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Biomedical subjects

R A Dykman

Publications and source records attributed to R A Dykman.

At least 19 recordsLinked to original sources
PubMed1999

Behavioral state affects heart rate response to low-intensity sound in human fetuses.

The cardiac orienting reflex is elicited by a low-intensity sound, it consists of a sustained heart rate (HR) deceleration, and it is a specific physiological correlate of cognitive processing. In this study we examined the relationship between behavioral state and the cardiac orienting reflex in 75 human fetuses between 36 and 40 weeks gestation. Each fetus was stimulated with a 30-s speech sound at an average intensity of 83 dB SPL in quiet sleep (QS) and active sleep (AS). The fetal cardiac electrical signal was captured transabdominally at a rate of 1024 Hz and fetal R-waves were extracted using adaptive signal processing. Fetal behavioral states were assigned based on HR pattern and the presence or absence of eye and general body movements. We found that a significant HR deceleration occurred, in both QS and AS, following stimulus onset. However, HR decelerations occurred more often in QS than AS; and for fetuses exhibiting a HR deceleration, the magnitude of the deceleration was greater in AS compared to QS. In addition, in AS female fetuses exhibited a larger, more sustained HR deceleratory response than male fetuses, but the seconds x gender interaction in QS was not significant. Based on these results, we concluded that behavioral state is an important determinant of the HR deceleratory response in human fetuses.

Acoustic Stimulation↗
PubMed1998

Event-related brain potentials elicited during phonological processing differentiate subgroups of reading disabled adolescents.

Visual and auditory rhyme judgment tasks were administered to adolescent dyslexics and normal readers while event-related brain potentials were recorded. Reading disabled subjects were split into two groups based on a median split of scores on a visual non-word decoding test. The better decoders were called Phonetics and the poorer decoders were referred to as Dysphonetics. Single syllable, real word stimuli were used, and both rhyming and non-rhyming targets had a 50% chance for matching orthography. In the visual paradigm the normal readers exhibited a left frontal CNV before targets, a large reduction in frontal N400 for matching orthography (orthographic priming), and a large reduction in parietal N400 for rhyming targets (phonological priming). Dysphonetics had an intact CNV and orthographic priming, but the group's phonological priming was very reduced. Phonetics showed both orthographic and phonological priming but had a marked reduction in their CNV. In the auditory task, controls showed a left parietal N400 priming effect for rhyming targets. Dysphonetics showed a similar bilateral effect. The Phonetics did not show a normal priming effect, but produced evidence for priming at a longer latency. Additionally, the Phonetic group responded more slowly than either of the other two groups, who responded with similar latencies. These results support the separation of the reading disabled into a group that has difficulty translating orthography into phonology, and a group that is slower functioning and has reduced capacity in preparing for a response.

Adolescent↗
PubMed1998

Prevalence of post traumatic stress disorder and other psychiatric diagnoses in three groups of abused children (sexual, physical, and both).

OBJECTIVE: The purpose of this study was to compare the prevalence of Post Traumatic Stress Disorder and other diagnoses in three groups of abused children, sexual only (N = 127), physical only (N = 43), and BOTH (N = 34). METHOD: The children, aged 7 to 13 years, were referred to the project from several sources at Arkansas Children's Hospital and from associated local agencies. The victims and caregivers were separately administered the Diagnostic Interview for Children and Adolescents, Revised Version (DICA). Additionally, caregivers and classroom teachers completed the Child Behavior Checklist (CBCL). Characteristics of the abuse were obtained from an investigative questionnaire. RESULTS: Both victims and caregivers endorsed high rates of disorders, with caregivers generally giving higher rates than children and boys having more externalizing diagnoses than girls. Children in the BOTH group had more diagnoses overall. Concordance between victims and caregivers was modest. PTSD was significantly comorbid with most affective disorders. On the CBCL, caregivers rated girls less disturbed than boys and the sexually abused only group less disturbed than the other groups. Teachers rated the boys more adversely than girls but did not see differences by abuse group. A younger age of onset of sexual abuse and coercion to maintain secrecy predicted a higher number of total diagnoses. Also, children who were physically abused by males had more diagnoses than those physically abused by females. CONCLUSIONS: Children who have been both physically/sexually abused appear to be at highest risk of psychiatric disturbance. PTSD, though common (circa one-third of victims), is generally comorbid with other affective disorders.

Adolescent↗
PubMed1998

Neuropsychological patterns in pediatric epilepsy.

Results from comprehensive neuropsychological assessments of children diagnosed with epilepsy have rarely been reported. Previous research has generally focused on the measurement of overall intellectual ability and achievement skills. In the present study, neuropsychological evaluations including memory, attention, language, achievement, fine motor, executive function, visual motor integration, and behavior were completed on children (n = 79) diagnosed with epilepsy. Neurocognitive skills were within expectations for measured intelligence with the exception of verbal and visual attention skills, which were significantly below expectations based on measured ability. Behaviorally, children were rated by their parents as demonstrating clinically elevated attentional problems. Differences in cognitive and behavioral function were not found according to seizure type. Findings suggested a more diffuse effect of childhood epilepsy reflected in a pattern of decreased attention skills.

Adolescent↗
PubMed1997

The heart rate deceleratory response in low-risk human fetuses: effect of stimulus intensity on response topography.

The purpose of this study was to determine the effect of stimulus intensity on heart rate response in 18 low-risk human fetuses between 37 and 40 weeks gestation. Each fetus was stimulated in quiet sleep with a 30-s voice sound at intensities of 80 dB and 90 dB. The fetal cardiac electrical signal was captured transabdominally at a rate of 1024 Hz and fetal R-waves were extracted using adaptive signal-processing techniques. We found that fetuses generally exhibited a 5- to 10-s decrease in heart rate following stimulus onset at an intensity of 80 dB. The response pattern changed from deceleratory to acceleratory when stimulus intensity was increased to 90 dB. Our findings suggest that a heart rate deceleration at low-stimulus intensity may be a component of the orienting reflex in the human fetus.

Analysis of Variance↗
PubMed1995

EEG power spectra of dysphonetic and nondysphonetic poor readers.

Two subtypes of poor readers, dysphonetic and phonetic, were compared on EEG spectral values obtained as they viewed strings of letters and short words. Dysphonetic poor readers had significantly higher values than phonetics in the theta and delta bands. Both phonetic and dysphonetic poor readers had lower beta values than adequate reading children with Attention Deficit Disorder. This evidence indicates that poor readers, especially dysphonetics, were less actively engaged in the task.

Achievement↗
PubMed1994

Heart rate changes following habituation testing of the motor response in normal human fetuses.

We examined the heart rate (HR) response immediately following habituation testing in 54 normal human fetuses between 34 and 40 weeks of gestation to determine if cardiac self-regulation was a function of the rate of motor habituation. All fetuses received eight trials of a 1-s vibroacoustic stimulus (VAS) with a 10-s interstimulus interval. A score of 0-10 was assigned for each trial based on subjective assessment of intensity and duration of the fetal motor response. Motor habituation was evaluated in terms of the rate of response decrement over trials. For each fetus the average post-VAS HR was calculated in 1-min blocks for the first 7 min following habituation testing. When subjects were divided into slow and fast motor habituators, we found that fetuses who were slow habituators displayed a significantly greater increase in HR above baseline at each of the first 7 min following habituation testing as compared to fetuses whose motor response habituated more rapidly, F(1,52) = 4.88, P = 0.03. However, there was no difference between slow and fast motor habituators in the rate at which the HR returned toward prestimulus levels. To further examine these results, we divided the 54 fetuses into four groups based on the medians of the slope of the post-VAS HR regression line and the variability in HR about this line. We found that fetuses whose HR decreased slowly after habituation testing displayed significantly greater variability in their cardiac response as compared to fetuses whose HR decreased more rapidly (chi 2 = 4.74, P = 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

Female↗
PubMed1994

Motor and cardiac response during habituation testing: demonstration of exaggerated cardiac reactivity in a subgroup of normal human fetuses.

In this study we wanted to determine: (1) whether or not a relationship existed between the rate of habituation of the fetal motor response and changes in the fetal heart rate (FHR), and (2) if this relationship could be used to identify a subgroup of fetuses who exhibited exaggerated cardiac reactivity during habituation testing. Thirty-nine normal human fetuses between 34 and 40 weeks of gestation were evaluated. Habituation testing consisted of a 1 second vibroacoustic stimulus with a 10 second interstimulus interval for eight trials. The motor response was observed using real-time sonography, and a score of 0 to 10 was assigned for each trial based on subjective assessment of the fetal response. Motor habituation was evaluated in terms of the rate of response decrement in movement over trials (Re). Subjects were initially divided into slow and fast motor habituators based on the median of Re, and it was found that fetuses whose motor response habituated slowly displayed a significantly greater increase in heart rate compared with fetuses who habituated more rapidly (F1,37 = 8.61; P = 0.0057). Cardiac reactivity was then defined as "the average increase in FHR above the mean prestimulus value during the last half of the testing period." When the data were divided into quadrants based on medians, we identified seven (18%) fetuses who habituated rapidly but who also displayed high cardiac reactivity. We conclude that there is a significant relationship between the magnitude of the increase in FHR above baseline and the rate of motor habituation in normal human fetuses.

Acoustic Stimulation↗
PubMed1994

Visual event-related potentials of dyslexic children to rhyming and nonrhyming stimuli.

In a visual event-related potential (ERP) study, children diagnosed as dyslexic in terms of both age and IQ discrepancy criteria were compared with two contrast groups: poor for age (SLOW) readers and normal reading children with Attention Deficit Disorder (ADD). The children viewed 200 stimulus pairs and judged whether the second stimulus of each pair rhymed with the first. The first stimulus was always a three-letter word, while half of the second stimuli were pronounceable nonsense words and half were real words. Rhyme probability was 50%. The ERP waveforms of the dyslexics were significantly different from those of the ADD group in showing less late negativity. The SLOW group's waveforms more closely paralleled those of the ADD group. The major anomalous feature of the dyslexics' waveform was a pronounced late positive peak (P500), which followed an attenuated N450 peak. Over all groups, the N450 peak was sensitive to the rhyme manipulation, as has been found in adults (Rugg, 1984a, 1984b). Real words and nonsense words produced similar waveforms. Hemispheric effects were found but did not interact with group. Results suggest non-automatic visual cognitive processing of rhyme in dyslexics.

Arousal↗
PubMed1994

EEG power spectra of children with dyslexia, slow learners, and normally reading children with ADD during verbal processing.

EEG power spectra were studied in two poor reader groups (with dyslexia and slow learning) and a normally reading clinic control group (with attention deficit disorder) as the children viewed strings of words and letters (seven categories). The children ranged in age from 7.5 to 12 years; 33 were girls, 86 were boys. Bilateral temporal and parietal sites and four midline sites were used. The major difference between groups was in the low beta band, where the ADD group had greater power at the parietal and midline sites. Also, the slow learner group had marginally greater low beta at the left than right temporal site, with the opposite trend found for the dyslexic and ADD groups. Across groups, power was greater at the right than at the left parietal site in the delta and alpha bands and at the right than at the left temporal site in the low beta band. Stimulus category effects were modest, with some alpha suppression to word strings, relative to letter strings, found in the poor readers. In correlational analyses, the combination of greater low beta and less theta power significantly predicted better reading and spelling. Results indicate that the adequate readers more actively processed the stimuli than did the poor readers.

Attention↗
PubMed1993

Phonological processes, confrontational naming, and immediate memory in dyslexia.

A group of poor readers classified as dyslexic by age/IQ discrepancy criteria (n = 42) were contrasted with two clinic control groups: 56 adequate-for-age readers with attention deficit disorder (ADD) and 21 poor-for-age readers not meeting the IQ discrepancy criterion (slow/borderline group). The children (33 girls, 86 boys) ranged in age from 7.5 years to 12 years. Variables chosen for study included simple and complex phonological processing, speech rate, continuous naming speed, running memory span, serial memory span, and mental addition. Evidence is presented that the two poor reader groups are distinguishable. Unlike the dyslexic group, the slow/borderline group did not differ from the ADD group on three key measures: simple auditory phonological sensitivity, continuous naming speed, and running memory span. Stepwise regression to predict word list reading level showed that once age and verbal IQ were removed (51% of variance), these three key measures accounted for an additional 22% of the variance (R = 0.86, R2 = 0.73). The single best predictor of word list reading level was nonsense word list reading level, which was explained by the same set of five variables that explained real word reading (R = 0.77, R2 = .60). Severity of attentional problems was not linearly related to reading skill in this clinic sample.

Analysis of Variance↗
PubMed1991

Attention deficit disorder and specific reading disability: separate but often overlapping disorders.

Within a large (N = 182) heterogeneous sample of clinic-referred children with DSM-III-diagnosed attention deficit disorder (ADD), three behavioral subgroups were identified via cluster analysis of teacher ratings: 40% of the children had ADD with hyperactivity (ADDH), 30% had ADD with hyperactivity and aggressivity (ADDHA), and 31% had ADD without hyperactivity or aggressivity. Proportionally more girls were in the ADD-only subgroup. Over half the sample (n = 94) were poor readers, with 82 meeting discrepancy criteria for specific reading disability (RD). Proportionately more boys than girls met the RD criteria (9.2:1.0), whereas the sex ratio of males to females for the whole sample was 5.1 to 1.0. Focusing just on white males, the three behavioral subgroups were significantly different on convergent validity measures, such as other teacher ratings, parent ratings, and interview-elicited ratings of externalizing behavior, but were not different on such divergent validity measures as IQ and achievement scores, self-ratings, and laboratory performance tasks. Boys in the ADD sample who did not meet criteria for RD had significantly higher IQs than those who did, but subgroups with and without RD still differed significantly on WRAT-R reading and spelling scores with IQ covaried out. Both groups with and without RD could be differentiated from a control group on laboratory measures of sustained attention and impulse control. Methylphenidate benefited all subgroups equally, whether RD or not, and whether given a low (0.3 mg/kg) or high (0.6 mg/kg) dose.

Arousal↗
PubMed1991

A trial of piracetam in two subgroups of students with dyslexia enrolled in summer tutoring.

Sixty children with dyslexia (41 boys, 19 girls; ages 9 to 13) were enrolled in a 10-week summer tutoring program that emphasized word-building skills. They were randomly and blindly assigned to receive either placebo or piracetam, a purportedly memory-enhancing drug that has been reported to facilitate reading skill acquisition. The children were subtyped as "dysphonetic" or "phonetic" on the basis of scores from tests of phonological sensitivity and phoneme-grapheme correspondence skills. Of the 53 children who completed the program, 37 were classified as dysphonetic and 16 as phonetic. The phonetic group improved significantly more in word-recognition ability than the dysphonetic group. Overall, the children on medication did not improve more than the nonmedicated ones in any aspect of reading. The phonetic subgroup on piracetam gained more in word recognition than any subgroup but did not improve significantly more than the phonetic subgroup on placebo. Results are discussed in relation to findings from previous studies of piracetam in children with dyslexia.

Adolescent↗
PubMed1990

The frequency and significance of additional self-reported psychiatric diagnoses in children with attention deficit disorder.

The frequency of additional self-reported diagnoses in a large, heterogeneous sample of attention deficit disorder (ADD) children (N = 182) was determined using the Diagnostic Interview for Children and Adolescents (DICA). Over half the children had additional DICA diagnoses, with oppositional disorder and anxiety/mood disorders the most frequent. ADD boys with internalizing-type diagnoses had lower verbal IQs and arithmetic scores and performed more poorly on attention tasks than those without; parents also rated them more adversely. Those with externalizing-type diagnoses were rated as more aggressive by teachers and had sociopathic, thrill-seeking profiles on paper-pencil self-ratings. Over 40% of the children were dyslexic or slow learners but they had no higher rate of DICA diagnoses than those who read adequately.

Achievement↗
PubMed1990

Blink rates in schizophrenia.

In schizophrenia, blink rates are frequently elevated and the peak of the electroencephalographic alpha rhythm is often absent or of a lower frequency. Emerging evidence suggests that both blinks and the alpha rhythm may be controlled by a linked neuroanatomical circuit that begins in rostral pons and involves several subcortical structures as well as the occipital cortex. Blink-alpha abnormalities in schizophrenia further suggest that this blink-alpha neurocircuit may be a locus of the pathophysiological process of this disorder.

Arousal↗
PubMed1990

ADD students with and without dyslexia differ in sensitivity to rhyme and alliteration.

Children with attention deficit disorder (ADD) and dyslexia (n = 82) made significantly more errors than normally reading children with ADD (n = 83) on a simple auditory test of phonological sensitivity to rhyme and alliteration (Bradley, 1984). A subgroup of children with dyslexia who were sensitive to rhyme and alliteration had higher scores on the Wechsler Intelligence Scale for Children-Revised (WISC-R) Spatial factor than a dyslexic subgroup who were phonologically insensitive. In multiple regression analyses, age-corrected phonological sensitivity scores contributed significantly to the prediction of both reading and spelling Wide Range Achievement Test (WRAT) scores, this beyond the contribution of WISC-R variables. Of interest for dyslexia subtyping theories, Spatial factor scores had a subtractive effect in these regression analyses.

Achievement↗