Chronic uveitis in Gaucher's disease

Thirty patients with Gaucher's disease have been examined in the authors' clinic; 29 of them suffered from the adult form and one had the juvenile type of the disease. The authors found intraocular abnormalities in four patients: three suffered from uveitis and in one, multiple vitreous opacities were observed. Two of the three patients had bilateral uveitis, while in one the uveitis was confined to the right eye only. In two of the three patients the manifestations of Gaucher's disease were present before the onset of uveitis. In one of the three, however, bilateral uveitis with spontaneous hyphema in the left eye was the presenting symptom. The diagnosis of Gaucher's disease in this case was arrived at during the work-up investigations for the etiology of the ocular manifestations. Initially the ocular symptoms in these three patients manifested as acute anterior uveitis, becoming chronic and involving also the posterior segments at a later stage.

Convulsions and retinal haemorrhage: should we look further?

BACKGROUND AND AIMS

The prevalence of retinal haemorrhages after convulsions is not well established. As these haemorrhages are considered characteristic of child abuse, we investigated their occurrence after convulsive episodes to see whether the finding of haemorrhage should prompt further investigation.

METHODS

Prospective study of 153 children (aged 2 months to 2 years), seen in the emergency department after a convulsive episode. After a thorough history and physical examination, a retinal examination was performed by an ophthalmologist. If findings were positive, further investigation was undertaken to rule out systemic disorder or child abuse.

RESULTS

One child was found with unilateral retinal haemorrhages following an episode of a simple febrile convulsion. A thorough investigation uncovered no other reason for this finding.

CONCLUSION

Retinal haemorrhages following a convulsive episode are rare. Such a finding should trigger an extensive search for other reasons, including child abuse.

Effect of schizophrenia on frontotemporal activity during word encoding and recognition: a PET cerebral blood flow study

OBJECTIVE

Neuropsychological studies have shown that deficits in verbal episodic memory in schizophrenia occur primarily during encoding and retrieval stages of information processing. The current study used positron emission tomography to examine the effect of schizophrenia on change in cerebral blood flow (CBF) during these memory stages.

METHOD

CBF was measured in 23 healthy comparison subjects and 23 patients with schizophrenia during four conditions: resting baseline, motor baseline, word encoding, and word recognition. The motor baseline was used as a reference that was subtracted from encoding and recognition conditions by using statistical parametric mapping.

RESULTS

Patients' performance was similar to that of healthy comparison subjects. During word encoding, patients showed reduced activation of left prefrontal and superior temporal regions. Reduced left prefrontal activation in patients was also seen during word recognition, and additional differences were found in the left anterior cingulate, left mesial temporal lobe, and right thalamus. Although patients' performance was similar to that of healthy comparison subjects, left inferior prefrontal activation was associated with better performance only in the comparison subjects.

CONCLUSIONS

Left frontotemporal activation during episodic encoding and retrieval, which is associated with better recognition in healthy people, is disrupted in schizophrenia despite relatively intact recognition performance and right prefrontal function. This may reflect impaired strategic use of semantic information to organize encoding and facilitate retrieval.

Effects of check size on visual cortex activation studied by functional magnetic resonance imaging

We studied functional magnetic resonance imaging (fMRI) of visual cortex during checkerboard visual stimulation with three standard check sizes to examine whether activation in the visual cortex varied among these sizes. We acquired fMRI at 1.5 T in 8 normal subjects, each receiving the best refractive correction. Each subject underwent an experiment consisting of four conditions: black and white checkerboards with three check sizes (0.25-, 0.5-, and 1.0-degree) flickering at 8 Hz, and a black screen. SPM96 was used for a group data analysis with a random effects model after each of the subject's data was motion-corrected and spatially normalized to a standard brain. The activation in the visual cortex showed the greatest signal changes with the 0.5-degree check among the three check sizes. When standard check sizes are used to stimulate visual cortex in fMRI experiments, our results suggest that 0.5-degree checks flickering at 8 Hz produce the most vigorous activation in visual cortex.

Reproducibility of visual activation during checkerboard stimulation in functional magnetic resonance imaging at 4 Tesla

PURPOSE

To investigate the reproducibility of visual activation by checkerboard stimulation, we used functional magnetic resonance imaging (fMRI) at 4 Tesla (T).

METHODS

Four subjects were studied with fMRI at 4 T during checkerboard visual stimulation. The functional images were realigned and spatially normalized to the standard brain. For each subject, statistical parametric maps were made for each study, and the reproducibility was determined based on the number of supra-threshold voxels (Z > 3.5, 4.5, and 5.5).

RESULTS

The mean ratio for the number of supra-threshold (Z > 4.5) voxels was 0.75, and the mean ratio for the overlapping voxels was 0.61. Restricting the region of interest within the posterior half of the brain improved reproducibility values at the low threshold (Z > 3.5), but did not improve the values at the higher thresholds.

CONCLUSIONS

Despite the fact that more than half of the supra-threshold voxels were found to be active for the repeated scans, visual activation with checkerboard stimulation seems to be less reproducible than that by flash stimulation.

Visual activation in functional magnetic resonance imaging at very high field (4 Tesla)

OBJECTIVES

Functional magnetic resonance imaging (fMRI) at very high field strengths provides functional brain mapping with the enhanced signal to noise ratio and the larger blood oxygenation level-dependent (BOLD) effect. We report activated areas in the standard space detected by fMRI at 4 Tesla (T) during simple visual stimulation.

MATERIALS AND METHODS

Twelve healthy young subjects were scanned using a 4 T scanner during binocular flashing visual stimulation. Functional images were realigned to the first scan and then spatially normalized. Individual and group data analyses were performed to identify areas of visual activation.

RESULTS

Activation of the bilateral primary visual cortex (V1/V2) was observed along the entire calcarine fissure in all subjects. The activated area extended to the extrastriate cortex in all subjects. Activation of the bilateral lateral geniculate nucleus (LGN) was detected in all subjects. The group data showed activation of the bilateral primary visual cortex and the bilateral lateral geniculate nucleus.

CONCLUSIONS

Robust activation of the vision-related areas was successfully obtained in all subjects using a 4 T magnetic resonance scanner. These results suggest that fMRI at very high field strengths may be effective in showing visual system physiology, and that it can be a promising method to assess visual function of human subjects.

Reproducibility of visual activation in functional magnetic resonance imaging at very high field strength (4 Tesla)

PURPOSE

The reproducibility of functional magnetic resonance imaging (fMRI) has been studied on 1.5 Tesla (T) (high field strength) scanners. We report the reproducibility of visual activation in fMRI at 4 T (very high field strength).

METHODS

Five healthy subjects were scanned twice in the same session with a 4 T scanner during binocular flashing visual stimulation. The activated areas during the first and second acquisition were compared.

RESULTS

Activation of the visual cortex was observed in all subjects and activation of lateral geniculate nucleus was also detected in four subjects. The ratio of overlapping activated voxels in the first and second acquisition was 0.81 +/- 0.05.

CONCLUSIONS

Reproducibility of visual activation using fMRI at 4 T was found to be acceptable, and the results from 4T scanners show a reliability similar to those at 1.5 T.

Functional magnetic resonance imaging of lateral geniculate nucleus at 1.5 tesla

Although activation of the lateral geniculate nucleus has been detected by functional magnetic resonance imaging with magnetic field strengths higher than 2.0 Tesla, there have been no reports of functional magnetic resonance imaging of the lateral geniculate nucleus with the more widely available 1.5 Tesla scanner. The authors used functional magnetic resonance imaging techniques at 1.5 Tesla to detect lateral geniculate nucleus activation in five of seven healthy subjects. This study shows that visual activation of the lateral geniculate nucleus can be obtained with functional magnetic resonance imaging using conventional 1.5 Tesla scanners.

Contralateral monocular dominance in anterior visual cortex confirmed by functional magnetic resonance imaging

PURPOSE

Although it is known that the damage to anterior striate cortex results in temporal peripheral visual field loss of the contralateral eye in patients with cerebral visual disturbance, the monocularity of anterior striate cortex has not been demonstrated in normal living humans. The aim of this study was to investigate whether this could be shown noninvasively using functional magnetic resonance imaging of the human visual cortex.

METHODS

Eleven normal volunteers were studied with functional magnetic resonance imaging during alternating monocular visual stimulation using a 1.5 Tesla scanner. The data were motion corrected and spatially normalized to the standard brain. The monocular activation of the visual cortex was compared with the activation by the other eye.

RESULTS

In the individual data analysis, contralateral eye dominance was always observed in the anterior striate cortex. In the group analysis from 11 subjects, the area with contralateral eye dominance was found in the most anterior part of primary visual cortex where the calcarine fissure merged with the parieto-occipital sulcus.

CONCLUSIONS

This study shows that the contralateral eye dominance of anterior striate cortex can be detected noninvasively with functional magnetic resonance imaging during monocular visual stimulation. The finding confirms that the anterior striate cortex, where the monocular temporal crescent is represented, is primarily monocular, but the fact that greatest density of retinal ganglion cells and photoreceptors is in the nasal hemiretina must also be taken into account when interpreting these results.

A nonsense mutation (W9X) in CRYAA causes autosomal recessive cataract in an inbred Jewish Persian family

PURPOSE

To identify the genetic defect causing autosomal recessive cataract in two inbred families.

METHODS

Linkage analysis was performed with polymorphic markers close to 14 loci previously shown to be involved in autosomal dominant congenital cataract. In one of the families a gene segregating with the disease was analyzed by single-strand conformation polymorphism (SSCP) and eventually sequenced.

RESULTS

Three polymorphic markers close to the CRYAA gene located on chromosome 21q segregated with the disease phenotype in one of the families, but not in the other. Sequencing of the CRYAA in this Jewish Persian family revealed a G-to-A substitution, resulting in the formation of a premature stop codon (W9X).

CONCLUSIONS

A nonsense mutation in the CRYAA gene causes autosomal recessive cataract in one family. This constitutes the first description of the molecular defect underlying nonsyndromic autosomal recessive congenital cataract. That there was no linkage to this locus in another family provides evidence for genetic heterogeneity.

Selective opiate modulation of nociceptive processing in the human brain

Fentanyl, a mu-opioid receptor agonist, produces analgesia while leaving vibrotactile sensation intact. We used positron emission tomography (PET) to study the mechanisms mediating this specific effect in healthy, right-handed human males (ages 18-28 yr). Subjects received either painful cold (n = 11) or painless vibratory (n = 9) stimulation before and after the intravenous injection of fentanyl (1.5 microgram/kg) or placebo (saline). Compared with cool water (29 degrees C), immersion of the hand in ice water (1 degrees C) is painful and produces highly significant increases in regional cerebral blood flow (rCBF) within the contralateral second somatosensory (S2) and insular cortex, bilaterally in the thalamus and cerebellum, and medially in the cerebellar vermis. Responses just below the statistical threshold (3.5 < Z < 4.0) are seen in the contralateral anterior cingulate, ipsilateral insular cortex, and dorsal medial midbrain. The contralateral primary sensory cortex (S1) shows a trend of activation. Except for slight changes in intensity, this pattern is unchanged following a saline placebo injection. Fentanyl reduces the average visual analogue scale ratings of perceived pain intensity (47%) and unpleasantness (50%), reduces pain-related cardioacceleration, and has positive hedonic effects. After fentanyl, but not placebo, all cortical and subcortical responses to noxious cold are greatly reduced. Subtraction analysis [(innocuous water + fentanyl) - (innocuous water + no injection)] shows that fentanyl alone increases rCBF in the anterior cingulate cortex, particularly in the perigenual region. Vibration (compared with mock vibration) evokes highly significant rCBF responses in the contralateral S1 cortex in the baseline (no injection) and placebo conditions; borderline responses (3.5 < Z < 4. 0) are detected also in the contralateral thalamus. Fentanyl has no effect on the perceived intensity or unpleasantness of vibratory stimulation, which continues to activate contralateral S1. Fentanyl alone [(mock vibration + fentanyl) - (mock vibration + no injection)] again produces highly significant activation of the perigenual and mid-anterior cingulate cortex. A specific comparison of volumes of interest, developed from activation peaks in the baseline condition (no injection), shows that fentanyl strongly attenuates both the contralateral thalamic and S1 cortical responses to noxious cold stimulation (P < 0.048 and 0.007, respectively) but fails to affect significantly these responses to vibrotactile stimulation (P > 0.26 and 0.91, respectively). In addition, fentanyl, compared with placebo, produces a unique activation of the mid-anterior cingulate cortex during fentanyl analgesia, suggesting that this region of the cingulate cortex participates actively in mediating opioid analgesia. The results are consistent with a selective, fentanyl-mediated suppression of nociceptive spinothalamic transmission to the forebrain. This effect could be implemented directly at the spinal level, indirectly through cingulate corticofugal pathways, or by a combination of both mechanisms.

Hemispheric activation of anterior and inferior prefrontal cortex during verbal encoding and recognition: a PET study of healthy volunteers

Evidence of bilateral prefrontal activation during memory encoding and retrieval has increased attention given to anatomical subdivisions within the prefrontal cortex. The current study examined anterior and inferior aspects of the prefrontal cortex to determine their degree of functional and hemispheric overlap during encoding and recognition. Cerebral blood flow of 25 healthy volunteers was measured using PET (15)O-water methods during four conditions: resting baseline, sequential finger movement, word encoding, and word recognition. Resting and motor images were averaged to provide a single reference that was subtracted from encoding and recognition using statistical parametric mapping (SPM96). Memory conditions were also subtracted from each other to identify differences in regional activity. Subjects performed well (86% correct) and had a slightly conservative response bias. Baseline subtraction from encoding revealed focal activation of left inferior prefrontal cortex (area 45) without significant contralateral activation. Recognition minus baseline subtraction produced a focal right anterior prefrontal activation (areas 9 and 10) that was not present in the left hemisphere. Bilateral effects were seen in area 45 during recognition. Subtraction of memory tasks from each other did not reveal any areas of greater activity during encoding. However, the recognition task produced greater activation in right area 9 extending into the anterior cingulate. Greater activity during recognition was also observed in left insula and bilateral visual integration areas. These results are discussed in relation to the prevailing model of prefrontal hemispheric asymmetry during episodic memory.

Reproducibility of visual activation in functional MR imaging and effects of postprocessing

BACKGROUND AND PURPOSE

Functional MR imaging studies of the brain should be interpreted in the context of their reproducibility. We assessed the reproducibility of visual activation measured by functional MR imaging and analyzed the effect of image transformation to standard space.

METHODS

Seven healthy volunteers were studied twice with echo-planner functional MR imaging at 1.5 T during visual stimulation. The studies were separated by an interval of 2 to 7 days. Functional images were analyzed after spatial normalization to the space described by Talairach and Tournoux and/or after coregistration of the images of the second study with the images of the first study. The number of active voxels for each study was determined at three thresholds. In addition, the change in the center of the mass of activation, the mean change in signal intensity, and the mean t value within the activated area were measured. These reproducibility indexes were calculated for the spatially normalized and nonnormalized data for each subject.

RESULTS

Variations in visual activation were observed between the two studies in the same individual as well as across subjects. There was no evidence of an effect from image transformation on reproducibility on any of the measures.

CONCLUSION

Our findings show that the reproducibility of activation in functional MR imaging may be much more variable across subjects than suggested in previous studies. The use of different types of image transformation (coregistration, spatial normalization) does not significantly affect the reproducibility of visual activation.

Neuroendocrine and psychophysiologic responses in PTSD: a symptom provocation study

Biological research on post-traumatic stress disorder (PTSD) has focused on autonomic, sympatho-adrenal, and hypothalamo-pituitary-adrenal (HPA) axis systems. Interactions among these response modalities have not been well studied and may be illuminating. We examined subjective, autonomic, adrenergic, and HPA axis responses in a trauma-cue paradigm and explored the hypothesis that the ability of linked stress-response systems to mount integrated responses to environmental threat would produce strong correlations across systems. Seventeen veterans with PTSD, 11 veteran controls without PTSD, and 14 nonveteran controls were exposed to white noise and combat sounds on separate days. Subjective distress, heart rate, skin conductance, plasma catecholamines, ACTH, and cortisol, at baseline and in response to the auditory stimuli, were analyzed for group differences and for patterns of interrelationships. PTSD patients exhibited higher skin conductance, heart rate, plasma cortisol, and catecholamines at baseline, and exaggerated responses to combat sounds in skin conductance, heart rate, plasma epinephrine, and norepinephrine, but not ACTH. The control groups did not differ on any measure. In canonical correlation analyses, no significant correlations were found between response systems. Thus, PTSD patients showed heightened responsivity to trauma-related cues in some, but not all, response modalities. The data did not support the integrated, multisystem stress response in PTSD that had been hypothesized. Individual response differences or differing pathophysiological processes may determine which neurobiological system is affected in any given patient.

Prenatal diagnosis of dacryocystocele: a possible marker for syndromes

We present our experience of the sonographic prenatal diagnosis of dacryocystocele and review the literature. This lesion can be distinguished from a facial hemangioma, dermoid or anterior encephalocele by the ultrasound findings and Doppler flow studies. These conditions are separate entities and their associated diagnosis and prognosis are very different in each case. As dacryocystocele may be part of numerous syndromes, its prenatal visualization raises the rare possibility of associated anomalies.

A wavelet packet model of evoked potentials

The standard methods for decomposition and analysis of evoked potentials are bandpass filtering, identification of peak amplitudes and latencies, and principal component analysis (PCA). We discuss the limitations of these and other approaches and introduce wavelet packet analysis. Then we propose the "single-channel wavelet packet model," a new approach in which a unique decomposition is achieved using prior time-frequency information and differences in the responses of the components to changes in experimental conditions. Orthogonal sets of wavelet packets allow a parsimonious time-frequency representation of the components. The method allows energy in some wavelet packets to be shared among two or more components, so the components are not necessarily orthogonal. The single-channel wavelet packet model and PCA both require constraints to achieve a unique decomposition. In PCA, however, the constraints are defined by mathematical convenience and may be unrealistic. In the single-channel wavelet packet model, the constraints are based on prior scientific knowledge. We give an application of the method to auditory evoked potentials recorded from cats. The good frequency resolution of wavelet packets allows us to separate superimposed components in these data. Our present approach yields estimates of component waveforms and the effects of experiment conditions on the amplitude of the components. We discuss future extensions that will provide confidence intervals and p values, allow for latency changes, and represent multichannel data.

Relationship of seizure duration to antidepressant efficacy in electroconvulsive therapy

BACKGROUND

A relationship between the anticonvulsant and antidepressant properties of electroconvulsive therapy (ECT) has been hypothesized. The goal of this study was to see whether the anticonvulsant effects of ECT could be measured in a clinical setting and whether there was any relationship between the anticonvulsant effects of ECT and the antidepressant response to it.

METHODS

We examined the temporal relationship between change in seizure duration (as an index of anticonvulsant activity) and improvement in Hamilton Rating Scale for Depression scores in a retrospective sample of 114 depressed patients who received 145 courses of ECT. A linear mixed effects model was utilized for analysis so that the repeated measures nature of the data could be taken into account.

RESULTS

Both seizure duration and depression scores decreased significantly through the course of ECT. However, no evidence was found for a relationship between decrease in seizure duration and clinical improvement as measured by Hamilton ratings.

CONCLUSIONS

The process underlying the reduction in seizure duration through a course of ECT may not be related to antidepressant efficacy.

Ethnic differences in the length of the menstrual cycle during the postmenarcheal period

In 1989, 125 African-American and 123 European-American girls aged 12-14 years were enrolled in a 2-year study in which they maintained a menstrual calendar, recording the date and amount of menstrual bleeding. Weight, exercise, and stress during the previous week were recorded at the start of each menstrual cycle. Although only minor ethnic differences were observed in expected cycle length (29.3 vs. 28.8 days for European-American and African-American girls, respectively), more prominent differences were observed in the between-subjects standard deviation of cycle length (2.9 vs. 2.2 days, respectively) and in the odds of having a cycle longer than 45 days (odds ratio=1.86, 95% confidence interval 1.17-2.97) for European-American compared with African-American girls. Low weight for height and high levels of exercise increased the probability of having a cycle longer than 45 days and decreased expected cycle length of 13- to 45-day cycles. Additional investigation of potential ethnic differences in menstrual cycle characteristics is warranted.

Linear mixed models with heterogeneous within-cluster variances

This paper describes an extension of linear mixed models to allow for heterogeneous within-cluster variances in the analysis of clustered data. Unbiased estimating equations based on quasilikelihood/pseudolikelihood and method of moments are introduced and are shown to give consistent estimators of the regression coefficients, variance components, and heterogeneity parameter under regularity conditions. Cluster-specific random effects and variances are predicted by the posterior modes. The method is illustrated through an analysis of menstrual diary data and its properties are evaluated in a simulation study.

Modeling NMR lineshapes using logspline density functions

Distortions in the FID and spin echo due to magnetic field inhomogeneity are proved to have a representation as the characteristic function of some probability distribution. In the special case that the distribution is Cauchy, the model reduces to the conventional Lorentzian model. A more general and flexible representation is presented using the Fourier transform of a logspline density. An algorithm for fitting the model is described, the performance of the model and algorithm is investigated in applications to real and simulated data sets, and the logspline approach is compared to a previous Hermitian spline approach and to the Lorentzian model. The logspline model is more parsimonious than the Hermitian spline model, provides a better fit to real data, and is much less biased than the Lorentzian model.

Intra-hemispheric alpha coherence decreases with increasing cognitive impairment in HIV patients

Inter-hemispheric and intra-hemispheric canonical coherences in the alpha range between EEG signals collected from frontal and posterior groups of electrodes were estimated for 38 HIV positive subjects and 23 uninfected controls. Neuropsychological testing was used to categorize the degree of cognitive impairment evident in each of the subjects. A linear regression analysis provided evidence that intra-hemispheric coherence decreased with increasing cognitive impairment in impaired HIV+ subjects, as measured by a Global Impairment Score (GIS). There was no evidence that cognitively unimpaired HIV+ subjects differed in coherence when compared to uninfected control subjects. Severely impaired HIV+ subjects showed significantly decreased coherence compared to uninfected controls. These data contradict previous work demonstrating increased intra-hemispheric and inter-hemispheric alpha coherence in impaired HIV subjects. In addition, they provide evidence that intra-hemispheric (and possibly inter-hemispheric) disconnection is associated with cognitive impairment in HIV.

Frequency domain estimation of covariate effects in multichannel brain evoked potential data

An evoked potential is the recorded brain electrical response to a stimulus such as an auditory click. In most evoked potential experiments, the response is studied as a function of covariates such as stimulus characteristics and drug states. We propose a frequency domain model of multichannel evoked potential data that includes parameters representing the effects of covariates on the amplitude and latency (time from stimulus presentation) of the response. The variability of the response among scalp electrodes is modeled by the activity of one or more equivalent electrical dipoles. The frequency domain representation allows considerable data reduction, facilitates modeling of the noise, and leads to a simple approximate expression for the latency effects. We describe maximum likelihood estimation of the model parameters and construction of approximate confidence intervals for the covariate effects. We report the results of a simulation study in which we evaluated the bias of the estimators and the coverage rate of the confidence intervals. We also report the results of an application to auditory evoked potentials recorded from five subjects.

Autosomal recessive colobomatous microphthalmia

Colobomatous microphthalmia was studied in multiple relatives of 5 families. In these families, the disorder was an autosomal recessive trait as opposed to the usual autosomal dominant form of the disorder. A relatively high incidence of this recessive allele is found in the Iranian Jewish community.

Frequency domain dipole localization: extensions of the method and applications to auditory and visual evoked potentials

We describe a statistical frequency domain approach to localizing equivalent dipole generators of human brain evoked potentials. The frequency domain representation allows considerable data reduction, constrains the magnitude function of the dipoles to be smooth, and accounts for the statistical properties of the background EEG. A previous paper described a restrictive model in which the dipole orientations were assumed to be fixed over time, and only one dipole was allowed. In this paper, we consider the more general model in which the orientation can vary over time, and which includes multiple dipole generators. The varying orientation model has the practical advantage of being more nearly linear and more flexible than the fixed orientation model, which facilitates convergence of the iterative fitting algorithm. We suggest a measure of goodness-of-fit that compares the likelihood of the dipole model with the likelihoods of saturated and null models. We report the results of fitting the model to recorded auditory and visual evoked potentials. A single dipole with fixed orientation seems to be an adequate model of the auditory midlatency response, while two dipoles with varying orientation are needed to fit the later P200 component. Analysis of the visual P100 response to unilateral stimulation localized a generator in the contralateral occipital cortex, as expected from anatomical considerations. A two-dipole model fit the visual P100 response of bilateral stimulations, and the locations of the two dipoles were similar to the locations obtained by single-dipole fits to the responses to left and right unilateral stimuli.

Behr's syndrome and 3-methylglutaconic aciduria

We examined three patients from two families of Jewish-Iraqi origin who had progressive reduction of visual acuity and childhood onset of bilateral optic nerve atrophy without additional retinal abnormalities. They had neurologic symptoms compatible with Behr's syndrome. Neurologic signs included increased tendon reflexes, a positive Babinski sign, progressive spastic paraplegia, dysarthria, head nodding, and horizontal nystagmus. Neurologic involvement varied between affected siblings. The patients excreted excessive amounts of 3-methylglutaconic acid and 3-methylglutaric acid in their urine. We compared the characteristic ophthalmic features and the spectrum of neurologic signs encountered in this recently delineated autosomal recessive clinical entity with those of previously described entities associated with 3-methylglutaconic aciduria. Patients with early-onset optic atrophy should be examined for neurologic signs and screened for organic aciduria. A detailed ophthalmic examination is important in patients with neurologic abnormalities compatible with Behr's syndrome.

EEG spectra in dyslexic and normal readers during oral and silent reading

EEGs of extensively screened dyslexics and normal readers were recorded while they read easy and difficult texts silently and orally, and during two other verbal tasks which also differed in overt speaking but had no reading component: narrative speaking and listening to a story. Mid-temporal, central and parietal leads were referenced to linked ears and to Cz. Large differences between tasks and between groups were found. With the linked ears reference, power was higher in all bands in oral reading than in silent reading, with the largest change occurring in the temporal leads. In the theta and low beta bands the difference between oral and silent reading was greater for controls than for dyslexics. These effects were not accounted for by differences in reading speed or in difficulty. Similar results were found in two cohorts of subjects. The difference between groups in theta was found only in the reading tasks. In contrast, the group difference in low beta was also found in the change from listening to speaking. This implies that the oral-silent group difference in theta is related to some aspect of the reading tasks other than the presence or absence of overt speaking, and that the low beta group difference is related to some aspect of overt speaking rather than to reading per se. With the Cz reference no group differences were found. It is suggested that the groups differ in the reading strategies they use, and the degree to which they shift strategy between the silent and oral tasks. We hypothesize that these cognitive differences are reflected in the theta activity from the temporal lobe. While there were many differences between the tasks in alpha power and asymmetry, no group differences involving alpha were found.

Artifactually high coherences result from using spherical spline computation of scalp current density

Coherence computed from common reference montages inextricably confounds true coherence with power and phase at the recording and reference electrodes. Direct measurement of coherence requires reference-free EEG data, such as data from EEG scalp current densities (SCDs), which estimate the potential gradient perpendicular to the scalp. Perrin et al. (1989) presented a method for computing SCDs by taking the Laplacian of the scalp potential surface generated by spherical spline interpolation. When this method of computing SCDs was applied to EEG data gathered from young adults, very high values were observed for inter-electrode coherences computed from the spherical spline derived SCD data but not from coherences computed from the common reference data. These high coherences prompted further examination of the properties of the spherical spline function and of spherical spline derived SCDs. Simulated data were constructed, and coherence was computed on the simulated data and on the SCDs derived from the spherical spline procedure and from the Hjorth (1980) procedure. The results of those simulations are presented, which demonstrate that a major artifact is introduced by using the spherical spline procedure. This artifact results from the spline weighting matrix used to derive the SCDs and strongly inflates the inter-electrode coherences of the SCD transformed data.

Representation of multi-channel evoked potential data using a dipole component model of intracranial generators: application to the auditory P300

A number of procedures have been employed to decompose recorded scalp potential wave forms into their hypothesized constituent elements. The shortcomings of the various decomposition methods (principal components analysis, topographic components modeling, inverse dipole localization and spatio-temporal dipole modeling) are reviewed and a new dipole components model, which incorporates the strengths of the topographic components model and the spatio-temporal dipole model, is presented. This model decomposes ERPs into subcomponents reflecting the activity of dipole sources with location and orientation fixed across subjects and with the temporal activity of each dipole modeled as a decaying sinusoid. The requirement that the equivalent dipole generators be the same across subjects and experimental conditions permits analysis of inter-group differences and of the effects of experimental variables. An application of the model to data from a 3-tone auditory target detection task is presented, and equivalent dipole sources of the components of the auditory evoked potential are described. Assumptions inherent in the model, as well as practical obstacles to its widespread implementation, are discussed.

Estimation of trial-to-trial variation in evoked potential signals by smoothing across trials

Averaging single trial evoked potential data to produce an estimate of the underlying signal obscures trial-to-trial variation in the response. We describe a method for estimating slow changes in the evoked potential signal by smoothing the data over trials. We discuss the crucial issue of deciding how much to smooth and suggest that an appropriate smoothing parameter is one that minimizes the estimated mean average square error of the smoothed data. Equations to estimate the mean average square error for a one-dimensional local linear regression smoother are presented. Performance of the method is assessed using simulated evoked potential data with several different models of a changing signal and different values of the signal-to-noise ratio. We find that the method rarely imputes trial-to-trial variation to data sets that have an unchanging signal, while it almost always produces less error than averaging when estimating a varying signal. The ability of the method to reveal signal heterogeneity is hampered by very low signal-to-noise ratios. When applied to real auditory evoked potential data from a sample of elderly subjects, the method indicated a changing signal in 35% of all subjects and in 56% of subjects with signal-to-noise ratios above 0.6. Consistent patterns of variation in the auditory evoked potential were present in this sample.

Selecting the smoothing parameter for estimation of slowly changing evoked potential signals

Brain evoked potential (EP) data consist of a true response ("signal") and random background activity ("noise"), which are observed over repeated stimulus presentations ("trials"). A signal that changes slowly from trial to trial can be estimated by smoothing across trials and over time within trials. We present a method for selecting the smoothing parameter by minimizing an estimate of the mean average squared error (MASE). We evaluate the performance of this method using simulated EP data, and apply the method to an example set of real flash evoked potentials.

Analysis of repeated measurements using nonparametric smoothers and randomization tests

The mixed-model analysis of variance (ANOVA), which is commonly applied to repeated measurements taken over time, depends on specialized assumptions about the error distribution and fails to exploit information contained in the ordering of the data points over time. This paper describes a procedure that overcomes these disadvantages while preserving familiar features of the mixed-model ANOVA. Group profiles are estimated by nonparametric smoothing of observed mean profiles. Group and time main effects, and the group by time interaction effect, are tested using randomization tests. Results of Zerbe (1979, Journal of the American Statistical Association 74, 215-221) are used to construct F-test approximations for the randomization tests of the group and group by time effects. A new approximate F-test for time effect is proposed. A simulation study demonstrates that the approximations perform well and that smoothing increases the power of the tests for time main effect and group by time interaction. The procedure is applied to data on hormone levels in cows.

Noise and signal power and their effects on evoked potential estimation

Signal power, noise power and their ratio (SNR) are important variables underlying estimation of evoked potential signals, yet, they are rarely explicitly considered in the design or analysis of EP experiments. A model is developed which relates the reliability of the average evoked potential (AEP) wave form to signal power, noise power, SNR, and the number of single trials included in the average. Measurements taken from auditory and visual EP experiments in elderly subjects show that noise power is highly reliable across experimental conditions and probably reflects global CNS anatomic or physiologic factors. In contrast, signal power and SNR are variable across conditions and sensory modalities, but are stable across replications. Thus signal power reflects CNS processes specific to the experimental paradigm. These results have importance for EP estimation. The expected reliability of the AEP cannot be adequately predicted from estimates of a subject's noise power, or from SNR estimated under different experimental conditions. These findings suggest the need for on-line estimation of SNR during data acquisition to ensure adequate reliability of AEPs.

Common reference coherence data are confounded by power and phase effects

Coherence analysis of the EEG is used to study the coupling between cortical regions. High coherence between signals recorded at 2 electrodes is interpreted as evidence for neuroanatomic connections between the cortical areas underlying the electrodes. When common reference recordings are used, coherence measures the relationship between 2 time series, each of which is the difference between 2 signals measured at the scalp and is confounded by spectral power and phase at the recording and reference electrodes. Using multi-channel EEG data from 3 subjects, we illustrate the confounding of common reference data coherence computations and demonstrate the extreme effects of power and phase changes on coherence by simulating these changes in the EEG data. Common reference coherence data can be either inflated or deflated as a consequence of activity (i.e., spectral power) at the reference. Phase relationships among the reference and recording time series modulate the power effects on coherence. Both the power and phase effects can vary dramatically across frequencies, having profound and complicated effects on the shape of the coherence function. Based on these considerations, we conclude that common reference coherence data must be interpreted very cautiously and recommend that a new body of EEG coherence data must be gathered using reference-free recording methods before the utility of EEG coherence analysis for understanding brain function can be determined.

Obesity prognosis: a longitudinal study of children from the age of 6 months to 9 years

The development of body fatness and leanness is examined in an ongoing prospective nutrition and growth study. Individual skinfold thicknesses, relative weights, weight gains, activity levels, and caloric intakes were examined at seven ages between 6 months and 9 years. Changes in body fatness in this group of children provide evidence that the obese infant usually does not become the obese child. Weight gain in infancy is also a poor predictor of 9-year old obesity. Changes from obese to non-obese or lean are often not linear. There is evidence that impending or actual obesity begins at ages 6 to 9 years with some predictability provided as early as age 2 years for girls, age 3 years for boys.