Biomedical subjects

Cameron S Carter

Publications and source records attributed to Cameron S Carter.

At least 37 records · Page 2Linked to original sources

PubMed2005

Prefrontal and striatal activation during sequence learning in geriatric depression.

BACKGROUND: Frontostriatal dysfunction is a primary hypothesis for the neurocognitive changes of depression in late life. The aim of the present study was to test this hypothesis with the use of functional magnetic resonance imaging (fMRI) tasks that are known to engage the prefrontal and neostriatal cognitive circuits. METHODS: Twenty-three elderly subjects (mean age, 69.9 years) participated: 11 subjects with a current major depressive episode and 12 nondepressed elderly control subjects. Subjects underwent fMRI while performing a concurrent implicit and explicit sequence learning task. Region of interest (ROI)-based analyses were conducted, focusing on the dorsal anterior cingulate cortex, the dorsolateral prefrontal cortex, and the neostriatum. RESULTS: As expected, both the control and depressed subjects learned the sequence during both implicit and explicit conditions. During explicit learning, decreased prefrontal activation was found in the depressed subjects, along with increased striatal activation. The increased striatal activity in the depressed subjects was due to increased activity on the trials that violated the sequence. During implicit learning, no significant differences were found between the groups in the identified ROIs. CONCLUSIONS: The increased striatal activation on trials that violated the sequence demonstrates a greater response to negative feedback for depressed compared with control subjects. Our observations of significant differences in both prefrontal and striatal regions in the depressed elderly subjects relative to elderly control subjects supports the frontostriatal dysfunction hypothesis of late-life depression.

Aged↗

PubMed2005

Prefrontal functioning during context processing in schizophrenia and major depression: an event-related fMRI study.

Patients with schizophrenia frequently demonstrate hypofrontality in tasks that require executive processing; however questions still remain as to whether prefrontal cortex dysfunctions are specific to schizophrenia, or a general feature of major psychopathology. Context processing is conceptualized as an executive function associated with attention and working memory processes. Impairment in the ability of patients with schizophrenia to represent and maintain context information has been previously reported in a number of studies. To examine the question of the specificity of a context processing deficit to schizophrenia, we used functional MRI and an expectancy AX continuous performance task designed to assess context processing in a group of healthy controls (n=9), depressed patient controls (n=10), and patients with schizophrenia (n=7). The behavioral performance was consistent with a context processing deficit in patients with schizophrenia, but not those with depression. The imaging data replicate previous results in showing abnormal activity in the right middle frontal gyrus (BA9) in schizophrenia patients related to context processing.

Adult↗

PubMed2005

Prefrontal and striatal activation in elderly subjects during concurrent implicit and explicit sequence learning.

Decreased function in the prefrontal cortex (PFC) is regarded as a primary mechanism of cognitive aging. However, despite a strong association between the prefrontal cortex and the neostriatum, the role of the neostriatum in cognitive aging is less certain. In the current study, event-related functional MRI was used to distinguish the cognitive contributions of neostriatal and prefrontal function in elderly versus young subjects. Twenty healthy subjects, 9 elderly (mean age 67.6 years), and 11 young (mean age 22 years) performed a concurrent implicit and explicit sequence learning task while undergoing functional MR imaging. Both groups showed learning in both the implicit and explicit task conditions. Relative to the young subjects, the elderly subjects showed decreased activation in the left PFC during both implicit and explicit learning, decreased activation in the right putamen during implicit learning, and increased activation in the right PFC during explicit learning. Our results support the theory that changes in a network of brain regions, including the dorsolateral prefrontal cortex and the striatum, are related to cognitive aging. Moreover, these changes are observed during an implicit task, and thus do not seem to be mediated by awareness.

Adult↗

PubMed2005

Event-related functional magnetic resonance imaging investigation of executive control in very old individuals with mild cognitive impairment.

BACKGROUND: Attentional control of executive cognitive function (ECF) decreases in older individuals with Alzheimer Disease (AD). In order to examine early AD-related changes in the neural substrates of ECF attentional control, we measured activation dorsolateral prefrontal (dLPFC), posterior parietal (PPC), and anterior cingulate cortex (ACC) in adults with mild cognitively impairment (MCI) and in cognitively normal (CN) adults. METHODS: Functional magnetic resonance imaging analysis of brain activation in MCI (n = 8, mean age 79.5) and CN (n = 8 mean age 81.5) during increasing loads of attentional demands. RESULTS: MCI and CN older adults performed with similar accuracy and reaction time. MCI had greater activation than CN in PPC (right p = .03 and left p = .05) and dlPFC areas (right p = .002 and left p = .004), while activation in ACC was similar in the two groups. Response to increasing loads of the task differed by group: MCI selectively engaged bilateral PPC (right p = .03, left p = .04), while CN subjects increased bilateral dlPFC activation (right p = .005 and left p = .02) and ACC activation (p = .04). Among MCI, greater load-related changes in PPC activity were associated with smaller load-related changes in accuracy rates (r = -.85, p = .07) and greater increases in reaction times (r = .97, p = .01). In CN subjects, load-related change in PPC activation was associated with load-related change in reaction time (r = .76, p = .02) but not with changes in accuracy rates. CONCLUSIONS: PPC and dlPFC may show early functional changes associated with MCI.

Aged↗

PubMed2005

An information-processing model of three cortical regions: evidence in episodic memory retrieval.

ACT-R (Anderson, J.R., et al., 2003. An information-processing model of the BOLD response in symbol manipulation tasks. Psychon. Bull. Rev. 10, 241-261) relates the inferior dorso-lateral prefrontal cortex to a retrieval buffer that holds information retrieved from memory and the posterior parietal cortex to an imaginal buffer that holds problem representations. Because the number of changes in a problem representation is not necessarily correlated with retrieval difficulties, it is possible to dissociate prefrontal-parietal activations. In two fMRI experiments, we examined this dissociation using the fan effect paradigm. Experiment 1 compared a recognition task, in which representation requirement remains the same regardless of retrieval difficulty, with a recall task, in which both representation and retrieval loads increase with retrieval difficulty. In the recognition task, the prefrontal activation revealed a fan effect but not the parietal activation. In the recall task, both regions revealed fan effects. In Experiment 2, we compared visually presented stimuli and aurally presented stimuli using the recognition task. While only the prefrontal region revealed the fan effect, the activation patterns in the prefrontal and the parietal region did not differ by stimulus presentation modality. In general, these results provide support for the prefrontal-parietal dissociation in terms of retrieval and representation and the modality-independent nature of the information processed by these regions. Using ACT-R, we also provide computational models that explain patterns of fMRI responses in these two areas during recognition and recall.

Adolescent↗

PubMed2005

Outcome representations, counterfactual comparisons and the human orbitofrontal cortex: implications for neuroimaging studies of decision-making.

Recent research suggests that the primate orbitofrontal cortex (OFC) is critical for representations of outcomes of actions and their subsequent impact on the control of behavior. In parallel, a recent theory of decision-making called decision affect theory (Mellers, Schwartz, and Ritov, Psychological Science, 1997) emphasizes the role of anticipated affective impact of outcomes in guiding choices, and the effects of comparisons with alternative outcomes (i.e., counterfactual effects). In the context of decision affect theory, we present results from two event-related functional MRI experiments consistent with two hypotheses regarding the role of the human OFC in guiding behavior through outcome representation: (1) counterfactual effects are manifested in the human OFC during expectation of outcomes, such that the anticipated affective impact of outcomes is modulated by the nature of the various possible alternative outcomes; (2) a regional specialization exists in the human prefrontal cortex, such that affective impact of potential negative outcomes of actions is represented mainly by the lateral areas of the OFC, while areas situated progressively more medial and dorsal on the ventral and medial PFC are specifically involved in representing the impact of positively valenced outcomes. We also discuss some of the implications that these hypotheses have for neuroimaging studies of reward processing and decision-making, and for studies of neuropsychiatric disorders in which these processes are thought to be disturbed.

Adult↗

PubMed2005

Separating semantic conflict and response conflict in the Stroop task: a functional MRI study.

Attentive behavior requires the ability to perform in the face of distraction. Distracting information can cause conflict at any level along the information processing stream. However, it is not yet known whether the brain has distinct subsystems dedicated to detecting and resolving these different forms of distraction. Although previous studies have localized brain activity during semantic and response conflict, no prior study has specifically determined whether these activations occur in distinct or overlapping regions. We used a modified version of the Stroop color-word task, by which we were able to separate semantic from response conflict. Behavioral data indicate that these two kinds of conflict both contribute to the overall Stroop interference effect, while fMRI data indicate that they elicit non-overlapping activation in anterior cingulate, prefrontal, and parietal brain regions. These results suggest that the brain has distinct but parallel attentional mechanisms for resolving these different forms of cognitive interference.

Adult↗

PubMed2005

A convergent-divergent approach to context processing, general intellectual functioning, and the genetic liability to schizophrenia.

Convergent and divergent validity are critically important in developing psychological measures that reveal interpretable deficits in disordered populations. This article reports on 2 studies that evaluated the validity of context processing measures. In Experiment 1, a confirmatory factor analysis of data from 481 healthy adults established the convergent validity of 2 context processing measures and showed that context processing accounted for significant amounts of variance in standard IQ and working memory measures. In Experiment 2, 20 schizophrenia patients, 16 of their healthy siblings, and 28 controls were evaluated using a novel, short context processing measure, the dot pattern expectancy (DPX) task. The DPX was sensitive to specific deficits in schizophrenia patients and their healthy siblings. These findings support the construct validity of context processing measures, suggest context processing is a component of intellectual functioning, and demonstrate that brief context processing measures remain sensitive to psychopathological deficits.

Adult↗

PubMed2005

Decreased conflict- and error-related activity in the anterior cingulate cortex in subjects with schizophrenia.

OBJECTIVE: People with schizophrenia have exhibited reduced functional activity in the anterior cingulate cortex during the performance of many types of cognitive tasks and during the commission of errors. According to conflict theory, the anterior cingulate cortex is involved in the monitoring of response conflict, acting as a signal for a need for greater cognitive control. This study examined whether impaired conflict monitoring in people with schizophrenia could underlie reduced anterior cingulate activity during both correct task performance and error-related activity. METHOD: Functional activity in the anterior cingulate of 13 schizophrenia patients and 13 healthy comparison subjects was investigated by using event-related fMRI and a Stroop task that allowed simultaneous examination of activity during both conflict (incongruent trials) and error (commission of error trials). RESULTS: In the presence of comparable reaction time measures for conflict as well as comparable error rates, the schizophrenia subjects showed both decreased conflict- and error-related activity in the same region of the anterior cingulate cortex. Moreover, those with schizophrenia did not exhibit significant post-conflict or post-error behavioral adjustments. CONCLUSIONS: Concurrently reduced conflict- and error-related activity in the anterior cingulate cortex along with reduced trial-to-trial adjustments in performance has not previously been reported in schizophrenia. The current results suggest that impaired conflict monitoring by the anterior cingulate cortex might play an important role in contributing to cognitive control deficits in patients with schizophrenia.

Adult↗

PubMed2005

Lateral and medial hypofrontality in first-episode schizophrenia: functional activity in a medication-naive state and effects of short-term atypical antipsychotic treatment.

OBJECTIVE: The dorsolateral prefrontal cortex and the anterior cingulate cortex are critical components of the brain circuitry underlying executive control. The objective of this study was to investigate control-related dorsolateral prefrontal cortex functioning and conflict-related anterior cingulate cortex functioning in a group of never medicated first-episode schizophrenia patients to determine whether both regions show dysfunction at illness onset. A second objective was to assess short-term effects of atypical antipsychotic medication on dorsolateral prefrontal cortex and anterior cingulate cortex functioning. METHOD: First-episode schizophrenia patients (N=23) and healthy comparison subjects (N=24) underwent event-related fMRI and performed a cognitive task designed to functionally dissociate the two regions. Four weeks after initiation of pharmacotherapy for patients, a subset of 11 patients and 16 comparison subjects underwent a repeat assessment. RESULTS: At baseline, patients exhibited hypoactivation in the dorsolateral prefrontal cortex and anterior cingulate cortex. After 4 weeks of antipsychotic treatment, the patients demonstrated improved functioning in the anterior cingulate cortex but not in the dorsolateral prefrontal cortex. CONCLUSIONS: These findings confirm the presence of dorsolateral prefrontal cortex dysfunction early in the course of schizophrenia and suggest that anterior cingulate cortex functioning may be altered at illness onset as well. Results also suggest that anterior cingulate cortex functioning may be especially sensitive to remedial antipsychotic treatment effects. These findings are consistent with an emerging literature documenting short-term benefits of atypical antipsychotic medication for the neural circuitry underlying cognitive deficits in schizophrenia.

Adult↗

PubMed2005

Specificity of prefrontal dysfunction and context processing deficits to schizophrenia in never-medicated patients with first-episode psychosis.

OBJECTIVE: Context processing is a cognitive construct associated with activity in the middle frontal gyrus. Schizophrenia-related deficits in context processing tasks have been associated with prefrontal cortical dysfunction. This study evaluated whether prefrontal cortical dysfunction related to context processing occurred in first-episode, never-medicated schizophrenia patients, whether this dysfunction also occurred in patients with nonschizophrenia psychosis, and whether this dysfunction was related to psychotic symptom expression. METHOD: A modified version of the AX continuous performance task was conducted during event-related functional magnetic resonance imaging in 18 never-medicated, first-episode schizophrenia patients, 12 never-medicated patients with first-episode nonschizophrenia psychosis, and 28 comparison participants without psychiatric disorder. RESULTS: In-scanner measures of errors and interference reaction time showed that the schizophrenia patients had a specific deficit in context processing. Trials with greater context processing demands corresponded to activity in the middle frontal gyrus (Brodmann's area 9) in the comparison subjects and in the patients with nonschizophrenia psychosis, but not in the schizophrenia patients. Individual differences in prefrontal cortical dysfunction were associated with context processing measures and disorganization symptoms. The schizophrenia patients also showed increased activity in the anterior (Brodmann's area 10) and inferior prefrontal cortices (Brodmann's area 45/46) when they were maintaining context over a delay. CONCLUSIONS: Prefrontal dysfunctions related to context processing were found only in schizophrenia patients early in the course of the illness, and these dysfunctions were related to disorganization symptoms. Instead of using context processing during a continuous performance task, schizophrenia patients may use an inefficient encoding and retrieval strategy.

Adult↗

PubMed2004

Behavioral equivalence, but not neural equivalence--neural evidence of alternative strategies in mathematical thinking.

In a functional magnetic resonance imaging study, we investigated how people solve mathematically equivalent problems presented in two alternative formats: verbal, story format or symbolic, equation format. Although representation format had no effect on behavior, anterior prefrontal activation was greater in the story condition and posterior parietal activation was greater in the equation condition. These results show that there exist alternative neural pathways that implement different and yet equally efficient problem-solving strategies.

Behavior↗

PubMed2004

Cognitive control involved in overcoming prepotent response tendencies and switching between tasks.

A dissociable set of regions was active for the executive processing associated with overcoming a prepotent response tendency and task switching. Regions associated with overcoming prepotency were primarily frontal and may be part of a system involved in top-down biasing for conflict reduction. Posterior regions were recruited for switching between tasks and likely play a role in reconfiguring stimulus-response mappings. Precuneus activity was common to both manipulations and may reflect increased visual attention due to more difficult task demands.

Adult↗

PubMed2004

Prefrontal cortex guides context-appropriate responding during language production.

Although language processing is thought to frequently require cognitive control, little is known about the cognitive and neural basis of the control of language. Here, we demonstrate that processing of context by the PFC plays an important role in the control of language comprehension and production. Using a missing letter paradigm and fMRI, we found that increased activation in the PFC (but not in posterior regions), while encoding and maintaining context information, predicted context-appropriate responses. Furthermore, greater selection demands increased activity during responding in the same regions engaged during the encoding and maintenance of context. Overall, as in other cognitive task domains, these results suggest that PFC context processing plays an important role in the control of language.

Adult↗

PubMed2004

The change of the brain activation patterns as children learn algebra equation solving.

In a brain imaging study of children learning algebra, it is shown that the same regions are active in children solving equations as are active in experienced adults solving equations. As with adults, practice in symbol manipulation produces a reduced activation in prefrontal cortex area. However, unlike adults, practice seems also to produce a decrease in a parietal area that is holding an image of the equation. This finding suggests that adolescents' brain responses are more plastic and change more with practice. These results are integrated in a cognitive model that predicts both the behavioral and brain imaging results.

Adolescent↗

PubMed2004

Distinct portions of anterior cingulate cortex and medial prefrontal cortex are activated by reward processing in separable phases of decision-making cognition.

BACKGROUND: Choosing between actions associated with uncertain rewards and punishments is mediated by neural circuitry encompassing the orbitofrontal cortex, anterior cingulate cortex (ACC), and striatum; however, the precise conditions under which these different components are activated during decision-making cognition remain uncertain. METHODS: Fourteen healthy volunteers completed an event-based functional magnetic resonance imaging protocol to investigate blood-oxygenation-level-dependent (BOLD) responses during independently modeled phases of choice cognition. In the "decision phase," participants decided which of two simultaneous visually presented gambles they wished to play for monetary reward. The gambles differed in their magnitude of gains, magnitude of losses, and the probabilities with which these outcomes were delivered. In the "outcome phase," the result of each choice was indicated on the visual display. RESULTS: In the decision phase, choices involving large gains were associated with increased BOLD responses in the pregenual ACC, paracingulate, and right posterior orbitolateral cortex compared with choices involving small gains. In the outcome phase, good outcomes were associated with increased BOLD responses in the posterior orbitomedial cortex, subcallosal ACC, and ventral striatum compared with negative outcomes. There was only limited overlap between reward-related activity in ACC and orbitofrontal cortex during the decision and outcome phases. CONCLUSIONS: Neural activity within the medial and lateral orbitofrontal cortex, pregenual ACC, and striatum mediate distinct representations of reward-related information that are deployed at different stages during a decision-making episode.

Adult↗

PubMed2004

Event-related functional magnetic resonance imaging of reward-related brain circuitry in children and adolescents.

BACKGROUND: Functional disturbances in reward-related brain systems are thought to play a role in the development of mood, impulse, and substance-abuse disorders. Studies in nonhuman primates have identified brain regions, including the dorsal/ventral striatum and orbital-frontal cortex, in which neural activity is modulated by reward. Recent studies in adults have concurred with these findings by observing reward-contingent blood oxygen level-dependent (BOLD) responses in these regions during functional magnetic resonance imaging (fMRI) paradigms; however, no previous studies indicate whether comparable modulations of neural activity exist in the brain reward systems of children and adolescents. METHODS: We used event-related fMRI and a behavioral paradigm modeled on previous work in adults to study brain responses to monetary gains and losses in psychiatrically healthy children and adolescents as part of a program examining the neural substrates of anxiety and depression in youth. RESULTS: Regions and time-courses of reward-related activity were similar to those observed in adults with condition-dependent BOLD changes in the ventral striatum and lateral and medial orbital-frontal cortex; specifically, these regions showed larger responses to positive than to negative feedback. CONCLUSIONS: These results provide further evidence for the value of event-related fMRI in examining reward systems of the brain, demonstrate the feasibility of this approach in children and adolescents, and establish a baseline from which to understand the pathophysiology of reward-related psychiatric disorders in youth.

Adolescent↗

PubMed2004

Anterior cingulate conflict monitoring and adjustments in control.

Conflict monitoring by the anterior cingulate cortex (ACC) has been posited to signal a need for greater cognitive control, producing neural and behavioral adjustments. However, the very occurrence of behavioral adjustments after conflict has been questioned, along with suggestions that there is no direct evidence of ACC conflict-related activity predicting subsequent neural or behavioral adjustments in control. Using the Stroop color-naming task and controlling for repetition effects, we demonstrate that ACC conflict-related activity predicts both greater prefrontal cortex activity and adjustments in behavior, supporting a role of ACC conflict monitoring in the engagement of cognitive control.

Adult↗