Biomedical subjects

Cameron S Carter

Publications and source records attributed to Cameron S Carter.

64 records · Page 4Linked to original sources

PubMed2003

Fiswidgets: a graphical computing environment for neuroimaging analysis.

Current fMRI neuroimaging software programs offer the researcher a wealth of analysis methods and tools. However, the incompatibilities in user interface, data format, and computing environment in these tools make it difficult if not impossible for most researchers to take advantage of the full set of resources available for neuroimaging analyses. We describe a graphical computing environment, Functional Imaging Software Widgets (fiswidgets), which was developed to address these interoperability and usability problems. This environment provides a desktop style framework into which 100 subcomponents from a number of widely used fMRI analysis software packages (e.g., AFNI, AIR) are incorporated. It is an open-source, extensible environment available for reuse and modification by other software developers. A discussion of the design criteria (open architecture, modularity, wrapper technology, commercial utilities) that support such loosely integrative computing environments, and the problems entailed in maintaining them (development overhead, distribution logistics, format incompatibilities, graphics vs scripting tradeoffs, and appropriate acknowledgment of software developers) follows.

Computer Graphics↗

PubMed2003

An information-processing model of the BOLD response in symbol manipulation tasks.

Two imaging experiments were performed--one involving an algebraic transformation task studied by Anderson, Reder, and Lebiere (1996) and the other an abstraction symbol manipulation task studied by Blessing and Anderson (1996). ACT-R models exist that predict the latency patterns in these tasks. These models require activity in an imaginal buffer to represent changes to the problem representation, in a retrieval buffer to hold information from declarative memory, and in a manual buffer to hold information about motor behavior. A general theory is described about how to map activity in these buffers onto the fMRI blood oxygen level dependent (BOLD) response. This theory claims that the BOLD response is integrated over the duration that a buffer is active and can be used to predict the observed BOLD function. Activity in the imaginal buffer is shown to predict the BOLD response in a left posterior parietal region; activity in the retrieval buffer is shown to predict the BOLD response in a left prefrontal region; and activity in the manual buffer is shown to predict activity in a motor region. More generally, this article shows how to map a large class of information-processing theories (not just ACT-R) onto the BOLD response and provides a precise interpretation of the cognitive significance of the BOLD response.

Brain↗

PubMed2003

Context-processing deficits in schizophrenia: diagnostic specificity, 4-week course, and relationships to clinical symptoms.

Previous research on schizophrenia suggests that context-processing disturbances are one of the core cognitive deficits present in schizophia. However, it is not clear whether such deficits are specific to schizophrenia as compared with other psychotic disorders. To address this question, the authors administered a version of the AX Continuous Performance Test designed to assess context processing in a sample of healthy controls, patients with schizophrenia, and patients with other psychotic disorders. Participants were tested at index (when medication naive and experiencing their first contact with psychiatric services) and 4 weeks later, following medication treatment. At index, patients with schizophrenia and the psychotic comparison group demonstrated similar impairments in context processing. However, context-processing deficits improved in the psychotic comparison group at 4 weeks but did not improve in patients with schizophrenia.

Adult↗

PubMed2002

Developing novel treatments for mood disorders: accelerating discovery.

This review was generated from discussions by the Pharmacologic and Somatic Treatments Section of the National Institute of Mental Health Strategic Plan for Mood Disorders Committee on advancing novel pharmacologic and somatic treatments for mood disorders. The opening section of the article summarizes in broad strokes, current pharmacologic treatments, and new directions in the field. Thereafter the topics focus on specific research initiatives that could advance the current therapeutics for mood disorders including new basic and clinical research in vivo human imaging procedures, somatic therapeutics, and the vast new area of pharmacogenetics. New scientific and technical opportunities exist today based on advances in basic neuroscience, opportunities in clinical testing, industry interest in advancing central nervous system therapeutics, and on active consumer advocacy groups. The question of how to bring all of these positive forces together to accelerate discovery in mood disorder thera-peutics is the topic of this article.

Animals↗

PubMed2002

Attentional control and word inhibition in schizophrenia.

Previous studies have suggested that schizophrenia patients do not utilize contextual information efficiently to modulate attentional performance. The goal of the current study was to compare the utilization of context in modulating responses to irrelevant information on the Stroop task between a group of schizophrenia outpatients and matched controls. A single-trial version of the Stroop task was used to investigate performance on the Stroop task under three expectancy conditions. Eleven schizophrenia outpatients (on and off antipsychotic medication) and sixteen matched controls were tested. The schizophrenia patients showed: (1) augmented facilitation; (2) interference comparable to normals; and (3) normal ability to reduce interference under certain experimental circumstances. Schizophrenia patients were able to utilize contextual information under certain conditions and could modulate the magnitude of irrelevant word interference, although they were not able to overcome the prepotent tendency to read the word during the Stroop task as effectively as normals, which was reflected in greater Stroop facilitation. This suggests that the integrity or impairment of cognitive control functions in schizophrenia is related to the complexity of the context representation required to support that function.

Adult↗

PubMed2002

The timing of action-monitoring processes in the anterior cingulate cortex.

The anterior cingulate cortex (ACC) has been shown to respond to conflict between simultaneously active, incompatible response tendencies. This area is active during high-conflict correct trials and also when participants make errors. Here, we use the temporal resolution of high-density event-related potentials (ERPs) in combination with source localization to investigate the timing of ACC activity during conflict and error detection. We predicted that the same area of the ACC is active prior to high-conflict correct responses and following erroneous responses. Dipole modeling supported this prediction: The frontocentral N2, occurring prior to the response on correct conflict trials, and the ERN, occurring immediately following error responses, could both be modeled as having a generator in the caudal ACC, suggesting the same process to underlie both peaks. Modeling further suggested that the rostral area of the ACC was also active following errors, but later in time, contributing to the error positivity (P(E)), and peaking at 200-250 msec following the ERN peak. Despite the inherent limitations of source localization, these data may begin to shed light on the timing of action-monitoring processes. First, the time course of caudal ACC activity follows the time course as predicted by the conflict theory of this region. Second, caudal ACC activity might be temporally dissociated from rostral ACC activity during error trials, which possibly reflects a separate, affective component of the evaluative functions of the ACC.

Adult↗

PubMed2002

Can't shake that feeling: event-related fMRI assessment of sustained amygdala activity in response to emotional information in depressed individuals.

BACKGROUND: Previous research suggests that depressed individuals engage in prolonged elaborative processing of emotional information. A computational neural network model of emotional information processing suggests this process involves sustained amygdala activity in response to processing negative features of information. This study examined whether brain activity in response to emotional stimuli was sustained in depressed individuals, even following subsequent distracting stimuli. METHODS: Seven depressed and 10 never-depressed individuals were studied using event-related functional magnetic resonance imaging during alternating 15-sec emotional processing (valence identification) and non-emotional processing (Sternberg memory) trials. Amygdala regions were traced on high-resolution structural scans and co-registered to the functional data. The time course of activity in these areas during emotional and non-emotional processing trials was examined. RESULTS: During emotional processing trials, never-depressed individuals displayed amygdalar responses to all stimuli, which decayed within 10 sec. In contrast, depressed individuals displayed sustained amygdala responses to negative words that lasted throughout the following non-emotional processing trials (25 sec later). The difference in sustained amygdala activity to negative and positive words was moderately related to self-reported rumination. CONCLUSIONS: Results suggest that depression is associated with sustained activity in brain areas responsible for coding emotional features.

Adult↗

PubMed2002

Neural mechanisms of planning: a computational analysis using event-related fMRI.

To investigate the neural mechanisms of planning, we used a novel adaptation of the Tower of Hanoi (TOH) task and event-related functional MRI. Participants were trained in applying a specific strategy to an isomorph of the five-disk TOH task. After training, participants solved novel problems during event-related functional MRI. A computational cognitive model of the task was used to generate a reference time series representing the expected blood oxygen level-dependent response in brain areas involved in the manipulation and planning of goals. This time series was used as one term within a general linear modeling framework to identify brain areas in which the time course of activity varied as a function of goal-processing events. Two distinct time courses of activation were identified, one in which activation varied parametrically with goal-processing operations, and the other in which activation became pronounced only during goal-processing intensive trials. Regions showing the parametric relationship comprised a frontoparietal system and include right dorsolateral prefrontal cortex [Brodmann's area (BA 9)], bilateral parietal (BA 40/7), and bilateral premotor (BA 6) areas. Regions preferentially engaged only during goal-intensive processing include left inferior frontal gyrus (BA 44). The implications of these results for the current model, as well as for our understanding of the neural mechanisms of planning and functional specialization of the prefrontal cortex, are discussed.

Adult↗

PubMed2002

The anterior cingulate as a conflict monitor: fMRI and ERP studies.

We propose that the anterior cingulate cortex (ACC) contributes to cognition by detecting the presence of conflict during information processing, and to alert systems involved in top-down control to resolve this conflict. Here, we review several functional magnetic resonance imaging (fMRI) and event-related potential (ERP) studies that have used simple response interference tasks, and propose that ACC activity is activated prior to the response during correct conflict trials and reflected in the frontocentral N2, and immediately following error trials and reflected in the error-related negativity (ERN). Furthermore, we suggest that certain disturbances in cognition and behavior in common mental disorders such as schizophrenia and obsessive-compulsive disorder (OCD) can be understood as resulting from alteration in performance monitoring functions associated with this region of the brain.

Animals↗

PubMed2002

Cognitive experimental approaches to investigating impaired cognition in schizophrenia: a paradigm shift.

There has been a growing interest in cognitive deficits in schizophrenia in recent years. The use of traditional clinical neuropsychological measures of cognition in schizophrenia has the advantages of normative data and standardized administration, and remains the standard for cognitive assessment in clinical practice. However for the investigation of cognition in schizophrenia these methods have critical limitations in their ability to measure specific cognitive processes. In this paper we discuss solutions to these interpretive and measurement issues that can be provided by measures derived from experimental cognitive psychology. We suggest that the use of these measures will increasingly become the preferred approach to the investigation of the nature, neurobiology and genetics of impaired cognition in schizophrenia in the coming years.

Cognition Disorders↗