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Cameron S Carter

Publications and source records attributed to Cameron S Carter.

At least 55 records · Page 3Linked to original sources
PubMed2004

Errors without conflict: implications for performance monitoring theories of anterior cingulate cortex.

Recent theories of the neural basis of performance monitoring have emphasized a central role for the anterior cingulate cortex (ACC). Replicating an earlier event-related potential (ERP) study, which showed an error feedback negativity that was modeled as having an ACC generator, we used event-related fMRI to investigate whether the ACC would differentiate between correct and incorrect feedback stimuli in a time estimation task. The design controlled for response conflict and frequency and expectancy effects. Although participants in the current study adjusted their performance following error feedback, we did not observe error feedback-evoked ACC activity. In contrast, we did observe ACC activity while the same subjects performed the Stroop task, in which an area of the ACC activated during both conflict and error trials. These findings are inconsistent with previous dipole models of the error feedback negativity, and suggest the ACC may not be involved in the generation of this ERP component. These results question involvement of the ACC in the detection of errors per se when controlling for conflict.

Adult↗
PubMed2004

Neurocognitive mechanisms of cognitive control: the role of prefrontal cortex in action selection, response inhibition, performance monitoring, and reward-based learning.

Convergent evidence highlights the differential contributions of various regions of the prefrontal cortex in the service of cognitive control, but little is understood about how the brain determines and communicates the need to recruit cognitive control, and how such signals instigate the implementation of appropriate performance adjustments. Here we review recent progress from cognitive neuroscience in examining some of the main constituent processes of cognitive control as involved in dynamic decision making: goal-directed action selection, response activation and inhibition, performance monitoring, and reward-based learning. Medial frontal cortex is found to be involved in performance monitoring: evaluating outcome vis-a-vis expectancy, and detecting performance errors or conflicting response tendencies. Lateral and orbitofrontal divisions of prefrontal cortex are involved in subsequently implementing appropriate adjustments.

Animals↗
PubMed2004

Conflict monitoring and anterior cingulate cortex: an update.

One hypothesis concerning the human dorsal anterior cingulate cortex (ACC) is that it functions, in part, to signal the occurrence of conflicts in information processing, thereby triggering compensatory adjustments in cognitive control. Since this idea was first proposed, a great deal of relevant empirical evidence has accrued. This evidence has largely corroborated the conflict-monitoring hypothesis, and some very recent work has provided striking new support for the theory. At the same time, other findings have posed specific challenges, especially concerning the way the theory addresses the processing of errors. Recent research has also begun to shed light on the larger function of the ACC, suggesting some new possibilities concerning how conflict monitoring might fit into the cingulate's overall role in cognition and action.

Cognition↗
PubMed2004

Factors influencing Stroop performance in schizophrenia.

Recent studies suggest that individuals with schizophrenia show enhanced facilitation but similar interference in reaction times (RTs), compared with control participants, combined with increased error interference. This study examined the relationship between errors and RTs on the Stroop task among individuals with schizophrenia. The authors examined performance on a speeded Stroop task, designed to increase errors, in 29 individuals with schizophrenia and 29 nonpatient control participants. The authors also analyzed color-naming and word-reading estimates from process dissociation analyses. The findings suggest that a lack of increased RT interference among patients (compared with control participants) is not solely due to the increased number of errors they produce in the incongruent condition but is also influenced by a greater impact of the word even in the neutral condition.

Adult↗
PubMed2004

Regional brain activation during concurrent implicit and explicit sequence learning.

We used event-related fMRI to identify the brain regions engaged during explicit and implicit sequence learning (ESL and ISL, respectively). Twenty-four subjects performed a concurrent ESL and ISL task. Behavior showed learning in both conditions. Prefrontal (PFC), striatal, anterior cingulate cortex (ACC) and visual regions (V1, V2 and V3) were engaged during both ESL and ISL. With ESL there was increased activity in the visual regions on the predictable (i.e. learned pattern) trials. With ISL, however, there was a relative decrease in activity in visual regions. The opposite patterns in the visual regions highlight the different effects of ESL and ISL. The learning process was distinguished from the result of learning, by fitting subjects' functional magnetic resonance imaging data to their learning curve. This analysis revealed more extensive PFC activity during ESL and caudal ACC activity specific for the result of learning analysis, when the expected response was violated. Our results suggest a relative dissociation of the brain regions engaged during ESL and ISL, whereby ESL and ISL can be viewed as partially distinct but overlapping parallel processes.

Adolescent↗
PubMed2004

The relationship of three cortical regions to an information-processing model.

This research tests a model of the computational role of three cortical regions in tasks like algebra equation solving. The model assumes that there is a left parietal region-of-interest (ROI) where the problem expression is represented and transformed, a left prefrontal ROI where information for solving the task is retrieved, and a motor ROI where hand movements to produce the answer are programmed. A functional magnetic resonance imaging (fMRI) study of an abstract symbol-manipulation task was performed to articulate the roles of these three regions. Participants learned to associate words with instructions for transforming strings of letters. The study manipulated the need to retrieve these instructions, the need to transform the strings, and whether there was a delay between calculation of the answer and the output of the answer. As predicted, the left parietal ROI mainly reflected the need for a transformation and the left prefrontal ROI the need for retrieval. Homologous right ROIs showed similar but weaker responses. Neither the prefrontal nor the parietal ROIs responded to delay, but the motor ROI did respond to delay, implying motor rehearsal over the delay. Except for the motor ROI, these patterns of activity did not vary with response hand. In an ACT-R model, it was shown that the activity of an imaginal buffer predicted the blood oxygen level-dependent (BOLD) response of the parietal ROI, the activity of a retrieval buffer predicted the response of the prefrontal ROI, and the activity of a manual buffer predicted the response of the motor ROI.

Adolescent↗
PubMed2004

The BOLD hemodynamic response in healthy aging.

Several previous studies have compared the blood oxygen level-dependent (BOLD) hemodynamic response (HDR) in healthy elderly subjects to the HDR in young subjects. Some studies have found a relative decreased amplitude in the elderly in the visual cortex, whereas other studies have found the elderly HDR amplitude in the visual cortex to be nearly identical to that in young subjects. A possible explanation for the different findings is that the peak voxel HDR is similar between the groups, but that the HDR in the group-averaged region-of-interest (ROI) is "washed out" by the inclusion of less significant voxels (due to a smaller extent of activation in the elderly) or by the inclusion of negative-peaking voxels. We tested this hypothesis using event-related functional magnetic resonance imaging (fMRI ). While undergoing fMRI, subjects performed a simple visual and motor task, pressing with their index fingers in response to visual presentation of the word tap. Data from 18 subjects, 8 young and 10 elderly, were analyzed. For each subject, a visual and a motor ROI was selected by choosing the most significant positive voxels within the anatomically defined ROI. This individual subject approach excluded both low-significance and negative-peaking voxels. Similar peaks were found for the elderly and the young subjects in both motor and visual regions and a more sustained BOLD response was found for the elderly in both regions. Additionally, as predicted, a greater percentage of voxels with a negative HDR was found for the elderly in the visual region; this finding was also replicated in our reanalysis of an independent fMRI and aging study from the fMRI Data Center. Functional neuroimaging observations of negative HDRs in visual areas have been interpreted as the effect of unconstrained processing during rest. Our results suggest that the elderly may have more unconstrained visual processing during the rest condition in the scanner. The observation that the group differences in the BOLD response are sensitive to voxel selection (e.g., inclusion of low-significance and/or negative voxels) underscores the importance of ROI selection criteria in the interpretation of fMRI studies using elderly populations.

Adult↗
PubMed2004

ERP correlates of action monitoring in adolescence.

This study examines the development of action monitoring in adolescence by measuring the N200, the ERN (error-related negativity) and the P(E) (error positivity), which are event-related potentials (ERPs) that appear to be generated in the anterior cingulate cortex (ACC) and reflect action-monitoring processes. We predicted that amplitude would be significantly greater in late compared to early adolescence. Participants consisted of 11 adolescents that were divided into early (age 9-14) and late (age 14-17) adolescence groups. ERPs were recorded during an 840-trial arrow-flanker task and using 128-channel dense array EEG. Results indicated that there were no differences in P(E) amplitude but that N200 and ERN amplitudes were greater in the late adolescence group. According to the conflict monitoring hypothesis, this suggests that the ability to detect error-related conflict, which is involved in the modulation of cognitive control, appears to be fully developed later in adolescence and may be linked to the maturation of the ACC.

Adolescent↗
PubMed2003

The evaluation of brain activity in response to taste stimuli--a pilot study and method for central taste activation as assessed by event-related fMRI.

BACKGROUND: Brain pathways contribute to the regulation of appetite behaviors, and advancements in brain imaging offer new opportunities in determining whether disturbances of these pathways play a role in pathological feeding behaviors in humans. We developed a standardized method for the assessment of brain activation in response to taste stimuli. METHODS: Five healthy control women were positioned in a 1.5 T GE magnet resonance (MR) scanner for functional MR imaging (fMRI). They received 1.0 cm3 samples of 1 M glucose solution or artificial saliva (25 mM KCl, 2 mM NaHCO3). Fluid challenges were delivered by a programmable syringe pump (J-Kem Scientific, St. Louis, MO). E-Prime software (Psychology Software Tools Inc., Pittsburgh, PA) coordinated taste stimulation with MR scanning. Data were analyzed using NeuroImaging software (NIS). RESULTS: Healthy women showed increased orbitofrontal cortex activation when glucose was compared to artificial saliva. In addition, mesial and lateral temporal cortical regions contrasted glucose from artificial saliva. CONCLUSIONS: This study demonstrates a design for the systematic study of brain activation after taste stimulation using fMRI and computer controlled stimulus delivery. The results are consistent with previous studies, showing activation in higher order brain centers that are involved in emotional coding of taste experience.

Adult↗
PubMed2003

Competition and representation during memory retrieval: roles of the prefrontal cortex and the posterior parietal cortex.

In this functional-MRI study we examined the hypothesis that the prefrontal cortex responds differently to the extent of competition during retrieval, whereas the parietal cortex is responsible for problem representation that should not be directly related to the competition. Participants mastered arbitrary person-location pairs, and their recognition memory was tested in a functional-MRI session. The pairs were constructed such that a person was associated with one, two, or three different locations and vice versa. The recognition time increased with the number of associations, reflecting increased competition. A confirmatory analysis of imaging data with prespecified prefrontal and parietal regions showed that, although both regions were highly involved during memory retrieval, only the prefrontal region responded to the levels of competition. This result was consistent with predictions of an information-processing model as well as with an exploratory identification of regions of interest.

Adult↗
PubMed2003

Predicting the practice effects on the blood oxygenation level-dependent (BOLD) function of fMRI in a symbolic manipulation task.

Based on adaptive control of thought-rational (ACT-R), a cognitive architecture for cognitive modeling, researchers have developed an information-processing model to predict the blood oxygenation level-dependent (BOLD) response of functional MRI in symbol manipulation tasks. As an extension of this research, the current event-related functional MRI study investigates the effect of relatively extensive practice on the activation patterns of related brain regions. The task involved performing transformations on equations in an artificial algebra system. This paper shows that the base-level activation learning in the ACT-R theory can predict the change of the BOLD response in practice in a left prefrontal region reflecting retrieval of information. In contrast, practice has relatively little effect on the form of BOLD response in the parietal region reflecting imagined transformations to the equation or the motor region reflecting manual programming.

Adult↗
PubMed2003

Prefrontal cortex dysfunction mediates deficits in working memory and prepotent responding in schizophrenia.

BACKGROUND: Schizophrenic patients show deficits in working memory (WM) and inhibition of prepotent responses. We examined brain activity while subjects performed tasks that placed demands on WM and overriding prepotent response tendencies, testing predictions that both processes engage overlapping prefrontal cortical (PFC) regions and that schizophrenic patients show reduced PFC activity and performance deficits reflecting both processes. METHODS: Functional magnetic resonance imaging data were acquired while 16 schizophrenic and 15 healthy subjects performed the N-Back task that varied WM load and a version of the AX-CPT that required overriding a prepotent response tendency. RESULTS: Both tasks engaged overlapping cortical networks (e.g., bilateral dorsolateral PFC, Broca's area, parietal cortex). Increased WM load monotonically increased activity; preparation to override a prepotent response produced greater and more enduring activity. Group differences on each task emerged in a right dorsolateral PFC region: schizophrenic subjects showed lesser magnitude increases under conditions of high WM and prepotent response override demands, with concomitant performance impairments. CONCLUSIONS: Schizophrenic patients exhibit PFC-mediated deficits in WM and preparation to override prepotent responses. Findings are consistent with the operation of a single underlying PFC-mediated cognitive control mechanism and with physiologic dysfunction of the dorsolateral PFC in schizophrenic patients reflecting impairments in this mechanism.

Adult↗
PubMed2003

A specific deficit in context processing in the unaffected siblings of patients with schizophrenia.

BACKGROUND: Understanding the biological basis of complex, heritable illnesses such as schizophrenia is facilitated by sensitive and functionally specific measures of intermediate processes. Context processing is a theoretically motivated construct associated with executive function. Impairments in this process have been associated with dysfunction of the prefrontal cortex. In the present study, we evaluated whether a specific deficit in context processing could be associated with the unexpressed genetic liability to schizophrenia. METHODS: Twenty-four patients with schizophrenia, 24 unaffected siblings and 36 control subjects completed a version of the AX task with (1) a condition that required context processing and (2) an expectancy condition in which intact context processing could lead to errors. RESULTS: Patients and unaffected siblings performed relatively worse in the context processing condition, whereas controls performed relatively worse in the expectancy condition. A double dissociation between siblings and controls (F = 9.5, P<.005) constituted strong evidence of a specific deficit in context processing associated with a familial or genetic liability to schizophrenia. Preliminary evidence of high diagnostic efficiency was also noted (specificity, 38%; and sensitivity, 100%). CONCLUSIONS: Context processing deficits have been associated with dorsolateral prefrontal cortex dysfunctions in schizophrenia. Such a dysfunction may occur even when genetic liability to schizophrenia is unexpressed clinically. The present method of demonstrating a double dissociation may be a useful approach to exploring endophenotypes related to specific cognitive and neural processes that can be measured in ways sensitive to subtle group differences.

Adult↗
PubMed2003

Use of concurrent pupil dilation assessment to inform interpretation and analysis of fMRI data.

Potential contributions of concurrently acquired pupil dilation data to functional magnetic resonance imaging (fMRI) experiments were examined. Sixteen healthy participants completed a working memory task (digit sorting) during measurement of pupil dilation outside the fMRI environment and during concurrent 3T fMRI assessment. Pupil dilation increased parametrically with task difficulty inside and outside the scanner, on a similar time course, suggesting that task demand was similar in both environments. The time course of pupil dilation during digit sorting was similar to the time course of the fMRI signal in the middle frontal gyrus, suggesting that middle-frontal gyrus activity indexed the engagement working memory processes. Incorporating individual differences in pupil dilation improved the sensitivity and specificity of general linear modeling analyses of activity in the middle frontal gyrus, above and beyond standard analytic techniques. Results suggest concurrent pupil dilation during fMRI assessment can help to (1) specify whether task demand is the same inside and outside the fMRI environment, (2) resolve the extent to which fMRI signals reflect different aspects of event-related designs, and (3) explain variation in fMRI data due to individual differences in information processing.

Adult↗
PubMed2003

Event-related FMRI study of context processing in dorsolateral prefrontal cortex of patients with schizophrenia.

Context processing is conceptualized as an executive function involved in voluntary, complex actions such as overcoming automatic responses. The present study tested the hypothesis that context-processing deficits in patients with schizophrenia are associated with a dysfunction of left dorsolateral prefrontal cortex (DLPFC). Using event-related functional magnetic resonance imaging (fMRI), 17 controls and 17 medicated patients performed a version of the AX task in which a learned, automatic response had to be inhibited. In controls, left DLPFC activity increased when preparing to overcome an automatic response, whereas patients with schizophrenia showed no differential activation. In controls, context processing appeared to be associated with the differential representation of cues associated with the need to provide top-down support for overcoming automatic responses. This mechanism appeared to be impaired in patients with schizophrenia.

Adult↗
PubMed2003

Tryptophan depletion alters the decision-making of healthy volunteers through altered processing of reward cues.

While accumulating evidence suggests that effective real-life decision-making depends upon the functioning of the orbitofrontal cortex, much less is known about the involvement of the monoamine neurotransmitter systems and, in particular, serotonin. In the present study, we explored the impact of depleting the serotonin precursor, tryptophan, on human decision-making. Eighteen healthy volunteers consumed an amino-acid drink containing tryptophan and 18 healthy volunteers consumed an amino-acid drink without tryptophan, before choosing between simultaneously presented gambles, differing in the magnitude of expected gains (ie reward), the magnitude of expected losses (ie punishment), and the probabilities with which these outcomes were delivered. Volunteers also chose between gambles probing identified non-nomative biases in human decision-making, namely, risk-aversion when choosing between gains and risk-seeking when choosing between losses. Tryptophan-depleted volunteers showed reduced discrimination between magnitudes of expected gains associated with different choices. There was little evidence that tryptophan depletion was associated with altered discrimination between the magnitudes of expected losses, or altered discrimination between the relative probabilities with which these positive or negative outcomes were delivered. Risk-averse and risk-seeking biases were also unchanged. These results suggest that serotonin mediates decision-making in healthy volunteers by modulating the processing of reward cues, perhaps represented within the orbitofrontal cortex. It is possible that such a change in the cognition mediating human choice is one mechanism associated with the onset and maintenance of anhedonia and lowered mood in psychiatric illness.

Adult↗
PubMed2003

Overactive action monitoring in obsessive-compulsive disorder: evidence from functional magnetic resonance imaging.

The anterior cingulate cortex (ACC) in patients with obsessive-compulsive disorder (OCD) has been found to be hyperactive at rest, during symptom provocation, and after commission of errors in cognitive tasks. This hyperactivity might reflect an abnormality in conflict detection, a hypothesized basic mechanism for the action-monitoring function of the ACC. This hypothesis was tested using functional magnetic resonance imaging, by scanning 11 OCD patients and 13 matched control subjects while they performed a version of the continuous-performance task with four trial types that induced graded levels of response conflict. Although a behavioral index of conflict (i.e., accuracy) was similar for patients and control subjects, the ACC activation was increased in patients during high-conflict trials. The error-related activity in the same brain region was also higher in patients, consistent with previous electrophysiological findings. Both conflict- and error-related activity showed trends for positive correlations with severity of OCD symptoms, but not with anxiety. These findings suggest that as part of an overactive action-monitoring system, the ACC is more directly involved in the pathophysiology of OCD than previously thought.

Adult↗