Biomedical subjects

S Arndt

Publications and source records attributed to S Arndt.

At least 91 records · Page 5Linked to original sources

PubMed1996

Normalizing counts and cerebral blood flow intensity in functional imaging studies of the human brain.

Image intensity normalization is frequently applied to eliminate or adjust for subject or injection global blood flow (gCBF) and other sources of nuisance variation. Normalization has several other positive effects on the analysis of PET images. However, the choice of an intensity normalization technique affects the statistical and psychometric properties of the image data. We compared three normalization procedures, the ratio approach (regional (r)CBF/gCBF), histogram equalization, and ANCOVA, on both PET count and flow data sets. The ratio method presents the proportional increase of regions, the histogram equalization method offers the relative ranking of intensities over the image, and the ANCOVA method provides statistical deviations from an expected linear model of regional values from the subject's gCBF. The original study used 33 normal subjects in a standard subtraction paradigm. The normalization methods were evaluated on their ability to remove extraneous error variation, induce homogeneity of intersubject variation, and remove unwanted dependencies. In general, the normalization modified the subtraction image more than the individual condition images. All three methods worked well at removing the dependency of rCBF on gCBF in count and flow images. For count data, the three methods also reduced the amount of error variation equally well, improving the signal to noise ratio. For flow data, the histogram equalization and ratio methods worked best at reducing statistical error. All three methods dramatically stabilized the variance over the image.

Analysis of Variance↗

PubMed1996

A neural network model for stroboscopic alternative motion.

A neural network which models multistable perception is presented. The network consists of sensor and inner neurons. The dynamics is established by a stochastic neuronal dynamics, a formal Hebb-type coupling dynamics and a resource mechanism that corresponds to saturation effects in perception. From this a system of coupled differential equations is derived and analyzed Single stimuli are bound to exactly one percept, even in ambiguous situations where multistability occurs. The network exhibits discontinuous as well as continuous phase transitions and models various empirical findings, including the percepts of succession, alternative motion and simultaneity, the percept of oscillation is explained by oscillating percepts of a continuous phase transition.

Algorithms↗

PubMed1996

Reversibility of brain tissue loss in anorexia nervosa assessed with a computerized Talairach 3-D proportional grid.

We describe the results of our follow-up magnetic resonance imaging (MRI) study of underweight patients with anorexia nervosa, using rigorous methodology to control for head position across time. All subjects first underwent an initial scan and rescan to verify that our computerized three-dimensional co-planar grid method for volume measurement was reliable and accurate, regardless of head positioning. After a period of several months, subjects had a follow-up scan to assess for changes that may have occurred following significant weight gain. Ventricular and total brain volume measurements from the initial scans were compared with the scans from an age- and sex-matched normal control group to determine whether we could replicate previous findings of ventricular enlargement compared with controls and whether brain volume is reduced compared with controls. Anorexic subjects had significantly larger ventricles when compared with normal controls but did not differ significantly in total brain volume. Using a repeated measures analysis of variance, a priori contrasts compared the initial/rescan pair volumes with each other and the initial/rescan pair volumes with the follow-up volume. These analyses showed that ventricular and total brain volumes derived from the initial/rescan pair were nearly identical, but that at follow-up ventricular volume decreased significantly and total brain volume increased significantly after weight gain.

Adolescent↗

PubMed1996

Course of behavioral change in autism: a retrospective study of high-IQ adolescents and adults.

OBJECTIVE: The course of behavioral change in autistic behaviors has received little attention in previous research but is a potentially important parameter for study in autism. METHOD: Autistic behaviors were systematically examined in 38 high-IQ adolescent and adult autistic individuals at their current age (13 through 28 years) and retrospectively at age 5 years using a standardized interview for autism. RESULTS: Significant change over time in autistic behaviors, generally in the direction of improvement, was detected. The proportion of subjects showing improvement in communication and social behaviors was found to be significantly higher than the proportion showing improvement in ritualistic/repetitive behaviors. Five of 38 subjects who met DSM-IV criteria for autistic disorder at age 5 years no longer met criteria at their current age, although all five continued to have substantial impairment. CONCLUSIONS: The study of patterns of behavioral change over time in autism has practical implications for both diagnosis and prognosis as well as potential importance in defining biologically meaningful subgroups and clarifying fundamental mechanisms underlying this disorder.

Adolescent↗

PubMed1996

Regional brain enlargement in autism: a magnetic resonance imaging study.

OBJECTIVE: To determine whether increased brain volume in autism, suggested in previous studies, is the result of general or regional brain size differences and to study the effect of gender on brain size and pattern of enlargement. METHOD: Total brain volume and cerebral cortical lobe volumes were examined in 35 autistic and 36 comparison subjects using magnetic resonance imaging and an automated method of brain volume measurement. RESULTS: After controlling for height and nonverbal IQ, the authors detected a significant diagnosis x gender effect (F = 7.4; p = .009) for total brain volume. A repeated-measures analysis of variance indicated that the pattern of enlargement (brain region x diagnosis) in autistic subjects differed from that in controls (F = 4.88; p = .0004). Subsequent sex-specific analysis revealed significantly increased total brain volume in autistic males but not females. Analysis of lobe sizes showed significant enlargement in autistic subjects in temporal, parietal, and occipital, but not frontal lobes. CONCLUSIONS: These results suggest that brain size is increased in autism and that differences are not generalized but appear to be the result of a pattern of enlargement with increases in the size of specific cortical lobes.

Adolescent↗

PubMed1996

Quantitative EEG differences in a nonclinical sample of children with ADHD and undifferentiated ADD.

OBJECTIVE: To use quantitative electroencephalographic (EEG) techniques to identify electrophysiological differences between children with distinct disorders of attention and/or hyperactivity. METHOD: Forty children from a prescreened community sample were evaluated by means of both spectral EEG and evoked response potential (ERP) techniques. The children were 7 to 13 years of age and were selected on the basis of membership in one of the following DSM-III-R categories: attention-deficit hyperactivity disorder (ADHD) (n = 16), undifferentiated attention deficit disorder (UADD) (n = 12), or no disruptive disorder diagnosis (n = 12). RESULTS: Spectral EEG revealed that UADD subjects had less delta band relative percent power (RPP) (p < .01), more beta band RPP (p < .01), and ERP findings of a decreased rare tone P300 amplitude (p < .02) compared with the control group. ADHD subjects had spectral EEG findings of increased beta band RPP (p < .05) and ERP findings of an increased common tone N100 latency (p < .02) and a decreased rare tone P300 amplitude (p < .02). Interhemispheric asymmetries appeared to distinguish the groups: the UADD group had spectral EEG asymmetries; the ADHD group had only ERP asymmetries; and the control group had no asymmetries. CONCLUSION: Quantitative EEG techniques may prove useful in differentiating specific subtypes of ADHD.

Adolescent↗

PubMed1996

Sample size and statistical power in [15O]H2O studies of human cognition.

Determining the appropriate sample size is a crucial component of positron emission tomography (PET) studies. Power calculations, the traditional method for determining sample size, were developed for hypothesis-testing approaches to data analysis. This method for determining sample size is challenged by the complexities of PET data analysis: use of exploratory analysis strategies, search for multiple correlated nodes on interlinked networks, and analysis of large numbers of pixels that may have correlated values due to both anatomical and functional dependence. We examine the effects of variable sample size in a study of human memory, comparing large (n = 33), medium (n = 16,17), small (n = 11, 11, 11), and very small (n = 6,6,7,7,7) samples. Results from the large sample are assumed to be the "gold standard." The primary criterion for assessing sample size is replicability. This is evaluated using a hierarchically ordered group of parameters: pattern of peaks, location of peaks, number of peaks, size (volume) of peaks, and intensity of the associated t (or z) statistic. As sample size decreases, false negatives begin to appear, with some loss of pattern and peak detection; there is no corresponding increase in false positives. The results suggest that good replicability occurs with a sample size of 10-20 subjects in studies of human cognition that use paired subtraction comparisons of single experimental/baseline conditions with blood flow differences ranging from 4 to 13%.

Adult↗

PubMed1996

Tests for comparing images based on randomization and permutation methods.

Tests comparing image sets can play a critical role in PET research, providing a yes-no answer to the question "Are two image sets different?" The statistical goal is to determine how often observed differences would occur by chance alone. We examined randomization methods to provide several omnibus test for PET images and compared these tests with two currently used methods. In the first series of analyses, normally distributed image data were simulated fulfilling the requirements of standard statistical tests. These analyses generated power estimates and compared the various test statistics under optimal conditions. Varying whether the standard deviations were local or pooled estimates provided an assessment of a distinguishing feature between the SPM and Montreal methods. In a second series of analyses, we more closely simulated current PET acquisition and analysis techniques. Finally, PET images from normal subjects were used as an example of randomization. Randomization proved to be a highly flexible and powerful statistical procedure. Furthermore, the randomization test does not require extensive and unrealistic statistical assumptions made by standard procedures currently in use.

Computer Simulation↗

PubMed1996

Self-reported aggressive behavior in patients with stroke.

This study represents a first attempt to identify some of the clinical and pathoanatomical correlates of violent outbursts in patients with cerebrovascular accident. Subjects were selected from a population of patients hospitalized with acute stroke. Although we did not have behavioral measures of violent behavior, patients who reported having had violent outbursts were identified based on clinical ratings on a structured interview. Subjects were asked if they had experienced episodes of anger accompanied by behaviors ranging from shouting to violence during the time since their stroke. These patients were compared with controls matched for demographic variables. Violent patients had higher total Present State Exam and Hamilton-D scores. The percentage of patients with cognitive impairment in the angry outburst group (66%) was greater than the control group (22%). Outburst patients had a higher frequency of left-hemisphere lesions (46.7%) compared with controls (29.4%). When lesion volumes were statistically equated, proximity of lesion to the frontal pole was one of the factors related to the self-reported irritable/violent behavior. To determine whether depression explained our findings, we carried out two-way analyses of variance with angry outburst and major depression group membership as factors. Effects of left anterior lesion location and cognitive impairment on violence remained present. These findings suggest that the potential for anger and violence in patients with stroke has multiple clinical and neuropathological correlates, including greater cognitive impairment and left anterior hemisphere lesions.

Aggression↗

PubMed1996

Neural substrates of facial recognition.

Seventeen healthy normal volunteers performed three facial recognition tasks while their cerebral blood flow was measured with PET: categorizing faces according to gender, recognizing new faces, and recognizing familiar faces. These tasks activated three different pathways: respectively, the left inferior temporal lobe and left frontal cortex; a predominantly right frontal-right parietal-left cerebellar network; and left lingual and left and right fusiform gyri. These results suggest that humans use different brain regions in performing these three routine daily activities. The results are consistent with previous observations concerning organization of extrastriate visual cortex in human and nonhuman primate lesion studies, including studies of the unusual syndrome of prosopagnosia (loss of the ability to recognize familiar faces with intact ability to recognize a face as a face).

Adult↗

PubMed1995

Withdrawal-emergent dyskinesia in patients with schizophrenia during antipsychotic discontinuation.

We examined whether patients exhibiting withdrawal-emergent dyskinesia (WE-D) represent a group vulnerable to subsequent development of tardive dyskinesia (TD). WE-D was defined as moderate abnormal movements during antipsychotic withdrawal in persons without persistent TD. We assessed patients with schizophrenia-spectrum illness participating in withdrawal from antipsychotic medication. Patients with WE-D were compared to those without dyskinesia and to those with persistent TD. Clinical measures included duration of illness and antipsychotic exposure, negative symptoms, and neurologic soft signs. We hypothesized that WE-D patients would not differ from persistent-TD patients across the above variables, but would differ from non-TD patients. Patients without TD significantly differed from persistent TD in duration of illness, medication exposure and neurologic soft signs. WE-D did not differ from TD across these measures. No-TD patients also showed less duration of medication exposure and neurologic soft signs than those with WE-D.

Adolescent↗

PubMed1995

Premorbid adjustment as a predictor of phenomenological and neurobiological indices in schizophrenia.

Previous studies have demonstrated relationships between poor premorbid adjustment and a variety of phenomenological and neurobiological indices in schizophrenic patients. Using the Modified Premorbid Adjustment Scale we re-examined these relationships in a large sample (n = 131) of schizophrenic patients. Subjects were evaluated with the Comprehensive Assessment of Symptoms and History (CASH) and magnetic resonance imaging. Multiple correlation indicated that poor premorbid adjustment was significantly associated with prominence of negative symptoms, early age of onset, educational problems, chronicity, and neurological soft signs, but not with any MRI measures. These results confirm poor premorbid adjustment as an important predictor of a malignant form of schizophrenia as evidenced by an earlier age of onset, poorer educational performance, prominent negative symptoms, presence of soft signs, and chronicity of course.

Brain↗

PubMed1995

Short-term and long-term verbal memory: a positron emission tomography study.

Short-term and long-term retention of experimentally presented words were compared in a sample of 33 healthy normal volunteers by the [15O]H2O method with positron emission tomography (PET). The design included three conditions. For the long-term condition, subjects thoroughly studied 18 words 1 week before the PET study. For the short-term condition, subjects were shown another set of 18 words 60 sec before imaging, with instructions to remember them. For the baseline condition, subtracted from the two memory conditions, subjects read a third set of words that they had not previously seen in the experiment. Similar regions were activated in both short-term and long-term conditions: large right frontal areas, biparietal areas, and the left cerebellum. In addition, the short-term condition also activated a relatively large region in the left prefrontal region. These complex distributed circuits appear to represent the neural substrates for aspects of memory such as encoding, retrieval, and storage. They indicate that circuitry involved in episodic memory has much larger cortical and cerebellar components than has been emphasized in earlier lesion studies.

Adult↗

PubMed1995

Symptoms of schizophrenia. Methods, meanings, and mechanisms.

BACKGROUND: The "group of schizophrenias," normally referred to with a single nominative, is phenomenologically heterogeneous. Its symptoms represent multiple psychological domains, including perception, inferential thinking, language, attention, social interaction, emotion expression, and volition. Studies of psychopathology have simplified this complex array in several ways, one of which is a subdivision into positive and negative symptoms. METHODS: This study examined the positive vs negative distinction in a sample of 243 patients with schizophrenia or schizophreniform disorder who were evaluated with the Scale for the Assessment of Negative Symptoms and the Scale for the Assessment of Positive Symptoms. A two-stage factor analysis was applied, beginning with a principal components analysis applying varimax rotation, followed by an extension analysis. The purpose of these analyses was to evaluate the correlational relationships of the various symptoms of schizophrenia. RESULTS: The results confirmed previous reports by our group and others suggesting that the symptoms of schizophrenia fall into three natural dimensions, as assessed by the correlational interrelationships: positive symptoms subdivide into psychotic and disorganized dimensions, while a third negative dimension also emerges. CONCLUSION: Because these dimensions have impressive consistency across studies, future work must examine their relationship to clinically relevant concepts such as prognosis or etiology and examine four different aspects: longitudinal course, neural mechanisms, relationship to treatment, and interrelationships in other pathological conditions.

Age of Onset↗

PubMed1995

A longitudinal study of symptom dimensions in schizophrenia. Prediction and patterns of change.

BACKGROUND: Factor analytic studies have suggested that the symptoms of schizophrenia may be divided into three uncorrelated dimensions. This study examines the longitudinal course of the symptoms of schizophrenia using this three-dimensional perspective. METHODS: The sample was composed primarily of neuroleptic-naive patients suffering from schizophrenia. Subjects were studied in a prospective longitudinal design, with comprehensive structured assessments at index, discharge, and 6-month intervals after discharge over a 2-year period. RESULTS: Negative symptoms were already relatively prominent at the time of index evaluation; they tended to remain stable throughout the follow-up period. The two dimensions of positive symptoms, psychoticism and disorganization, although prominent at index evaluation, declined over the course of the follow-up period and tended to be less stable. A longitudinal factor analysis was conducted to determine whether the changes in symptoms followed any consistent pattern. We observed that all three groups of symptoms tended to change in unison and independently from one another. CONCLUSIONS: These results suggest that these three dimensions of psychopathology show different patterns of exacerbation and remission during the course of schizophrenia. This independent pattern of evolution suggests that these three dimensions should be studied further with respect to response to treatment, cognitive mechanisms, psychosocial correlates, and neural substrates.

Adult↗

PubMed1995

I. PET studies of memory: novel and practiced free recall of complex narratives.

Positron Emission Tomography (PET) with the tracer H215O was used to measure regional cerebral blood flow in 13 healthy volunteers during two experimental memory tasks, one of which was well-practiced and the other of which was novel. The materials used for the memory tasks consisted of two complex narratives (Story A and Story B from the Wechsler Memory Scale). Natural language materials were chosen because they similate experimentally the natural learning situation and permit study of the neural mechanisms by which recall memory becomes more fluid, automatic, or "rote." One week before the PET study, subjects were trained to perfect recall of Story A, while they were exposed to Story B only 60 s prior to PET data acquisition. Despite the substantial differences in level of familiarity (and in free recall performance), patterns of activation were quite similar; activations presumed to reflect recall in both tasks included frontal, inferior temporal, thalamic, anterior cingulate, and cerebellar regions. Many regions were smaller during recall of the familiar story, however, presumably reflecting greater neural efficiency due to practice. In addition, the novel task activated an additional left frontal region that is presumed to reflect more active encoding. The similarity and multiplicity of the activations in the two tasks suggest that the brain uses a multinodal general network for memory tasks such as free recall, while the differences suggest that some nodes in the network may be used for specific components of memory such as encoding and retrieval.

Adult↗

PubMed1995

II. PET studies of memory: novel versus practiced free recall of word lists.

Positron emission tomography (PET) with the tracer H215O was used to measure regional cerebral blood flow in 13 healthy volunteers while they engaged in free recall of 15-item word lists from the Rey Auditory Verbal Learning task. The study was designed so that recall of well-practiced versus novel material could be compared. One week before the PET study, subjects were trained to perfect recall of List A, while they were exposed to list B only 60 s prior to PET data acquisition. As in the companion study of free recall of complex narratives, we observed that practice tended to decrease the size of activations in regions involved in the memory component of the task; we also observed that the novel recall task produced greater activation in left frontal regions, probably due to active encoding. A commonality of other regions observed in this pair of studies, as well as other studies of memory in the literature, suggests that the human brain may contain a distributed multinodal general memory system. Nodes on this network include the frontal, parietal, and temporal cortices, the thalamus, the anterior and posterior cingulate, the precuneus, and the cerebellum. There appears to be a commonality of components across tasks (e.g., retrieval, encoding) that is independent of content, as well as differentiation of some components that may be content-specific or tasks-specific. In addition, these results support a significant role for the cerebellum in cognitive functions such as memory.

Adult↗

PubMed1995

Multi-center N400 ERP consistency using a primed and unprimed word paradigm.

A word priming paradigm involving primed, unprimed, and non-word experimental conditions was used to elicit event-related potentials (ERPs) in normal, young adult males in identically equipped electrophysiology laboratories located in 6 different cities in the USA. Analyses of the average amplitude of a specified latency window containing the N400, the N400 peak amplitude, or the latency of the N400 peak amplitude found no differences among laboratory locations. The shape of the N400 ERP wave form was also found to be highly correlated across laboratory sites for each experimental condition. Comparison of the data with analogous word priming paradigms revealed similar patterns for the N400 components and response times in both the primed and unprimed experimental conditions. These findings suggest that the data from all 6 laboratory locations are consistent with each other and are congruous with those found in other N400 studies and will permit pooling of subject data for future research.

Adolescent↗