Stephan Taylor - Academia.edu (original) (raw)

Papers by Stephan Taylor

Research paper thumbnail of Isolation of specific interference processing in the Stroop task: PET

NeuroImage

The Stroop task, in which subjects must name the color of letters that spell color words differen... more The Stroop task, in which subjects must name the color of letters that spell color words different than the color-to-be-named, provides an important experimental paradigm for the study of selective attention. Cerebral blood flow activation studies have not always demonstrated consistent activation patterns; inconsistent results may reflect nonspecific responses, such as arousal or anticipation, rather than cerebral networks specific to Stroop interference processing. In order to identify regions consistently implicated in Stroop interference processing, we undertook two experiments with a Stroop interference paradigm and contrasting lexical and nonlexical control conditions. In our first experiment, standard Stroop stimuli, e.g., the word ''RED'' displayed in a green font, were contrasted with color naming of the font of noncolor words and color naming of a false font. In our second experiment, we compared Stroop stimuli with colored symbols and a control condition designed to elicit nonspecific interference-taboo words displayed in color fonts. Only two brain regions showed a consistent CBF change in both experiments. Activation in the left inferior frontal gyrus reflected processing more specific to the Stroop task, while deactivation in the right superior temporal gyrus occurred for the Stroop and the taboo conditions, consistent with more nonspecific processing. Activation in the anterior cingulate cortex occurred in only one comparison in one experiment and may not reflect functions central to overcoming Stroop interference.

Research paper thumbnail of Automated detection of the intercommissural line for stereotaxic localization of functional brain images

Journal of Nuclear Medicine

CT) can be employed for this purpose. Accurate co registration between PET and the anatomical ref... more CT) can be employed for this purpose. Accurate co registration between PET and the anatomical reference image is crucial for this approach (3,5â€"9).

Research paper thumbnail of Intrinsic viscosity and partial specific volume of hyaluronic acid

Research paper thumbnail of Global Cerebral Blood Flow Increase Reveals Focal Hypoperfusion in Schizophrenia - Linear scaling and nonlinear warping of functional brain images

Neuropsychopharmacology

Recent functional neuroimaging strategies have evaluated cerebral blood flow (CBF) to determine s... more Recent functional neuroimaging strategies have evaluated cerebral blood flow (CBF) to determine specific sites of action of pharmacologic agents. Since many pharmacologic agents change global CBF, we investigated the effects of global CBF changes on regional perfusion with acetazolamide, which increases global CBF via non-neuronal mechanisms. We used the [15O]PET technique to measure CBF before and after we infused 8 schizophrenic patients and 10 healthy control subjects with acetazolamide. The rostral anterior cingulate cortex demonstrated a greater perfusion increase in the schizophrenic subjects after acetazolamide infusion, relative to other areas of the brain. During the baseline condition, this area showed relative hypoperfusion in our sample of schizophrenic subjects, consistent with previous functional neuroimaging studies. The results demonstrate the need for caution in interpreting CBF changes after pharmacologic challenge, because global CBF changes can confound the assessment of regionally-specific pharmacologic action.

Research paper thumbnail of PET study of greater visual activation in schizophrenia

American Journal of Psychiatry

The authors tested the hypothesis that photic visual stimuli cause a greater blood flow activatio... more The authors tested the hypothesis that photic visual stimuli cause a greater blood flow activation response in subjects with schizophrenia than in normal subjects. Eleven medicated patients with schizophrenia and 10 normal subjects were studied with [15O]H2O positron emission tomography to measure perfusion during photic stimulation at four different rates. The activation at three out of four rates of visual stimulation was greater for the patients with schizophrenia than it was for the normal subjects. Further investigation into the mechanisms of activation during sensory stimulation in schizophrenia is warranted.

Research paper thumbnail of Abnormal GABAergic function and face processing in schizophrenia: A pharmacologic-fMRI study

Schizophrenia Research, 2015

The involvement of the gamma-aminobutyric acid (GABA) system in schizophrenia is suggested by pos... more The involvement of the gamma-aminobutyric acid (GABA) system in schizophrenia is suggested by postmortem studies and the common use of GABA receptor-potentiating agents in treatment. In a recent study, we used a benzodiazepine challenge to demonstrate abnormal GABAergic function during processing of negative visual stimuli in schizophrenia. This study extended this investigation by mapping GABAergic mechanisms associated with face processing and social appraisal in schizophrenia using a benzodiazepine challenge. Fourteen stable, medicated schizophrenia/schizoaffective patients (SZ) and 13 healthy controls (HC) underwent functional MRI using the blood oxygenation level-dependent (BOLD) technique while they performed the Socio-emotional Preference Task (SePT) on emotional face stimuli ("Do you like this face?"). Participants received single-blinded intravenous saline and lorazepam (LRZ) in two separate sessions separated by 1-3weeks. Both SZ and HC recruited medial prefrontal cortex/anterior cingulate during the SePT, relative to gender identification. A significant drug by group interaction was observed in the medial occipital cortex, such that SZ showed increased BOLD signal to LRZ challenge, while HC showed an expected decrease of signal; the interaction did not vary by task. The altered BOLD response to LRZ challenge in SZ was significantly correlated with increased negative affect across multiple measures. The altered response to LRZ challenge suggests that abnormal face processing and negative affect in SZ are associated with altered GABAergic function in the visual cortex, underscoring the role of impaired visual processing in socio-emotional deficits in schizophrenia.

Research paper thumbnail of Clinical Equivalence of Generic Clozapine

Research paper thumbnail of Dexamethasone nonsuppression and short rapid eye movement (REM) latency in schizophrenia: Not due to an affective diathesis

Schizophrenia Research, 1995

Research paper thumbnail of Neural correlates of interpersonal feedback and modulatory effect of personality

Research paper thumbnail of Error-processing abnormalities in pediatric anxiety and obsessive compulsive disorders

CNS Spectrums, 2015

Anxiety and obsessive compulsive disorders are among the earliest occurring psychopathology and m... more Anxiety and obsessive compulsive disorders are among the earliest occurring psychopathology and may derive from atypical maturation of neural networks for error processing. Psychological models have alternately suggested that over-detection of errors, excessive caring about errors, or failure of errors to elicit regulatory control could associate with the expression of anxiety. In this review article, the potential relevance of error processing for anxiety and obsessive compulsive disorders is described in the context of neurophysiological and functional magnetic resonance imaging (fMRI) research demonstrating altered brain response to errors in pediatric and adult patients. Finally, hypotheses about developmentally sensitive mechanisms of anxiety and obsessive compulsive disorders are drawn from the extant literature, and avenues for clinical translation are discussed.

Research paper thumbnail of Poster Docent Selection: Face Processing in Pediatric Posttraumatic Stress Disorder

Research paper thumbnail of Altered Attentional and Perceptual Processes as Indexed by N170 During Gaze Perception in Schizophrenia: Relationship With Perceived Threat and Paranoid Delusions

Journal of abnormal psychology, Jan 20, 2015

Using gaze information to orient attention and guide behavior is critical to social adaptation. P... more Using gaze information to orient attention and guide behavior is critical to social adaptation. Previous studies have suggested that abnormal gaze perception in schizophrenia (SCZ) may originate in abnormal early attentional and perceptual processes and may be related to paranoid symptoms. Using event-related brain potentials (ERPs), this study investigated altered early attentional and perceptual processes during gaze perception and their relationship to paranoid delusions in SCZ. Twenty-eight individuals with SCZ or schizoaffective disorder and 32 demographically matched healthy controls (HCs) completed a gaze-discrimination task with face stimuli varying in gaze direction (direct, averted), head orientation (forward, deviated), and emotion (neutral, fearful). ERPs were recorded during the task. Participants rated experienced threat from each face after the task. Participants with SCZ were as accurate as, though slower than, HCs on the task. Participants with SCZ displayed enlarge...

Research paper thumbnail of Accepted Manuscript

Research paper thumbnail of Endothelial function, folate pharmacogenomics, and neurocognition in psychotic disorders

Schizophrenia research, Jan 23, 2015

Cardiovascular disease (CVD) is a well-described complication of schizophrenia, however, mechanis... more Cardiovascular disease (CVD) is a well-described complication of schizophrenia, however, mechanisms connecting CVD with other facets of psychotic disorders, such as neurocognition, are not understood. The current study examined folate metabolism as a potential mechanism of CVD and neurocognitive deficits by: 1) using endothelial dysfunction as a biomarker of CVD, and 2) comparing enzymes associated with neurocognition, CVD, and critical to folate metabolism, methylenetetrahydrofolate reductase (MTHFR) and catechol-o-methyl transferase (COMT). Endothelial function was assessed in 147 participants with schizophrenia, schizoaffective disorder, and psychotic disorder not otherwise specified grouped by MTHFR and COMT allele status. Regression models were used to compare neurocognitive performance based on the Brief Assessment of Cognition in Schizophrenia (BACS). Overall, endothelial function predicted BACS composite z-scores after controlling for age, race, level of education, serum fol...

Research paper thumbnail of The Persistence of Experience: Prior Attentional and Emotional State Affects Network Functioning in a Target Detection Task

Cerebral cortex (New York, N.Y. : 1991), Jan 5, 2014

Efficient, adaptive behavior relies on the ability to flexibly move between internally focused (I... more Efficient, adaptive behavior relies on the ability to flexibly move between internally focused (IF) and externally focused (EF) attentional states. Despite evidence that IF cognitive processes such as event imagination compromise a significant amount of awake cognition, the consequences of internal absorption on the subsequent recruitment of brain networks during EF tasks are unknown. The present functional magnetic resonance imaging (fMRI) study employed a novel attentional state switching task. Subjects imagined positive and negative events (IF task) or performed a working memory task (EF task) before switching to a target detection (TD) task also requiring attention to external information, allowing for the investigation of neural functioning during external attention based on prior attentional state. There was a robust increase of activity in frontal, parietal, and temporal regions during TD when subjects were previously performing the EF compared with IF task, an effect that wa...

Research paper thumbnail of Cerebral aging: integration of brain and behavioral models of cognitive function

Dialogues in clinical neuroscience, 2001

There are substantial declines in behavioral measures of cognitive function with age, including d... more There are substantial declines in behavioral measures of cognitive function with age, including decreased function of executive processes and long-term memory. There is also evidence that, with age, there is a decrease in brain volume, particularly in the frontal cortex. When young and older adults perform cognitive tasks that depend heavily on frontal function, neuroimaging evidence indicates that older adults recruit additional brain regions in order to perform the tasks. This additional neural recruitment is termed "dedifferentiation," and can take multiple forms. This recruitment of additional neural tissue with age to perform cognitive tasks was not reflected in the behavioral literature, and suggests that there is more plasticity in the ability to organize brain function than was previously suspected. We review both behavioral and neuroscience perspectives on cognitive aging, and then connect the findings in the two areas. From this integration, we suggest important ...

Research paper thumbnail of Conditional Differences in Mean Reaction Time Explain Effects of Response Congruency, but not Accuracy, on Posterior Medial Frontal Cortex Activity

Frontiers in human neuroscience, 2010

According to the conflict-monitoring model of cognitive control, the posterior medial frontal cor... more According to the conflict-monitoring model of cognitive control, the posterior medial frontal cortex (pMFC) plays an important role in detecting conflict between competing motor responses. Consistent with this view, pMFC activity is greater in high-conflict trials (e.g., incongruent trials and errors) than in low-conflict trials (e.g., congruent trials and correct responses) of distractor interference tasks. However, in both low- and high-conflict trials, pMFC activity increases linearly with reaction time (RT). Thus, heightened pMFC activity in high-conflict trials may simply reflect the fact that mean RT is longer in high-conflict than in low-conflict trials. To investigate this hypothesis, we reanalyzed data from a previously published fMRI study in which participants performed an event-related version of the multi-source interference task. Critically, after controlling for conditional differences in mean RT, effects of response congruency on pMFC activity were eliminated; in con...

Research paper thumbnail of Neural systems for error monitoring: recent findings and theoretical perspectives

The Neuroscientist : a review journal bringing neurobiology, neurology and psychiatry, 2007

Complex behavior requires a flexible system that maintains task performance in the context of spe... more Complex behavior requires a flexible system that maintains task performance in the context of specific goals, evaluating behavioral progress, adjusting behavior as needed, and adapting to changing contingencies. Generically referred to as performance monitoring, a key component concerns the identification and correction of differences between an intended and an executed response (i.e., an error). Brain mapping experiments have now identified the temporal and spatial components of a putative error-processing system in the large-scale networks of the human brain. Most of this work has focused on the medial frontal cortex and an associated electrophysiological component known as the error-related negativity (or error negativity). Although the precise role, or roles, of this region still remain unknown, investigations of error processing have identified a cluster of modules in the medial frontal cortex involved in monitoring/maintaining ongoing behavior and motivating task sets. Other r...

Research paper thumbnail of Effects of antipsychotic treatment on polysomnographic measures in schizophrenia: a replication and extension

The American journal of psychiatry, 1998

The authors sought to replicate and extend previous observations of improvement in some EEG sleep... more The authors sought to replicate and extend previous observations of improvement in some EEG sleep measures during the course of antipsychotic treatment in schizophrenia patients. Fourteen medication-free patients with schizophrenia underwent 2 nights of sleep EEG monitoring before and after 3-4 weeks of treatment with clinically determined doses of haloperidol or thiothixene. Measures of sleep continuity improved consistently. REM latency increased, although five of 14 patients continued to exhibit short REM latencies (less than 60 minutes). Stage 3 sleep increased during neuroleptic treatment, while stage 4 sleep did not change. These data demonstrate partial improvement of some but not all EEG sleep measures in schizophrenic patients through the course of neuroleptic treatment. They suggest that shortened REM latency and disturbed sleep continuity might represent reversible state abnormalities, while reduced slow-wave sleep may represent a more persistent trait abnormality in schi...

Research paper thumbnail of Automated detection of the intercommissural line for stereotactic localization of functional brain images

Journal of nuclear medicine : official publication, Society of Nuclear Medicine, 1993

A technique has been developed for automated detection of the intercommissural (AC-PC) line for p... more A technique has been developed for automated detection of the intercommissural (AC-PC) line for positron emission tomography (PET). The AC-PC line is estimated from the location of four internal landmarks; the frontal and occipital poles, the inferior aspect of the anterior corpus callosum, and the subthalamic point. The landmarks are detected automatically in PET mid-sagittal slices by combining edge detection, interpolation and profile curve analysis techniques. The anatomical relationships between the true and estimated AC-PC lines from the landmarks was confirmed by analysis of magnetic resonance (MR) images. Accuracy of the automated estimation technique was assessed in co-registered PET and MR images, which showed minimal angular differences and displacements of the estimated from the true AC-PC lines. The automated detection of the AC-PC line in a PET study enables accurate stereotactic localization of functional signals without the need for additional anatomical imaging and ...

Research paper thumbnail of Isolation of specific interference processing in the Stroop task: PET

NeuroImage

The Stroop task, in which subjects must name the color of letters that spell color words differen... more The Stroop task, in which subjects must name the color of letters that spell color words different than the color-to-be-named, provides an important experimental paradigm for the study of selective attention. Cerebral blood flow activation studies have not always demonstrated consistent activation patterns; inconsistent results may reflect nonspecific responses, such as arousal or anticipation, rather than cerebral networks specific to Stroop interference processing. In order to identify regions consistently implicated in Stroop interference processing, we undertook two experiments with a Stroop interference paradigm and contrasting lexical and nonlexical control conditions. In our first experiment, standard Stroop stimuli, e.g., the word ''RED'' displayed in a green font, were contrasted with color naming of the font of noncolor words and color naming of a false font. In our second experiment, we compared Stroop stimuli with colored symbols and a control condition designed to elicit nonspecific interference-taboo words displayed in color fonts. Only two brain regions showed a consistent CBF change in both experiments. Activation in the left inferior frontal gyrus reflected processing more specific to the Stroop task, while deactivation in the right superior temporal gyrus occurred for the Stroop and the taboo conditions, consistent with more nonspecific processing. Activation in the anterior cingulate cortex occurred in only one comparison in one experiment and may not reflect functions central to overcoming Stroop interference.

Research paper thumbnail of Automated detection of the intercommissural line for stereotaxic localization of functional brain images

Journal of Nuclear Medicine

CT) can be employed for this purpose. Accurate co registration between PET and the anatomical ref... more CT) can be employed for this purpose. Accurate co registration between PET and the anatomical reference image is crucial for this approach (3,5â€"9).

Research paper thumbnail of Intrinsic viscosity and partial specific volume of hyaluronic acid

Research paper thumbnail of Global Cerebral Blood Flow Increase Reveals Focal Hypoperfusion in Schizophrenia - Linear scaling and nonlinear warping of functional brain images

Neuropsychopharmacology

Recent functional neuroimaging strategies have evaluated cerebral blood flow (CBF) to determine s... more Recent functional neuroimaging strategies have evaluated cerebral blood flow (CBF) to determine specific sites of action of pharmacologic agents. Since many pharmacologic agents change global CBF, we investigated the effects of global CBF changes on regional perfusion with acetazolamide, which increases global CBF via non-neuronal mechanisms. We used the [15O]PET technique to measure CBF before and after we infused 8 schizophrenic patients and 10 healthy control subjects with acetazolamide. The rostral anterior cingulate cortex demonstrated a greater perfusion increase in the schizophrenic subjects after acetazolamide infusion, relative to other areas of the brain. During the baseline condition, this area showed relative hypoperfusion in our sample of schizophrenic subjects, consistent with previous functional neuroimaging studies. The results demonstrate the need for caution in interpreting CBF changes after pharmacologic challenge, because global CBF changes can confound the assessment of regionally-specific pharmacologic action.

Research paper thumbnail of PET study of greater visual activation in schizophrenia

American Journal of Psychiatry

The authors tested the hypothesis that photic visual stimuli cause a greater blood flow activatio... more The authors tested the hypothesis that photic visual stimuli cause a greater blood flow activation response in subjects with schizophrenia than in normal subjects. Eleven medicated patients with schizophrenia and 10 normal subjects were studied with [15O]H2O positron emission tomography to measure perfusion during photic stimulation at four different rates. The activation at three out of four rates of visual stimulation was greater for the patients with schizophrenia than it was for the normal subjects. Further investigation into the mechanisms of activation during sensory stimulation in schizophrenia is warranted.

Research paper thumbnail of Abnormal GABAergic function and face processing in schizophrenia: A pharmacologic-fMRI study

Schizophrenia Research, 2015

The involvement of the gamma-aminobutyric acid (GABA) system in schizophrenia is suggested by pos... more The involvement of the gamma-aminobutyric acid (GABA) system in schizophrenia is suggested by postmortem studies and the common use of GABA receptor-potentiating agents in treatment. In a recent study, we used a benzodiazepine challenge to demonstrate abnormal GABAergic function during processing of negative visual stimuli in schizophrenia. This study extended this investigation by mapping GABAergic mechanisms associated with face processing and social appraisal in schizophrenia using a benzodiazepine challenge. Fourteen stable, medicated schizophrenia/schizoaffective patients (SZ) and 13 healthy controls (HC) underwent functional MRI using the blood oxygenation level-dependent (BOLD) technique while they performed the Socio-emotional Preference Task (SePT) on emotional face stimuli ("Do you like this face?"). Participants received single-blinded intravenous saline and lorazepam (LRZ) in two separate sessions separated by 1-3weeks. Both SZ and HC recruited medial prefrontal cortex/anterior cingulate during the SePT, relative to gender identification. A significant drug by group interaction was observed in the medial occipital cortex, such that SZ showed increased BOLD signal to LRZ challenge, while HC showed an expected decrease of signal; the interaction did not vary by task. The altered BOLD response to LRZ challenge in SZ was significantly correlated with increased negative affect across multiple measures. The altered response to LRZ challenge suggests that abnormal face processing and negative affect in SZ are associated with altered GABAergic function in the visual cortex, underscoring the role of impaired visual processing in socio-emotional deficits in schizophrenia.

Research paper thumbnail of Clinical Equivalence of Generic Clozapine

Research paper thumbnail of Dexamethasone nonsuppression and short rapid eye movement (REM) latency in schizophrenia: Not due to an affective diathesis

Schizophrenia Research, 1995

Research paper thumbnail of Neural correlates of interpersonal feedback and modulatory effect of personality

Research paper thumbnail of Error-processing abnormalities in pediatric anxiety and obsessive compulsive disorders

CNS Spectrums, 2015

Anxiety and obsessive compulsive disorders are among the earliest occurring psychopathology and m... more Anxiety and obsessive compulsive disorders are among the earliest occurring psychopathology and may derive from atypical maturation of neural networks for error processing. Psychological models have alternately suggested that over-detection of errors, excessive caring about errors, or failure of errors to elicit regulatory control could associate with the expression of anxiety. In this review article, the potential relevance of error processing for anxiety and obsessive compulsive disorders is described in the context of neurophysiological and functional magnetic resonance imaging (fMRI) research demonstrating altered brain response to errors in pediatric and adult patients. Finally, hypotheses about developmentally sensitive mechanisms of anxiety and obsessive compulsive disorders are drawn from the extant literature, and avenues for clinical translation are discussed.

Research paper thumbnail of Poster Docent Selection: Face Processing in Pediatric Posttraumatic Stress Disorder

Research paper thumbnail of Altered Attentional and Perceptual Processes as Indexed by N170 During Gaze Perception in Schizophrenia: Relationship With Perceived Threat and Paranoid Delusions

Journal of abnormal psychology, Jan 20, 2015

Using gaze information to orient attention and guide behavior is critical to social adaptation. P... more Using gaze information to orient attention and guide behavior is critical to social adaptation. Previous studies have suggested that abnormal gaze perception in schizophrenia (SCZ) may originate in abnormal early attentional and perceptual processes and may be related to paranoid symptoms. Using event-related brain potentials (ERPs), this study investigated altered early attentional and perceptual processes during gaze perception and their relationship to paranoid delusions in SCZ. Twenty-eight individuals with SCZ or schizoaffective disorder and 32 demographically matched healthy controls (HCs) completed a gaze-discrimination task with face stimuli varying in gaze direction (direct, averted), head orientation (forward, deviated), and emotion (neutral, fearful). ERPs were recorded during the task. Participants rated experienced threat from each face after the task. Participants with SCZ were as accurate as, though slower than, HCs on the task. Participants with SCZ displayed enlarge...

Research paper thumbnail of Accepted Manuscript

Research paper thumbnail of Endothelial function, folate pharmacogenomics, and neurocognition in psychotic disorders

Schizophrenia research, Jan 23, 2015

Cardiovascular disease (CVD) is a well-described complication of schizophrenia, however, mechanis... more Cardiovascular disease (CVD) is a well-described complication of schizophrenia, however, mechanisms connecting CVD with other facets of psychotic disorders, such as neurocognition, are not understood. The current study examined folate metabolism as a potential mechanism of CVD and neurocognitive deficits by: 1) using endothelial dysfunction as a biomarker of CVD, and 2) comparing enzymes associated with neurocognition, CVD, and critical to folate metabolism, methylenetetrahydrofolate reductase (MTHFR) and catechol-o-methyl transferase (COMT). Endothelial function was assessed in 147 participants with schizophrenia, schizoaffective disorder, and psychotic disorder not otherwise specified grouped by MTHFR and COMT allele status. Regression models were used to compare neurocognitive performance based on the Brief Assessment of Cognition in Schizophrenia (BACS). Overall, endothelial function predicted BACS composite z-scores after controlling for age, race, level of education, serum fol...

Research paper thumbnail of The Persistence of Experience: Prior Attentional and Emotional State Affects Network Functioning in a Target Detection Task

Cerebral cortex (New York, N.Y. : 1991), Jan 5, 2014

Efficient, adaptive behavior relies on the ability to flexibly move between internally focused (I... more Efficient, adaptive behavior relies on the ability to flexibly move between internally focused (IF) and externally focused (EF) attentional states. Despite evidence that IF cognitive processes such as event imagination compromise a significant amount of awake cognition, the consequences of internal absorption on the subsequent recruitment of brain networks during EF tasks are unknown. The present functional magnetic resonance imaging (fMRI) study employed a novel attentional state switching task. Subjects imagined positive and negative events (IF task) or performed a working memory task (EF task) before switching to a target detection (TD) task also requiring attention to external information, allowing for the investigation of neural functioning during external attention based on prior attentional state. There was a robust increase of activity in frontal, parietal, and temporal regions during TD when subjects were previously performing the EF compared with IF task, an effect that wa...

Research paper thumbnail of Cerebral aging: integration of brain and behavioral models of cognitive function

Dialogues in clinical neuroscience, 2001

There are substantial declines in behavioral measures of cognitive function with age, including d... more There are substantial declines in behavioral measures of cognitive function with age, including decreased function of executive processes and long-term memory. There is also evidence that, with age, there is a decrease in brain volume, particularly in the frontal cortex. When young and older adults perform cognitive tasks that depend heavily on frontal function, neuroimaging evidence indicates that older adults recruit additional brain regions in order to perform the tasks. This additional neural recruitment is termed "dedifferentiation," and can take multiple forms. This recruitment of additional neural tissue with age to perform cognitive tasks was not reflected in the behavioral literature, and suggests that there is more plasticity in the ability to organize brain function than was previously suspected. We review both behavioral and neuroscience perspectives on cognitive aging, and then connect the findings in the two areas. From this integration, we suggest important ...

Research paper thumbnail of Conditional Differences in Mean Reaction Time Explain Effects of Response Congruency, but not Accuracy, on Posterior Medial Frontal Cortex Activity

Frontiers in human neuroscience, 2010

According to the conflict-monitoring model of cognitive control, the posterior medial frontal cor... more According to the conflict-monitoring model of cognitive control, the posterior medial frontal cortex (pMFC) plays an important role in detecting conflict between competing motor responses. Consistent with this view, pMFC activity is greater in high-conflict trials (e.g., incongruent trials and errors) than in low-conflict trials (e.g., congruent trials and correct responses) of distractor interference tasks. However, in both low- and high-conflict trials, pMFC activity increases linearly with reaction time (RT). Thus, heightened pMFC activity in high-conflict trials may simply reflect the fact that mean RT is longer in high-conflict than in low-conflict trials. To investigate this hypothesis, we reanalyzed data from a previously published fMRI study in which participants performed an event-related version of the multi-source interference task. Critically, after controlling for conditional differences in mean RT, effects of response congruency on pMFC activity were eliminated; in con...

Research paper thumbnail of Neural systems for error monitoring: recent findings and theoretical perspectives

The Neuroscientist : a review journal bringing neurobiology, neurology and psychiatry, 2007

Complex behavior requires a flexible system that maintains task performance in the context of spe... more Complex behavior requires a flexible system that maintains task performance in the context of specific goals, evaluating behavioral progress, adjusting behavior as needed, and adapting to changing contingencies. Generically referred to as performance monitoring, a key component concerns the identification and correction of differences between an intended and an executed response (i.e., an error). Brain mapping experiments have now identified the temporal and spatial components of a putative error-processing system in the large-scale networks of the human brain. Most of this work has focused on the medial frontal cortex and an associated electrophysiological component known as the error-related negativity (or error negativity). Although the precise role, or roles, of this region still remain unknown, investigations of error processing have identified a cluster of modules in the medial frontal cortex involved in monitoring/maintaining ongoing behavior and motivating task sets. Other r...

Research paper thumbnail of Effects of antipsychotic treatment on polysomnographic measures in schizophrenia: a replication and extension

The American journal of psychiatry, 1998

The authors sought to replicate and extend previous observations of improvement in some EEG sleep... more The authors sought to replicate and extend previous observations of improvement in some EEG sleep measures during the course of antipsychotic treatment in schizophrenia patients. Fourteen medication-free patients with schizophrenia underwent 2 nights of sleep EEG monitoring before and after 3-4 weeks of treatment with clinically determined doses of haloperidol or thiothixene. Measures of sleep continuity improved consistently. REM latency increased, although five of 14 patients continued to exhibit short REM latencies (less than 60 minutes). Stage 3 sleep increased during neuroleptic treatment, while stage 4 sleep did not change. These data demonstrate partial improvement of some but not all EEG sleep measures in schizophrenic patients through the course of neuroleptic treatment. They suggest that shortened REM latency and disturbed sleep continuity might represent reversible state abnormalities, while reduced slow-wave sleep may represent a more persistent trait abnormality in schi...

Research paper thumbnail of Automated detection of the intercommissural line for stereotactic localization of functional brain images

Journal of nuclear medicine : official publication, Society of Nuclear Medicine, 1993

A technique has been developed for automated detection of the intercommissural (AC-PC) line for p... more A technique has been developed for automated detection of the intercommissural (AC-PC) line for positron emission tomography (PET). The AC-PC line is estimated from the location of four internal landmarks; the frontal and occipital poles, the inferior aspect of the anterior corpus callosum, and the subthalamic point. The landmarks are detected automatically in PET mid-sagittal slices by combining edge detection, interpolation and profile curve analysis techniques. The anatomical relationships between the true and estimated AC-PC lines from the landmarks was confirmed by analysis of magnetic resonance (MR) images. Accuracy of the automated estimation technique was assessed in co-registered PET and MR images, which showed minimal angular differences and displacements of the estimated from the true AC-PC lines. The automated detection of the AC-PC line in a PET study enables accurate stereotactic localization of functional signals without the need for additional anatomical imaging and ...