
PubMed1995

Wrong move.

Explore the source record for details and available documents.

Academies and Institutes↗
PubMed1995

[Follow-up of cutaneous paradoxical vascular reactions in atopic patients during and after eczema manifestations].

In atopic eczema patients the well-known abnormal cutaneous reactivity of the blood vessels (white dermographism, delayed blanch after acetylcholine, paradoxical blanching after nicotinic acid application and diminished erythema after histamine injection) were observed during acute eczematous episodes and later in an exzema-free state in comparison with controls. In this follow-up study the use of different stimuli allowed us to demonstrate abnormal cutaneous vascular reactions in the patients depending on the severity of their atopic eczema. Severely affected patients showed persistence of the paradoxical vascular reactions even in an eczema-free cutaneous state.

Acetylcholine↗
PubMed1995

A novel allele of Saccharomyces cerevisiae RFA1 that is deficient in recombination and repair and suppressible by RAD52.

To understand the mechanisms involved in homologous recombination, we have performed a search for Saccharomyces cerevisiae mutants unable to carry out plasmid-to-chromosome gene conversion. For this purpose, we have developed a colony color assay in which recombination is induced by the controlled delivery of double-strand breaks (DSBs). Recombination occurs between a chromosomal mutant ade2 allele and a second plasmid-borne ade2 allele where DSBs are introduced via the site-specific HO endonuclease. Besides isolating a number of new alleles in known rad genes, we identified a novel allele of the RFA1 gene, rfa1-44, which encodes the large subunit of the heterotrimeric yeast single-stranded DNA-binding protein RPA. Characterization of rfa1-44 revealed that it is, like members of the RAD52 epistasis group, sensitive to X rays, high doses of UV, and HO-induced DSBs. In addition, rfa1-44 shows a reduced ability to undergo sporulation and HO-induced gene conversion. The mutation was mapped to a single-base substitution resulting in an aspartate at amino acid residue 77 instead of glycine. Moreover, all radiation sensitivities and repair defects of rfa1-44 are suppressed by RAD52 in a dose-dependent manner, and one RAD52 mutant allele, rad52-34, displays nonallelic noncomplementation when crossed with rfa1-44. Presented is a model accounting for this genetic interaction in which Rfa1, in a complex with Rad52, serves to assemble other proteins of the recombination-repair machinery at the site of DSBs and other kinds of DNA damage. We believe that our findings and those of J. Smith and R. Rothstein (Mol. Cell. Biol. 15:1632-1641, 1995) are the first in vivo demonstrations of the involvement of a eukaryotic single-stranded binding protein in recombination and repair processes.

Alleles↗