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R J Davidson

Publications and source records attributed to R J Davidson.

At least 19 recordsLinked to original sources
PubMed2005

Comparison of fMRI motion correction software tools.

Motion correction of fMRI data is a widely used step prior to data analysis. In this study, a comparison of the motion correction tools provided by several leading fMRI analysis software packages was performed, including AFNI, AIR, BrainVoyager, FSL, and SPM2. Comparisons were performed using data from typical human studies as well as phantom data. The identical reconstruction, preprocessing, and analysis steps were used on every data set, except that motion correction was performed using various configurations from each software package. Each package was studied using default parameters, as well as parameters optimized for speed and accuracy. Forty subjects performed a Go/No-go task (an event-related design that investigates inhibitory motor response) and an N-back task (a block-design paradigm investigating working memory). The human data were analyzed by extracting a set of general linear model (GLM)-derived activation results and comparing the effect of motion correction on thresholded activation cluster size and maximum t value. In addition, a series of simulated phantom data sets were created with known activation locations, magnitudes, and realistic motion. Results from the phantom data indicate that AFNI and SPM2 yield the most accurate motion estimation parameters, while AFNI's interpolation algorithm introduces the least smoothing. AFNI is also the fastest of the packages tested. However, these advantages did not produce noticeably better activation results in motion-corrected data from typical human fMRI experiments. Although differences in performance between packages were apparent in the human data, no single software package produced dramatically better results than the others. The "accurate" parameters showed virtually no improvement in cluster t values compared to the standard parameters. While the "fast" parameters did not result in a substantial increase in speed, they did not degrade the cluster results very much either. The phantom and human data indicate that motion correction can be a valuable step in the data processing chain, yielding improvements of up to 20% in the magnitude and up to 100% in the cluster size of detected activations, but the choice of software package does not substantially affect this improvement.

Algorithms↗
PubMed2004

Functional but not structural subgenual prefrontal cortex abnormalities in melancholia.

Major depression is a heterogeneous condition, and the search for neural correlates specific to clinically defined subtypes has been inconclusive. Theoretical considerations implicate frontostriatal, particularly subgenual prefrontal cortex (PFC), dysfunction in the pathophysiology of melancholia--a subtype of depression characterized by anhedonia--but no empirical evidence has been found yet for such a link. To test the hypothesis that melancholic, but not nonmelancholic depression, is associated with the subgenual PFC impairment, concurrent measurement of brain electrical (electroencephalogram, EEG) and metabolic (positron emission tomography, PET) activity were obtained in 38 unmedicated subjects with DSM-IV major depressive disorder (20 melancholic, 18 nonmelancholic subjects), and 18 comparison subjects. EEG data were analyzed with a tomographic source localization method that computed the cortical three-dimensional distribution of current density for standard frequency bands, allowing voxelwise correlations between the EEG and PET data. Voxel-based morphometry analyses of structural magnetic resonance imaging (MRI) data were performed to assess potential structural abnormalities in melancholia. Melancholia was associated with reduced activity in the subgenual PFC (Brodmann area 25), manifested by increased inhibitory delta activity (1.5-6.0 Hz) and decreased glucose metabolism, which themselves were inversely correlated. Following antidepressant treatment, depressed subjects with the largest reductions in depression severity showed the lowest post-treatment subgenual PFC delta activity. Analyses of structural MRI revealed no group differences in the subgenual PFC, but in melancholic subjects, a negative correlation between gray matter density and age emerged. Based on preclinical evidence, we suggest that subgenual PFC dysfunction in melancholia may be associated with blunted hedonic response and exaggerated stress responsiveness.

Adult↗
PubMed2001

Hippocampal morphometry in depressed patients and control subjects: relations to anxiety symptoms.

BACKGROUND: Although it has been hypothesized that glucocorticoid hypersecretion in depressed patients leads to neuronal atrophy in the hippocampus, magnetic resonance imaging (MRI) -based morphometry studies of the hippocampus to date have produced mixed results. METHODS: In our MRI study, hippocampal volumes were measured in 25 depressed patients (13 with melancholia and 12 without melancholia) and 15 control subjects. RESULTS: No significant differences in hippocampus volumes were found between any of the subject groups, although within subjects right hippocampal volumes were found to be significantly larger than left hippocampal volumes. Additionally, right and total (left + right) hippocampal volumes in control and depressed subjects were found to be positively correlated with trait anxiety as measured by the state/trait anxiety inventory. CONCLUSIONS: Because our subject group is younger than those in studies reporting hippocampal atrophy, we conclude that longitudinal studies will be necessary for investigation of the lifelong course of hippocampal volumetry.

Adult↗
PubMed2001

A nosocomial outbreak of fluoroquinolone-resistant Streptococcus pneumoniae.

Over the course of a 20-month period, in a hospital respiratory ward in which ciprofloxacin was often used as empirical antimicrobial therapy for lower respiratory tract infections (LRTIs), 16 patients with chronic bronchitis developed nosocomial LRTIs caused by penicillin- and ciprofloxacin-resistant Streptococcus pneumoniae (serotype 23 F). The minimum inhibitory concentration (MIC) of ciprofloxacin for all isolates from the first 9 patients was 4 microg/mL, in association with a parC mutation. Isolates from the subsequent 7 patients all had a ciprofloxacin MIC of 16 microg/mL, in association with an additional mutation in gyrA. The MICs for this isolate were 8 microg/mL of levofloxacin (resistant), 2 microg/mL of moxifloxacin and gatifloxacin (intermediately resistant), and 0.12 microg/mL of gemifloxacin. This outbreak demonstrates the ability of S. pneumoniae to acquire multiple mutations that result in increasing levels of resistance to the fluoroquinolones and to be transmitted from person to person.

Aged↗
PubMed2001

The primate amygdala mediates acute fear but not the behavioral and physiological components of anxious temperament.

Temperamentally anxious individuals can be identified in childhood and are at risk to develop anxiety and depressive disorders. In addition, these individuals tend to have extreme asymmetric right prefrontal brain activity. Although common and clinically important, little is known about the pathophysiology of anxious temperament. Regardless, indirect evidence from rodent studies and difficult to interpret primate studies is used to support the hypothesis that the amygdala plays a central role. In previous studies using rhesus monkeys, we characterized an anxious temperament endophenotype that is associated with excessive anxiety and fear-related responses and increased electrical activity in right frontal brain regions. To examine the role of the amygdala in mediating this endophenotype and other fearful responses, we prepared monkeys with selective fiber sparing ibotenic acid lesions of the amygdala. Unconditioned trait-like anxiety-fear responses remained intact in monkeys with >95% bilateral amygdala destruction. In addition, the lesions did not affect EEG frontal asymmetry. However, acute unconditioned fear responses, such as those elicited by exposure to a snake and to an unfamiliar threatening conspecific were blunted in monkeys with >70% lesions. These findings demonstrate that the primate amygdala is involved in mediating some acute unconditioned fear responses but challenge the notion that the amygdala is the key structure underlying the dispositional behavioral and physiological characteristics of anxious temperament.

Aggression↗
PubMed2001

Progenitor cells from patients with advanced phase chronic myeloid leukaemia respond to STI571 in vitro and in vivo.

STI571 targets p210(BCR-ABL) in chronic myeloid leukaemia (CML). In vitro, STI571 reduces self-replication (replating ability) by chronic-phase CML CFU-GM. Here, we studied CFU-GM in advanced-phase (accelerated and blast crisis) CML. The numbers and self-replication of CFU-GM in advanced phase were greater than in the chronic phase. Self-replication by CFU-GM from advanced phase patients was reduced by STI571 or IFN alfa to the same extent as in the chronic phase. The reduced replating ability induced by STI571 correlated with that induced by IFN alpha (r=0.73). STI571 treatment in vivo also reduced replating ability and the numbers of CFU-GM/ml of blood.

Antineoplastic Agents↗
PubMed2001

Peripheral blood progenitor cell mobilisation alters myeloid, but not erythroid, progenitor cell self-renewal kinetics.

Transplantation of progenitor cells which have been mobilised into the bloodstream (PBPC) following the administration of G-CSF results in more rapid neutrophil recovery than transplantation of bone marrow (BM). The reasons for the accelerated neutrophil engraftment are not clear, but would be explained by increased self-replication of myeloid progenitor cells (CFU-GM). We have used a CFU-GM replating assay to investigate myeloid progenitor self-replication, and quantification of subcolony formation during erythroid burst formation to quantify erythroid progenitor self-renewal. Secondary colony formation by CFU-GM, grown from PBPC and then replated was increased compared with secondary colony formation by BM CFU-GM (P = 0.0001); erythroid subcolony formation was not altered. There was no difference between the replating abilities of PBPC CFU-GM derived from allogeneic donors (normal individuals) and autologous donors (patients with malignant disease) although differences were found between subgroups of autologous donors. The increased replication of PBPC could not be accounted for by a reduction in progenitor cell apoptosis; PBPC CFU-GM contained slightly fewer apoptotic CD34+ cells than BM CFU-GM. The increased replication by PBPC CFU-GM was reversible because it declined when CFU-GM colonies were passaged through three sequential CFU-GM replating cycles. This decline in self-replication was more rapid than the decline seen in replated BM CFU-GM. The self-replication of PBPC CFU-GM, and subcolony formation by BFU-E could be further enhanced by exposure to cytokines in vitro. We conclude that mobilisation alters the replication kinetics of myeloid, but not of erythroid, progenitor cells, that mobilisation-induced events are of limited duration and that in vitro exposure to cytokines may modify PBPC progenitor cell kinetics.

Blood Cells↗
PubMed2001

Toward a biology of personality and emotion.

For most of this past century, scholarship on the topics of personality and emotion has emerged from the humanities and social sciences. In the past decade, a remarkable change has occurred in the influence of neuroscience on the conceptualization and study of these phenomena. This article argues that the categories that have emerged from psychiatric nosology and descriptive personality theory may be inadequate, and that new categories and dimensions derived from neuroscience research may produce a more tractable parsing of this complex domain. The article concludes by noting that the discovery of these biological differences among individuals does not imply that the origins of these differences lie in heritable influences. Experiential shaping of the brain circuitry underlying emotion is powerful. The neural architecture provides the final common pathway through which culture, social factors, and genetics all operate together.

Affect↗
PubMed2001

Interspecies recombination contributes minimally to fluoroquinolone resistance in Streptococcus pneumoniae.

Analysis of 71 ciprofloxacin-resistant (MIC > or = 4 microg/ml) Streptococcus pneumoniae clinical isolates revealed only 1 for which the quinolone resistance-determining regions of the parC, parE, and gyrB genes were genetically related to those of viridans group streptococci. Our findings support the occurrence of interspecies recombination of type II topoisomerase genes; however, its contribution to the emergence of quinolone resistance among pneumococci appears to have been minimal.

Amino Acid Sequence↗
PubMed2001

Anterior cingulate activity as a predictor of degree of treatment response in major depression: evidence from brain electrical tomography analysis.

OBJECTIVE: The anterior cingulate cortex has been implicated in depression. Results are best interpreted by considering anatomic and cytoarchitectonic subdivisions. Evidence suggests depression is characterized by hypoactivity in the dorsal anterior cingulate, whereas hyperactivity in the rostral anterior cingulate is associated with good response to treatment. The authors tested the hypothesis that activity in the rostral anterior cingulate during the depressed state has prognostic value for the degree of eventual response to treatment. Whereas prior studies used hemodynamic imaging, this investigation used EEG. METHOD: The authors recorded 28-channel EEG data for 18 unmedicated patients with major depression and 18 matched comparison subjects. Clinical outcome was assessed after nortriptyline treatment. Of the 18 depressed patients, 16 were considered responders 4-6 months after initial assessment. A median split was used to classify response, and the pretreatment EEG data of patients showing better (N=9) and worse (N=9) responses were analyzed with low-resolution electromagnetic tomography, a new method to compute three-dimensional cortical current density for given EEG frequency bands according to a Talairach brain atlas. RESULTS: The patients with better responses showed hyperactivity (higher theta activity) in the rostral anterior cingulate (Brodmann's area 24/32). Follow-up analyses demonstrated the specificity of this finding, which was not confounded by age or pretreatment depression severity. CONCLUSIONS: These results, based on electrophysiological imaging, not only support hemodynamic findings implicating activation of the anterior cingulate as a predictor of response in depression, but they also suggest that differential activity in the rostral anterior cingulate is associated with gradations of response.

Adult↗
PubMed2000

Dysfunction in the neural circuitry of emotion regulation--a possible prelude to violence.

Emotion is normally regulated in the human brain by a complex circuit consisting of the orbital frontal cortex, amygdala, anterior cingulate cortex, and several other interconnected regions. There are both genetic and environmental contributions to the structure and function of this circuitry. We posit that impulsive aggression and violence arise as a consequence of faulty emotion regulation. Indeed, the prefrontal cortex receives a major serotonergic projection, which is dysfunctional in individuals who show impulsive violence. Individuals vulnerable to faulty regulation of negative emotion are at risk for violence and aggression. Research on the neural circuitry of emotion regulation suggests new avenues of intervention for such at-risk populations.

Affect↗
PubMed2000

Cerebrospinal fluid corticotropin-releasing hormone levels are elevated in monkeys with patterns of brain activity associated with fearful temperament.

BACKGROUND: Asymmetric patterns of frontal brain activity and brain corticotropin-releasing hormone (CRH) systems have both been separately implicated in the processing of normal and abnormal emotional responses. Previous studies in rhesus monkeys demonstrated that individuals with extreme right frontal asymmetric brain electrical activity have high levels of trait-like fearful behavior and increased plasma cortisol concentrations. METHODS: In this study we assessed cerebrospinal fluid (CSF) CRH concentrations in monkeys with extreme left and extreme right frontal brain electrical activity. CSF was repeatedly collected at 4, 8, 14, 40, and 52 months of age. RESULTS: Monkeys with extreme right frontal brain activity had increased CSF CRH concentrations at all ages measured. In addition, individual differences in CSF CRH concentrations were stable from 4 to 52 months of age. CONCLUSIONS: These findings suggest that, in primates, the fearful endophenotype is characterized by increased fearful behavior, a specific pattern of frontal electrical activity, increased pituitary-adrenal activity, and increased activity of brain CRH systems. Data from other preclinical studies suggests that the increased brain CRH activity may underlie the behavioral and physiological characteristics of fearful endophenotype.

Aging↗
PubMed2000

While a phobic waits: regional brain electrical and autonomic activity in social phobics during anticipation of public speaking.

BACKGROUND: Recent studies have highlighted the role of right-sided anterior temporal and prefrontal activation during anxiety, yet no study has been performed with social phobics that assesses regional brain and autonomic function. This study compared electroencephalograms (EEGs) and autonomic activity in social phobics and controls while they anticipated making a public speech. METHODS: Electroencephalograms from 14 scalp locations, heart rate, and blood pressure were recorded while 18 DSM-IV social phobics and 10 controls anticipated making a public speech, as well as immediately after the speech was made. Self-reports of anxiety and affect were also obtained. RESULTS: Phobics showed a significantly greater increase in anxiety and negative affect during the anticipation condition compared with controls. Heart rate was elevated in the phobics relative to the controls in most conditions. Phobics showed a marked increase in right-sided activation in the anterior temporal and lateral prefrontal scalp regions. These heart rate and EEG changes together accounted for > 48% of the variance in the increase in negative affect during the anticipation phase. CONCLUSIONS: These findings support the hypothesis of right-sided anterior cortical activation during anxiety and indicate that the combination of EEG and heart rate changes during anticipation account for substantial variance in reported negative affect.

Adult↗
PubMed2000

Six-month test-retest reliability of MRI-defined PET measures of regional cerebral glucose metabolic rate in selected subcortical structures.

Test-retest reliability of resting regional cerebral metabolic rate of glucose (rCMR) was examined in selected subcortical structures: the amygdala, hippocampus, thalamus, and anterior caudate nucleus. Findings from previous studies examining reliability of rCMR suggest that rCMR in small subcortical structures may be more variable than in larger cortical regions. We chose to study these subcortical regions because of their particular interest to our laboratory in its investigations of the neurocircuitry of emotion and depression. Twelve normal subjects (seven female, mean age = 32.42 years, range 21-48 years) underwent two FDG-PET scans separated by approximately 6 months (mean = 25 weeks, range 17-35 weeks). A region-of-interest approach with PET-MRI coregistration was used for analysis of rCMR reliability. Good test-retest reliability was found in the left amygdala, right and left hippocampus, right and left thalamus, and right and left anterior caudate nucleus. However, rCMR in the right amygdala did not show good test-retest reliability. The implications of these data and their import for studies that include a repeat-test design are considered.

Adult↗
PubMed2000

Probing emotion in the developing brain: functional neuroimaging in the assessment of the neural substrates of emotion in normal and disordered children and adolescents.

Virtually all developmental neuropsychiatric disorders involve some dysfunction or dysregulation of emotion. Moreover, many psychiatric disorders with adult onset have early subclinical manifestations in children. This essay selectively reviews the literature on the neuroimaging of affect and disorders of affect in children. Some critical definitional and conceptual issues are first addressed, including the distinctions between the perception and production of emotion and between emotional states and traits. Developmental changes in morphometric measures of brain structure are then discussed and the implications of such findings for studies of functional brain activity are considered. Data on functional neuroimaging and childhood depression are then reviewed. While the extant data in this area are meager, they are consistent with studies in adults that have observed decreased left-sided anterolateral prefrontal cortex activation in depression. Studies in children on the recognition of emotion and affective intent in faces using functional magnetic resonance imaging are then reviewed. These findings indicate that the amygdala plays an important role in such affective face processing in children, similar to the patterns of activation observed in adults. Moreover, one study has reported abnormalities in amygdala activation during a task requiring the judgment of affective intent from the eye region of the face in subjects with autism. Some of the methodological complexities of developmental research in this area are discussed, and directions for future research are suggested.

Adolescent↗
PubMed2000

Prefrontal brain electrical asymmetry predicts the evaluation of affective stimuli.

Measures of left-right asymmetry in resting brain activity were derived from spectral estimates of electroencephalogram (EEG) alpha-band power density in 13 homologous scalp electrode pairs from 81 right-handed individuals (43 F) on two occasions separated by 6 weeks. At a third, later session, these individuals completed a cognitive task, comparing word-pairs that systematically differed in affective tone. For an extended series of paired-comparisons, the subject chose the one word-pair that 'went together best'. Objectively, associative strength was comparable for both word-pairs. Individuals with relatively greater left-sided anterior frontal resting activity were more likely to select the more pleasant word-pair. Relations between word-pair selection and asymmetry in resting brain activity at central and posterior sites were not significant.

Adult↗