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Biomedical subjects

W S Brown

Publications and source records attributed to W S Brown.

At least 19 recordsLinked to original sources
PubMed1992

Confabulation in Alzheimer's disease.

Confabulation is present when memory is disturbed, but does it occur in Alzheimer's disease (AD) where memory abnormalities are often severe? In this study, confabulation was assessed prospectively in 26 AD patients and 15 normal elderly (NE) controls using a neuropsychological battery specifically designed to assess different types of memory errors. The results indicated that the AD group made significantly more verbal intrusions than the NE group. These findings provide evidence for the feasibility of eliciting confabulatory-type behavior during clinical assessment and support previous reports which have documented verbal intrusions as a common accompaniment of the memory impairment manifested by AD patients.

Aged↗
PubMed1991

Reduced attention-related negative potentials in schizophrenic children.

ERPs were recorded from normal and schizophrenic children during performance of a reaction time task (RT) followed by a complex visual discrimination, the span of apprehension task (Span), sensitive to vulnerability factors in schizophrenia. Subjects responded rapidly to the onset of the visual arrays in the RT condition and differentially to the presence of 1 of 2 target letters in the Span condition. The EEG was recorded at 19 scalp sites and ERPs included activity 1 sec before through 1 sec after Span array onset. Difference potentials (Span-RT) were computed to remove unvarying exogenous activity, thus isolating endogenous activity associated with the processing demands of the Span task. When RT and Span task ERPs are compared, schizophrenic children produced a significantly smaller than normal increment in endogenous negative activity. This endogenous negativity differed in its topography and time course from the exogenous components (P1, N1 and P2), and most likely reflects attentional effort associated with serial search, pattern recognition and stimulus identification. We believe that the current results support the position that schizophrenics are impaired in their ability to allocate adequate attentional resources for the processing of the Span stimuli. It is important to note that this deficit is apparent quite early in discriminative processing.

Analysis of Variance↗
PubMed1991

Cognitive function, mood and P3 latency: effects of the amelioration of anemia in dialysis patients.

Attention difficulties and psychomotor slowing associated with depressed mood affect the ability of individuals to perform on most neuropsychological tests. It has been suggested that latency of the P3 (P300) component of the event-related EEG potential is an index of neurocognitive status which is not affected by mood. Dialysis patients, who experience diminished dysphoric mood with the reversal of anemia when treated with recombinant human erythropoietin (rHuEPO), were tested for neurocognitive performance, mood and latency of P3. Prior to rHuEPO treatment mood was dysphoric, and neurocognitive testing showed mild deficits, but P3 latency was normal. After treatment, mood improved and neurocognitive test performance was normal. P3 amplitude increased over frontal areas, while P3 latency remained unchanged. Thus, in the case of dysphoric mood, P3 latency may provide a more accurate index of cognitive capacity (as opposed to level of functioning) than neurocognitive test measures.

Affect↗
PubMed1991

rHuEPO treatment improves brain and cognitive function of anemic dialysis patients.

Twenty-four patients with chronic renal failure, stabilized on hemodialysis, were treated with recombinant human erythropoietin. Before treatment, all patients were anemic (mean Hct = 23.7%). Hematocrits reached normal levels (36.5%) after three months of treatment. Brain event-related potentials and neuropsychological tests were used to assess changes in brain and cognitive functions associated with the correction of anemia. Assessments were done prior to and after three and twelve months of rHuEPO treatment. The P3 component of the event-related potential increased in amplitude significantly with treatment, while its latency was unaffected. Of the four neuropsychological tests administered, scores on two improved significantly with treatment, and the other two approached significance. Taken together, these findings suggest that the correction of anemia to hematocrits near normal in uremic patients by rHuEPO treatment improves brain and cognitive function by raising levels of sustained attention, thus increasing speed and efficiency of scanning and perceptual-motor functions and enhancing learning and memory. These findings also suggest that anemia, either directly or indirectly, may impair brain function.

Anemia↗
PubMed1991

Probing the time-course of the auditory oddball P3 with secondary reaction time.

An elementary neural model of the P3 is proposed in which the P3 is held to manifest a brief, widely-distributed, inhibitory event. A preliminary and indirect test of the model is described using secondary-task methodology. Manual reaction times were measured to probe clicks delivered during the presumed time-course of an auditory oddball P3. We observed that reaction times to probes presented after oddball stimuli were significantly slowed as compared to reaction times to probes presented after standards. The latency of maximum reaction time slowing corresponded generally to the latency of the P3. The latency of maximum reaction time slowing did not respond to a manipulation varying the latency of the P3. Thus, some of the obtained results were consistent with the P3-inhibition hypothesis, whereas others were not. Secondary-task methodology may provide a valuable new approach to understanding the late event-related potentials.

Adult↗
PubMed1990

Event-related potential correlates of impaired attention in schizophrenic children.

Electrophysiological correlates of focused attention were studied in 13 schizophrenic and 19 age- and gender-matched children. Subjects performed a version of the Continuous Performance Task (CPT) in which a target was designated as any digit from 0 through 9 occurring on two successive stimulus presentations. Signal digits were surrounded by distractor digits which varied in position, value, and number. Event-related potentials (ERPs) elicited by each stimulus of a target pair were recorded from midline and homologous parietal, temporal, and occipital electrode placements. Schizophrenic children made significantly more errors of omission and commission than normal children. The amplitude and time course of the intertrial CNV was the same for both groups. There was a circumscribed amplitude asymmetry, left smaller than right, for the P1/N1 and P2 measures which was greater in normal than in schizophrenic children. The P3 component was significantly larger to the second stimulus of the target pair than to the first for both groups, and larger for the normal than the schizophrenic children to both stimuli.

Arousal↗
PubMed1989

Using phytoplankton and flow cytometry to analyze grazing by marine organisms.

Phytoplankton can, through their autofluorescent characteristics, be thought of as tracer particles in much the same way as fluorescent microspheres when used in particle uptake experiments. Flow cytometric techniques can be used to differentiate phytoplankton from other suspended particles by the two primary autofluorescing photosynthetic pigments, chlorophyll and phycoerythrin. Based on these characteristics, phytoplankton assemblages have been used to assess grazing rates, particle selectivity, and endocytotic abilities in various marine species, from single-celled organisms to higher invertebrates.

Animals↗
PubMed1989

Longitudinal P300 latency changes in Alzheimer's disease.

A longitudinal study of the changes in latency of the P300 (P3) wave of the auditory event-related brain potential was undertaken in a group of 18 thoroughly screened and diagnosed possible and probable Alzheimer's disease (pAD) patients and 15 normal controls. On initial recording, P3 latency was significantly prolonged in the pAD group by more than 1.5 standard deviations (40 msec) beyond the normal group. Over the course of the next 3 years, the rate of increase in P3 latency was significantly greater for the patient group than for the controls. The rate of change in P3 latency may reflect accelerated senescence in Alzheimer's disease. Development of the auditory P300 as a marker of neurobiological processes in aging and dementia is discussed.

Aged↗
PubMed1989

Stratus automated creatine kinase-MB assay evaluated: identification and elimination of falsely increased results associated with a high-molecular-mass form of alkaline phosphatase.

We compared the performance of an automated assay of creatine kinase MB isoenzyme (CK-MB) mass (Stratus) with that of a CK-MB enzymatic assay routinely used at our institutions. Both of these assays use the same CK-MB-specific monoclonal antibody to immunocapture CK-MB, thus providing a direct means of comparing a mass assay with an activity assay. Routine CK-MB measurements for 206 samples within the analytical range of both assays revealed the following relationship: Stratus (micrograms/L) = 0.67 (activity U/L) + 0.18 (r = 0.95, Sx.y = 4.45). The linearity, sensitivity, and precision of the Stratus assay were acceptable for routine clinical use. Icteric, lipemic, and hemolyzed samples do not interfere with the assay. During our evaluation we identified a single, clinically significant false-positive sample. Because this patient had alkaline phosphatase values greater than 1100 U/L, we investigated additional samples with increased activities of alkaline phosphatase and found that samples from 12 of 23 patients selected for alkaline phosphatase values greater than 460 U/L produced falsely increased CK-MB values. We determined that a membrane-associated, high-molecular-mass form of alkaline phosphatase was a cause of these falsely increased values and instituted an approach to identify falsely increased Stratus CK-MB values. Samples from 23 of 1933 patients were falsely increased, the increase being clinically significant in samples from 14 of these patients. Consultation with the manufacturer resulted in the successful reformulation of the substrate/wash solution to minimize interferences from high-molecular-mass forms of alkaline phosphatase.

Alkaline Phosphatase↗
PubMed1988

The relationship between auditory sensitivity and ear asymmetry on a dichotic listening task.

Using an adaptive forced-choice procedure, the average absolute sensitivity of the right ears of a group of right-handed males was found to be slightly greater than that of their left ears. There was no ear difference in performance on a monaural syllable-identification task using easily detectable stimuli, however. The magnitude of the ear difference in absolute sensitivity was significantly correlated with performance on a dichotic-listening task. In a second experiment, the adaptive forced-choice procedure was used to assess differences in absolute sensitivity in a group of left-handed males. The right ears of those left-handers showing a right-ear advantage on the dichotic-listening task were slightly more sensitive than their left ears. The left ears of those left-handers showing a dichotic left-ear advantage were slightly, but not significantly, more sensitive than their right ears. The correlation of the ear differences in absolute sensitivity with performance on the dichotic-listening task for the left-handers was not significantly different from zero. Results of both experiments are discussed in terms of their implications for the nature of hemispheric asymmetry of function, and the interpretation of dichotic and monaural asymmetries.

Adult↗
PubMed1988

Individual differences in cognitive strategy and personality traits as measured by the Sixteen Personality Factor Questionnaire.

The relationship between personality and preference for use of the right or left hemisphere of the brain in cognitive processing was investigated. Lateral eye movements were recorded as 50 female and 20 male right-handed subjects considered questions requiring reflection. The questions were not obviously "verbal" or "spatial" in nature but did require differing levels of reflection. Questions requiring higher levels of reflection produced a higher rate of lateral eye movement responses. Percent right eye movement for individual subjects was then correlated with scores on the Sixteen Personality Factor Questionnaire, using both first-order factors and the second-order factor Cortertia, which has some face validity as describing the personality generally ascribed to those who produce mostly right lateral eye movements. No correlation was found between the preferred directions of eye movements and 16 PF factors, which suggests that the lateral eye movements reflect thinking and problem-solving strategies but are not associated with personality styles.

Adolescent↗
PubMed1987

The effects of continuous phonation on 133xenon-inhalation air curves (of the kind used in deriving regional cerebral blood flow).

Regional cerebral blood flow (rCBF) may be measured with inhalation techniques that use end-expired values of radioactivity to estimate the isotope concentration in arterial blood. These end-expired data are used as an input function in a mathematical equation to derive rCBF. End-expired air is assumed normally to be in equilibrium with the arterial blood at the alveolar surface of the lung during regular (passive) breathing; this assumption may not be valid during continuous phonation. We therefore have analyzed breathing (inhalation/exhalation) patterns and end-expired radioactivity (133Xe) during (1) speaking, (2) singing, and (3) humming of the national anthem, and also during (4) passive breathing. Statistically significant differences in breathing patterns were measured between a group of nonmusicians and two groups of musicians (singers) during the phonation tasks: The nonmusicians breathed more often (and more rapidly) and exhibited less variability in their breathing patterns than did the musicians. Notwithstanding these differences, the shapes of smoothed functions derived from the end-expired values were not influenced appreciably during phonation (except possibly during talking). The latter finding suggests that estimates of rCBF derived with these data should not be confounded seriously because of the continuous phonation.

Adolescent↗
PubMed1987

Judgments of emotion in words and faces: ERP correlates.

Visual event-related potentials (ERPs) to two types of stimuli (faces and words) were analyzed to determine the effects of the perceived emotional connotations of the stimuli (positive, neutral, or negative) in 10 right-handed normal functioning adult males. Principal component analysis (PCA) of the ERPs reveals 5 factors accounting for over 90% of the ERP waveform variance for both faces and words. In the facial data, two ERP components varied in amplitude according to the perceived emotional connotation of the stimulus. For the P3 component, neutrally rated stimuli produced significantly larger amplitudes than stimuli rated as positive or negative. This effect was lateralized to the left hemisphere. A later positive component, the slow wave (448-616 ms), manifested complementary effects, i.e. faces perceived as positive and negative produced larger amplitudes than those perceived as neutral over the right hemisphere. The verbal stimuli did not result in significant main effects for perceived emotional connotation, but produced subtle connotation-related differences in slow wave topography. Hemispheric asymmetries, unrelated to affective connotation, were evident in the verbal data, manifesting different patterns of lateralization depending on the ERP component. The results suggest that differential processing of emotional connotation affects ERP waveforms and that the effects can be understood in terms of ERP components known to be associated with more general aspects of cognitive processing.

Adult↗
PubMed1987

Neural temporal coding of low pitch. I. Human frequency-following responses to complex tones.

The neural basis of low pitch was investigated in the present study by recording a brainstem potential from the scalp of human subjects during presentation of complex tones which evoke a variable sensation of pitch. The potential recorded, the frequency-following response (FFR), reflects the temporal discharge activity of auditory neurons in the upper brainstem pathway. It was used as an index of neural periodicity in order to determine the extent to which the low pitch of complex tones is encoded in the temporal discharge activity of auditory brainstem neurons. A tone composed of harmonics of a common fundamental produces a sensation of pitch equal to that of the 'missing' fundamental. Such signals generate brainstem potentials which are spectrally similar to FFR recorded in response to sinusoidal signals equal in frequency to the missing fundamental. Both types of signals generate FFR which are periodic, with a frequency similar to the perceived pitch of the stimuli. It is shown that the FFR to the missing fundamental is not the result of a distortion product by recording FFR to a complex signal in the presence of low-frequency bandpass noise. Neither is the FFR the result of neural synchronization to the waveform envelope modulation pattern. This was determined by recording FFR to inharmonic and quasi-frequency-modulated signals. It was also determined that the 'existence region' for FFR to the missing fundamental lies below 2 kHz and that the most favorable spectral region for FFR to complex tones is between 0.5 and 1.0 kHz. These results are consistent with the hypothesis that far-field-recorded FFR does reflect neural activity germane to the processing of low pitch and that such pitch-relevant activity is based on the temporal discharge patterns of neurons in the upper auditory brainstem pathway.

Acoustic Stimulation↗