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R Cohen

Publications and source records attributed to R Cohen.

At least 91 records · Page 5Linked to original sources
PubMed2000

Event-related potentials in a working-memory task in schizophrenics and controls.

Event-related potentials (ERPs) were recorded from 65 channels in 12 schizophrenics and 12 age- and sex-matched controls during a delayed matching-to-sample design with variation of working-memory (WM) challenge: following a 500 ms visual sample stimulus (called S1, two diamonds varying in size, rotation angle and vertical position), the same pattern was either presented throughout a 6s retention interval (no challenge) or a diamond pattern differing from the first one in at least one dimension was presented during this interval (WM challenge). The 500 ms matching stimulus (called S2) comprised one diamond, which had to be matched for identity to either the left or the right diamond of the sample stimulus. The topographical distribution of ERPs during an interval of 500 ms after S1-onset, 5s of the retention interval, a 500 ms-interval preceding the S2, and a 1s postimperative interval were evaluated. No WM challenge during the retention interval induced a right-posterior accentuation of the slow negative potentials in either group, while WM challenge evoked a tendency for left-hemispheric negativity in controls, but not in patients. Patients exhibited a postimperative negative variation (PINV) with left-anterior focus irrespective of the preceding WM challenge, while in controls, the left-anterior PINV was found only following WM challenge. In schizophrenic patients the lack of a left-anterior accentuation of negative ERPs under WM challenge might be related to WM dysfunction, and the condition-independent PINV might be considered either the consequence of this dysfunction or indication of processes related more to the diagnoses than to WM-challenge and -dysfunction.

Adult↗
PubMed2000

Interhemispheric cooperation during word processing: evidence for callosal transfer dysfunction in schizophrenic patients.

Functional lateralization and interhemispheric interaction during word processing were investigated in schizophrenic patients (n=12) and matched healthy controls (n=18). Words and phonologically regular pseudowords were presented tachistoscopically either in the left or right visual field (unilateral conditions), or simultaneously in both visual hemifields (bilateral condition). Consistent with earlier findings, healthy controls showed a right visual field advantage (RVFA), indicating left-hemispheric dominance for language. The patients showed a RVFA similar to that of controls, consistent with normal left-hemispheric language dominance. Importantly, controls performed much better on words presented in the bilateral condition, when two copies of the same word appeared twice, compared to stimulation in only one of the visual hemifields. This bilateral advantage, which has been interpreted as evidence for cooperation between the hemispheres, was absent in schizophrenics. These data show that schizophrenic patients can exhibit similar lateralization patterns as healthy controls. Their specific functional deficit may be a lack of cooperation between the hemispheres.

Adult↗
PubMed2000

Resilience of the internet to random breakdowns

A common property of many large networks, including the Internet, is that the connectivity of the various nodes follows a scale-free power-law distribution, P(k) = ck(-alpha). We study the stability of such networks with respect to crashes, such as random removal of sites. Our approach, based on percolation theory, leads to a general condition for the critical fraction of nodes, p(c), that needs to be removed before the network disintegrates. We show analytically and numerically that for alpha</=3 the transition never takes place, unless the network is finite. In the special case of the physical structure of the Internet (alpha approximately 2.5), we find that it is impressively robust, with p(c)>0.99.

Journal Article↗
PubMed2000

Impact of antimicrobial therapy on nasopharyngeal carriage of Streptococcus pneumoniae, Haemophilus influenzae, and Branhamella catarrhalis in children with respiratory tract infections.

We conducted a multicenter prospective study to document changes in nasopharyngeal carriage of Streptococcus pneumoniae, Haemophilus influenzae, and Branhamella catarrhalis during antibiotic therapy. A cohort of 629 children with respiratory tract infections underwent nasopharyngeal sampling before and after antibiotic treatment. Susceptibility testing, serotyping, arbitrarily primed polymerase chain reaction, and pulsed-field gel electrophoresis were used to compare pretreatment and posttreatment strains of S. pneumoniae. A significant decrease in carriage of all 3 species (especially S. pneumoniae and B. catarrhalis) was recorded. The increase in the proportion of penicillin-resistant pneumococci (PRP; 66% vs. 44%) was due to the decreased carriage of penicillin-susceptible pneumococci (71 of 629 vs. 176 of 629). The risk of PRP carriage in a given child did not increase. None of the children was found to harbor genetically related strains with increased minimum inhibitory concentrations. Given the multiple resistance of PRP, beta-lactam antibiotic therapy also increased the incidence of macrolide-resistant strains, whereas macrolides selected both macrolide- and penicillin-resistant strains.

Anti-Bacterial Agents↗
PubMed2000

The incidence of lymphoma in first-degree relatives of patients with Hodgkin disease and non-Hodgkin lymphoma: results and limitations of a registry-linked study.

BACKGROUND: The precise incidence of familial Hodgkin disease (HD) and non-Hodgkin lymphoma (NHL) in first-degree relatives is unknown. Through record linkage using two population-based sources, the authors estimated the risk of HD and NHL in family members of lymphoma probands. METHODS: The authors identified 8,037 first-degree relatives of 2,606 lymphoma cases (28.5% HD, 71.5% NHL) treated between 1970 and 1993 in 3 hospitals in Israel via the family file of the Population Registry. The authors linked this file with the Israel Cancer Registry, then calculated the standardized incidence ratio (SIR) by dividing the observed number of cases with the expected, adjusting for age, gender, calendar year, and continent of origin. RESULTS: The family file yielded incomplete ascertainment of relatives (for 771 probands, no relatives were identified). Twenty cases of lymphoma--6 HD and 14 NHL--were identified among relatives of lymphoma patients. The SIR for HD was 1.15 (95% confidence interval [CI]: 0.42-2.51) and for NHL 1.71 (95% CI: 0.93-2.87), considering the entire population of first-degree relatives. SIRs among siblings of lymphoma probands were 3.12 (95% CI: 1.01-7.29) for HD, 2.16 (95% CI: 0.45-6.31) for NHL, and 2.68 (95% CI: 1.15-5.27) for all lymphomas. There were 4 HD/HD, 1 NHL/NHL, and 3 NHL/HD sibling pairs. For HD/HD and NHL/NHL sibling pairs, the interval between lymphoma occurrence in proband and sibling was 1-4 years, whereas for HD/NHL pairs this ranged from 16 to 21 years. CONCLUSIONS: The risk of lymphoma among siblings of lymphoma probands was over 2.5-fold that of the general population and lower among other family members. The temporal proximity of HD/HD and NHL/NHL sibling pairs argues for environmental as well as genetic etiology. This method was hampered by incomplete data.

Adolescent↗
PubMed2000

Parathyroid xenotransplantation without immunosuppression in experimental hypoparathyroidism: long-term in vivo function following microencapsulation with a clinically suitable alginate.

Permanent hypoparathyroidism is one of the most difficult of all endocrine disorders to treat medically. Because this deficiency syndrome rarely is a life-threatening condition, systemic immunosuppression for recipients of transgenic transplants is not justified. An alternative would be protecting the tissue to be transplanted from the immunologic response (immunoisolation) by coating it with a semipermeable membrane- microencapsulation. Unfortunately, prior to the first clinical use, further analysis of the coating substance (alginate) demonstrated that it has potential cancerogenic properties. Using a purified amitogenic alginate suitable for clinical use, we accomplished allotransplantation in a long-term animal model and reported the first clinical cases without postoperative immunosuppression recently. In view of the potential clinical use, we investigated the ability of the microencapsulation technology with the novel amitogenic alginate in experimental hypoparathyroidism (80 parathyroidectomized rats) to enable transgenic transplantation across the highest immunologic barrier (xenotransplantation: human to rat) to ensure intact transplant function without immunosuppression. In a controlled, long-term animal study, the effect of microencapsulation on xenotransplanted human parathyroid tissue was evaluated over a period of 30 weeks (microencapsulated and naked hyperplastic parathyroid tissue, respectively). Functionally, human parathyroid tissue was able to replace that of rats. More than 6 months after xenotransplantation 32 of 40 animals that had received microencapsulated transplants were normocalcemic. In contrast, serum calcium concentrations dropped to postparathyroidectomy levels within 3 weeks in the animals that had received naked tissue only. Correspondingly, normocalcemic animals showed vital parathyroid tissue inside the microcapsules, which were surrounded by a small rim of fibroblasts. When combining microencapsulation with an improved tissue culture method, xenotransplantation of human parathyroid tissue and maintenance of its physiologic function is reproducibly achieved over the highest transplantation barrier. Using the amitogenic alginate may be a crucial step toward the first clinical use of this technique for parathyroid xenotransplantation without immunosuppression.

Alginates↗
PubMed2000

Electroencephalographic activity over temporal brain areas during phonological encoding in picture naming.

OBJECTIVES: The present study examined electroencephalographic (EEG) correlates of phonological encoding during picture naming with special emphasis on hemispheric asymmetries of these EEG correlates. We also examined whether a small set of stimuli was sufficient to study the phonological encoding, and to what extent the complexity of the produced message affects the EEG responses. METHODS: Event-related electrical brain activity during the covert and overt production of names and nominal phrases derived from 16 variants from 4 different pictures was compared with that during passive viewing of the same pictures. RESULTS: Topographical and source analyses of the differential EEG activity (naming versus passive viewing) indicated that the N1 and P2 components of the visual evoked potential resulted from the same brain areas, but were activated stronger during naming as compared to passive viewing. In contrast, the differential EEG activity from 275 to 400 ms suggested the involvement of additional brain areas during naming with more pronounced left- than right-hemispheric activation in middle and posterior temporal regions for both overt and covert naming. CONCLUSIONS: Results suggest the involvement of Wernicke's area in the phonological encoding of a message during speech production, which can even be obtained with a small set of pictures and a large number of repetitions.

Adult↗
PubMed2000

Side-to-side isoperistaltic strictureplasty in extensive Crohn's disease: a prospective longitudinal study.

OBJECTIVE: To report on the results of a prospective longitudinal study of a new bowel-sparing procedure (side-to-side isoperistaltic strictureplasty [SSIS]) in patients with extensive Crohn's disease. METHODS: Between January 1992 and April 1999, the authors operated on 469 consecutive patients for Crohn's disease of the small bowel. Seventy-one patients (15.1%) underwent at least one strictureplasty; of these, 21 (4.5%; 12 men, 9 women; mean age 39) underwent an SSIS. The long-term changes occurring in the SSIS were studied radiographically, endoscopically, and histopathologically. RESULTS: The indication for surgical intervention was symptomatic partial intestinal obstruction in each of the 21 patients. Fourteen SSISs were constructed in the jejunum, four in the ileum, and three with ileum overlapping colon. The average length of the SSIS was 24 cm. Performance of an SSIS instead of a resection resulted in preservation of an average of 17% of small bowel length. One patient suffered a postoperative gastrointestinal hemorrhage. All patients were discharged on oral feedings after a mean of 8 days. In all cases, SSIS resulted in resolution of the preoperative symptoms. With follow-up extending to 7.5 years in 20 patients (one patient died of unrelated causes), radiographic, endoscopic, and histopathologic examination of the SSIS suggests regression of previously active Crohn's disease. CONCLUSIONS: SSIS is a safe and effective procedure in patients with extensive Crohn's disease. The authors' results provide radiographic, endoscopic, and histopathologic evidence that active Crohn's disease regresses at the site of the SSIS.

Adult↗
PubMed2000

Five vs. ten days of antibiotic therapy for acute otitis media in young children.

BACKGROUND: Many publications in recent years have argued in favor of shortened therapy for acute otitis media. However, doubt persists regarding children younger than 2 years, and some authors therefore restrict short course therapy to children older than 2 years. METHODS: In a prospective, comparative, double blind, randomized, multicenter trial we compared cefpodoxime-proxetil, 8 mg/kg/day in two divided doses for 10 days, with an identical 5-day regimen followed by a 5-day placebo period. RESULTS: Between October, 1996, and April, 1997, 450 children (mean age, 14.3 months) were enrolled, 227 in the 5-day group and 223 in the 10-day group. In the per protocol analysis clinical success was obtained on Days 12 to 14 after the beginning of treatment (main analysis) in 175 (84.1%) of the 208 children receiving the 5-day regimen and 194 (92.4%) of the 210 children receiving the 10-day regimen (P = 0.009). The superiority of the standard regimen was more marked among children cared for outside their homes (92.5% vs. 81.5%). Clinical success persisted on Days 28 to 42 among 134 (85.4%) of the 157 assessable patients in the 5-day group and 144 (83.7%) of the 172 assessable patients in the 10-day group (P = 0.68). CONCLUSIONS: The 10-day regimen resulted in a higher success rate at the conclusion of therapy, but there were no differences between the two study groups 4 to 6 weeks after enrollment in the study protocol.

Acute Disease↗
PubMed2000

Epidemiology of pneumococcal infections in French children.

UNLABELLED: Since 1977, resistance to beta-lactams and other families of antibiotics among isolates of Streptococcus pneumoniae has increased alarmingly worldwide. France is particularly affected by this phenomenon; in 1997 the French National Reference Centre for Pneumococci reported that 44% of S. pneumoniae strains were penicillin non-susceptible (PNSS). Furthermore, resistance to macrolides (53%) and sulphonamides (37%) was comparable; in addition, >50% of PNSS had a high level of resistance to penicillin and were multiresistant. The highest frequency of resistance is observed in children, particularly those with acute otitis media (AOM). CONCLUSION: The clinical consequences of increasing antibiotic resistance are evident for meningitis and AOM, prompting clinicians to consider alternative agents such as high-dose cefotaxime (300 mg/ kg/d) or ceftriaxone (100mg/kg/d) plus vancomycin (60 mg/kg/d) for meningitis, and high-dose amoxicillin (> 80 mg/kg/d) or ceftriaxone (50 mg/kg/d) for AOM.

Acute Disease↗
PubMed2000

Resistance to macrolides in Streptococcus pyogenes in France in pediatric patients.

A total of 1,500 recent throat isolates of Streptococcus pyogenes collected between 1996 and 1999 from children throughout France were tested for their susceptibility to erythromycin, azithromycin, josamycin, clindamycin, and streptogramin B. The erythromycin-resistant isolates were further studied for their genetic mechanism of resistance, by means of PCR. The clonality of these strains was also investigated by means of serotyping and ribotyping. In all, 6.2% of the strains were erythromycin resistant, and 3.4 and 2.8% expressed the constitutive MLS(B) and M resistance phenotypes and harbored the ermB and mefA genes, respectively; ermTR was recovered from one isolate which also harbored the ermB gene. Ten serotypes and 8 ribotypes were identified, but we identified 17 strains by combining serotyping with ribotyping. Among the eight ribotypes, the mefA gene was recovered from six clusters, one being predominant, while the ermB gene was recovered from four clusters, of which two were predominant.

Anti-Bacterial Agents↗