PubMed Health⌕ Search

Biomedical subjects

Phan Luu

Publications and source records attributed to Phan Luu.

9 recordsLinked to original sources
PubMed2005

Dynamics of task sets: evidence from dense-array event-related potentials.

Prior research suggests that task sets facilitate coherent, goal-directed behavior by providing an internal, contextual frame that biases selection toward context-relevant stimulus attributes and responses. Questions about how task sets are engaged, maintained, and shifted have recently become a major focus of research on executive control processes. We employed dense-array (128-channel) event-related potential (ERP) methodology to examine the dynamics of brain systems engaged during the preparation and implementation of task switching. The EEG was recorded while participants performed letter and digit judgments to pseudorandomly-ordered, univalent (#3, A%) and bivalent (G5) stimulus trials, with the appropriate task cued by a colored rectangle presented 450 ms before target onset. Results revealed spatial and temporal variations in brain activity that could be related to preparatory processes common to both switch and repeat trials, switch-specific control processes engaged to reconfigure and maintain task set under conflict, and visual priming benefits of task repetition. Despite extensive practice and improvement, both behavioral and ERP results indicated that subjects maintained high levels of executive control processing with extended task engagement. The patterns of ERP activity obtained in the present study fit well with functional neuroanatomical models of self-regulation of action. The frontopolar and right-lateralized frontal switch effects obtained in the present study are consistent with the role of these regions in adapting to changing contextual contingencies. In contrast, the centroparietal P3b and N384 effects related to the contextual ambiguity of bivalent trials are consistent with the context monitoring and updating functions associated with the posterior cingulate learning circuit.

Adolescent↗
PubMed2005

Geodesic photogrammetry for localizing sensor positions in dense-array EEG.

OBJECTIVE: An important goal for functional brain studies using EEG technology is to estimate the location of brain sources that produce the scalp-recorded signals. The accuracy of source estimates is dependent upon many variables, one of which is the accurate description of the scalp positions of the EEG sensors. The objective of the present research was to develop a photogrammatic method for sensor localization that is fast, accurate, and easy to use. METHODS: With the novel photogrammetric method, multiple cameras were arranged in a geodesic array, and images of the sensors on the subject's head were acquired allowing for the reconstruction of the 3D sensor positions. RESULTS: Data from the photogrammetric method were compared with data acquired with the conventional electromagnetic method. The accuracy of the photogrammatic method, quantified as RMS of the measured positions and the actual known positions, was similar (mean error = 1.27 mm) to the electromagnetic method (mean error = 1.02 mm), and both approximated the localization error of the calibration object (mean error = 0.56 mm). CONCLUSIONS: Accurate determination of 3D sensor positions can be accomplished with minimal demands on the time of the subject and the experimenter using the photogrammetric method.

Electrodes↗
PubMed2005

Love hurts: the evolution of empathic concern through the encephalization of nociceptive capacity.

Empathic concern for others is an essential motive for challenges of self-regulation at all developmental stages. A child who never develops the capacity for empathic concern may become an ineffective parent, such that developmental psychopathology propagates across generations. We draw on evidence and theory by Panksepp and associates that indicates that infant-mother bonding is mediated by opiate mechanisms. We review the neural systems of pain perception and find these are closely aligned with those for attentional and cognitive self-regulation. Analysis of the limbic and neocortical representations for interpersonal reasoning suggests there are important contributions from visceral, affective, and somatic and cognitive levels. We draw on modern learning theory to propose a critical role for frustration training in development to allow the child to achieve the capacity for tolerating psychological pain that allows effective empathic concern in later relationships.

Attention↗
PubMed2004

Frontal midline theta and the error-related negativity: neurophysiological mechanisms of action regulation.

OBJECTIVE: The error-related negativity (ERN) is an event-related potential (ERP) peak occurring between 50 and 100 ms after the commission of a speeded motor response that the subject immediately realizes to be in error. The ERN is believed to index brain processes that monitor action outcomes. Our previous analyses of ERP and EEG data suggested that the ERN is dominated by partial phase-locking of intermittent theta-band EEG activity. In this paper, this possibility is further evaluated. METHODS: The possibility that the ERN is produced by phase-locking of theta-band EEG activity was examined by analyzing the single-trial EEG traces from a forced-choice speeded response paradigm before and after applying theta-band (4-7 Hz) filtering and by comparing the averaged and single-trial phase-locked (ERP) and non-phase-locked (other) EEG data. Electrical source analyses were used to estimate the brain sources involved in the generation of the ERN. RESULTS: Beginning just before incorrect button presses in a speeded choice response paradigm, midfrontal theta-band activity increased in amplitude and became partially and transiently phase-locked to the subject's motor response, accounting for 57% of ERN peak amplitude. The portion of the theta-EEG activity increase remaining after subtracting the response-locked ERP from each trial was larger and longer lasting after error responses than after correct responses, extending on average 400 ms beyond the ERN peak. Multiple equivalent-dipole source analysis suggested 3 possible equivalent dipole sources of the theta-bandpassed ERN, while the scalp distribution of non-phase-locked theta amplitude suggested the presence of additional frontal theta-EEG sources. CONCLUSIONS: These results appear consistent with a body of research that demonstrates a relationship between limbic theta activity and action regulation, including error monitoring and learning.

Adult↗
PubMed2003

Frontolimbic response to negative feedback in clinical depression.

Functional neuroimaging suggests that limbic regions of the medial frontal cortex may be abnormally active in individuals with depression. These regions, including the anterior cingulate cortex, are engaged in both action regulation, such as monitoring errors and conflict, and affect regulation, such as responding to pain. The authors examined whether clinically depressed subjects would show abnormal sensitivity of frontolimbic networks as they evaluated negative feedback. Depressed subjects and matched control subjects performed a video game in the laboratory as a 256-channel EEG was recorded. Speed of performance on each trial was graded with a feedback signal of A, C, or F. By 350 ms after the feedback signal, depressed subjects showed a larger medial frontal negativity for all feedback compared with control subjects with a particularly striking response to the F grade. This response was strongest for moderately depressed subjects and was attenuated for subjects who were more severely depressed. Localization analyses suggested that negative feedback engaged sources in the anterior cingulate and insular cortices. These results suggest that moderate depression may sensitize limbic networks to respond strongly to aversive events.

Adult↗
PubMed2003

Corticolimbic mechanisms in emotional decisions.

Midline frontolimbic networks are engaged in monitoring simple actions. They may also provide evaluative control for more complex decisions. Subjects read a trait-descriptive word and responded either "yes" or "no" within 1,500 ms whether it was self-descriptive. By 300 ms, an electrophysiological discrimination between good and bad words was seen over centromedial regions of the frontal lobe for both friend and self-decisions. By 350 ms, an interaction effect between evaluation and endorsement appeared, and by 500 ms, activity specific to self-evaluation was seen in both anterior and posterior midline sites. An evaluative decision thus begins by recruiting motivational and semantic influences within limbic networks, and these influences appear to shape the development of the decision within multiple neocortical regions.

Adult↗
PubMed2003

Electrophysiological responses to errors and feedback in the process of action regulation.

The anterior cingulate cortex (ACC) is believed to be involved in the executive control of actions, such as in monitoring conflicting response demands, detecting errors, and evaluating the emotional significance of events. In this study, participants performed a task in which evaluative feedback was delayed, so that it was irrelevant to immediate response control but retained its emotional value as a performance indicator. We found that a medial frontal feedback-related negativity similar to the error-related negativity (ERN) tracked affective response to the feedback and predicted subsequent performance. Source analysis of the feedback-related negativity and ERN revealed a common dorsomedial ACC source and a rostromedial ACC source specific to the ERN. The oscillatory nature of these sources provides further evidence that the ERN reflects ongoing theta activity generated in the mediofrontal regions. These results suggest that action regulation by the cingulate gyrus may require the entrainment of multiple structures of the Papez corticolimbic circuit.

Affect↗
PubMed2000

Mood, personality, and self-monitoring: negative affect and emotionality in relation to frontal lobe mechanisms of error monitoring.

A fundamental question in frontal lobe function is how motivational and emotional parameters of behavior apply to executive processes. Recent advances in mood and personality research and the technology and methodology of brain research provide opportunities to address this question empirically. Using event-related-potentials to track error monitoring in real time, the authors demonstrated that variability in the amplitude of the error-related negativity (ERN) is dependent on mood and personality variables. College students who are high on negative affect (NA) and negative emotionality (NEM) displayed larger ERN amplitudes early in the experiment than participants who are low on these dimensions. As the high-NA and -NEM participants disengaged from the task, the amplitude of the ERN decreased. These results reveal that affective distress and associated behavioral patterns are closely related with frontal lobe executive functions.

Adolescent↗