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Biomedical subjects

D M Barch

Publications and source records attributed to D M Barch.

At least 19 recordsLinked to original sources
PubMed2001

Increased amygdala response to masked emotional faces in depressed subjects resolves with antidepressant treatment: an fMRI study.

BACKGROUND: The amygdala has a central role in processing emotions, particularly fear. During functional magnetic resonance imaging (fMRI) amygdala activation has been demonstrated outside of conscious awareness using masked emotional faces. METHODS: We applied the masked faces paradigm to patients with major depression (n = 11) and matched control subjects (n = 11) during fMRI to compare amygdala activation in response to masked emotional faces before and after antidepressant treatment. Data were analyzed using left and right amygdala a priori regions of interest, in an analysis of variance block analysis and random effects model. RESULTS: Depressed patients had exaggerated left amygdala activation to all faces, greater for fearful faces. Right amygdala did not differ from control subjects. Following treatment, patients had bilateral reduced amygdala activation to masked fearful faces and bilateral reduced amygdala activation to all faces. Control subjects had no differences between the two scanning sessions. CONCLUSIONS: Depressed patients have left amygdala hyperarousal, even when processing stimuli outside conscious awareness. Increased amygdala activation normalizes with antidepressant treatment.

Adolescent↗
PubMed2001

Selective deficits in prefrontal cortex function in medication-naive patients with schizophrenia.

BACKGROUND: Previously we proposed that dorsolateral prefrontal cortex (PFC) supports a specific working memory (WM) subcomponent: the ability to represent and maintain context information necessary to guide appropriate task behavior. By context, we mean prior task-relevant information represented in such a form that it supports selection of the appropriate behavioral response. Furthermore, we hypothesized that WM deficits in schizophrenia reflect impaired context processing due to a disturbance in dorsolateral PFC. We use functional magnetic resonance imaging to examine PFC activation in medication-naive, first-episode patients with schizophrenia during a WM, task-isolating context processing. METHODS: Fourteen first-episode, medication-naive patients with schizophrenia and 12 controls similar in age, sex, and parental education underwent functional magnetic resonance imaging during performance of an A-X version of the Continuous Performance Test. RESULTS: Patients with schizophrenia demonstrated deficits in dorsolateral PFC activation in task conditions requiring context processing but showed intact activation of posterior and inferior PFC. In addition, patients demonstrated intact activation of the primary motor and somatosensory cortex in response to stimulus processing demands. CONCLUSIONS: These results demonstrate selectivity in dorsolateral PFC dysfunction among medication-naive first-episode patients with schizophrenia, suggesting that a specific deficit in PFC function is present at illness onset, prior to the administration of medication or the most confounding effects of illness duration. Furthermore, these results are consistent with the hypothesis that WM deficits in patients with schizophrenia reflect an impairment in context processing due to a disturbance in dorsolateral PFC function.

Adult↗
PubMed2001

Direct comparison of prefrontal cortex regions engaged by working and long-term memory tasks.

Neuroimaging studies have suggested the involvement of ventrolateral, dorsolateral, and frontopolar prefrontal cortex (PFC) regions in both working (WM) and long-term memory (LTM). The current study used functional magnetic resonance imaging (fMRI) to directly compare whether these PFC regions show selective activation associated with one memory domain. In a within-subjects design, subjects performed the n-back WM task (two-back condition) as well as LTM encoding (intentional memorization) and retrieval (yes-no recognition) tasks. Additionally, each task was performed with two different types of stimulus materials (familiar words, unfamiliar faces) in order to determine the influence of material-type vs task-type. A bilateral region of dorsolateral PFC (DL-PFC; BA 46/9) was found to be selectively activated during the two-back condition, consistent with a hypothesized role for this region in active maintenance and/or manipulation of information in WM. Left frontopolar PFC (FP-PFC) was also found to be selectively engaged during the two-back. Although FP-PFC activity has been previously associated with retrieval from LTM, no frontopolar regions were found to be selectively engaged by retrieval. Finally, lateralized ventrolateral PFC (VL-PFC) regions were found to be selectively engaged by material-type, but uninfluenced by task-type. These results highlight the importance of examining PFC activity across multiple memory domains, both for functionally differentiating PFC regions (e.g., task-selectivity vs material-selectivity in DL-PFC and VL-PFC) and for testing the applicability of memory domain-specific theories (e.g., FP-PFC in LTM retrieval).

Adult↗
PubMed2001

Conflict monitoring and cognitive control.

A neglected question regarding cognitive control is how control processes might detect situations calling for their involvement. The authors propose here that the demand for control may be evaluated in part by monitoring for conflicts in information processing. This hypothesis is supported by data concerning the anterior cingulate cortex, a brain area involved in cognitive control, which also appears to respond to the occurrence of conflict. The present article reports two computational modeling studies, serving to articulate the conflict monitoring hypothesis and examine its implications. The first study tests the sufficiency of the hypothesis to account for brain activation data, applying a measure of conflict to existing models of tasks shown to engage the anterior cingulate. The second study implements a feedback loop connecting conflict monitoring to cognitive control, using this to simulate a number of important behavioral phenomena.

Cognition↗
PubMed2001

Anterior cingulate cortex and response conflict: effects of frequency, inhibition and errors.

Anterior cingulate cortex (ACC) may play a key role in cognitive control by monitoring for the occurrence of response conflict (i.e. simultaneous activation of incompatible response tendencies). Low-frequency responding might provide a minimal condition for eliciting such conflict, as a result of the need to overcome a prepotent response tendency. We predicted that ACC would be selectively engaged during low-frequency responding, irrespective of the specific task situation. To test this hypothesis, we examined ACC activity during the performance of simple choice-discrimination tasks, using rapid event-related functional magnetic resonance imaging. Subjects were scanned while performing three tasks thought to tap different cognitive processes: 'Go/No-go' (response inhibition), 'oddball' (target detection), and two-alternative forced- choice (response selection). Separate conditions manipulated the frequency of relevant task events. Consistent with our hypothesis, the same ACC region was equally responsive to low-frequency events across all three tasks, but did not show differential responding when events occurred with equal frequency. Subregions of the ACC were also identified that showed heightened activity during the response inhibition condition, and on trials in which errors were committed. Task-sensitive activity was also found in right prefrontal and parietal cortex (response inhibition), left superior temporal and tempoparietal cortex (target detection), and supplementary motor area (response selection). Taken together, the results are consistent with the hypothesis that the ACC serves as a generic detector of processing conflict arising when low-frequency responses must be executed, but also leave open the possibility that further functional specialization may occur within ACC subregions.

Adolescent↗
PubMed2001

Anterior cingulate cortex and response conflict: effects of response modality and processing domain.

Studies of a variety of higher cognitive functions consistently activate a region of anterior cingulate cortex (ACC), situated posterior to the genu and superior to the corpus callosum. However, it is not clear whether the same ACC region is activated for all response modalities (e.g. vocal and manual) and/or all processing domains (e.g. verbal and spatial). To explore this question, we used rapid event-related functional magnetic resonance imaging and a spatial Stroop task with conditions tapping both verbal and spatial processing. We also employed novel methods that allowed us to acquire the accuracy and reaction times of both manual and vocal responses. We found one large ACC region that demonstrated significant response conflict effects with both vocal and manual responses, and three ACC regions that demonstrated significant response conflict effects with both spatial and verbal processing. We did not find any ACC regions that demonstrated activity selective to either a specific response modality or processing domain. Thus, our results suggest that the same regions of ACC are responsive to conflict arising with both manual and vocal output and with both spatial and verbal processing.

Adult↗
PubMed2001

Context processing in older adults: evidence for a theory relating cognitive control to neurobiology in healthy aging.

A theory of cognitive aging is presented in which healthy older adults are hypothesized to suffer from disturbances in the processing of context that impair cognitive control function across multiple domains, including attention, inhibition, and working memory. These cognitive disturbances are postulated to be directly related to age-related decline in the function of the dopamine (DA) system in the prefrontal cortex (PFC). A connectionist computational model is described that implements specific mechanisms for the role of DA and PFC in context processing. The behavioral predictions of the model were tested in a large sample of older (N = 81) and young (N = 175) adults performing variants of a simple cognitive control task that placed differential demands on context processing. Older adults exhibited both performance decrements and, counterintuitively, performance improvements that are in close agreement with model predictions.

Adult↗
PubMed2000

Anterior cingulate and the monitoriing of response conflict: evidence from an fMRI study of overt verb generation.

Studies of a range of higher cognitive functions consistently activate a region of anterior cingulate cortex (ACC), typically posterior to the genu and superior to the corpus collosum. In particular, this ACC region appears to be active in task situations where there is a need to override a prepotent response tendency, when responding is underdetermined, and when errors are made. We have hypothesized that the function of this ACC region is to monitor for the presence of "crosstalk" or competition between incompatible responses. In prior work, we provided initial support for this hypothesis, demonstrating ACC activity in the same region both during error trials and during correct trials in task conditions designed to elicit greater response competition. In the present study, we extend our testing of this hypothesis to task situations involving underdetermined responding. Specifically, 14 healthy control subjects performed a verb-generation task during event-related functional magnetic resonance imaging (fMRI), with the on-line acquisition of overt verbal responses. The results demonstrated that the ACC, and only the ACC, was more active in a series of task conditions that elicited competition among alternative responses. These conditions included a greater ACC response to: (1) Nouns categorized as low vs. high constraint (i.e., during a norming study, multiple verbs were produced with equal frequency vs. a single verb that produced much more frequently than any other); (2) the production of verbs that were weak associates, rather than, strong associates of particular nouns; and (3) the production of verbs that were weak associates for nouns categorized as high constraint. We discuss the implication of these results for understanding the role that the ACC plays in human cognition.

Adolescent↗
PubMed1999

Increased stroop facilitation effects in schizophrenia are not due to increased automatic spreading activation.

Studies using the single trial Stroop task consistently reveal increased reaction time (RT) facilitation effects among schizophrenia patients. One possible mechanism underlying this effect is increased automatic spreading activation in semantic networks. The current study was designed to test this hypothesis. We administered the Stroop task and two semantic priming tasks to the same subjects. Patients showed greater Stroop RT facilitation than controls, no evidence of increased semantic priming at short stimulus onset asynchronies (SOAs), and reduced semantic priming at long SOAs. In addition, abnormal Stroop performance was related to the severity of Disorganization symptoms. These results are inconsistent with the spreading activation hypothesis. Alternative hypotheses regarding the source of Stroop task performance deficits in schizophrenia are discussed.

Adult↗
PubMed1999

Cognition and control in schizophrenia: a computational model of dopamine and prefrontal function.

Behavioral deficits suffered by patients with schizophrenia in a wide array of cognitive domains can be conceptualized as failures of cognitive control, due to an impaired ability to internally represent, maintain, and update context information. A theory is described that postulates a single neurobiological mechanism for these disturbances, involving dysfunctional interactions between the dopamine neurotransmitter system and the prefrontal cortex. Specifically, it is hypothesized that in schizophrenia, there is increased noise in the activity of the dopamine system, leading to abnormal "gating" of information into prefrontal cortex. The theory is implemented as an explicit connectionist computational model that incorporates the roles of both dopamine and prefrontal cortex in cognitive control. A simulation is presented of behavioral performance in a version of the Continuous Performance Test specifically adapted to measure critical aspects of cognitive control function. Schizophrenia patients exhibit clear behavioral deficits on this task that reflect impairments in both the maintenance and updating of context information. The simulation results suggest that the model can successfully account for these impairments in terms of abnormal dopamine activity. This theory provides a potential point of contact between research on the neurobiological and psychological aspects of schizophrenia, by illustrating how a particular physiological disturbance might lead to precise and quantifiable consequences for behavior.

Cognition Disorders↗
PubMed1999

Word production in schizophrenia and its relationship to positive symptoms.

We explored relationships between positive symptoms of schizophrenia and neurocognitive functions (language and memory). The semantic and phonemic associations among words produced in a verbal fluency task by 26 participants diagnosed with DSM-III-R schizophrenia were examined. Formal thought disorder was associated with producing fewer contextually related words and with producing more unrelated words. In contrast, hallucinations were associated with producing more related words. Our results suggest associations between formal thought disorder and impaired memory, and between hallucinations and increased lexical activation/excessive synaptic pruning.

Adult↗
PubMed1999

Overt verbal responding during fMRI scanning: empirical investigations of problems and potential solutions.

This paper presents a pair of studies designed to empirically explore the severity of potential artifacts associated with overt verbal responding during fMRI scanning and to examine several different solutions to these artifacts. In Study One, we compared susceptibility artifacts, signal-to-noise ratios, and activation patterns when overt versus covert verbal responses were elicited during fMRI scanning, using both individual and group analyses. The results indicated that different patterns of brain activation were elicited during covert as compared to overt verbal responses. This suggests that covert responses cannot be used as a simple substitute for overt verbal responses. Further, the results suggested that the use of overt verbal responses during fMRI scanning can produce interpretable results if: (1) the primary comparison is between two conditions that both use overt verbal responses, and (2) analyses are conducted on pooled group data rather than individual participant data. In Study Two, we evaluated the feasibility and validity of a method for acquiring participants' overt responses during fMRI scanning. The results indicated that our method was very accurate in acquiring the content of participant's responses. Further, inspection of the responses demonstrated that participants do not always comply with task instructions and highlighted the importance of obtaining behavioral performance measures during fMRI scanning.

Adult↗
PubMed1999

Context-processing deficits in schizophrenia: converging evidence from three theoretically motivated cognitive tasks.

To test the hypothesis that the ability to actively represent and maintain context information in a central function of working memory and that a disturbance in this function contributes to cognitive deficits in schizophrenia, the authors modified 3 tasks--the AX version of the Continuous Performance Test, Stroop, and a lexical disambiguation task--and administered them to patients with schizophrenia as well as to depressed and healthy controls. The results suggest an accentuation of deficits in patients with schizophrenia in context-sensitive conditions and cross-task correlations of performance in these conditions. However, the results do not definitively eliminate the possibility of a generalized deficit. The significance of these findings is discussed with regard to the specificity of deficits in schizophrenia and the hypothesis concerning the neural and cognitive mechanisms that underlie these deficits.

Adult↗
PubMed1999

The "benefits" of distractibility: mechanisms underlying increased Stroop effects in schizophrenia.

Recent studies of selective attention in schizophrenia patients suggest a particular pattern of single-trial Stroop performance: increased facilitation but not interference in reaction times (RTs), combined with increased error interference. Our Stroop task analysis suggests that this pattern can be explained by a selective attention deficit if one accounts for (1) performance in the congruent condition; (2) the nature of the neutral stimulus; (3) the relationship between accuracy and RT; and (4) response set effects. To test these hypotheses, we examined Stroop performance in 40 DSM-IV schizophrenia patients and 20 healthy control subjects, using a range of neutral stimuli (color patches, noncolor words, color words not in the response set). The findings confirmed several of our predictions and the results were consistent with the hypothesis that abnormal Stroop performance in schizophrenia reflects a failure to adequately attend to the task-appropriate stimulus dimension (color). This inattention affects both the congruent and incongruent conditions and multiple points in the information processing pathway.

Adult↗
PubMed1998

Selective attention in schizophrenia: relationship to verbal working memory.

In previous work using the Stroop task to examine cognitive function in schizophrenia, we have suggested that reaction time (RT) facilitation and error interference should be more sensitive measures of cognitive function than RT interference. We examined this hypothesis in 36 DSM-IV schizophrenia and schizoaffective patients, who performed both the Stroop and the Speaking Span, a measure of verbal working memory. The results supported our hypotheses, demonstrating that RT facilitation and error interference were associated more strongly with working memory performance than RT interference. The robust correlations between these measures of selective attention and Speaking Span performance has implications for understanding the nature and selectivity of cognitive dysfunction in schizophrenia. We present several different hypotheses that may explain this relationship, including: (1) a generalized deficit; (2) a common cognitive disturbance; and (3) a common neurobiological dysfunction.

Adult↗
PubMed1998

Anterior cingulate cortex, error detection, and the online monitoring of performance.

An unresolved question in neuroscience and psychology is how the brain monitors performance to regulate behavior. It has been proposed that the anterior cingulate cortex (ACC), on the medial surface of the frontal lobe, contributes to performance monitoring by detecting errors. In this study, event-related functional magnetic resonance imaging was used to examine ACC function. Results confirm that this region shows activity during erroneous responses. However, activity was also observed in the same region during correct responses under conditions of increased response competition. This suggests that the ACC detects conditions under which errors are likely to occur rather than errors themselves.

Brain Mapping↗
PubMed1998

The Stroop task and attention deficits in schizophrenia: a critical evaluation of card and single-trial Stroop methodologies.

The Stroop task, considered by many to be a paradigmatic measure of selective attention, has often been employed to investigate attention deficits in schizophrenia. Card and single-trial versions of this task have yielded different results. In this study both card and single-trial versions were administered to healthy controls (n = 24) and patients with schizophrenia (n = 55). No differences in reaction time (RT) interference were found on either version. On the single-trial version, patients showed greater RT facilitation and error rate interference, evidence for a deficit in selective attention. Methodologic and analytic issues that account for the mixed results from earlier card Stroop studies are addressed. It is concluded that single-trial versions provide greater sensitivity to selective attention pathology in schizophrenia.

Adult↗