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Biomedical subjects

S Arndt

Publications and source records attributed to S Arndt.

At least 109 records · Page 6Linked to original sources
PubMed1995

Abnormalities in midline attentional circuitry in schizophrenia: evidence from magnetic resonance and positron emission tomography.

The syndrome of schizophrenia presents with a complex array of symptoms that are difficult to explain at the neural level. Data collected using magnetic resonance (MR) and positron emission tomography (PET) suggest that this complex array could occur as a consequence of misconnections and mismatches in midline circuitry that is reticular-thalamic-cingulate-cortical. MR studies have shown a variety of abnormalities, including callosal agenesis, cavum septi pellucidi, decreased thalamic size, decreased frontal size, and changes in signal intensity in white matter tracts between the thalamus and the frontal cortex. PET studies using a dichotic listening paradigm suggest that patients suffering from schizophrenia have brain blood flow abnormalities consistent with a difficulty in focusing or shifting attention, which may reflect the functional substrate of the anatomic abnormalities.

Attention↗
PubMed1995

Infestation of rodents with larval Ixodes ricinus (Acari: Ixodidae) is an important factor in the transmission cycle of Borrelia burgdorferi s.l. in German woodlands.

The ecology of Borrelia burgdorferi Johnson et al. s.l. was investigated from 1987 to 1993 in a preserved woodland in western Germany near Bonn. In selected biotopes, host-seeking Ixodes ricinus L. were regularly collected by blanket dragging in 1987, 1988, and 1989 and screened for infection with B. burgdorferi. Rodents were trapped monthly between April and October in 1988, 1990, 1991, and in the winter of 1992-1993, examined for antibodies to B. burgdorferi s.l., and inspected for feeding ticks. Ticks collected from rodents were screened for spirochete infection. High numbers of host-seeking nymphs were consistently collected within a biotope characterized by humid and acid soils. The mean number of ticks was significantly lower in biotopes with permeable soils. All small mammals captured belonged to the species Apodemus flavicollis Melchior, A. sylvaticus L., and Clethrionomys glareolus Schreber. Of 11,680 ticks obtained from rodents, 11,674 were I. ricinus, with 97.9% of the ticks being larvae, 2.0% nymphs, and 0.1% females. Mean numbers of feeding ticks ranged from 3.4 to 117 larvae per rodent and from 0.0 to 0.64 nymph per rodent, respectively. High levels of larval infestation on rodents were recorded in the same biotope where high numbers of host-seeking nymphs were present. Members of the genus Apodemus were more heavily infested with I. ricinus larvae than C. glareolus. The mean infection prevalence in host-seeking ticks was found to be 1% for larvae, 5% for nymphs, and 10-20% for adults. The infection prevalence in host-seeking nymphs ranged from 1.1 to 15.4% according to the particular biotope. The values for specific infectivity for the Apodemus populations were positively correlated with the mean larval infestation, but not with nymphal infestation. The respective estimates for C. glareolus were much higher than those for Apodemus spp. in biotopes with low tick densities. However, specific infectivity of C. glareolus was substantially reduced at sites with high tick abundances. In biotopes with high numbers of infected I. ricinus, significantly more rodents were found to have antibodies to B. burgdorferi than in biotopes with low abundances of ticks. The data show that C. glareolus plays a different role as reservoir host species compared with the 2 Apodemus species. This and previous studies suggest that the degree of infestation with larval I. ricinus differentially modulates infectivity of host species for ticks. We conclude that immune processes in natural reservoir hosts induced by B. burgdorferi or I. ricinus bites (or both) are important regulatory factors in the transmission cycle(s) of B. burgdorferi.

Animals↗
PubMed1995

Correlational studies of the Scale for the Assessment of Negative Symptoms and the Scale for the Assessment of Positive Symptoms: an overview and update.

The interrelationships between the various symptoms of schizophrenia may be explored by examining their intercorrelations. Five different factor analytic studies, which examine these interrelationships, are summarized. Three major factors emerge consistently: psychotic, disorganized, and negative. These three factors appear to represent three dimensions of the psychopathology of schizophrenia.

Factor Analysis, Statistical↗
PubMed1995

Remembering the past: two facets of episodic memory explored with positron emission tomography.

OBJECTIVE: This study used positron emission tomography to examine two kinds of personal memory that are used in psychiatric evaluation: focused episodic memory (recall of past experience, employed in "taking a history") and random episodic memory (uncensored thinking about experience, examined during analytic therapy using free association). For comparison, a third memory task was used to tap impersonal memory that represents general information about the world ("semantic memory"). METHOD: Thirteen subjects were studied using the [15O]H2O method to obtain quantitative measurements of cerebral blood flow. The three conditions were subtracted and their relative relationships examined. RESULTS: The random episodic condition produced activations in widely distributed association cortex (right and left frontal, parietal, angular/supramarginal, and posterior inferior temporal regions). Focused episodic memory engaged a network that included the medial inferior frontal regions, precuneus/retrosplenial cingulate, anterior cingulate, thalamus, and cerebellum. The use of medial frontal regions and the precuneus/retrosplenial cingulate was common to both focused and random episodic memory. The major difference between semantic and episodic memory was activation of Broca's area and the left frontal operculum by semantic memory. CONCLUSIONS: These results indicate that free-ranging mental activity (random episodic memory) produces large activations in association cortex and may reflect both active retrieval of past experiences and planning of future experiences. Focused episodic memory shares some components of this circuit (inferior frontal and precuneus), which may reflect the time-linked components of both aspects of episodic memory, and which permit human beings to experience personal identity, consciousness, and self-awareness.

Adult↗
PubMed1995

Neurological soft signs in neuroleptic-naive and neuroleptic-treated schizophrenic patients and in normal comparison subjects.

OBJECTIVE: The goal of this study was to assess neurological soft signs and developmental reflexes in schizophrenic patients who had never received neuroleptic medication and those who were receiving neuroleptic medication. METHOD: Neurological soft signs and developmental reflexes were examined in 26 schizophrenic patients who had never received a neuroleptic, 126 schizophrenic patients who were currently receiving neuroleptics, and 117 normal subjects. RESULTS: Soft signs were present in 23% of the neuroleptic-naive and 46% of the medicated schizophrenic patients. Developmental reflexes were present in 19% of the neuroleptic-naive and 12% of the medicated patients. Both soft signs and developmental reflexes were absent in the normal subjects. There were significant differences between patients and normal subjects in neurological soft signs and developmental reflexes. The possibly confounding variables of age, age at onset, duration of illness, number of hospitalizations, Abnormal Involuntary Movement Scale (AIMS) scores, and Simpson-Angus Scale extrapyramidal symptom scores were assessed by using logistic regression in the patients who were receiving neuroleptics. AIMS scores and Simpson-Angus Scale scores correlated with soft signs in these patients. CONCLUSIONS: The presence of neurological soft signs in schizophrenic patients who had never received neuroleptics indicates that these signs are present independent of medication effects, but it is possible that neuroleptics contribute to the prevalence of these abnormalities, as demonstrated by the patients who were receiving neuroleptics.

Adult↗
PubMed1995

An MRI study of brain size in autism.

OBJECTIVE: This study was undertaken to obtain detailed measurements of the volume of the brain, using magnetic resonance imaging (MRI), in a carefully selected group of autistic subjects and comparison subjects. METHOD: Twenty-two male autistic subjects and 20 male volunteer comparison subjects were examined with detailed (1.5-mm slices) MRI throughout the entire brain. Total brain, total brain tissue, and total lateral ventricle volumes were measured by using manual tracing and automated techniques. RESULTS: After height and performance IQ were controlled, autistic subjects had significantly greater total brain, total tissue, and total lateral ventricle volumes than comparison subjects. CONCLUSIONS: These findings suggest that male autistic subjects have enlarged brains and that enlargement is a result of both greater brain tissue volume and greater lateral ventricle volume.

Adolescent↗
PubMed1995

A comparison of approaches to the statistical analysis of [15O]H2O PET cognitive activation studies.

This study compares two of the most widely used statistical techniques for analyzing data obtained from [15O]H2O PET studies of brain function. The Friston method (SPM94) and the Worsley (Montreal) method were applied to a single data set of 33 subjects who were studied in a paradigm designed to evaluate memory for word lists. Neither of these methods emerged as either strikingly different or strikingly preferable, although the occasional differences may be important in some experiments. In general, the two methods were found to produce similar results in identifying brain regions active during long-term memory: frontal, parietal, cingulate, and cerebellar. Underlying assumptions of the two methods, as well as their strengths and weaknesses, are discussed.

Arousal↗
PubMed1994

Regional brain abnormalities in schizophrenia measured with magnetic resonance imaging.

OBJECTIVE: To determine general and regional indices of structural brain abnormality in schizophrenia. DESIGN: Case-control comparison study. SUBJECTS: Fifty-two patients diagnosed as having schizophrenia according to the criteria of the Diagnostic and Statistical Manual of Mental Disorders, Revised Third Edition, were compared with 90 healthy volunteers recruited from the community. MEASUREMENTS: Structural brain images were acquired using magnetic resonance; measurements were obtained using three-dimensional visualization of volume-rendered brains and an automated atlas-based dissection of specific regions. General measures included the volume of total brain tissue, total cerebrospinal fluid (CSF), and CSF within the ventricular system. Regional measures included the volume of tissue and CSF in the frontal, temporal, parietal, and occipital lobes and the cerebellum. RESULTS: Compared with the controls, the patients had a smaller average volume of total brain tissue and a greater average volume of total and ventricular CSF. A specific relative decrease in brain tissue was found only in the frontal lobes, although the volume of CSF was greater in patients than in controls in all brain regions. CONCLUSION: In addition to the generalized brain abnormalities observed in schizophrenia, a regional abnormality may be present in frontal regions. Since the frontal lobes integrate multimodality information and perform a variety of "higher" cognitive and emotional functions that are impaired in schizophrenia, the frontal abnormality noted is consistent with the clinical presentation of the illness. Impaired frontal function and a disruption in its complex circuitry (including thalamocortical projections) may explain why patients with schizophrenia often have significant deficits in formulating concepts and organizing their thinking and behavior.

Adult↗
PubMed1994

Thalamic abnormalities in schizophrenia visualized through magnetic resonance image averaging.

Schizophrenia is a complex illness characterized by multiple types of symptoms involving many aspects of cognition and emotion. Most efforts to identify its underlying neural substrates have focused on a strategy that relates a single symptom to a single brain region. An alternative hypothesis, that the variety of symptoms could be explained by a lesion in midline neural circuits mediating attention and information processing, is explored. Magnetic resonance images from patients and controls were transformed with a "bounding box" to produce an "average schizophrenic brain" and an "average normal brain." After image subtraction of the two averages, the areas of difference were displayed as an effect size map. Specific regional abnormalities were observed in the thalamus and adjacent white matter. An abnormality in the thalamus and related circuitry explains the diverse symptoms of schizophrenia parsimoniously because they could all result from a defect in filtering or gating sensory input, which is one of the primary functions of the thalamus in the human brain.

Brain↗
PubMed1994

Techniques for measuring sulcal/gyral patterns in the brain as visualized through magnetic resonance scanning: BRAINPLOT and BRAINMAP.

A method for measuring sulcal and gyral patterns, using data derived from magnetic resonance (MR) scanning, is described. This method can be applied through two newly developed computer programs, BRAINPLOT and BRAINMAP. These programs provide quantitative measures of brain surface pattern. The method has been validated with postmortem brains, phantoms, and human MR data. The method is robust to detecting differences in brain surface anatomy between atrophic and nonatrophic brains. It appears to offer an efficient, fully automated, and accurate method for analyzing the large amounts of information generated through in vivo neuroimaging techniques.

Autopsy↗
PubMed1994

Evaluating and validating two methods for estimating brain structure volumes: tessellation and simple pixel counting.

Developments in imaging technology have made three-dimensional visualization of internal brain structures possible with excellent resolution. Since improved visualization implies improved measurement, these advances hold promise to more accurately measure the volumes of internal structures. As new technologies and techniques emerge, evaluating the relative benefits of measurement methods becomes necessary. We compared and evaluated two methods of estimating volumes from images of brain structures. One method counted pixels within a region of interest, while the other method tessellated the surface between tracings on adjacent slices. Our study assessed both measurement error for true phantom volumes and method disparity for in vivo structures in a randomly selected sample of subjects (n = 100). For our comparisons, we focused on the temporal lobe, ventricular system, and hippocampus. Bias, independence of measurement errors and maximal discrimination of individual differences are properties that are relevant to validating and evaluating measurements of cerebral structure. Pixel counting proved to be the more robust of the two methods, being less sensitive to nuisance-interactions between size of object, shape, and slice thickness. Clinical and research applications of imaging techniques may have distinctive but overlapping needs when evaluating and validating new developments in imaging.

Adult↗
PubMed1994

Stability of cognitive functioning early in the course of schizophrenia.

This study evaluated the longitudinal course of neuropsychological deficits in a group of patients with new or recent onset schizophrenia. Thirty-five inpatients with DSM-III-R diagnoses of schizophrenia were administered a comprehensive battery of neuropsychological tests during their index hospitalization, and either 1 or 2 years after intake. Cognitive function remained stable in most domains, including motor speed, verbal and nonverbal memory, and verbal learning. Significant improvement in neuropsychological performance was observed on a task of complex attention (Trails B) and a set response shifting task (Stroop). These improvements were correlated with changes in clinical symptoms, but not with changes in medication dose. These findings suggest that most of the neuropsychological functioning in schizophrenia is stable over the first few years of the illness. Moreover, those neuropsychological deficits that remain unchanging appear to be independent of significant change in clinical symptoms, suggesting they may be a trait of the illness. However, a small subset of functions such as complex attention and response inhibition appear to fluctuate with time, and in particular, with clinical symptomatology, and may be considered 'state' dependent.

Adult↗
PubMed1994

Effect of antipsychotic withdrawal on negative symptoms in schizophrenia.

Although it is generally accepted that antipsychotic treatment improves the negative symptoms of schizophrenia in the context of improvement of positive symptoms, exactly how and to what extent they effect "primary" negative symptoms remains controversial. Antipsychotic treatment may reduce only those negative symptoms secondary to positive or depressive symptoms, and may have minimal, if any effect, on negative symptoms that represent a primary psychopathological trait manifestation of schizophrenia. In an effort to further examine this issue, we prospectively assessed negative, positive, depressive, and extrapyramidal symptoms following the discontinuation of antipsychotic medication. Fifty-nine DSM III-R schizophrenic patients underwent a three-week drug wash as part of our neuroimaging protocols. We assessed psychopathological status and adverse effects utilizing various rating instruments (i.e., Scale for Assessment of Positive Symptoms [SAPS], Scale for Assessment of Negative Symptoms [SANS], Hamilton Rating Scale for Depression, and Simpson-Angus Extrapyramidal) at baseline and weekly during this three-week period. Negative symptoms, as measured by the SANS, worsened significantly during the three-week drug wash. Positive symptoms showed a less consistent change with symptoms of disorganization worsening and with psychotic symptoms remaining the same. The changes in negative symptoms during the drug-free period were correlated with the changes in psychosis and disorganization, but not with changes in depression or extrapyramidal side effects. We were not able to substantiate if the worsening in negative symptoms was a direct result of the worsening of positive symptoms or if they were changing simultaneously, but independent of each other.

Adult↗
PubMed1994

Examining the sexual assault victim: a new model for nursing care.

1. A sexual assault nurse clinician or examiner is a registered nurse who has been specially trained to provide comprehensive care to sexual assault survivors. She usually is certified by her local institution after completing a training program of approximately 40 hours. Demonstrated competence in conducting a comprehensive evidential examination also is required. 2. All forensic examinations of the sexual assault survivor in the emergency department should include treatment and documentation of injuries, treatment and evaluation of sexually transmitted diseases, pregnancy risk evaluation and prevention, crisis intervention and arrangements for follow-up counseling, and collection of medicolegal evidence while maintaining the proper chain of evidence. 3. The role of the nurse examiner involves providing comprehensive care for the survivor and working cooperatively with other individuals in the legal system.

Adult↗
PubMed1994

Tricyclic antidepressant concentrations in plasma: an estimate of their sensitivity and specificity as a predictor of response.

An analysis of the literature on tricyclic antidepressant level in blood using receiver operating characteristics curves as the primary statistical tool was performed. For nortriptyline, a significant curvilinear relationship between therapeutic response and nortriptyline was observed that ranged from 58 to 148 ng/ml. The sensitivity and specificity for the nortriptyline therapeutic window were 78 and 61%, respectively. The response rate within the therapeutic range was 66% versus 26% outside the therapeutic range. For desipramine, a significant linear relationship between therapeutic response and desipramine concentration in plasma was observed. The threshold concentration in plasma for therapeutic response was 116 ng/ml. The sensitivity and specificity for the desipramine threshold level in blood were 81 and 59%, respectively. The response rate above the threshold level was 51% versus 15% below the therapeutic threshold concentration. For imipramine, a significant curvilinear relationship between therapeutic response and total imipramine (imipramine+desipramine) concentration in plasma was observed between 175 and 350 ng/ml. The sensitivity and specificity for the total imipramine concentrations in plasma were 52 and 74%, respectively. The response rate within the therapeutic range was 67% versus 39% outside the therapeutic range. For amitriptyline, a significant curvilinear relationship between therapeutic response and total amitriptyline (amitriptyline+nortriptyline) concentration in plasma was observed between 93 and 140 ng/ml. The sensitivity and specificity for the total imipramine concentrations in plasma were 37 and 80%, respectively. The response rate within the therapeutic range was 50% versus 30% outside the therapeutic range.

Adolescent↗