Biomedical subjects

Natalia S Lawrence

Publications and source records attributed to Natalia S Lawrence.

6 recordsLinked to original sources

PubMed2006

Neural responses to facial expressions of disgust but not fear are modulated by washing symptoms in OCD.

BACKGROUND: Washing symptoms in Obsessive-Compulsive Disorder (OCD) are associated with increased trait sensitivity to disgust. This study explored neural systems underlying sensitivity to symptom-unrelated disgust and fear in OCD using functional neuroimaging. METHODS: Seventeen OCD subjects and 19 controls viewed facial expressions of disgust and fear (versus neutral) presented just above the level of conscious awareness in a backward masking paradigm. RESULTS: The OCD group showed greater activation than controls in the left ventrolateral prefrontal cortex, but reduced activation in the thalamus, to facial expressions of disgust. There were no between-group differences in response to fear. Further analysis using a median-split to divide OCD subjects into high and low washers suggested that the enhanced ventrolateral prefrontal cortex response was being driven by predominantly female OCD subjects with high washing symptoms. These subjects also reported higher levels of trait sensitivity to disgust. CONCLUSIONS: These findings are consistent with previous reports of increased response to symptom-relevant and generally disgusting stimuli in neural regions associated with disgust and autonomic response processing in OCD patients with prominent washing symptoms. Together, these findings point to increased sensitivity to disgust stimuli as a component of the pathophysiology of the washing/contamination symptom dimension of OCD.

Adult↗

PubMed2006

Decision making and set shifting impairments are associated with distinct symptom dimensions in obsessive-compulsive disorder.

Obsessive-compulsive disorder (OCD) is clinically heterogeneous. The authors examined how specific OCD symptom dimensions were related to neuropsychological functions using multiple regression analyses. A total of 39 OCD patients and 40 controls completed the Iowa Gambling Task (IGT; A. Bechara, A. R. Damasio, H. Damasio, & S. W. Anderson, 1994), which is a test of decision making, and the Wisconsin Card Sorting Test (R. K. Heaton, 1981), which is a test of set shifting. OCD patients and controls showed comparable decision making. However, patients with prominent hoarding symptoms showed impaired decision making on the IGT as well as reduced skin conductance responses. OCD patients had poorer set shifting abilities than controls, and symmetry/ordering symptoms were negatively associated with set shifting. These results help explain previous inconsistent findings in neuropsychological research in OCD and support recent neuroimaging data showing dissociable neural mechanisms involved in mediating the different OCD symptom dimensions.

Adolescent↗

PubMed2006

Stroop performance in bipolar disorder: further evidence for abnormalities in the ventral prefrontal cortex.

OBJECTIVES: Bipolar patients are impaired in Stroop task performance, a measure of selective attention. Structural and functional abnormalities in task-associated regions, in particular the prefrontal cortex (PFC), have been reported in this population. We aimed to examine the relationship between functional abnormalities, impaired task performance and the severity of depressive symptoms in bipolar patients. METHODS: Remitted bipolar patients (n = 10; all medicated), either euthymic or with subsyndromal depression, and age-matched control subjects (n = 11) viewed 10 alternating blocks of incongruent Stroop and control stimuli, naming the colour of the ink. Neural response was measured using functional magnetic resonance imaging. We computed between-group differences in neural response and within-group correlations with mood and anxiety. RESULTS: There were no significant between-group differences in task performance. During the Stroop condition, controls demonstrated greater activation of visual and dorsolateral and ventrolateral prefrontal cortical areas; bipolar patients demonstrated relative deactivation within orbital and medial prefrontal cortices. Depression scores showed a trend towards a negative correlation with the magnitude of orbitofrontal cortex deactivation in bipolar patients, whereas state anxiety correlated positively with activation of dorsolateral PFC and precuneus in controls. CONCLUSIONS: Our findings confirm previous reports of decreased ventral prefrontal activity during Stroop task performance in bipolar patients, and suggest a possible negative correlation between this and depression severity in bipolar patients. These findings further highlight the ventromedial PFC as a potential candidate for illness related dysfunction in bipolar disorder.

Adult↗

PubMed2004

Subcortical and ventral prefrontal cortical neural responses to facial expressions distinguish patients with bipolar disorder and major depression.

BACKGROUND: Bipolar disorder (BD) is characterised by abnormalities in mood and emotional processing, but the neural correlates of these, their relationship to depressive symptoms, and the similarities with deficits in major depressive disorder (MDD) remain unclear. We compared responses within subcortical and prefrontal cortical regions to emotionally salient material in patients with BP and MDD using functional magnetic resonance imaging. METHODS: We measured neural responses to mild and intense expressions of fear, happiness, and sadness in euthymic and depressed BD patients, healthy control subjects, and depressed MDD patients. RESULTS: Bipolar disorder patients demonstrated increased subcortical (ventral striatal, thalamic, hippocampal) and ventral prefrontal cortical responses particularly to mild and intense fear, mild happy, and mild sad expressions. Healthy control subjects demonstrated increased subcortical responses to intense happy and mild fear, and increased dorsal prefrontal cortical responses to intense sad expressions. Overall, MDD patients showed diminished neural responses to all emotional expressions except mild sadness. Depression severity correlated positively with hippocampal response to mild sadness in both patient groups. CONCLUSIONS: Compared with healthy controls and MDD patients, BD patients demonstrated increased subcortical and ventral prefrontal cortical responses to both positive and negative emotional expressions.

Adult↗

PubMed2003

Multiple neuronal networks mediate sustained attention.

Sustained attention deficits occur in several neuropsychiatric disorders. However, the underlying neurobiological mechanisms are still incompletely understood. To that end, functional MRI was used to investigate the neural substrates of sustained attention (vigilance) using the rapid visual information processing (RVIP) task in 25 healthy volunteers. In order to better understand the neural networks underlying attentional abilities, brain regions where task-induced activation correlated with task performance were identified. Performance of the RVIP task activated a network of frontal, parietal, occipital, thalamic, and cerebellar regions. Deactivation during task performance was seen in the anterior and posterior cingulate, insula, and the left temporal and parahippocampal gyrus. Good task performance, as defined by better detection of target stimuli, was correlated with enhanced activation in predominantly right fronto-parietal regions and with decreased activation in predominantly left temporo-limbic and cingulate areas. Factor analysis revealed that these performance-correlated regions were grouped into two separate networks comprised of positively activated and negatively activated intercorrelated regions. Poor performers failed to significantly activate or deactivate these networks, whereas good performers either activated the positive or deactivated the negative network, or did both. The fact that both increased activation of task-specific areas and increased deactivation of task-irrelevant areas mediate cognitive functions underlying good RVIP task performance suggests two independent circuits, presumably reflecting different cognitive strategies, can be recruited to perform this vigilance task.

Adolescent↗

PubMed2002

Cognitive mechanisms of nicotine on visual attention.

Understanding nicotine's neurobiological and cognitive mechanisms may help explain both its addictive properties and potential therapeutic applications. As such, functional MRI was used to determine the neural substrates of nicotine's effects on a sustained attention (rapid visual information-processing) task. Performance was associated with activation in a fronto-parietal-thalamic network in both smokers and nonsmokers. Along with subtle behavioral deficits, mildly abstinent smokers showed less task-induced brain activation in the parietal cortex and caudate than did nonsmokers. Transdermal nicotine replacement improved task performance in smokers and increased task-induced brain activation in the parietal cortex, thalamus, and caudate, while nicotine induced a generalized increase in occipital cortex activity. These data suggest that nicotine improves attention in smokers by enhancing activation in areas traditionally associated with visual attention, arousal, and motor activation.

Administration, Cutaneous↗