Monique Ernst - Academia.edu (original) (raw)
Papers by Monique Ernst
Emotion, 2016
Anxiety can be broken down into multiple facets including behavioral components, such as defensiv... more Anxiety can be broken down into multiple facets including behavioral components, such as defensive reactivity, and cognitive components, such as distracting anxious thoughts. In a previous study, we showed that anticipation of unpredictable shocks facilitated response inhibition to infrequent no-go trials during a go/no-go task. The present study extends this work to examine the distinct contribution of defensive reactivity, measures with fear-potentiated startle, and anxious thought, assessed with thought probes, on go and no-go performance. Consistent with our prior findings, shock anticipation facilitated response inhibition (i.e., reduced errors of commission) on the no-go trials. Regression analyses showed that (a) no-go accuracy was positively associated with fear-potentiated startle and negatively associated with threat-related/task-unrelated thoughts and (b) go accuracy correlated negatively with fear-potentiated startle. Thus, while the present findings confirm the influence of anxiety on response inhibition, they also show that such influence reflects the balance between the positive effect of defensive reactivity and the negative effect of distracting anxious thoughts. (PsycINFO Database Record
Objective: While adolescent anxiety disorders represent prevalent, debilitating conditions, few s... more Objective: While adolescent anxiety disorders represent prevalent, debilitating conditions, few studies have explored their brain physiology. Using event-related functional magnetic resonance imaging (fMRI) and a behavioral measure of attention to angry faces, the authors evaluated differences in response between healthy adolescents and adolescents with generalized anxiety disorder.
The anterior cingulate cortex (ACC) and lateral prefrontal (LPFC) cortex are brain regions import... more The anterior cingulate cortex (ACC) and lateral prefrontal (LPFC) cortex are brain regions important to executive cognitive functions (ECF). We determined ACC and LPFC function in 23-day abstinent cocaine abusers using positron emission tomography (PET H 2 15 O) during performance of a modified version of the Stroop Task. Cocaine abusers showed less activation than non-drugusing comparison subjects in the left ACC and the right LPFC and greater activation in the right ACC. Average amount of cocaine used per week was negatively correlated with activity in the rostral ACC and right LPFC. Disruption of ECF in substance abusers could interfere with attempts to stop drug use and undermine treatment. Since impairment in ECF may be a common feature of various neuropsychiatric disorders, these findings have applicability beyond the neurobiology of addiction.
Biological Psychiatry, Jan 10, 2009
Background: While adverse rearing is thought to alter threat responding, the effects on appetitiv... more Background: While adverse rearing is thought to alter threat responding, the effects on appetitive behavior remains minimally explored. This study examines the effects that early life emotional adversity has on response to both threatening and appetitive stimuli in juvenile rhesus monkeys.
![Research paper thumbnail of DOPA decarboxylase activity in attention deficit hyperactivity disorder adults. A [fluorine-18]fluorodopa positron emission tomographic study](https://attachments.academia-assets.com/52548772/thumbnails/1.jpg)
](The Journal of Neuroscience the Official Journal of the Society For Neuroscience, Aug 1, 1998
Converging evidence implicates the dopaminergic system and the prefrontal and nigrostriatal regio... more Converging evidence implicates the dopaminergic system and the prefrontal and nigrostriatal regions in the pathophysiology of attention deficit hyperactivity disorder (ADHD). Using positron emission tomography (PET) with [fluorine-18]fluorodopa (F18-DOPA), we compared the integrity of the presynaptic dopaminergic function between 17 ADHD adults and 23 healthy controls. The ratio of the isotope concentration of specific regions to that of nonspecific regions reflects DOPA decarboxylase activity and dopamine storage processes. Of three composite regions (prefrontal cortex, striatum, and midbrain), only the prefrontal cortex showed significantly different F18-DOPA ratios in ADHD as compared with control adults ( p Ͻ 0.01). The medial and left prefrontal areas were the most altered (lower F18-DOPA ratios by 52 and 51% in ADHD as compared with controls). Similarly, the interaction [sex ϫ diagnosis] was sig-nificant only in the prefrontal cortex ( p Ͻ 0.02): lower ratios in men than in women in ADHD and vice versa in controls. These findings suggest that a prefrontal dopaminergic dysfunction mediates ADHD symptoms in adults and that gender influences this abnormality. On the basis of previous neuroimaging findings in ADHD showing discrepant findings in adults and adolescents and on evidence for midbrain dopaminergic defect in adolescents, we hypothesize that the prefrontal dopaminergic abnormality in ADHD adults is secondary and results from an interaction of the primary subcortical dopaminergic deficit with processes of neural maturation and neural adaptation.
Psn Psychiatrie Sciences Humaines Neurosciences, Oct 20, 2009
ABSTRACT
Biological Psychiatry, Jan 6, 2004
Background: Females appear to be more sensitive and responsive to social cues, including threat s... more Background: Females appear to be more sensitive and responsive to social cues, including threat signals, than are males. Recent theoretical models suggest that developmental changes in brain functioning play important roles in the emergence of such gender differences. Methods: We used functional magnetic resonance imaging to examine developmental and gender differences in activation of neural structures thought to mediate attention to emotional faces depicting varying degrees of threat. Analyses focused on the orbitofrontal cortex, amygdala, and anterior cingulate cortex during the evaluation of threat conveyed by faces. Healthy adolescents (n ϭ 17; 53% male) and adults (n ϭ 17; 53% male) were scanned while they rated how threatening pictures of neutral and emotional (angry, fearful, or happy) faces appeared. Results: Results indicate significant interactions among age, gender, and face type for activation during explicit threat monitoring. In particular, adult women activated orbitofrontal cortex and amygdala selectively to unambiguous threat (angry) cues, while adult men showed a less discriminating pattern of activation. No gender differences were evident for adolescents, who as a group resembled adult males. Conclusions: These findings suggest that there are gender differences in patterns of neural responses to emotional faces that are not fully apparent until adulthood.
Journal of Child and Adolescent Psychopharmacology, Aug 1, 2005
Anxiety disorders in adults involve aberrant processing of emotional information that is hypothes... more Anxiety disorders in adults involve aberrant processing of emotional information that is hypothesized to reflect perturbations in the amygdala. This study examines the relationship between face-emotion recognition and anxiety in a sample of children and adolescents participating in a brain-imaging study of amygdala structure and function. This study recruited 15 children and adolescents with ongoing anxiety disorders and 11 psychiatrically healthy comparisons group-matched on age, gender, and IQ. Face-emotion recognition was assessed using the Diagnostic Analysis of Nonverbal Accuracy Scale (DANVA). Children and adolescents with anxiety disorders exhibited significantly poorer performance on the face-emotion recognition task compared to healthy controls (z = 2.2; p < 0.05). This difference was found only for expressions posed by adults but not children. Reduced accuracy on a face-emotion recognition test is consistent with perturbed amygdala function in pediatric anxiety disorders. As this study was conducted in a sample undergoing a neuroimaging investigation of amygdala integrity, future analyses will examine associations among amygdala function, clinical anxiety, and face-recognition abilities.
Psn Psychiatr Sci Hum Neurosc, 2009
Risk-taking behavior is a major cause of morbidity and mortality in adolescence. In the context o... more Risk-taking behavior is a major cause of morbidity and mortality in adolescence. In the context of decision theory and motivated (goal-directed) behavior, risk-taking reflects a pattern of decision-making that favors the selection of courses of action with uncertain and possibly harmful consequences. We present a triadic, neuroscience systems-based model of adolescent decision-making. We review the functional role and neurodevelopmental findings of three key structures in the control of motivated behavior, i.e. amygdala, nucleus accumbens, and medial/ventral prefrontal cortex. We adopt a cognitive neuroscience approach to motivated behavior that uses a temporal fragmentation of a generic motivated action. Predictions about the relative contributions of the triadic nodes to the three stages of a motivated action during adolescence are proposed. The propensity during adolescence for reward/novelty seeking in the face of uncertainty or potential harm might be explained by a strong reward system (nucleus accumbens), a weak harm-avoidant system (amygdala), and/or an inefficient supervisory system (medial/ventral prefrontal cortex). Perturbations in these systems may contribute to the expression of psychopathology, illustrated here with depression and anxiety. A triadic model, integrated in a temporally organized map of motivated behavior, can provide a helpful framework that suggests specific hypotheses of neural bases of typical and atypical adolescent behavior.
J Statist Phys, 1984
Diffusion of moving particles in stationary disordered media is studied using a phenomenological ... more Diffusion of moving particles in stationary disordered media is studied using a phenomenological mode-coupling theory. The presence of disorder leads to a generalized diffusion equation, with memory kernels having power law long time tails. The velocity autocorrelation function is found to decay like t-(d/2+1), while the time correlation function associated with the super-Burnett coefficient decays like t -d/2 for long times. The theory is applicable to a wide variety of dynamical and stochastic systems including the Lorentz gas and hopping models. We find new, general expressions for the coefficients of the long time tails which agree with previous results for exactly solvable hopping models and with the low-density results obtained for the Lorentz gas. Finally we mention that if the moving particles are charged, then the long time tails imply that there is an ω d/2 contribution to the low-frequency part of the frequency-dependent electrical conductivity.
The American Journal of Psychiatry, Aug 1, 1999
Attention deficit hyperactivity disorder (ADHD) is a highly prevalent childhood psychiatric disor... more Attention deficit hyperactivity disorder (ADHD) is a highly prevalent childhood psychiatric disorder characterized by impaired attention, excessive motor activity, and impulsivity. Despite extensive investigation of the neuropathophysiology of ADHD by a wide array of methodologies, the neurobiochemical substrate of this disorder is still unknown. Converging evidence, however, suggests a primary role of the dopaminergic system. This study examined the integrity of presynaptic dopaminergic function in children with ADHD through use of positron emission tomography and the tracer [18F]fluorodopa ([18F]DOPA). Accumulation of [18F]DOPA in synaptic terminals, a measure of dopa decarboxylase activity, was quantified in regions rich in dopaminergic innervation, including caudate nucleus, putamen, frontal cortex, and midbrain (i.e., substantia nigra and ventral tegmentum). Accumulation of [18F]DOPA in the right midbrain was higher by 48% in 10 children with ADHD than in 10 normal children. Despite its magnitude, this difference would not have reached statistical significance if corrected by the Bonferroni test for multiple comparisons. However, [18F]DOPA in the right midbrain was correlated with symptom severity. No other dopamine-rich regions significantly differed between groups. These findings are suggestive of dopaminergic dysfunction at the level of the dopaminergic nuclei in children with ADHD. Abnormality in dopa decarboxylase activity may be primary or secondary to deficits in other functional units of the dopamine pathway (e.g., receptor, uptake transporter, vesicular transporter, degradation enzymes). Efforts toward defining the origin of this abnormality should help delineate mechanisms of midbrain control of attention and motor behavior important for the understanding of the causes and treatment of ADHD.
The Journal of Neuropsychiatry and Clinical Neurosciences, Nov 9, 2014
Using positron emission tomography and [18F]-2-fluoro-2-deoxy-D-glucose, the authors determined c... more Using positron emission tomography and [18F]-2-fluoro-2-deoxy-D-glucose, the authors determined cerebral metabolic rates for glucose (CMRglc) in 39 adults (18-51 years old) with attention-deficit/hyperactivity disorder (ADHD) and 56 healthy control adults (19-56 years old) during the performance of a continuous attention task. Increased age was associated with reduced global CMRglc in ADHD women, but not in ADHD men, control men, or control women. Better performance on the attention task was significantly associated with increased age only in the ADHD female group. Determining the role of behavioral, hormonal, and genetic factors is a challenge for future research.
Neuropsychologia 42 1585 1597, Feb 1, 2004
We examined neural activations during decision-making using fMRI paired with the wheel of fortune... more We examined neural activations during decision-making using fMRI paired with the wheel of fortune task, a newly developed two-choice decision-making task with probabilistic monetary gains. In particular, we assessed the impact of high-reward/risk events relative to low-reward/risk events on neural activations during choice selection and during reward anticipation. Seventeen healthy adults completed the study. We found, in line with predictions, that (i) the selection phase predominantly recruited regions involved in visuo-spatial attention (occipito-parietal pathway), conflict (anterior cingulate), manipulation of quantities (parietal cortex), and preparation for action (premotor area), whereas the anticipation phase prominently recruited regions engaged in reward processes (ventral striatum); and (ii) high-reward/risk conditions relative to low-reward/risk conditions were associated with a greater neural response in ventral striatum during selection, though not during anticipation. Following an a priori ROI analysis focused on orbitofrontal cortex, we observed orbitofrontal cortex activation (BA 11 and 47) during selection (particularly to high-risk/reward options), and to a more limited degree, during anticipation. These findings support the notion that (1) distinct, although overlapping, pathways subserve the processes of selection and anticipation in a two-choice task of probabilistic monetary reward; (2) taking a risk and awaiting the consequence of a risky decision seem to affect neural activity differently in selection and anticipation; and thus (3) common structures, including the ventral striatum, are modulated differently by risk/reward during selection and anticipation. Published by Elsevier Ltd.
American Journal of Psychiatry, Nov 9, 2014
The characteristics of attention deficit hyperactivity disorder (ADHD) include abnormalities in r... more The characteristics of attention deficit hyperactivity disorder (ADHD) include abnormalities in reward responsivity that may interfere with decision making. The study examined reward responsivity in ADHD by comparing the neural correlates of decision making in adults with childhood-onset ADHD and in healthy adults.
Biological Psychiatry, Jan 11, 2006
Background: Although major depressive disorder (MDD) represents one of the most serious psychiatr... more Background: Although major depressive disorder (MDD) represents one of the most serious psychiatric problems afflicting adolescents, efforts to understand the neural circuitry of adolescent MDD have lagged behind those of adult MDD. This study tests the hypothesis that adolescent MDD is associated with abnormal amygdala activity during evocative-face viewing. Methods: Using functional magnetic resonance imaging (fMRI), between-group differences among MDD (n ϭ 10), anxious (n ϭ 11), and non-psychiatric comparisons (n ϭ 23) were examined during successful vs. unsuccessful face encoding, with encoding success measured post-scan. Results: Compared to healthy adolescents, MDD patients exhibited poorer memory for faces. fMRI analyses accounted for this performance difference through event-related methods. In an analysis comparing successful vs. unsuccessful face encoding, MDD patients exhibited greater left amygdala activation relative to healthy and anxious youth. Conclusions: Given prior findings among adults, this study suggests that adolescent and adult MDD may involve similar underlying abnormalities in amygdala functioning.
Pediatrics 117 2030 2039, Jun 1, 2006
OBJECTIVE. Our goal was to examine substance-use initiation in healthy adolescents and in adolesc... more OBJECTIVE. Our goal was to examine substance-use initiation in healthy adolescents and in adolescents who have been diagnosed with attention-deficit/hyperactivity disorder. METHODS. Seventy-eight adolescents (28 healthy and 50 with attention-deficit/hyperactivity disorder) participated in an ongoing longitudinal study of predictors of substance use. The substances most commonly reported were tobacco, alcohol, and marijuana. Aggression, conduct problems, hyperactivity, impulsivity, inattention, anxiety/depression, social difficulties, and somatic complaints were assessed at study entry and tested as predictors for later substance use. RESULTS. With an average of 4 years into the study, 37 adolescents had not used any substances, 41 had experimented with at least 1 substance, and 29 experimented with > 1 substance. Psychiatric diagnoses (attention-deficit/hyperactivity disorder, attention-deficit/ hyperactivity disorder and conduct disorder, and attention-deficit/hyperactivity disorder and depression/anxiety) did not influence reports of substance use. Distinct behavioral measures collected at study entry predicted use of different substances. In a multivariate analysis, aggression had the greatest association with tobacco smoking and marijuana use. Impulsivity was associated with alcohol use. Severity of drug exposure, indexed by the number of substances eScholarship provides open access, scholarly publishing services to the University of California and delivers a dynamic research platform to scholars worldwide. used, was predicted by aggression. CONCLUSIONS. This 4-year longitudinal study captured the onset of substance use, not abuse. Behavioral predictors differed with the type of substance used. These behavioral characteristics may raise suspicion among pediatricians for enhanced risk for substance-use initiation.
Some reports indicate that cigarette smoking can help smokers focus attention, even when they hav... more Some reports indicate that cigarette smoking can help smokers focus attention, even when they have not abstained from smoking for a substantial period of time (eg, >1 h). Understanding the mechanisms by which smoking affects attention may help in designing smoking cessation treatments. Thirteen nonsmokers and nine smokers participated in two tests of blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI). During fMRI, the participants performed the Stroop Task. There was a 15-min break between the two tests. During the break, each smoker smoked one cigarette. For smokers, the first test began 45-60 min after the last cigarette of ad libitum smoking. The differences in BOLD signal changes between Stroop conditions (ie, incongruent minus congruent) showed a group × test interaction in the right precentral sulcus, including the putative human frontal eye field (FEF). Smokers, but not nonsmokers, showed greater changes (relative to rest) in BOLD signal in the incongruent than in the congruent condition in the first fMRI test but not in the second. Even after brief abstinence from smoking, therefore, smokers exhibit compromised functional efficiency in the right FEF and adjacent precentral sulcus in a test of selective attention; and smoking ameliorates this condition.
Emotion, 2016
Anxiety can be broken down into multiple facets including behavioral components, such as defensiv... more Anxiety can be broken down into multiple facets including behavioral components, such as defensive reactivity, and cognitive components, such as distracting anxious thoughts. In a previous study, we showed that anticipation of unpredictable shocks facilitated response inhibition to infrequent no-go trials during a go/no-go task. The present study extends this work to examine the distinct contribution of defensive reactivity, measures with fear-potentiated startle, and anxious thought, assessed with thought probes, on go and no-go performance. Consistent with our prior findings, shock anticipation facilitated response inhibition (i.e., reduced errors of commission) on the no-go trials. Regression analyses showed that (a) no-go accuracy was positively associated with fear-potentiated startle and negatively associated with threat-related/task-unrelated thoughts and (b) go accuracy correlated negatively with fear-potentiated startle. Thus, while the present findings confirm the influence of anxiety on response inhibition, they also show that such influence reflects the balance between the positive effect of defensive reactivity and the negative effect of distracting anxious thoughts. (PsycINFO Database Record
Objective: While adolescent anxiety disorders represent prevalent, debilitating conditions, few s... more Objective: While adolescent anxiety disorders represent prevalent, debilitating conditions, few studies have explored their brain physiology. Using event-related functional magnetic resonance imaging (fMRI) and a behavioral measure of attention to angry faces, the authors evaluated differences in response between healthy adolescents and adolescents with generalized anxiety disorder.
The anterior cingulate cortex (ACC) and lateral prefrontal (LPFC) cortex are brain regions import... more The anterior cingulate cortex (ACC) and lateral prefrontal (LPFC) cortex are brain regions important to executive cognitive functions (ECF). We determined ACC and LPFC function in 23-day abstinent cocaine abusers using positron emission tomography (PET H 2 15 O) during performance of a modified version of the Stroop Task. Cocaine abusers showed less activation than non-drugusing comparison subjects in the left ACC and the right LPFC and greater activation in the right ACC. Average amount of cocaine used per week was negatively correlated with activity in the rostral ACC and right LPFC. Disruption of ECF in substance abusers could interfere with attempts to stop drug use and undermine treatment. Since impairment in ECF may be a common feature of various neuropsychiatric disorders, these findings have applicability beyond the neurobiology of addiction.
Biological Psychiatry, Jan 10, 2009
Background: While adverse rearing is thought to alter threat responding, the effects on appetitiv... more Background: While adverse rearing is thought to alter threat responding, the effects on appetitive behavior remains minimally explored. This study examines the effects that early life emotional adversity has on response to both threatening and appetitive stimuli in juvenile rhesus monkeys.
The Journal of Neuroscience the Official Journal of the Society For Neuroscience, Aug 1, 1998
Converging evidence implicates the dopaminergic system and the prefrontal and nigrostriatal regio... more Converging evidence implicates the dopaminergic system and the prefrontal and nigrostriatal regions in the pathophysiology of attention deficit hyperactivity disorder (ADHD). Using positron emission tomography (PET) with [fluorine-18]fluorodopa (F18-DOPA), we compared the integrity of the presynaptic dopaminergic function between 17 ADHD adults and 23 healthy controls. The ratio of the isotope concentration of specific regions to that of nonspecific regions reflects DOPA decarboxylase activity and dopamine storage processes. Of three composite regions (prefrontal cortex, striatum, and midbrain), only the prefrontal cortex showed significantly different F18-DOPA ratios in ADHD as compared with control adults ( p Ͻ 0.01). The medial and left prefrontal areas were the most altered (lower F18-DOPA ratios by 52 and 51% in ADHD as compared with controls). Similarly, the interaction [sex ϫ diagnosis] was sig-nificant only in the prefrontal cortex ( p Ͻ 0.02): lower ratios in men than in women in ADHD and vice versa in controls. These findings suggest that a prefrontal dopaminergic dysfunction mediates ADHD symptoms in adults and that gender influences this abnormality. On the basis of previous neuroimaging findings in ADHD showing discrepant findings in adults and adolescents and on evidence for midbrain dopaminergic defect in adolescents, we hypothesize that the prefrontal dopaminergic abnormality in ADHD adults is secondary and results from an interaction of the primary subcortical dopaminergic deficit with processes of neural maturation and neural adaptation.
Psn Psychiatrie Sciences Humaines Neurosciences, Oct 20, 2009
ABSTRACT
Biological Psychiatry, Jan 6, 2004
Background: Females appear to be more sensitive and responsive to social cues, including threat s... more Background: Females appear to be more sensitive and responsive to social cues, including threat signals, than are males. Recent theoretical models suggest that developmental changes in brain functioning play important roles in the emergence of such gender differences. Methods: We used functional magnetic resonance imaging to examine developmental and gender differences in activation of neural structures thought to mediate attention to emotional faces depicting varying degrees of threat. Analyses focused on the orbitofrontal cortex, amygdala, and anterior cingulate cortex during the evaluation of threat conveyed by faces. Healthy adolescents (n ϭ 17; 53% male) and adults (n ϭ 17; 53% male) were scanned while they rated how threatening pictures of neutral and emotional (angry, fearful, or happy) faces appeared. Results: Results indicate significant interactions among age, gender, and face type for activation during explicit threat monitoring. In particular, adult women activated orbitofrontal cortex and amygdala selectively to unambiguous threat (angry) cues, while adult men showed a less discriminating pattern of activation. No gender differences were evident for adolescents, who as a group resembled adult males. Conclusions: These findings suggest that there are gender differences in patterns of neural responses to emotional faces that are not fully apparent until adulthood.
Journal of Child and Adolescent Psychopharmacology, Aug 1, 2005
Anxiety disorders in adults involve aberrant processing of emotional information that is hypothes... more Anxiety disorders in adults involve aberrant processing of emotional information that is hypothesized to reflect perturbations in the amygdala. This study examines the relationship between face-emotion recognition and anxiety in a sample of children and adolescents participating in a brain-imaging study of amygdala structure and function. This study recruited 15 children and adolescents with ongoing anxiety disorders and 11 psychiatrically healthy comparisons group-matched on age, gender, and IQ. Face-emotion recognition was assessed using the Diagnostic Analysis of Nonverbal Accuracy Scale (DANVA). Children and adolescents with anxiety disorders exhibited significantly poorer performance on the face-emotion recognition task compared to healthy controls (z = 2.2; p < 0.05). This difference was found only for expressions posed by adults but not children. Reduced accuracy on a face-emotion recognition test is consistent with perturbed amygdala function in pediatric anxiety disorders. As this study was conducted in a sample undergoing a neuroimaging investigation of amygdala integrity, future analyses will examine associations among amygdala function, clinical anxiety, and face-recognition abilities.
Psn Psychiatr Sci Hum Neurosc, 2009
Risk-taking behavior is a major cause of morbidity and mortality in adolescence. In the context o... more Risk-taking behavior is a major cause of morbidity and mortality in adolescence. In the context of decision theory and motivated (goal-directed) behavior, risk-taking reflects a pattern of decision-making that favors the selection of courses of action with uncertain and possibly harmful consequences. We present a triadic, neuroscience systems-based model of adolescent decision-making. We review the functional role and neurodevelopmental findings of three key structures in the control of motivated behavior, i.e. amygdala, nucleus accumbens, and medial/ventral prefrontal cortex. We adopt a cognitive neuroscience approach to motivated behavior that uses a temporal fragmentation of a generic motivated action. Predictions about the relative contributions of the triadic nodes to the three stages of a motivated action during adolescence are proposed. The propensity during adolescence for reward/novelty seeking in the face of uncertainty or potential harm might be explained by a strong reward system (nucleus accumbens), a weak harm-avoidant system (amygdala), and/or an inefficient supervisory system (medial/ventral prefrontal cortex). Perturbations in these systems may contribute to the expression of psychopathology, illustrated here with depression and anxiety. A triadic model, integrated in a temporally organized map of motivated behavior, can provide a helpful framework that suggests specific hypotheses of neural bases of typical and atypical adolescent behavior.
J Statist Phys, 1984
Diffusion of moving particles in stationary disordered media is studied using a phenomenological ... more Diffusion of moving particles in stationary disordered media is studied using a phenomenological mode-coupling theory. The presence of disorder leads to a generalized diffusion equation, with memory kernels having power law long time tails. The velocity autocorrelation function is found to decay like t-(d/2+1), while the time correlation function associated with the super-Burnett coefficient decays like t -d/2 for long times. The theory is applicable to a wide variety of dynamical and stochastic systems including the Lorentz gas and hopping models. We find new, general expressions for the coefficients of the long time tails which agree with previous results for exactly solvable hopping models and with the low-density results obtained for the Lorentz gas. Finally we mention that if the moving particles are charged, then the long time tails imply that there is an ω d/2 contribution to the low-frequency part of the frequency-dependent electrical conductivity.
The American Journal of Psychiatry, Aug 1, 1999
Attention deficit hyperactivity disorder (ADHD) is a highly prevalent childhood psychiatric disor... more Attention deficit hyperactivity disorder (ADHD) is a highly prevalent childhood psychiatric disorder characterized by impaired attention, excessive motor activity, and impulsivity. Despite extensive investigation of the neuropathophysiology of ADHD by a wide array of methodologies, the neurobiochemical substrate of this disorder is still unknown. Converging evidence, however, suggests a primary role of the dopaminergic system. This study examined the integrity of presynaptic dopaminergic function in children with ADHD through use of positron emission tomography and the tracer [18F]fluorodopa ([18F]DOPA). Accumulation of [18F]DOPA in synaptic terminals, a measure of dopa decarboxylase activity, was quantified in regions rich in dopaminergic innervation, including caudate nucleus, putamen, frontal cortex, and midbrain (i.e., substantia nigra and ventral tegmentum). Accumulation of [18F]DOPA in the right midbrain was higher by 48% in 10 children with ADHD than in 10 normal children. Despite its magnitude, this difference would not have reached statistical significance if corrected by the Bonferroni test for multiple comparisons. However, [18F]DOPA in the right midbrain was correlated with symptom severity. No other dopamine-rich regions significantly differed between groups. These findings are suggestive of dopaminergic dysfunction at the level of the dopaminergic nuclei in children with ADHD. Abnormality in dopa decarboxylase activity may be primary or secondary to deficits in other functional units of the dopamine pathway (e.g., receptor, uptake transporter, vesicular transporter, degradation enzymes). Efforts toward defining the origin of this abnormality should help delineate mechanisms of midbrain control of attention and motor behavior important for the understanding of the causes and treatment of ADHD.
The Journal of Neuropsychiatry and Clinical Neurosciences, Nov 9, 2014
Using positron emission tomography and [18F]-2-fluoro-2-deoxy-D-glucose, the authors determined c... more Using positron emission tomography and [18F]-2-fluoro-2-deoxy-D-glucose, the authors determined cerebral metabolic rates for glucose (CMRglc) in 39 adults (18-51 years old) with attention-deficit/hyperactivity disorder (ADHD) and 56 healthy control adults (19-56 years old) during the performance of a continuous attention task. Increased age was associated with reduced global CMRglc in ADHD women, but not in ADHD men, control men, or control women. Better performance on the attention task was significantly associated with increased age only in the ADHD female group. Determining the role of behavioral, hormonal, and genetic factors is a challenge for future research.
Neuropsychologia 42 1585 1597, Feb 1, 2004
We examined neural activations during decision-making using fMRI paired with the wheel of fortune... more We examined neural activations during decision-making using fMRI paired with the wheel of fortune task, a newly developed two-choice decision-making task with probabilistic monetary gains. In particular, we assessed the impact of high-reward/risk events relative to low-reward/risk events on neural activations during choice selection and during reward anticipation. Seventeen healthy adults completed the study. We found, in line with predictions, that (i) the selection phase predominantly recruited regions involved in visuo-spatial attention (occipito-parietal pathway), conflict (anterior cingulate), manipulation of quantities (parietal cortex), and preparation for action (premotor area), whereas the anticipation phase prominently recruited regions engaged in reward processes (ventral striatum); and (ii) high-reward/risk conditions relative to low-reward/risk conditions were associated with a greater neural response in ventral striatum during selection, though not during anticipation. Following an a priori ROI analysis focused on orbitofrontal cortex, we observed orbitofrontal cortex activation (BA 11 and 47) during selection (particularly to high-risk/reward options), and to a more limited degree, during anticipation. These findings support the notion that (1) distinct, although overlapping, pathways subserve the processes of selection and anticipation in a two-choice task of probabilistic monetary reward; (2) taking a risk and awaiting the consequence of a risky decision seem to affect neural activity differently in selection and anticipation; and thus (3) common structures, including the ventral striatum, are modulated differently by risk/reward during selection and anticipation. Published by Elsevier Ltd.
American Journal of Psychiatry, Nov 9, 2014
The characteristics of attention deficit hyperactivity disorder (ADHD) include abnormalities in r... more The characteristics of attention deficit hyperactivity disorder (ADHD) include abnormalities in reward responsivity that may interfere with decision making. The study examined reward responsivity in ADHD by comparing the neural correlates of decision making in adults with childhood-onset ADHD and in healthy adults.
Biological Psychiatry, Jan 11, 2006
Background: Although major depressive disorder (MDD) represents one of the most serious psychiatr... more Background: Although major depressive disorder (MDD) represents one of the most serious psychiatric problems afflicting adolescents, efforts to understand the neural circuitry of adolescent MDD have lagged behind those of adult MDD. This study tests the hypothesis that adolescent MDD is associated with abnormal amygdala activity during evocative-face viewing. Methods: Using functional magnetic resonance imaging (fMRI), between-group differences among MDD (n ϭ 10), anxious (n ϭ 11), and non-psychiatric comparisons (n ϭ 23) were examined during successful vs. unsuccessful face encoding, with encoding success measured post-scan. Results: Compared to healthy adolescents, MDD patients exhibited poorer memory for faces. fMRI analyses accounted for this performance difference through event-related methods. In an analysis comparing successful vs. unsuccessful face encoding, MDD patients exhibited greater left amygdala activation relative to healthy and anxious youth. Conclusions: Given prior findings among adults, this study suggests that adolescent and adult MDD may involve similar underlying abnormalities in amygdala functioning.
Pediatrics 117 2030 2039, Jun 1, 2006
OBJECTIVE. Our goal was to examine substance-use initiation in healthy adolescents and in adolesc... more OBJECTIVE. Our goal was to examine substance-use initiation in healthy adolescents and in adolescents who have been diagnosed with attention-deficit/hyperactivity disorder. METHODS. Seventy-eight adolescents (28 healthy and 50 with attention-deficit/hyperactivity disorder) participated in an ongoing longitudinal study of predictors of substance use. The substances most commonly reported were tobacco, alcohol, and marijuana. Aggression, conduct problems, hyperactivity, impulsivity, inattention, anxiety/depression, social difficulties, and somatic complaints were assessed at study entry and tested as predictors for later substance use. RESULTS. With an average of 4 years into the study, 37 adolescents had not used any substances, 41 had experimented with at least 1 substance, and 29 experimented with > 1 substance. Psychiatric diagnoses (attention-deficit/hyperactivity disorder, attention-deficit/ hyperactivity disorder and conduct disorder, and attention-deficit/hyperactivity disorder and depression/anxiety) did not influence reports of substance use. Distinct behavioral measures collected at study entry predicted use of different substances. In a multivariate analysis, aggression had the greatest association with tobacco smoking and marijuana use. Impulsivity was associated with alcohol use. Severity of drug exposure, indexed by the number of substances eScholarship provides open access, scholarly publishing services to the University of California and delivers a dynamic research platform to scholars worldwide. used, was predicted by aggression. CONCLUSIONS. This 4-year longitudinal study captured the onset of substance use, not abuse. Behavioral predictors differed with the type of substance used. These behavioral characteristics may raise suspicion among pediatricians for enhanced risk for substance-use initiation.
Some reports indicate that cigarette smoking can help smokers focus attention, even when they hav... more Some reports indicate that cigarette smoking can help smokers focus attention, even when they have not abstained from smoking for a substantial period of time (eg, >1 h). Understanding the mechanisms by which smoking affects attention may help in designing smoking cessation treatments. Thirteen nonsmokers and nine smokers participated in two tests of blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI). During fMRI, the participants performed the Stroop Task. There was a 15-min break between the two tests. During the break, each smoker smoked one cigarette. For smokers, the first test began 45-60 min after the last cigarette of ad libitum smoking. The differences in BOLD signal changes between Stroop conditions (ie, incongruent minus congruent) showed a group × test interaction in the right precentral sulcus, including the putative human frontal eye field (FEF). Smokers, but not nonsmokers, showed greater changes (relative to rest) in BOLD signal in the incongruent than in the congruent condition in the first fMRI test but not in the second. Even after brief abstinence from smoking, therefore, smokers exhibit compromised functional efficiency in the right FEF and adjacent precentral sulcus in a test of selective attention; and smoking ameliorates this condition.