Biomedical subjects

M Koivisto

Publications and source records attributed to M Koivisto.

At least 37 records · Page 2Linked to original sources

PubMed2000

The effects of memory load on event-related EEG desynchronization and synchronization.

OBJECTIVES: To examine the effects of working memory load on the event-related desynchronization (ERD) and synchronization (ERS) of several narrow EEG frequency bands. METHODS: ERD/ERS responses of the 4-6, 6-8, 8-10 and 10-12 Hz EEG frequency bands were studied in 24 normal subjects performing a visual sequential letter task (so-called n-back task) in which memory load was varied from 0 to 2. RESULTS: In the 4-6 Hz theta frequency band, a long-lasting synchronization was observed in the anterior electrodes, especially after the presentation of targets. In the 6-8 and 8-10 Hz frequency bands, anterior ERS was elicited especially in the 2-back condition (highest memory load). In contrast to the responses of the 8-10 Hz frequency band, in the 10-12 Hz frequency band the 2-back experimental condition elicited the greatest ERD. CONCLUSIONS: In the highest memory load (2-back) experimental condition the attentional capacities were most probably exceeded, resulting in 6-8 and 8-10 Hz ERS. This might reflect an inhibition of such brain areas (frontal cortices) no longer involved in task completion when alternative strategies are needed and utilized. These more 'cognitive' strategies were then reflected as an increase in 10-12 Hz ERD. Additionally, our results support the assumption that the simultaneously recorded ERD/ERS responses of different narrow EEG frequency bands differ and reflect distinct aspects of information processing.

Adult↗

PubMed2000

Effects of electromagnetic fields emitted by cellular phones on the electroencephalogram during a visual working memory task.

PURPOSE: To examine the effects of electromagnetic fields (EMF) emitted by cellular phones on the event-related desynchronization/synchronization (ERD/ERS) responses of the 4-6, 6-8, 8-10 and 10-12Hz EEG frequency bands during cognitive processing. MATERIALS AND METHODS: Twenty-four subjects performed a visual sequential letter task (n-back task) with three different working memory load conditions: zero, one and two items. All subjects performed the memory task both with and without exposure to a digital 902 MHz EMF in counterbalanced order. RESULTS: The presence of EMF altered the ERD/ERS responses in the 6-8 and 8-10 Hz frequency bands but only when examined as a function of memory load and depending also on whether the presented stimulus was a target or not. CONCLUSIONS: The results suggest that the exposure to EMF modulates the responses of EEG oscillatory activity approximately 8 Hz specifically during cognitive processes.

Adult↗

PubMed2000

Preterm delivery for maternal or fetal indications: maternal morbidity, neonatal outcome and late sequelae in infants.

OBJECTIVE: To assess maternal morbidity, and neonatal outcome and especially long term sequelae in infants born preterm due to maternal or fetal indications. DESIGN: Analysis of retrospective cohort. SETTING: Oulu University Central Hospital, Finland. POPULATION: One hundred and three women, who were between the 24th and the 33rd week of pregnancy, delivered by caesarean delivery because of maternal or fetal indications. They were matched with 103 women who had spontaneous preterm delivery at corresponding gestational weeks between 1990-1997. MAIN OUTCOME MEASURES: Maternal morbidity, reasons for caesarean delivery, neonatal mortality and morbidity rates, and later development of the infants. RESULTS: Pre-eclampsia was diagnosed in 57% of the women in the indicated group and only in one woman in the control group. All infants in the indicated group and almost a third in the control group were born by caesarean birth; the main indication was threatening fetal asphyxia. There was a significant difference in neonatal mortality rates between the groups (175 vs 78 per thousand live births in the indicated vs control infants; RR 2.3, 95% CI 1.02, 4.9) and the main cause of death was respiratory insufficiency: 64% in the indicated group and 22% in the controls; RR 2.9, 95% CI 0.8, 10. Respiratory distress syndrome occurred more often (73% vs 53%, RR 1.4, 95% CI 1.1, 1.7) and it was more severe and more complicated in infants in the indicated group, compared with those in the control group. Symptomatic chronic lung disease at one year of age was more common in infants in the indicated group than in the control group (15% vs 3%; RR 4.6, 95% CI 1.4, 15.9). CONCLUSIONS: Not only the risks of neonatal mortality and morbidity but also long term pulmonary consequences, appear to be greater in infants born preterm by indicated delivery than in preterm infants born spontaneously at corresponding weeks.

Asphyxia Neonatorum↗

PubMed1999

Strategies of semantic categorization in the cerebral hemispheres.

Strategies of semantic categorization in intact cerebral hemispheres were studied in two experiments by presenting names of typical and atypical category instances to the left visual field (LVF) (right hemisphere) or to the right visual field (RVF) (left hemisphere). The results revealed that the typicality of instances had a large effect on categorization times in the LVF in both experiments, suggesting that the right hemisphere relies strongly on a holistic, similarity-based comparison strategy. In Experiment 1, the typicality effect was weaker in the RVF than in the LVF. In Experiment 2, a typicality effect in the RVF was observed for the "four-footed animal" category but not for the "bird" category. The hypothesis that the left hemisphere employs a strategy based on defining or necessary features is not supported by the observed typicality effect in the "four-footed animal" category. Instead, it is suggested that the left hemisphere may be able to categorize on the basis of prestored instance-category knowledge. When such knowledge is not available (e.g., as for four-footed animals), a similarity-based comparison strategy is employed by the left hemisphere.

Adolescent↗

PubMed1999

Nephrocalcinosis in full-term infants receiving furosemide treatment for congestive heart failure: a study of the incidence and 2-year follow up.

UNLABELLED: In order to study the incidence and course of nephrocalcinosis in full-term infants with congestive heart failure receiving long-term furosemide treatment, 36 such infants (median age 2.9 months, range 1.2-8.0) and 36 full-term control infants not receiving any diuretics (median age 3.4 months, range 1.1-8.4) were studied by renal ultrasonography and random urine calcium variables. The infants with nephrocalcinosis were followed at 3-6 month intervals up to 2 years of age, or until ultrasonic resolution. Nephrocalcinosis was found in 5 out of the 36 (14%) treated infants, but in none of the controls (P = 0.03). The dose of furosemide was higher in the infants with nephrocalcinosis than in those without (1.9+/-0.6 vs. 1.3+/-0.4 mg/kg per day; P = 0.01). The urinary calcium concentration was higher in the infants receiving furosemide than in controls and a similar trend was observed in the urinary calcium/creatinine ratio, but these variables did not differ between the study infants with and without nephrocalcinosis. Ultrasonic resolution of nephrocalcinosis was observed in 3 of the 5 infants at 12 months, but in the other 2 the condition still persisted at 24 months. CONCLUSIONS: Long-term furosemide treatment in full-term infants with congestive heart failure entails a considerable risk of developing nephrocalcinosis. Renal ultrasonography is warranted in these patients within a few months after initiation of the treatment and in the case of nephrocalcinosis alteration of the diuretic regimen is to be considered.

Calcium↗

PubMed1999

Prematurity-associated nephrocalcinosis and kidney function in early childhood.

To assess the impact of prematurity-associated nephrocalcinosis on kidney function later in life, 20 premature children with neonatal nephrocalcinosis and 20 controls, matched for birth weight and postnatal age but without nephrocalcinosis, were examined (birth weight 905+/-209 vs. 957+/-226 g; study age 4.7+/-1.1 vs. 4.6+/-0.9 years). Distal tubular acidification capacity was measured with the oral acetazolamide test, in which the response was abnormal in 1 out of the 20 children with a history of nephrocalcinosis, but in none of the controls. Urinary calcium and beta(2)-microglobulin excretion were higher in the children with nephrocalcinosis, but no differences were found in fractional excretion of sodium and potassium or tubular reabsorption of phosphate. Estimated creatinine clearance was not different between the groups. Of the 6 children with nephrocalcinosis lasting beyond 2 years of age, 5 had had chronic lung disease neonatally and exhibited a tendency for compensated respiratory acidosis at the time of the examination. Neonatal nephrocalcinosis seems to lead to some signs of renal tubular dysfunction in early childhood of preterm infants. Glomerular function, however, appears not to be specifically disturbed by nephrocalcinosis.

Calcium↗

PubMed1999

Short versus prolonged indomethacin therapy for patent ductus arteriosus in preterm infants.

OBJECTIVE: To evaluate whether a prolonged low-dose course of indomethacin would produce an improved closure rate and have fewer side effects compared with a short standard dosage schedule in the management of patent ductus arteriosus (PDA) in preterm infants. STUDY DESIGN: Sixty-one infants of gestational ages 24 to 32 weeks with a PDA confirmed with echocardiography were randomized to receive 0.2 to 0.1 to 0.1 mg/kg indomethacin in 24 hours (short course, n = 31) or 0.1 mg/kg every 24 hours 7 times (long course, n = 30). Echocardiography was done 3, 9, and 14 days after the treatment was started, and side effects were monitored. RESULTS: Primary PDA closure occurred more often in the short course group (94% vs 67%, P =.011), but the sustained closure rates were not different (74% vs 60%). Surgical PDA ligations were less frequent in the short course group than in the long course group. The short course group had a shorter duration of oxygen supplementation, less frequent symptoms of necrotizing enterocolitis, and a lower rate of urea retention. Mortality and other neonatal morbidity rates were similar. CONCLUSION: A prolonged low-dosage indomethacin regimen offers no advantage compared with a standard-dosage short course in the management of a hemodynamically significant PDA in preterm infants.

Cyclooxygenase Inhibitors↗

PubMed1999

Hemispheric dissociations in controlled lexical-semantic processing.

Cognitive mechanisms of semantic priming in individuals with intact cerebral hemispheres were studied using the visual half-field method and lexical-decision tasks. In Experiment 1, unidirectionally associated word pairs were presented in a forward direction (e.g., BEAVER-TAIL) to isolate priming attributable to automatic activation or expectancy-based processing. Forward priming was restricted to the right visual field-left hemisphere, and it occurred only when expectancy-based processing was encouraged in the instructions. Experiments 2 and 3 found backward priming (e.g., TAIL-BEAVER) only in the left visual field, indicating that the right hemisphere contributes to retrospective semantic matching of the target back to the prime. The results suggest that the 2 hemispheres have different roles in controlled processing of semantic relations.

Adult↗

PubMed1999

Incidence, ultrasonic patterns and resolution of nephrocalcinosis in very low birthweight infants.

This longitudinal study was undertaken in order to elucidate the incidence and natural course of nephrocalcinosis in preterm infants and to evaluate whether the ultrasonic classification for nephrocalcinosis used here is suitable for predicting subsequent resolution of the condition. A total of 129 very low birthweight infants were screened for nephrocalcinosis by renal ultrasonography at 2 wk, 6 wk and 3 mo. The pyramidal changes were classified as peripheral, scattered or extensive. Follow-up renal ultrasonography was performed on the infants with nephrocalcinosis at 6, 12, 18 and 24 mo, and thereafter annually up to 6 y of age, or until ultrasonic resolution. The overall incidence of nephrocalcinosis was 20% (26/129). Nephrocalcinotic changes were peripheral in 14 out of the 26 infants (54%), scattered in 7 (27%) and extensive in 5 (19%). Ultrasonic resolution had taken place in all the cases with peripheral nephrocalcinosis by 12 mo, but 3 of the 7 infants with the scattered pattern and 3 of the 4 with the extensive pattern (1 died) were still affected at 24 mo. In two cases with extensive nephrocalcinosis the condition still persisted at 5-6 y of age. We conclude that about 20% of very low birthweight infants develop nephrocalcinosis during the first 3 mo of life. In about half of the affected infants renal changes are restricted and transient, but more extensive forms may last several years. The classification of nephrocalcinosis used here is appropriate for predicting later ultrasonic resolution.

Anti-Inflammatory Agents↗

PubMed1998

Lexical access to inflected words as measured by lateralized visual lexical decision.

In two lateralized visual lexical decision experiments conducted with normal subjects, we studied hemispheric performance in the recognition of case-inflected Finnish nouns. Previous research employing mainly locative cases has indicated that such noun forms undergo morphological decomposition. The present experiments extend this finding to syntactic cases by showing that nouns with partitive or genitive endings take longer to recognize and elicit more errors than otherwise comparable monomorphemic nominative singular nouns. Morpheme-based recognition of all case-inflected forms would be a particularly appropriate solution for mental lexicon in highly inflecting languages like Finnish: it saves storage space and enables fast recognition of inflected forms not encountered before. In real words, morphological structure did not interact with visual field. However, particularly demanding, morphologically decomposable nonwords elicited more errors in the left visual field/right hemisphere than did nondecomposable nonwords. Our results suggest that at least in Finnish, both hemispheres are capable of morpheme-based access, but this mechanism is more accurate in the left than in the right hemisphere.

Adult↗

PubMed1998

Automatic influences of memory in Alzheimer's disease.

Automatic and controlled influences of memory were examined in 12 patients with early Alzheimer's disease (AD) and 12 control subjects. The subjects studied a list of words and then received three-letter word stems in three different retrieval tasks. In an indirect memory task (word-stem completion priming), they were asked to produce the first word that came to mind in response to each stem. In an inclusion task, they were required to produce a studied word in response to each stem, and in an exclusion task they were asked to produce a new, unstudied word for each stem. The performance of the subjects with AD was equal in the inclusion and exclusion conditions, showing no evidence of controlled recollection for the studied words, while their automatic memory as well as priming were preserved. The results provide neuropsychological support for the distinction between controlled and automatic memory processes.

Aged↗

PubMed1998

Categorical priming in the cerebral hemispheres: automatic in the left hemisphere, postlexical in the right hemisphere?

Automatic and postlexical semantic processing in the cerebral hemispheres was studied by presenting categorically related but nonassociated word pairs (e.g., TABLE-BED) to the left visual field (LVF) or to the right visual field (RVF) in semantic priming experiments. Experiment 1 examined automatic priming across stimulus onset asynchronies (SOAs) of 165 and 750 ms with a low proportion of related pairs and a low nonword ratio, employing a GO-NOGO lexical decision task. In contrast to an earlier view that a larger range of meanings is automatically activated in the right than in the left hemisphere, priming was observed in the RVF/left hemisphere only. SOA did not exert any effects. In Experiment 2, postlexical semantic matching of the prime and the target was encouraged by requiring subjects to respond to both of them at the same time. Now there was priming in the LVF, suggesting that a postlexical matching process works in the right hemisphere. The earlier studies showing a right hemisphere advantage in categorical priming are reinterpreted according to the postlexical right hemisphere hypothesis.

Adult↗

PubMed1998

Perinatal and neonatal outcome and late pulmonary sequelae in infants born after preterm premature rupture of membranes.

OBJECTIVE: To evaluate fetal outcome and long-term impact of very early preterm premature rupture of membranes (PROM). METHODS: In a retrospective cohort study, 78 women with singleton pregnancies who delivered at the Oulu University Central Hospital between 1990 and 1996 and who had early PROM, between the 17th and 30th gestational weeks, were matched with 78 women with spontaneous preterm delivery during the same time (control group). The main outcome measures were maternal morbidity, interval from early PROM to delivery, perinatal and neonatal mortality rates and neonatal morbidity, need for primary and recurrent hospitalization and later pulmonary complications of the infants, and growth and neurologic findings at 1 year of corrected age. RESULTS: The perinatal mortality was 282 per 1000 births in the early PROM group and 256 per 1000 births in the control group. Histopathologically defined chorioamnionitis and puerperal infections were significantly more common in the early PROM group than in controls (51 versus 29%, odds ratio [OR] 2.5, 95% confidence interval [CI] 1.3, 4.9 and 38 versus 22%, OR 2.3, 95% CI 1.1, 5.1, respectively). There were no differences in neonatal infections between groups. Pulmonary hypoplasia was detected more often in the early PROM group (in nine infants) compared with the control group (no infants). The duration of rehospitalization up to 1 year of age due to respiratory problems was a mean of 5 days in the early PROM group and a mean of 1 day in the control group (P = .01; 95% CI 0.9, 6.9). Symptomatic chronic lung disease at 1 year of age was detected more often in the early PROM group than in controls (22 versus 9%; OR 2.4, 95% CI 0.9, 6.5). CONCLUSION: Early PROM seems to be a major obstetric and neonatal problem with pulmonary ramifications extending beyond the neonatal period. However, most of these infants can be saved.

Adolescent↗

PubMed1998

Type I and type III procollagen propeptides in amniotic fluid of normal pregnancies and in a case of mild osteogenesis imperfecta.

BACKGROUND: The propeptides derived from type I and III procollagens, PICP, PINP and PIIINP, indicate the synthesis of the corresponding collagens. Their circulating concentrations reflect the growth velocity in infants and children METHODS: We measured these propeptides in 145 samples of amniotic fluid of normal pregnancy. In addition, we have analysed an amniotic fluid and serum sample from a mother with osteogenesis imperfecta, and later the infant's serum sample was also collected for procollagen propeptide analysis. RESULTS: High concentrations of propeptides, 100-1000 times higher than those in adult serum, were found in early second trimester, decreasing significantly towards term, reflecting the decreased foetal growth rate. Interestingly, the amino-terminal propeptide of type I procollagen, PINP, decreased more that the corresponding carboxy-terminal propeptide, PICP, although both are in principle derived from the same protein. At both stages of pregnancy, the discrepant ratio of PICP to PINP indicated a molar excess of PINP. Abnormally low concentrations of PICP and PINP with normal PIIINP concentrations measured in amniotic fluid and in the serum indicated decreased synthesis of type I procollagen in a foetus/infant with mild osteogenesis imperfecta. CONCLUSIONS: Our data show a decrease in collagen synthesis with the stage of pregnancy and lower values of type I procollagen propeptides in a case of OI.

Adult↗

PubMed1997

Time course of semantic activation in the cerebral hemispheres.

Recent visual half-field studies using relatively long stimulus onset asynchronies (SOAs) and non-associated category members (e.g. deer-pony) as word pair stimuli have indicated that with a low proportion of related stimuli, automatic priming of non-associated category information is larger in the right than in the left hemisphere [Chiarello and co-workers]. The present study examined semantic priming of non-associated category members, with a low proportion of related stimuli in the visual fields/hemispheres across SOAs of 165, 250, 500, and 750 msec. Eighty normal, right-handed subjects were tested (20 subjects/SOA). The results revealed a left hemisphere advantage in priming at the 165 msec SOA, whereas the right hemisphere advantage reported in earlier studies was observed at the longest 750 msec SOA only. The results challenge the view that a larger range of related meanings is activated in the right than in the left hemisphere. Rather, the time course of semantic activation may be different in the hemispheres.

Adult↗

PubMed1996

Perceptual priming in Alzheimer's and Parkinson's diseases.

The present study focused on perceptual identification priming (implicit memory) in early stages of dementia by studying demographically and cognitively matched patients with Alzheimer's disease (AD) and Parkinson's disease (PD). The AD and PD groups performed normally on perceptual identification priming, whereas their explicit recognition memory was equally impaired compared to normal controls. These results imply that priming in perceptual identification relies on the perceptual memory system which can resist not only impairments of explicit memory but also widespread cognitive deterioration induced by the neurodegenerative processes in AD or PD.

Adolescent↗

PubMed1996

Form-specific priming and functional brain asymmetries in perceptual identification.

Word form representations in intact cerebral hemispheres were studied by a lateralized perceptual identification priming task. During the study phase, word forms were primed by displaying words visually in uppercase or lowercase letters. During the test phase, perceptual identification of non-studied baseline words and studied words (presented in same or different lettercase as studied) was tested by displaying targets in the left or right visual field. Experiment 1 showed that the hemispheric pattern of priming effects was dependent on the lettercase at test. For uppercase test items, only the left visual field/right hemisphere was sentitive to study-test changes in lettercase, replicating an earlier result obtained in word-stem completion (Marsolek, Kosslyn and Squire, 1992). However, lowercase test items did not reveal any asymmetries in the form-dependent priming component indicating that in some conditions form-specific representations are computed in the left hemisphere also. No asymmetries were found in the abstract, form-independent component of priming. Experiment 2 revealed that use of explicit memory in the perceptual identification task eliminated the form-specific priming effects and suggested that the results of Experiment 1 were uncontaminated by explicit memory.

Adult↗

PubMed1995

On functional brain asymmetries in perceptual priming.

Brain asymmetries in implicit memory were studied using a perceptual identification priming paradigm. At the study phase, Subjects rated either the readability or the likeability of words. At the test phase, perceptual priming for these words was measured by presenting stimuli briefly either in the left or in the right visual hemifield. The typeface of the words was varied between the study and test. The orientation task manipulation at the study phase did not influence priming, although it had a powerful effect on a test of explicit memory. Priming effects were form-specific: words which were studied in the same typeface as they were tested were primed more strongly than words which were studied in a different typeface. No hemispheric asymmetries were observed in form-specific priming, but in general, priming was greater in the right hemifield/left hemisphere. These findings suggest that the hemispheres are equally effective in analysing and storing form-specific information at the early stages of word recognition process. Asymmetries favoring the left hemisphere may develop at a higher, more abstract level of presemantic visual word form processing.

Adult↗